The migrations of birds

^

,*^'" ^

The zyxtigrations of^irds

LONDON : HUMPHREY MILFORD

OXFORD UNIVERSITY PRESS

Figure i

Wooden image of swallow used in Macedonia as an emblem of spring
(After Keller.)

1/^

THE MIGRATIONS
OF BIRDS

BY

ALEXANDER WETMORE

ASSISTANT SECRETARY, SMITHSONIAN INSTITUTION
FELLOW, AMERICAN ORNITHOLOGISTS' UNION

CAMBRIDGE
HARVARD UNIVERSITY PRESS

1927

COPYRIGHT, 1926

BY THE PRESIDENT AND FELLOWS OF

HARVARD COLLEGE

Second impression

PRINTED AT THE HARVARD UNIVERSITY PRESS
CAMBRIDGE, MASS., U.S.A.

PREFACE

THE observations on the migration of birds pre-
sented in the following pages were delivered in
six lectures before the Lowell Institute in Boston on
October 26 and 28, and November 2, 4, 16 and 18,
1925. The manuscript as here published is un-
changed except for the inclusion of a few para-
graphs that time did not permit to be presented
during the course of the lectures.

The material included is based on study and ob-
servation on the part of the author during a period
of more than twenty years. It is intended as a sum-
mary of present knowledge of migration, with the
various factors that affect it in its broader aspects,
without entering upon precise statistics of move-
ment for the many species involved. Such figures
may be left for treatises of another character.

After careful consideration of the subject the
writer is profoundly impressed by the mass of detail
regarding the movements of birds that has been
assembled and the little that has been definitely
ascertained regarding the underlying principles that
control migration. There is much that remains to be
established in this phase of the subject.

In conclusion the author desires to express appre-
ciation to the Bureau of Biological Survey, United

vi PREFACE

States Department of Agriculture, for permission to
reproduce plates from its publications, and to the
Museum of Vertebrate Zoology, University of Cali-
fornia, for the privilege of reprinting a map by Mr.
H. S. Swarth to show the distribution of fox spar-
rows. Mr. Gregory Mathews, the well-known au-
thority on Australian birds, has read the sections
dealing with Australia, and I am indebted to other
friends for suggestions.

Alexander Wetmore

Washington, D. C.
May I, 1926.

CONTENTS

CHAPTER I

Introduction 3

Historical Account 4

Theories of Migration 15

Superstitious Beliefs 15

Scientific Hypotheses of Migration 21

CHAPTER II

Nocturnal and Diurnal Migration 39

Altitudes at which Migrating Birds Travel ... 46

Weather and Migration 52

Speed of Flight in Birds 58

The Sense of Direction in Birds 62

CHAPTER III

Regularity of Migration 73

Segregation during Migration 79

Migration Among Supposedly Resident Birds . . 84

Irregular or Vagrant Migration 89

Casual Records 99

CHAPTER IV

Altitudinal or Vertical Migration 106

Rapidity of Migration Movement no

Distances Travelled by Migrants 115

Mortality Among Migrant Birds 121

9 Q o o Q

viii CONTENTS

CHAPTER V

General Observations on Lines of Migratory
Flight 134

CHAPTER VI

Migration Among Shore-birds 165

The Seasonal Flight of Ducks 180

The Migrations of Some Other Birds 195

Conclusion 217

The zyXCigraiions of^irds

CHAPTER I
Introduction

THE regular movements of birds during their
migratory flights between their summer and
winter homes are among the striking natural phe-
nomena of the temperate regions of the earth that
attract almost universal attention. Lines of geese,
ducks, or cranes crossing the sky stir the heart of
civilized and savage man alike, and in all quarters
are greeted as indicators of changing season. The
return of robins to our lawns, almost as soon as the
ground is bare in spring, or the cheerful warblings of
the bluebird from roadside fences, are events re-
corded in speech and in the press, and are greeted
with pleasure as the vanguard of advance against
winter. The country dweller in Europe, Africa,
Argentina, or Australia welcomes a swallow as the
certain harbinger of warmer weather, and rejoices
accordingly. Movements among nomadic peoples,
migratory themselves in one sense of the word, have
been controlled by the flights of birds. Savage
tribes have named months for birds that regularly
appear during their course; and migratory flights of

4 THE MIGRATIONS OF BIRDS

different species in former times were used as omens,
a custom that prevails to-day in certain sections of
the earth.

Historical Account

Historical allusions to the migratory flights of
birds are innumerable, and we may suppose that
these regular movements have been observed by
man and correlated with the change of season since
the Pleistocene. On turning to the Bible, we find in
the Old Testament what is considered the earliest
definite written reference to migration when Job
(XXXIX, 26) remarks: "Doth the hawk fly by thy
wisdom, and stretch her wings toward the south?"
Jeremiah (VIII, 7), in an exhortation to Judah, is
more explicit in the statement, "Yea, the stork in
the heaven knoweth her appointed times; and the
turtle and the crane and the swallow observe the
time of their coming." The Israelites wandering in
Sinai were saved from starvation when "at even the
quails came up and covered the camp" {Exodus ^
XVI, 13) ; and again, a year later, when " there went
forth a wind from the Lord, and brought quails from
the sea." {Numbers XI, 31.) Canon Tristram has
calculated that this occurred in spring when migra-
tory quail were in flight to the north from their
winter home in Africa. Further, he has indicated
the date as in the month of April, about 1580 b. c.

HISTORICAL ACCOUNT 5

which, if authentic, would seem to be our earliest
definite migration record.

Apparently quails came in tremendous abun-
dance, since it is stated in the book oi Numbers (XI,
32), that "the people stood up all that day and all
that night, and all the next day, and they gathered
the quails: he that gathered least gathered ten
homers." Hugh Gladstone ' informs us that the
capacity of the unit of measure called the homer has
been estimated variously at from 48 to 80 gallons.
He assumes that 600 men (said to be the number of
heads of households or "tent-holders" that took
part in the exodus) were engaged in the capture of
birds; on these data the Israelites during thirty-six
hours may have taken over 9,000,000 quails!

Persians and Arabs formed part of their calendar
en data taken from the movements of birds, and,
with other ancient peoples, celebrated with song and
festival the return of spring as marked by the arrival
of migrants. In Macedonia to-day, on the first of
March, children pass from house to house carrying
the figure of a swallow carved from wood, while they
sing that the swallow comes and with it spring.
(See Fig. i .)

The Chippeway and various tribes of Plains
Indians, transposing cause and eflFect, believed that
the bluebird (in this case the Arctic bluebird) bore

^ Record Bags and Shooting Records (1922), pp. 59, 60.

6 THE MIGRATIONS OF BIRDS

summer to them on its azure wings, and they noted
its arrival with appropriate pleasure. The Eskimo
of the lower Yukon call the season comprising the
latter part of March and the first days of April "the
coming of the birds," and the succeeding period,
embracing a portion of April and May, "the arrival
of the geese." South of the Yukon Delta, October is
known as "the month of the flying away," because
of the departure of birds.

In the vast Chaco of Paraguay, when the north-
ward flight of shore-birds starts these voyagers on
their long journey from their winter homes in South
America to their breeding grounds near the Arctic
Circle, the Anguete and Lengua Indians, hunting
tribes governed in their movements by the availabil-
ity of water and the presence of game, resort to cer-
tain river channels where, from the shelter of low
sand-banks, they waylay passing sandpipers and
kill them in quantity with throw-sticks of light
wood hurtled through the closely flying flocks.

In the writings of Homer, we find reference to the
flight of cranes at the approach of winter, and the
gathering at that season of hordes of aquatic birds
on the marshes of Asiatic rivers. To Hesiod, in the
eighth century before Christ, the cries of the crane
were a summons to the laborer to plough his land,
while Herodotus (about 525 b. c.) supposed that
the hawks he saw must have come from some distant

HISTORICAL ACCOUNT 7

land. Anacreon sings of the return of the swallow in
spring to its nesting-place.

Aristotle, the first to discourse fully on migration,
in his writings on natural history, gives definite
accounts of a number of migrant birds. He tells us
that the crane flies from the steppes of Scythia to the
marshlands at the source of the Nile, south of Egypt;
that pelicans migrate, as do the quails, the rock-dove,
and the turtle-dove, though of the last three a few
may linger during cold weather in protected locali-
ties. The swan, the land-rail, and the lesser goose
likewise pass toward warmer regions, while the
cuckoo goes away in July about the time that Sirius
the Dog-star rises. Pliny, the Roman, in his His-
toria Naturalis, written in the earliest years of the
Christian era, in treating of migration repeats
much of what has been said by Aristotle, but adds
that blackbirds (in this case the common thrush of
Europe), thrushes, and starlings pass to neighboring
countries; the ring-dove also is migratory to an
unknown winter home, as are the storks and cranes,
which he believes go to a great distance.

The few known writings during the Dark Ages
that pertain to natural history, which include the
Bestiaries, accounts of hawking or falconry', and a
few other scattered manuscripts, contain little that

^ The peregrine falcon {Falco peregrinus) was so called by falconers
because it was secured when grown as a "pilgrim" or migrant, and
was not taken from the nest when young as were other hawks used
in hunting.

8 THE MIGRATIONS OF BIRDS

refers to migration except casual mention of species
of birds that we know to be migratory. Matthew
Paris, monk of St. Albans, in a manuscript pre-
served at Corpus Christi College, Cambridge, in the
year 1251 wrote of an invasion of crossbills, and
referred to them as birds never before seen in Eng-
land. Chaucer, in the fourteenth century, des-
cribed the field-fare, a species of thrush, as "frosty,"
in allusion to its presence in England only during
winter.

Glaus Magnus, Archbishop of Upsala, in 1555
speaks of the flights of swallows, Francis Willoughby
in his Ornithology published in 1678, mentions vari-
ous migratory birds; and the writings of Gilbert
White, Thomas Pennant, and George Edwards in
the succeeding century carry much of interest on
this subject. These men in fact kept regular records
of arrival and departure. The observations of George
Edwards on the migration of birds were collected in
his Essays upon Natural History^ published in Lon-
don in 1770; while in 1780 appeared a Discourse on
the Emigration of British Birds, printed anony-
mously, but since attributed to John Legg, a nat-
uralist previously unknown.

From the beginning of the nineteenth century
records of arrival and departure of migratory birds
were gathered by many observant naturalists in the
northern hemisphere, and the mass of data increased
in bulk yearly.

HISTORICAL ACCOUNT 9

Dr. MiddendorfF, in 1855 published a summary of
migration records for the Russian Empire, in which
he attempted to trace isepipteses^ or Hnes of simul-
taneous arrival, for individuals of the same species.'
Professor Palmen, in 1874,^ outlined many supposed
routes of migration in Europe, which led to con-
troversy on the subject with von Homeyer, who
combated some of his views. SeverzofF,^ in 1880,
prepared a similar treatise covering central Asia,
and Menzbier ^ wrote of routes of travel for Eastern
Europe.

Bibliographical material dealing with the subject
after 1880 is so voluminous that space permits bare
mention of only a few authors. Among the most
famous records of migratorial phenomena are the
observations of Heinrich Gatke, covering fifty
years intensive study on the little island of Heligo-
land standing solitary in the North Sea. These
records, published first in German, were in 1895
translated into English,^ and stand as a classic on
the subject. Though modern naturalists do not hold
with some of Gatke's theories, his account is rich in

^ Die Isepiptesen Russlands. Grundlagen zur Erforschung der Zug-
zeiten und Zugrichtungen der Vogel Russlands. St. Petersburg, 1855.

' Im Foglarnes Flyttningvdgar. Helsingfors, 1 874.

3 Bulletin de la Societe Imperiah des Naturalistes de Moscou (1880),
pp. 234-287.

< Ibid. (1886), pp. 291-369.

s Heligoland as an Ornithological Observatory. Edinburgh, 1895;
pp. i-xii, 1-599.

lo THE MIGRATIONS OF BIRDS

valuable information. Wallace and Newton in turn
wrote upon migration, followed by Charles Dixon,
and by W. E. Clarke whose two volumes' sum-
marize observations begun as a member of a special
committee on Bird Migration, of the British Asso-
ciation for the Advancement of Science, and con-
tinued at length after preparation of the reports that
cover the voluminous data assembled by that com-
mittee. The Hungarian, German, French, and a
number of other ornithological organizations have
been responsible for cooperative efforts leading to
the assembling of much information, which has been
published in a long series of papers.

The phenomena of bird migration were so evi-
dent to early colonists on the eastern coasts of
North xAmerica that notes on the movements of
birds found a natural place in many accounts that
touch on the indigenous life of the region. Water-
fowl swarmed in rivers and marshes in such numbers
that their migratory movements forced themselves
on attention, aside from the regular appearance and
disappearance of smaller birds that came in friendly
fashion about the crude homes of the pioneers. There
were in addition, in those days, great flights of the
passenger pigeon, which illustrated migration move-
ment of maximum magnitude.

Data on the migration of North American birds

* Studies in Bird Migration. London, 191 2, 1 vols.

HISTORICAL ACCOUNT ii

were early summarized by Spencer Fullerton Baird,
writing in the American Journal of Science in 1866/
and from that time increased steadily in volume
year by year. Tremendous impetus was given this
branch of ornithology by the formation of the Amer-
ican Ornithologists' Union. At its first congress,
held in New York City in September, 1883, there
was appointed a committee on the Migration of
Birds, with Dr. C. Hart Merriam of Locust Grove,
New York, as chairman. This committee began
active work immediately and during its first year,
through a corps of observers scattered through the
eastern half of the continent, assembled many data.
It was realized within a year that financial assistance
would be required to handle the rapidly growing
work, which led to a petition to Congress by the
Council of the Union, and resulted in the appropria-
tion of five thousand dollars for a Division of Eco-
nomic Ornithology under the United States De-
partment of Agriculture, estabHshed July i, 1885,
with Dr. Merriam as Chief. Though the scope of
the work undertaken by the new division rapidly
broadened into the present Biological Survey, study
of the migration of birds continued to receive its due
measure of attention. Professor Wells W. Cooke,
who had organized cooperative observation in the

^ "The Distribution and Migrations of North American Birds";
Amer. Journ. Set. ser. 2, vol. xli (1866), pp. 78-90, 184-192, 337-347»

12 THE MIGRATIONS OF BIRDS

Mississippi Valley in 1881, and whose endeavors
were incorporated with those of the A. O. U. Com-
mittee on its formation in 1883, became associated
early with the work under government auspices, and
continued these investigations until his death in
1 91 6. As a result of his endeavors augmented by the
efforts of others, there has been amassed in Wash-
ington the most comprehensive mass of data on the
subject ever brought together, much of which Pro-
fessor Cooke summarized in his many publications
dealing with the subject.

Literature of the past fifty years dealing with
migratory movement in birds is truly enormous and
must be left without further comment. It remains
to notice briefly the growth of bird-banding as ap-
plied to this study. Sporadic attempts to mark in-
dividual birds so that they might be identified later
began over one hundred and twenty years ago, and
have ranged from tiny bells, bits of colored yarn,
marks made with indelible inks or paint on certain
feathers, metal disks glued to the wing or tail
feathers, plain rings of wire and celluloid, and strips
of metal on which were stamped texts from the
scriptures, to bands of aluminum marked with a
serial number and the name and address of the per-
son or organization responsible. Lincoln has called
attention to a great gray heron {Ardea cinered) cap-
tured in Germany in 17 10, which carried on the

HISTORICAL ACCOUNT 13

tarsus several metal rings, one of which is stated to
have been placed on the bird in Turkey several
years earlier. This seems to be the first recorded use
in bird-marking of a metal ring placed on the tarsus.
Sporadic records of birds marked in various ways
occur in literature at random, but scientific use of
this method did not begin until 1899, when C. C.
Mortensen in Denmark began systematically to
band storks, teal, starlings, and other birds. The
results to be obtained from this method were so
obvious that it became popular almost at once, so
that by 1914 eighteen or twenty distinct projects for
the marking of birds were in progress or in contem-
plation in Europe. The work was checked in part by
the World War, but is now again in full progress. In
the United States early attempts at banding birds,
fostered in part by Dr. L. J. Cole, crystallized in
1909 in the organization of the American Bird-Band-
ing Association, conducted from 191 1 until 1920 by
the Linnaean Society of New York, and then taken
over by the Bureau of Biological Survey, of the
United States Department of Agriculture. Under
the present organization bands are issued to mem-
bers, who report to W^ashington, with all necessary
data, the birds on which they are placed. The work
is regularly advertised through the press so that the
bands are often recognized when found, or, if not,
the finder usually has sufficient interest or curiosity

14 THE MIGRATIONS OF BIRDS

to notify the Biological Survey to learn the source of
the marker. In this way many thousands of bands
have been used, and returns have come from many
hundreds. At the present time the work of bird-
banding has become so widespread and popular that
four regional associations of interested persons have
been formed in the United States and Canada, to
consolidate the work by geographic areas.

During development of this work attempts at
banding birds were directed first mainly to the
marking of nestlings, but in the last few years this
has been supplemented and largely replaced by the
use of traps for the capture of grown individuals.
The marking of nestlings, while fruitful, has many
disappointments, since mortality among young
birds during the fledgling period, before they are
sufficiently alert to escape their many enemies, is
so heavy that many bands are wasted. Trapping
methods at present used were developed early by
Mr. S. P. Baldwin, and have attained a high degree
of efficiency. The trap is especially valuable since it
does not injure the bird and enables consecutive
records of the same individual. The method has
been extended until now trapping devices are made
for the capture of species of the most diverse form
and habit.

The great value of bird-banding to the student of
migration lies in the data that it affords on the move-

HISTORICAL ACCOUNT 15

ments of individual birds, as contrasted with mass
observation of a species as a whole. This modern
development of the study while still in its infancy-
has already yielded highly valuable results, and will
be steadily productive of new information that will
aid in the solution of many problems.

Theories of Migration

Superstitious Beliefs

The migratory movements of larger birds, evident
in their accomplishment, were understood by the lay
mind with comparative ease; but to account for the
travels of smaller species, which appeared or disap-
peared between suns, was a matter of greater diffi-
culty. In 1740, J. G. Gmelin was assured by the
Tartars of Krasnojarsk, and the Assanians, in
Siberia, that each crane carried a corn crake on its
back to some warmer land. In southern Europe the
peasants hold that the smaller birds congregate on
the shores of the Mediterranean Sea, where they
await suitable opportunity for passage to Africa on
the commodious pinions of storks and cranes — a
superstition further correlated with the belief of the
Egyptian laborer that these great birds on their
journeys carry a living freight of their smaller com-
panions.

i6 THE MIGRATIONS OF BIRDS

Somewhat more startling is a theory of migration
elaborated in an anonymous treatise published in
London in 1703, "By a Person of Learning and
Piety," entitled in part An Essay I'owards the Prob-
able Solution of this Question: Whence come the Stork
and the T!urtle^ the Crane and the Swallow^ when they
know and Observe the appointed time of their Coming.
This author in a wordy statement announces his
belief that migratory birds, on leaving England, go
direct to the moon, where they pass the winter sea-
son — truly an outstanding expression of faith in
the power of flight of dehcate creatures which, ac-
cording to others, are not able to span the moderate
expanse of one of the seas ! To continue, this tract
sets forth that the journey may require sixty days,
during which the voyagers may have no need of food
in the rarefied ether through which they pass, or may
subsist on their stored-up body supplies of fat as
"bears are said to live upon their summer fat all the
winter long in Greenland." The matter of restful
sleep is easily arranged since, as they fly "where
they have no objects to divert them, [they] may
shut their eyes, and so swing on fast asleep." The
tract continues that as the moon is not a stationary
body, if birds leave at the time of full moon they
may fly directly in a straight line upward, and at the
end of the allotted sixty days the moon will again be
full and at the proper location in the heavens to

THEORIES OF MIGRATION 17

receive them. The author concludes with the sage
remark that "if the Moon will not be allowed, some
other place must be found out for them" — a state-
ment that we may accept, and that we may hope to
confirm in the course of the pages to follow.

In early times, disappearance of certain birds was
attributed to hibernation, in which they passed into
a torpid state and remained thus through the season
of cold, hidden in caves or hollow trees, or embedded
in the mud at the bottom of streams, ponds, or
marshes. The theory of hibernation seems to find
its first expression more than three hundred years
before Christ, in the writings of Aristotle, where it is
stated that some or all individuals of the swallow,
kite, stork, ouzel, turtle-dove, lark, and a number
of other species become torpid during winter. Al-
though in early times related of many species, this
bizarre custom was attributed later mainly to swal-
lows, swifts, and, in the United States, to the sora
rail; and prolonged and learned were the discussions
setting forth the merits of both sides of the case; so
that Coues in 1878 cited more than 175 titles dealing
directly with hibernation in swallows alone. One
early writer published several treatises on the sub-
ject, under the pseudonym of "Philochelidon^"

The sora rail frequented marshes in abundance
until between suns it suddenly disappeared. This

^ Thomas Foster, an author who wrote on othersubjects than birds.

i8 THE MIGRATIONS OF BIRDS

strange trait was explained by the statement that
overnight the birds had turned to frogs or had sunk
in the mud. Naturalists gravely related seeing
swallows congregate on reeds until their weight bent
down the slender support and the birds were sub-
merged beneath the water. Glaus Magnus wrote
that fishermen often found swallows fastened in
bunches in the mud of marshes, and gave an illustra-
tion depicting two men drawing a net filled with
mingled swallows and fishes. (See fig. 2.)

During the eighteenth and early part of the nine-
teenth century this question was argued with es-
pecial vigor, and many instances in which hiberna-
tion was alleged were brought forward. Men re-
ported seeing swallows fly into the water, or told of
torpid individuals drawn up in seines. It is related
in Williams's History of Vermont , published in 1794,
that about the year 1760 a torpid swallow was dug
from a depth of two feet in the salt marsh on the
banks of the Charles River at Cambridge, Mass-
achusetts, during the latter part of February, and
that this bird revived in half an hour! Several
papers on the subject were read before the French
Academy, and the Royal Society in London, and
John Hunter, the anatomist, as an experiment, one
autumn shut several swallows in an outhouse, with
tubs of water floored with mud in which rushes had
been planted, with death to the birds by starvation

Figure 2

Fishermen drawing nets with a mixed catch of fishes and hibernating swallows.
Taken from Olaus Magnus. (After Eagle Clarke.)

THEORIES OF MIGRATION 19

as the only result. Those to whom the theory of
submersion in marshes did not appeal stated that
swallows and swifts remained in a torpid state in
hollow trees or clefts in rocks; and numerous per-
sons in our own country have related with great cir-
cumstance the finding of such birds, the manner of
their reviving, and their subsequent death if not
permitted to resume their slumbers. Even the cau-
tious Coues apparently was inclined to place a cer-
tain amount of behef in hibernation, mainly since in
his day the chimney swift disappeared in the
autumn to some unknown place.

As final comment, attention may be drawn to the
fact that hibernation, or its correlate aestivation, is
of common occurrence among mammals, reptiles,
and amphibians, and even among fishes, if we accept
the burrowing of lung-fishes and of some forms of
minnows in moist mud during periods of drought as
related to the phenomenon under consideration. It
is strange indeed, therefore, that hibernation in
birds has never yet been scientifically proved in
spite of the many cases that have been claimed. The
frequent connection of this superstition with swal-
lows is probably explained by the fact that these birds
regularly resort to growths of rushes in marshes and
swamps for roosts and shelter during late summer
and autumn, and that during storms many perish,
and fall into the mud and water, but never revive
on the approach of more clement weather.

20 THE MIGRATIONS OF BIRDS

There may be mentioned here also a transmuta-
tion theory held in early centuries which supposed
the change of one species to another at the coming of
cold and the assumption of proper form with return
of summer. This again may be traced to Aristotle,
who propounded the belief that the redbreast, or
European robin, changed to the redstart, a species of
similar size but different color, since the latter was
present in winter and the former in summer. Simi-
larly he informs us that the beccafico^ possibly the
garden warbler, became the blackcap, a related
species, and that at the proper seasons birds in
transition between the two could be observed.
Pliny repeated these tales, and later in popular be-
lief they were still further embroidered by the al-
leged transformation of certain marsh birds to
frogs. In our own country this shift from warm-
blooded bird to cold-blooded amphibian has been
attributed in many quarters to the sora rail, which
migrates by night so that its departure is unseen.

All these beliefs, which seem strange and curious
to modern vision, arose in the attempt of the human
mind to explain observations which demonstrated
conclusively that many birds were present one day
and had vanished on the one that followed, while
their return came in a fashion equally mysterious.
With recognition of nocturnal flight as fact, such
stories lost credence immediately, save in the case of

THEORIES OF MIGRATION 21

hibernation, which has been alleged sporadically to
account for various circumstances at the time not
fully understood.

Scientific Hypotheses of Migration

With the migration of birds recognized as a regu-
lar accompaniment of the changing seasons, there
arises for consideration the manner in which migra-
tion had its origin, and the reasons that lie behind
its continuation — matters still of considerable
dispute. The various theories that have been ad-
vanced may be outlined briefly.

The most commonly accepted explanation of the
seasonal movement of birds is that of shifting food-
supply. Failure of food in northern areas in autumn
forces certain birds to travel; it is only in a southerly
direction that amelioration of the unfavorable con-
dition is encountered, so that the birds affected move
south to an area where food is abundant. With the
coming of spring the need for reproduction to per-
petuate the species becomes paramount. The food-
supply of the southern regions to which these birds
have migrated does not permit the easy support of
the host of young that must be reared to perpetuate
each species, so that the individuals that have come
from the north press out in that direction until they
arrive at a suitable spot for settlement for the breed-
ing season.

22 THE MIGRATIONS OF BIRDS

But little different is the theory that migration is
due to changes in temperature through which, with
the colder air of autumn warning of the approaching
extremes of winter, birds pass south, to return when
the season has changed again, so that a period of
warmth is approaching. In this hypothesis some
have held that the migratory birds originated in the
north, were driven south by the advance of ice in the
Pleistocene, and have returned to the north with the
coming of milder conditions. A love of birthplace
calls them now each year to return to the natal home.
Observation shows, however, that many birds re-
main a very brief period on the breeding-ground, —
merely long enough to permit the rearing of young,
— and then immediately begin the return journey
south, — so that the period spent in the northern
home is short. Many in fact return south long be-
fore there is need for them to do so; so that the argu-
ment of love of birthplace hardly seems substan-
tiated.

According to a somewhat different hypothesis, all
species have arisen in the south and have spread to
the north through the natural impact of individual
upon individual in the struggle for existence; that
this pressure is at its highest point during the period
of reproduction, so that individuals then must fare
afield to find space in which their families may be
reared, and that with this duty accomplished they

THEORIES OF MIGRATION 23

may withdraw once more to their ancient home.
According to this conception migrant birds retire in
autumn to the original home, and there remain for
the winter. With the advent of spring the impulse
for reproduction drives them irresistibly out to the
area that forms the summer home, where they settle
to rear their young. With this accomplished they
are again actuated by an overpowering impulse to
return to the area from which they originally came,
and so return in the autumn migration to the winter
home. This has been alleged especially to explain
early autumn migration before there is any practical
necessity for a shift in base. It is also alleged to ex-
plain those instances in which birds tend to follow
migration routes that do not carry them directly
north and south. The theory has in its favor the
fact that many birds breed in areas where they
cannot winter, a sufficient basis for migration. To
suppose that all have originated in the south is,
however, going to a considerable length, as many, if
not most of them, in their evolution must antedate
the Pleistocene, when physical conditions regulating
their distribution were far different from those en-
countered at present.

Mr. J. T. Nichols,' has summarized certain mi-
gration theories akin to this in consideration of the
irregular southward flights of the red-breasted nut-

I Science^ Aug. 16, 1918, pp. 168-170.

24 THE MIGRATIONS OF BIRDS

hatch, a species that comes south in abundance at
irregular intervals. He considers that these flights
take place only when the species has increased to a
point where it is crowding its northern range. It
then scatters over a broad area and is found in
abundance in regions to the southward. He con-
siders that the majority of these migrants fail to re-
turn to their original home. Such movement he
terms centrifugal, in distinction from a centripetal
movement in which a species has separate breeding
and wintering grounds between which its individuals
perform regular migratory flights. He considers the
condition of indiscriminate wandering the original
one, in which the bird may succeed in returning oc-
casionally to its original home, perhaps from a short
distance only. With this established as habit, the
distance between the winter and summer homes may
become greater and greater until the area inhabited
in winter may lie without the limits where the
species breeds. This in brief is an outline of what has
unquestionably taken place in the development of
migratory habit, without attempt at explanation of
the principles that have controlled it.

A somewhat different belief is alleged by those
who support the theory of phototropism, in which it
is considered that birds naturally turn to the region
of greatest light and retreat from one in which light
is curtailed. According to this belief, migratory

THEORIES OF MIGRATION 25

birds simply follow the sun in spring as the centre of
its path advances beyond the Equator, and after
rearing their young follow the retreating rays of the
heavenly orb as it moves southward, to winter
quarters where light is at its maximum intensity.
The course of migration is, in general, correlated
with the advance and retreat of the sun, but it
seems that light is a secondary cause, which reacts
on the bird through its effect in producing a change
in season, and not directly through any organic re-
action to the light rays themselves. On the basis of
light we cannot, for example, explain a migration
south among northern shorebirds during July, as the
maximum amount of light, though on the wane, is
still to be found in their northern breeding-ground.
Also in the case of the few migrant nocturnal birds,
for example, various goatsuckers, it would seem ad-
vantageous to react against light rather than to fol-
low it, since prolonged darkness is better suited to
their activities, which are actually curtailed by
lengthening days. In fact, this is probably one of
the factors that limits the summer range of some of
the strictly nocturnal species. A whippoorwill, for
example, would be decidedly out of place near the
Arctic Circle, where the hours of night are elimi-
nated or greatly curtailed by the movements of the
midnight sun. Further, we should expect birds of
such habits to find their optimum conditions as re-

26 THE MIGRATIONS OF BIRDS

gards life in equatorial regions, where the hours of
the day remain evenly divided between daylight and
darkness, and where the favorable period of night is
not curtailed as it is in June in the North Temperate
Zone.

Among other theories, it has been suggested that
migration is the natural outcome of power of flight,
a faculty that is so pleasurable and so easy in execu-
tion that birds migrate naturally from place to
place when not bound by home ties. It has been
asserted also that migration has its impetus in a
desire for solitude, which causes birds to seek remote
islands, isolated lakes, marshes, or distant forests,
where they may be free from all disturbing factors
during the period of reproduction. Though many
birds, particularly those of shy habit, do seek isola-
tion while breeding, there are others with exactly
opposite tendency, as the many birds that nest
familiarly about the homes of man; so that there
are as many points against this argument as for it.

Dr. Alvin R. Cahn, in a recent article ' on the
migration of animals, has discussed migratory
movements in a highly interesting and instructive
manner. He points out that the movements of birds
in north and south migration correspond, in general,
to advance and retreat to or from the breeding-
station, and considers migration due to physiological

^ American Naturalist (1925), lix, 539-566,

THEORIES OF MIGRATION 27

change in the gonads, and thus directly activated by
the sex hormones. It appears true that the migration
north from the winter home is instigated by this
factor, which is of powerful influence in maintaining
and directing present migration movement; but,
though a prime influence at present, this cannot be
considered as the ultimate underlying principle that
has given rise to migration as we now see it.

The evolutionary line of the bird is tremendously
long: on the basis of present knowledge it is known
to go back through an enormous reach of time to
Archaeopteryx and Archaeornis of the Jurassic
period.

That these earliest known birdlike creatures pro-
gressed through the air is certain from their struc-
ture, but the extent of their powers of flight is prob-
lematical. In the Cretaceous, however, we find in
Ichthyornis a bird with ability to fly strongly de-
veloped, and the flying type has been the dominant
one in the millions of years during which our present
avian forms have been evolved. The evidence re-
corded by fossils indicates that many of our modern
types of birds were found during the Miocene. It
seems probable that the forms shown in many, if not
most, of our modern genera, were in existence at
that time, though our fossil record is highly incom-
plete. Bones of many birds not certainly distin-
guishable from those of living forms are found in the
early part of the Pleistocene.

28 THE MIGRATIONS OF BIRDS

Habits and reaction to environment in birds must
date back through this same long period of years, so
that what we now recognize as definite instincts
among them, which are merely reactions to the
usual stimuli of everyday life, must have had their
beginning back in the same remote periods. Birds
sought for food, fought for territory, and produced
their kind, were subject to seasonal changes, shifts
in environment, ecological successions among plants
and trees, and climatic variations, then as now. We
must consider the present migratory instinct as an
outcome of all the various complex circumstances
that have affected birds, and for its origin must look'
to remote ages. The actual migrations now found in
the northern hemisphere have been influenced pro-
foundly by the climatic changes of the Pleistocene,
but the cause of migratory flight goes so far back in
time that we may discuss it, but may not hope to
offer more than guess or supposition as to its actual
origin.

With this statement in mind it will be understood
that hypotheses advanced regarding the origin of
migration are merely attempts to explain it on the
basis of what may have happened, judging from the
observations of our limited human experience.
There can be no final proof of the validity of the
arguments. They stand as scientific guesses at what
is supposed to be the truth.

THEORIES OF MIGRATION 29

Let us now return to the hypotheses that have
been outlined. Objection may be raised to any of
them;, but it appears that an explanation of the phe-
nomena under discussion may be found in a com-
bination of the various forces suggested, working in
unison. The entire act of migration is so utterly
complex that no single factor may be ascribed as the
absolute cause. A logical explanation may, however,
be attempted if we hold that the origin of these
movements is multiple. It may be advanced as a
working hypothesis that migration has arisen from
movement induced by seasonal and climatic change
developed in certain species until it has become
hereditary instinct.

It will suffice to turn to everyday observations on
the habit of brief post-breeding wanderings of some
of our common birds to record what may have con-
stituted a beginning of migration. A pair of robins,
tufted titmice, or white-breasted nuthatches, select
a home site, prepare a nest, incubate eggs, and rear
a brood of young to maturity. During this period
foraging for food is confined to a limited space. As
the young grow, the surrounding area must be
scanned intensively to procure a sufficient supply of
food. When the fledglings leave the nest they may
linger for a time in the vicinity; but as the young
grow stronger, they begin to wander, at first for a
few yards, but gradually extend their area until it

30 THE MIGRATIONS OF BIRDS

may cover several miles. This shifting is often noted
at the time when the young are thrown on their own
resources, as the parents, wearying of importunate
calls for food, may harry their offspring and drive
them from the immediate vicinity, or may accom-
pany them to some nearby area where food for all is
easily procured. In part, the wandering that comes
at this period may be considered merely the expres-
sion of a restless instinct for exploration on the part
of creatures endowed with wonderful freedom of
movement, while in part it is necessity subservient
to a search for food.

The house wrens of my door-yard form ready
examples of the statement just made. They rear a
brood in a small bird-house and for several weeks
incessantly scan the shrubbery and herbage for food.
Spiders disappear from beneath porches and other
shelter, multitudes of aphids on the nasturtiums
melt away, and with tiny beetles, caterpillars, and
moths from grass and vines, go to feed a hungry,
growing family. When that family is safely on the
wing, the wrens may move to another locality, per-
haps only to a neighboring yard, perhaps farther,
where a less carefully explored territory is open to
them. At intervals the adults may return or may
linger to rear other broods, until the time arrives for
them to make their retreat to the south; but the
young usually disappear. This is movement in its

THEORIES OF MIGRATION 31

simplest phase, a matter often of yards, though it
may extend to greater distances.

In some forms of bird-life found in tropical regions
the succeeding step may be exemplified. Climatic
conditions there are quite uniform, divergence from
a level mean being found mainly in the amount of
precipitation that marks wet and dry seasons. In
careful observation over a limited area certain birds
may appear extremely rare for the greater part of a
year. Suddenly some forest tree will come into
flower or fruit, and immediately these same birds
flock, at times in abundance, to feed. They remain
common for a period and then disappear. These
shiftings among tropical forms are little understood.
Many ant-thrushes, flycatchers, and other small
brush-birds undoubtedly are wholly sedentary from
year to year; but many others are certainly erratic
in their occurrence. Years ago Dr. C. W. Richmond
found the beautiful snow-white cotinga known as the
holy-ghost bird of rare occurrence in a certain sec-
tion of Nicaragua for a period of several months.
Later with a slight change in the season it became
almost common. The little euphonias, brilliant gems
in the group of tanagers, are governed in their wan-
derings by the ripening seeds of mistletoes, which
form their sole food. Hummingbirds appear and dis-
appear with the flowering of vines, trees, or certain
epiphytes, their presence being governed wholly by
these phenomena.

32 THE MIGRATIONS OF BIRDS

The movement is most easily seen on tropical
islands, as in the West Indies, where certain large
pigeons shift from the uplands to the coastal plain,
or cross between neighboring islands. The white-
crowned pigeon flies between Porto Rico, Vieques,
and Culebra with the ripening of the beach plum
{Chrysobalanus icaco). The squamated pigeon, in
the same manner, crosses the stretch of water that
separates Desecheo and Mona from the main is-
lands adjacent. Whether the birds come from Porto
Rico or Santo Domingo is open to question. Flocks
of parrots wander extensively, but usually return to
certain quarters to roost each night. Thrushes, as in
temperate regions, follow ripening small fruits and
berries, and swifts and swallows shift from place to
place.

As yet we have only hints of the migratory move-
ments of birds in the heavily forested areas in the
Tropics, hints in many instances so indefinite that
many have been prone to consider tropical birds as
wholly sedentary. To date the bulk of observations
in such regions has been made by collectors who
remain for short periods at suitable points and then
pass on. Data that will lead to full knowledge of the
situation may be expected from prolonged studies at
some of the jungle laboratories — as, for example,
the one at Barro Colorado — established in recent
years.

THEORIES OF MIGRATION 3^

For further understanding of the problem of the
origin of migration let us turn to Australia, where
data are available through records furnished by an
increasing number of keenly observant naturalists.
This island continent, while it does not have the
extremes of climate found in the larger land masses
of the northern hemisphere, has sufficient extent
for a considerable difference between north and
south. The winter in the south, though marked by
lowered temperature, is not rigorously severe. Some
forms of birds are regularly migratory, but many
others may be termed only nomadic, as across broad
areas their presence depends upon rains. In some
sections, during periods of drought extending some-
times over several years, bird life practically dis-
appears. Rains come and turn the country once
more green, trees flower, and plants mature their
seeds. Flocks of parrots return to regions from
which they have long been absent; honey-eaters
appear in the eucalyptus; coots swarm in marshes
and swamps, and with ducks and other waterfowl
proceed to breed and rear their young. Proper con-
ditions may continue for several years, when these
birds will remain common. With the shifting of
rains to other sections the birds dependent upon
them follow, and desert the area that has given
them temporary sustenance.

Though this seems mere vagrancy, it is migration

34 THE MIGRATIONS OF BIRDS

of a kind, and needs only to become synchronized
with seasonal climatic change to assume the usual
rhythm of migration with which we are familiar in
the northern hemisphere, and which in Australia is
pursued regularly by a number of species, notably
swallows and cuckoos.

Migration may also be explained, in part, in
terms of what has recently been called "Territory in
Bird-life." During much of the year birds have no
other responsibilities than search for food, with rea-
sonable alertness to avoid death at the claws of pre-
dators. They may be social or solitary according to
habit, and may wander, or may remain sedentary.
Individuals of the same or different species may
range in reasonable proximity without undue bicker-
ing or quarrelling. With the approach of the breed-
ing season all this changes. Each male seeks an area
on his breeding-ground within which later will be
constructed his nest, which he guards closely against
encroachment. This is his particular and private
domain, within which he permits no prolonged in-
trusion by rival males of his own kind. In the case
of such gregarious species as the sooty tern, which
nests in tremendous colonies, this bit of territory
may be likened to the narrow quarters of the human
dweller in city squares, as it is merely sufficient to
permit each individual space to stand free from
actual physical contact with its neighbors; in the

THEORIES OF MIGRATION 35

tern its extent is governed by the reach of the
daggerlike bill that threatens all who crowd within
reach. The cardinal, the mocking-bird, the thrush,
meadowlark, or vireo, on the other hand, controls a
larger area, a tree or a group of trees, or a stretch of
thicket or grassland. Intruders of the same species
may come near, but may not tarry within the limits
of this tract without doing battle with the one who
has preempted it.

Let us now turn back some hundreds of thousands
of years, to a period in the Tertiary near the close of
the Pliocene. Geologists inform us that during the
Miocene and Pliocene, when the genera to which our
modern birds belong were attaining their develop-
ment, in North America and elsewhere in the north-
ern hemisphere climatic conditions, though perhaps
not especially warm, were more or less equable from
the Equator to within the boundary of the Arctic
Circle. Zonal bands increasing regularly in warmth
to the southward were not as strongly indicated as
at the present day, and in those epochs there would
not have been necessity for regular migration of the
birds then in existence, further than a retreat from
the far northern regions of extended night, when the
sun was south of the Equator, a seasonal shifting
with changing food-supply, or change with expand-
ing range among dominant species such as is found
in the Tropics to-day, or as is recorded in the conti-
nent of Australia.

2,6 THE MIGRATIONS OF BIRDS

In the next geological period, the Pleistocene or
Ice Age, huge sheets or glacial ice spread down from
the north across the land, advancing and retreating
during tens of thousands of years. Periods of glacial
invasion were followed for unknown reasons by
times of warmth, during which the ice retreated,
when forms that we now consider tropical and sub-
tropical were able to flourish in arctic regions. Fol-
lowing these, the ice again came south. The ad-
vance of the glacial front was slow, probably almost
imperceptible, so that the hand of cold crept slowly
over the land. Life, both plant and animal, shivered
in the unwonted chill. Some forms, possibly of wide
range and adaptability, retreated slightly; others
less pliant, unable to change from their accustomed
habit and range, perished and disappeared, leaving
no record except as their harder portions were en-
tombed and preserved beneath the ice. Congestion
in the steadily decreasing land area toward the
Equator crowded others, and through an increasing
competition brought about further extermination of
individuals and species.

Let us look now for a moment at conditions during
the first, or Wisconsin, stage when ice extended
across Canada and the northern United States as far
as New Jersey, Pennsylvania, and Illinois. With the
exception of a few islands of land left bare through
some freak or accident, ice covered a vast area where

THEORIES OF MIGRATION 37

to-day there are thousands of square miles of forest,
prairie, lake, and marsh. Practically all life had been
driven from this space, or, in some cases, had been ex-
terminated in it. Species that persisted had been
forced into the open region to the south of the glacial
front. Let us suppose now that after a period the ice,
through some change in conditions, begins to recede.
The shift is slow. Each year there are regressions in
which the ice king seeks to hold his own. Gradually,
however, new territory is released, to which vegeta-
tion slowly spreads, followed by insects and other
invertebrates, with which come the birds.

The dominant species, the one that is successful in
life, produces in greater abundance than the home
areas can maintain. The surplus individuals are
crowded away from the centre of production, and so
are forced out to other regions where conditions are
perhaps a little less to their liking at first, but to
which conditions they adapt themselves. These we
may suppose, in the Pleistocene and later, crowded
up into the spaces to the north following the re-
treating glaciers. Summer conditions were such that
they might breed. As winter approached they found
food scarce, and wandered. Their wandering was
restricted to three cardinal directions — east, west,
and south. If they went north, they perished. To
the south conditions were most favorable, so the
majority wandered southward. Seasonal change in

38 THE MIGRATIONS OF BIRDS

climate continued; and as centuries passed, mo-
mentary necessity became habit, and regular lines
of migration were established.

Where glacial action has not figured definitely, we
may look to other factors, which affect similar eco-
logic changes, to explain migratory movements
among birds. Extension of forest areas, or of plains,
or growth of marshes may permit extension among
avian species that seize on the new range as terri-
tory in which they may breed. After young are
reared, they may wander or withdraw — move-
ments which, with the passage of time, become
fixed and hereditary.

Such to me seem logical hypotheses, which afford
explanation of the wonderful phenomenon of bird
migration. It is admitted that they are not fully
satisfactory and that there are a number of points
that are not definitely covered. Explanation of these
cannot now be attempted. We must recognize that
Man's actual experience of these happenings, to
which we may look for assistance in considering
them, is wholly negligible, since the number of years
of our recorded study and observation do not repre-
sent a dot of perceptible size in the long procession
of centuries that have covered the development of
these things.

CHAPTER II
Nocturnal and Diurnal Migration

MIGRATORY flight among birds is performed
by day or by night, or occasionally during
either, according to the species concerned. As a
general rule, the smaller birds migrate by night and
the larger ones by day, or by day or night indiffer-
ently. Geese and ducks often fly in migrating flocks
by day, but also pass in numbers after dark, especi-
ally during great rushes of migration when their
movement is at its height. The calls of geese are a
common sound from the darkened skies above cities,
heard most often in autumn, when a sudden change
in weather is hastening their departure for the south.
In the city of Washington it is not unusual in March
to hear the barking calls of swans at night as these
great birds pass in their northward travels. Among
my vivid memories of residence and observation on
the broad marshes at the northern end of Great Salt
Lake in Utah are the flights of ducks that passed
overhead in the moonlight, or the multitudes, her-
alded by whistling wings, that came hurtling down
before dawn when severe weather in the north
started the flight from regions in Canada.

40 THE MIGRATIONS OF BIRDS

Loons and cranes migrate regularly by day, as
do pelicans, shore-birds, gulls, and hawks. The
stirring bugle calls of the sandhill crane herald the
approach of flocks before they are actually within
view, and continue faintly to reach the ear long after
the birds have passed beyond the range of vision.
Flights of large hawks in the Middle West, in which
hundreds passed in wheeling flocks across the sky,
were common sights twenty years ago, but now are
rare because of the gradual extermination of these
fine birds. Red-tailed, Swainson's, and rough-
legged hawks travel regularly in bands through the
western region of plains and prairies, and at times
the turkey vulture may be seen migrating, in con-
siderable flocks. In the Eastern States sharp-
shinned and Cooper's hawks fly by day, but, though
often common, seldom associate in actual bands.
Nighthawks regularly, and various blackbirds occa-
sionally, migrate by day.

The majority of small birds, the great hosts that
form the bulk of the migrant hordes that come to our
attention, travel by night. We wake in the morning
to find groves, hedges, and fields filled with a multi-
tude of warblers, flycatchers, and sparrows, which
on the following morning, may have largely dis-
appeared. Rails pursue the same secretive method
of travel as do cuckoos, migrant species of wood-
peckers, Old World warblers, vireos, and a host of

NOCTURNAL MIGRATION 41

others. The method followed by swifts and hum-
mingbirds is uncertain, but it is probable that the
former usually move by day. The ruby-throated
hummer has been seen flying by day from Point
Pelee, Ontario, across Lake Erie.

It has been stated that small birds migrate by
night to escape the enemies that otherwise might
destroy them. Bluebirds, jays, and blackbirds fly
regularly by day without fear of attack, as do king-
birds, fork-tailed flycatchers, and waxwings. It is
highly probable, however, that small species, as
wrens, chats, ground- or thicket-haunting warblers,
and the small flycatchers that inhabit thickets or
dense woodland, habitually living in concealment,
feel safer under the protecting cover of darkness
during their prolonged flights above the earth.

The procurement of food is perhaps a much more
weighty factor than timidity in regulating flight by
night. The stomach of a bird killed during the day
invariably contains remains of food, and often is full,
unless the bird is sick, or injured, or is in a situation
where food may not be obtained. Digestion is very
rapid, so that, to ensure a proper replacement of
the energy expended by the bird during its rapid
and sprightly movements, it is necessary that food
be secured at comparatively short intervals. In
studies of the food of starlings Kalmbach and
Gabrielson found that stomachs of a considerable

42 THE MIGRATIONS OF BIRDS

number taken between eight and ten in the evening,
when the birds had been at roost for three to five
hours, were almost entirely empty. Stomachs of
birds killed by striking obstructions during night
flight are nearly always empty, from which fact at
times has come the belief that the wanderers had
died of starvation. It appears, therefore, that diges-
tion empties the stomach completely when food is
not taken at short intervals. If tiny migrant way-
farers flew by day across the great stretches of land
and sea that they must necessarily compass in their
migrations, they would arrive at nightfall, tired, per-
haps almost exhausted, at some destination where
they would be unable to procure food until the fol-
lowing morning, as they are diurnal in habit. Such
circumstance might lead to unnecessary exhaustion
of their powers and so delay their further flights.
Or might, if coincident with unusual cold, or expo-
sure to heavy rains or snows, prove fatal, as in a
condition of reduced vigor sufficient bodily heat
and vital energy might not be available to enable
them to weather the unseasonable condition. On the
other hand, where migrational flights are pursued by
night, when the travellers pause at daybreak, they
may rest for a brief space and then may begin a
search for food. The entire day may be occupied
alternately in feeding and resting, and the travellers
may so recuperate that, if it is desired, further flight
may be begun at nightfall.

NOCTURNAL MIGRATION 43

Swallows, swifts, and nighthawks feed as they
travel. Hawks and vultures are so large and robust
that fasting for a day or so is no hardship. Ducks
feed regularly by night, especially when there is
moonlight, and so are not hampered by the time of
day of their arrival. Such birds as shore-birds and
gulls must be able to endure without food, or must
curtail their journey when sustenance is required.
We must suppose that the same is true of migrants
among strictly nocturnal species like the goat-
suckers, of which our whippoorwill and chuckwills-
widow, and the nightjars of the Old World, are
familiar examples.

Though among most small birds extensive flights
are made at night, the close observer soon becomes
aware of migration movement among them by day,
particularly during the period from the height to
near the close of migration. Flocks of warblers,
feeding seemingly without particular objective
through the tops of the trees, often pursue a regular
course in their search for food. Flights are made in
the direction in which the change of season is lead-
ing them. At times they travel hurriedly and must
cover an appreciable amount of territory during the
day. These movements may be noted with especial
ease at points where there are well-marked migra-
tion routes. At Point Pelee on Lake Erie, in the
autumn. Swales and Taverner have noted regular

44 THE MIGRATIONS OF BIRDS

passage along the sides of the point, which finally
terminated in many cases in a flight directly out
across the open lake. I have observed this same
action on islands in the West Indies where there
were established lines of flight, or in continental
river valleys that were regular routes of travel for
many birds.

Under proper conditions observations on noc-
turnal flights may be made without particular diffi-
culty. The sight of birds crossing the face of the
larger heavenly bodies has undoubtedly been fa-
miliar to astronomers since the days of Galileo and
the first telescopes, but seems to have come to the
notice of zoologists only in recent years. Tennant,
while studying the face of the sun at Roorkee in
1875, noted what he thought were kites soaring at a
great height.^ W. E. D. Scott, during casual inspec-
tion in an observatory at Princeton in October, 1880,
saw a considerable number of birds cross the moon
and was able even to identify a few of them. Addi-
tional notes were secured by Scott and J. A. Allen in
the spring of 188 1, and by F. M. Chapman in Sep-
tember, 1887, while observations were made in
greater detail by O. G. Libby in 1898,^ at Washburn
Observatory in the City of Madison, Wisconsin.
This author gives a record at considerable length of
studies made during the height of the autumn migra-

"■ Stray Feathers^ iii, 1875, P- 4i9' ^ ^"^> ^^99j PP- H^-U^.

NOCTURNAL MIGRATION 45

tion in September, and estimates that birds passed
the point of observation at the rate of approximately
9,000 per hour — an indication of the enormous
extent of the nocturnal movement.

Similar observations may be made by anyone at
the proper season by means of small telescopes or
powerful binoculars, though in my own experience
as a boy I found such instruments somewhat unsat-
isfactory, as the field of vision was so small that the
moving dots representing birds crossed the illumi-
nated area and disappeared with great rapidity. It
is possible to identify an occasional individual
among the birds that are detected; but efforts made
to estimate the height at which the birds are travel-
ling seem to me to yield highly uncertain results, as
there is no simple, definite method of determining
the actual distance between passing birds and the
point of observation in the brief space in which they
are on view.

Records of nocturnal flight are made easily by the
ear, as many birds call during these flights by night.
During the rush at the height of migration these
notes, coming constantly from the darkness, pro-
duce a profound effect upon the imagination. Calls
come from near and far, some of them easily recog-
nized, and some so distant or so mingled with others
that they are indistinct. At times there may be a
medley in which half a dozen species may join, or

46 THE MIGRATIONS OF BIRDS

again a band of some particular form may pass with
their cries coming from all points of the air, to the
exclusion of others. The impression given at times is
so vivid that instinctively one strains the eyes
against the darkness in a vain attempt to pick out
the migrants whose vibrant calls come from so near
at hand that the birds seem almost within reach.

Though migration flights at times are recorded
at lighthouses, and by means of call notes, steadily
all night long, usually the bulk of birds pass during
the earlier hours of the night and toward day-break
in the morning. From eight to twelve in the even-
ing seems to be the favorite period for nocturnal
flight, though on a number of occasions particularly
in autumn, I have noticed heavy migration between
four and six in the morning.

Altitudes at which Migrating Birds Travel

Actual evidence of the heights above the earth
sought by birds during their migrations is scanty,
and only since the development of the airplane have
definite altitudinal observations become available.
Early records have been based largely on inference,
or on calculations into which entered a wide margin
of estimate.

The older observers, holding firmly that most
normal migration took place at heights above 15,000
feet, attempted as a rule to justify their faith in these

NOCTURNAL MIGRATION 47

statements by a somewhat uncertain belief that
flying became easier as altitude was gained, and
increased in difficulty as the earth was neared. Ex-
perience of aviators, however, is directly opposed to
this theory, as it is found that with greater altitude
there is increasing difficulty in maintaining height
and speed. Though part of this difficulty may be
due to the changing mixture offered for combustion
in the motor, more of it unquestionably comes from
the difference in buoyancy as the air becomes more
and more rarefied. Birds are not afflicted with the
engine troubles that beset humans who invade the
air, but must nevertheless feel keenly the lack of
buoyancy of the upper reaches. Though less effec-
tive in the case of broad-winged hawks, vultures,
pelicans, and cranes, whose great pinions afford a
large supporting surface compared to the weight of
the body, we must believe that the difference in-
dicated would operate more heavily in smaller
migrants, who are under necessity of keeping their
smaller, shorter wings in constant rapid motion to
hold a proper altitude even when flying near the
earth.

Observations on the altitudes at which birds fly
have been summarized recently by Colonel R.
Meinertzhagen,^ who gives a considerable number of
records based on the experiences of airpilots. His

I Ibis, 1920, pp. 920-936.

48 THE MIGRATIONS OF BIRDS

findings^ in brief, are that it is exceptional in flying
to meet with birds above an altitude of 5,000 feet,
and that the bulk of migration is performed below a
height of 3,000 feet from the earth. Though most of
the observations that he cites were made during the
day, he holds with reason that there is no evident
cause for considering that nocturnal migrants pass
at a higher plane than those observed by day. Since
the observations that he cites were made by pilots
who, during several years of war, had the air across
broad areas in the Palaearctic region under constant
close surveillance, we must accept them as conclu-
sive. In several hundred records by airplane it ap-
pears that there were only 32 observations of birds
above 5,000 feet, and only seven above 8,000 feet.
Meinertzhagen considers that ordinarily birds prefer
to descend below cloud level, though this is not uni-
versally true. On nights of fog or rain birds pass
very near the earth, and it is then that we may ob-
tain some idea of the vast hordes of migrants that
fill the air, as their notes and calls come drifting
down from the sky.

Day migrants among shore-birds may pass at con-
siderable altitudes, as it is common experience in
shooting, particularly in arid regions where suitable
feeding grounds are widely separated, to have
yellowlegs or black-bellied plover come swiftly
down to the decoys from heights at which the eye

NOCTURNAL MIGRATION 49

did not perceive them. Aviators have recorded such
birds at 10,000 and 12,000 feet. Pelicans, cranes,
ducks, and geese often pass at 3,000 to 8,000 feet in
travelling from one feeding ground to another, and
when crossing mountain chains mayfly at enormous
heights. Donald notes that in the Himalayas, at
14,000 feet above sea-level, he observed storks and
cranes flying to the northeast at the end of May,
when they were so high that they could be seen only
through glasses. Meinertzhagen considers that, if
these birds were beyond unaided vision, they must
have been at least 6,000 feet above the earth, placing
them at an actual altitude of 20,000 feet above the
mean level of the sea.

Captain C. Ingram ^ has assembled other observa-
tions by aviators, and has obtained results fully in
agreement with those given above. It is of interest
to examine the greatest altitudinal records that he
gives. Lapwings and ducks were noted up to 8,500
feet, though rarely seen above 6,000 feet. Geese
were seen at 9,000 feet, and sandpipers of unknown
species at 10,000 and 12,000 feet, above the battle-
front in France. Small birds with undulating flight
were recorded once at 10,000 feet. These, however,
were such unusual occurrences that the aviators
making the records took special note of them. Dr.
A. F. R. Wollaston, when on the Mount Everest

I Ibis, 1 91 9, pp. 321-325.

50 THE MIGRATIONS OF BIRDS

Expedition in 1921, recorded a lammergeier at
24,000 or 25,000 feet, and distinguished passing god-
wits and curlews at 20,000 feet.' In this instance,
however, the birds were flying above elevated land
masses, and were forced upward to cross the moun-
tains. Finally, it is recorded that an observer mak-
ing photographic observations of the sun at Dehra
Dun in India obtained a photograph of geese which,
it was estimated, were flying at an altitude of 29,000
feet.=*

The observations above are given to illustrate
extremes, and to indicate that birds may occasion-
ally fly at great heights. That there is no apparent
advantage in altitude is indicated by the fact that
comparatively few attempt it.

I have observed autumn flights of sandpipers
crossing the Gulf of Alaska, south of Kodiak Island
and the Kenai Peninsula, at heights of not more than
500 feet above the sea, with many at only a few
yards above the waves. In fact, a Peale*s falcon re-
mained with our ship for a day, perching on a mast-
head and flying out at intervals to seize some poor
sandpiper that came swinging up to examine our
vessel. Other observations certify to these results,
since where migrants are heard calling at night,
if directly overhead, many are within easy range

' Country Life, March 25, 1922, p. 419.
== the Field, Dec. 18, 1920, p. 876.

NOCTURNAL MIGRATION 51

of the ear. Some in fact seem barely above the
trees. Where small birds have been seen flying by
day, as at Point Pelee, Ontario, they are usually at
very moderate heights, and numerous recorders of
migrants crossing stretches of open water note them
frequently as passing barely above the waves. Re-
cords from lighthouses also indicate birds flying at
comparatively low levels, as do notes made on
diurnal movements among small birds at islands.
Eagle Clarke, in observations at the Kentish Knock
lightship, in the North Sea off the mouth of the
River Thames, noted small birds of various sorts
passing barely above the crests of the waves — a
sort of flight that prevailed even when there was fog
or mist, when it would have seemed advantageous
to attempt to rise to an altitude where the air was
clear.

Weather conditions must affect the heights at
which birds travel, as on clear warm days, when
warmed air is rising from broad areas, — such days
for example as birds of powerful flight use in soaring,
— it would be easy to fly at high altitudes, while in
periods when the atmosphere is dead and lifeless,
high flight would be more difficult. Since rising air
currents ordinarily prevail only during the day, and
slacken or disappear by night, we may see in this an
indication that birds do not travel at excessive alti-
tudes after nightfall.

52 THE MIGRATIONS OF BIRDS

Ingram ^ has noted that normally the velocity of
the wind increases as one rises above the earth, so
that it may be doubled in strength at 1,500 feet.
Beyond this the amount of increase is lessened. In
his experience (apparently mainly in France) an
east wind attained its maximum strength at 3,000
feet, while winds from other quarters of the compass
may increase up to 30,000 feet. In ascending, the
directions of the winds also vary, so that they may
be reversed within a few hundred feet of altitude.
Both of the factors mentioned are of great impor-
tance in considering bird migration.

We may conclude from the evidence that has been
presented that the bulk of migration passes below
3,000 feet, and that as a rule only birds of strong
flight travel at greater heights unless weather condi-
tions may, for brief periods, favor greater altitudes.

Weather and Migration

Cooke has well observed that weather conditions
have little to do with the migrations of birds, except
to permit them to travel or to hold them back, as the
case may be. Parula warblers or redstarts wintering
in the West Indies, or Old World warblers or wag-
tails spending the cold season in central Africa,
notice no difference in temperature or climatic con-
ditions between November and April, yet in the

^ 7^/^,1919, p. 323.

NOCTURNAL MIGRATION , ^3

latter month they regularly move north toward the
summer home. Though we may theorize as to the
actual origin of migration, the annual movements of
migratory birds are now a part of the life-cycle of
the individual, and as such occur at the regularly
appointed time, actuated by physiological condi-
tions. The spring migration especially has its in-
ception and course distinctly connected with the
necessity for reproduction. Food is as abundant in
the winter home in spring as through the winter
months, so there is no necessity for movement to
search for it. Winter is a resting period, during
which the bird has no cares save to avoid enemies
and search for food. With the approach of spring
the reproductive impulse awakens, and the individ-
ual is irresistibly driven to initiate a journey that
ends in its summer home.

We?ther makes only this difference, that the life-
cycle has been so adjusted, and the migrations so
synchronized, that they agree with major phe-
nomena of weather and climate through the year.
Some species find that cold means little to them, so
that their northern limit in winter is in regions
where the climate is severe. This is true with juncos
and tree sparrows, and a number of other birds in the
United States, and with many small birds in north-
ern Europe and Asia. Certain waterbirds are hardy
and are restricted in winter range only by the line of

54 THE MIGRATIONS OF BIRDS

ice. Thousands of canvasbacks, bluebills, and other
ducks remain on the Potomac River in winter, even
though a large part of the channel is frozen. Mal-
lards and pintails in the Missouri River drainage
move north and south regularly during winter with
fluctuation in the southern limit of ice, and in spring
press northward with every thaw, retreating again
if need arise because of freezing weather.

Birds that are not accustomed to cold respond
variously to it, some seeming wholly indifferent so
long as food is available, unless subjected to undue
exposure. This is true even in certain tropical
species that normally never encounter cold, as when
transported to another climate some do not seem
particularly affected. The red blue and yellow
macaw {Ara macao)^ native in tropical America, has
lived in outdoor flight cages in the National Zoologi-
cal Park at Washington during severe winters. Dur-
ing the winter of 1924-25 a great white heron from
southern Florida was kept in an outdoor cage, shel-
tered from northerly and westerly winds but with-
out artificial heat, and seemed as oblivious of cold as
a great blue heron that lived as its neighbor. Even
the snowy heron and American egret in a wild state
are not so sensitive to cold as we usually imagine,
since I have seen the former flying in snowstorms in
Utah, and the latter penetrates regularly to Pata-
gonia, where the summers are anything but warm.

NOCTURNAL MIGRATION 55

Other species, however, have no reaction against
cold. The blue and yellow macaw {Ara ararauna)
cannot withstand a fall in temperature, and I have
a captive blue-headed parrot {Pionus menstruus)
from Bolivia, that is sensitive to a degree, and com-
plains of the shghtest degree of cold.

Wind is as much a deterrent to migration as rain
or snow, as head winds greatly increase the labor
of flight and, if at all strong, cut down the speed
at which migrants are able to travel. Similarly,
strong winds blowing in the direction in which the
birds are travelling are equally bad, since they
interfere seriously with balance, and disarrange
feathers, thus hindering flight. Moderate cross,
quartering, or light winds from other directions,
seem to off'er the best air-movement conditions.

Cooke has indicated that migration among birds
is so adjusted to mean weather conditions that each
species moves north in spring at a time when the
average weather encountered is not unsupportable.
Hardy forms move early, unafraid to brave the
blasts of retreating winter. More delicate ones
come later, when there is less danger of encountering
prolonged cold spells. Occasionally, as in the
Canada goose, it is found that the advance in migra-
tion coincides with advance of certain isothermal
lines. The goose keeps closely abreast of the line of
35 degrees average temperature, and moves north as

56 THE MIGRATIONS OF BIRDS

this line advances. The majority of species allow
spring to forge ahead, and then, travelling rapidly,
overtake it, or, in some cases, outstrip it. Hardy
forms among our smaller birds press northward with
the first indication of spring, so that robins appear
as soon as the ground is bare, and blackbirds when
the marshes open. Recurrent cold means a certain
amount of hardship, but has no other effect unless
too prolonged. Delicate species, of necessity, ad-
vance more slowly, as they must wait until spring
weather is settled.

The northward flight of migrants in general is
initiated when wind and temperature are favorable.
If a sudden storm arises, the weaker migrants, if
over land, must descend to await better conditions.
If over water, they may be lost. Storms coming late
in spring often overtake the height of the small-bird
migration, and may entail much suffering, destitu-
tion, and loss of life. Yet such conditions are so
regularly met that most species pass through them
with discomfort but without particular danger, ex-
cept when they are unwontedly severe. On many
occasions snows during the first week in May greet
warblers and flycatchers in the northern states, and
for a day or two these small creatures may be seen
hopping about in unusual situations where there
may be a chance for food or shelter. Though many
may perish, usually the weather moderates before

NOCTURNAL MIGRATION 57

there Is great mortality. Such storms are more
dangerous in their effect on food-supply than in the
cold that they bring, as most species of birds can
endure cold if they are properly fed.

With some species the return southward in au-
tumn comes long before there is any cold. Yellow
warblers, Baltimore orioles, kingbirds, the Euro-
pean cuckoo, and many shore-birds, in both eastern
and western hemispheres, crowd south before the
close of summer, when there is no meteorological
change to warrant it. Others linger until cold nights
and frosts warn of approaching extremes, and then
move south rapidly. Some linger until cold storms
actually strike their northern ranges.

Movement among these later migrants is noticed
especially in areas immediately south of the belt
where cold winters are prevalent. In southeastern
Kansas, at the northern edge of the Austro-riparian
life-zone, during November and December new
arrivals among migrant sparrows, thrushes, and
blackbirds are noted with every storm reported in
the north, indicating that many birds linger in the
north to the last possible moment. Similarly, freez-
ing weather far north is frequently responsible for
great flights of ducks or of Wilson's snipe to southern
areas, where the birds arrive in abundance before
the press of severe conditions in regions to the
northward.

58 THE MIGRATIONS OF BIRDS

Speed of Flight in Birds

The speed that birds regularly make in flight, a
subject of considerable speculation and theory in the
past, but one concerning which there has been little
definite information available until recent years, is a
matter of pertinent inquiry when considering
migration.

Early observers had few definite data at hand
regarding speed, but were conservative in their
estimates. Gatke, however, in his studies on Heligo-
land, became obsessed with the idea that most birds
performed the greater part of their migration flight
in a single night, and with this as a basis, deduced
extraordinary rates of travel, which, unfortunately,
have been widely quoted and copied. Through in-
genious but misleading estimates he rates the mi-
gratory flight of the northern blue-throat, a thrush
smaller than the American hermit thrush, at i8o to
240 miles per hour, the hooded crow at 108 miles,
the golden plover at 212 miles, and plovers, curlews,
and godwits in general at about 4 miles per minute,
or 240 miles per hour ! These tremendous speeds he
believed possible through flight at great altitudes, up
to 40,000 feet above the earth, where he supposed
that the rarefied air offered less resistance! His
statements are exceeded by a correspondent of "The
Field" who considers that the "cave-swallow" of

NOCTURNAL MIGRATION 59

Ceylon (probably a species of swift) is the fastest-
flying bird since he states that the noise made by
flocks of these birds may be heard as they pass, but
that the birds themselves move so rapidly that they
may not be seen ! ^ These statements, it is hardly
necessary to say, are wholly erroneous.

During the past ten years reliable data on the
subject of flight have accumulated slowly. In 191 6 I
published records secured by timing the flight of a
number of birds by means of the speedometer of an
automobile, and in such diverse forms as herons,
hawks, horned larks, ravens, and shrikes found the
rate to vary from 22 to 28 miles per hour. Flight in
all these cases was normal and unhurried. Records
of another observer, H. B. Wood,=' show speeds of
only 10 to 17 miles per hour for Arkansas kingbirds
and scissor-tailed flycatchers. Hugh Gladstone cites
other records 2 in which it was found that the willow-
warbler travelled at 23 J miles per hour, the pied wag-
tail at 25, the European blackbird over 22, missel
thrush 23, and the cuckoo 23 miles per hour.

Passing over scattered notes that verify the
figures just cited we come to a far more comprehen-
sive study by Col. R. Meinertzhagen in the "Ibis'*

^ Quoted by Gladstone, Record Bags and Shooting Records (1922),
p. 189.

» Bird-Lore, 1923, p. 121.

3 Record Bags and Shooting Records (1922), p. 185.

6o THE MIGRATIONS OF BIRDS

for 1 921 (pages 228-238), based on observations by
means of theodolites designed to estimate the speed
of airplanes at anti-aircraft stations, by stop
watches along measured courses, and by readings
from travelling airplanes. From these notes the fol-
lowing records of speed in flight may be cited.

Miles per hour

Members of the crow family (Corvidae) 31 to 45

Smaller perching birds (as larks, pipits, buntings) . 20 to 37

Starlings 38 to 49

Geese 42 to 55

Ducks 44 to 59

Falcons 40 to 48

Sand Grouse 43 to 47

The greatest speed recorded definitely was that of
swifts (apparently the common swift of Eurasia)
recorded from an airplane in Mesopotamia. These
passed the observing plane and circled about it
easily when it was travelling at 68 miles per hour.
This and other observations seem to give approxi-
mately 70 miles per hour as the normal rate at
which some swifts feed and travel, a speed that can
be accelerated to fully 100 miles per hour for pleas-
ure, or in case necessity arises to escape from dan-
ger. E. C. Stuart-Baker ^ in India timed two species
of swifts [Chaetura nudipes and C. cochinchinensis)
with stop watches over a two-mile course and found
that they were able to cover this distance in from 36

^ British Birds i xvi, 1922, p. 31.

NOCTURNAL MIGRATION 6i

to 42 seconds, or at the rate of 17 1.4 to 200 miles per
hour. These jfigures may offer some solace to those
who, like myself, have expended considerable am-
munition in collecting specimens of the white-
throated and other swifts as they circled in the wind
over high ridges or mountain headlands.

Most birds when frightened are capable of in-
creasing their speed above the figures indicated, to
enable them to escape momentary perils, • — per-
haps for short distances to double the normal rates,
— but cannot long maintain such exaggerated
efforts. It is certain that migrations are performed
at the usual rate of normal flight, as by pursuing
this steady course birds conserve their strength and
avoid the fatigue and exhaustion that undue speed
would entail. Eagle Clarke has recorded that mi-
grants passing lightships flew without hurry or
strain to attain speed, though their flight was at-
tended by businesslike method, without delay.

If we consider ten hours as a fair stretch of flight
over land, the speeds cited would carry crows 310 to
450 miles in a ten-hour day, the smaller birds from
200 to 370 miles, ducks from 440 to 590 miles, and
geese from 420 to 550 miles — considerable dis-
tances when direct airlines are considered, that
would cover the ordinary migration route from
Canada or the northern states south to the Gulf
Coast, Central America, the West Indies, or even

62 THE MIGRATIONS OF BIRDS

northern South America, in a relatively short time.
It is highly probable that most migrations are per-
formed in a leisurely manner, and that after a flight
of a few hours, the bird pauses to feed and rest for
one or several days if it finds itself in congenial sur-
roundings.

The Sense of Direction in Birds

No less wonderful than the fact of migration itself
is the regularity and system with which birds pursue
journeys that in many cases cover thousands of
miles across the earth's surface. Let us consider for
a moment the instance of a white-throated sparrow
(no. 38160), banded by Mr. S. P. Baldwin on an
estate near Thomasville, Georgia, on March 5, 191 6.
As the white-throat nests in the northern portion of
eastern North America, from Massachusetts, New
York, Michigan, Minnesota, and northeastern
Wyoming, north to Great Bear Lake and Labrador,
this individual was in its winter range when cap-
tured in Georgia. Subsequently this identical bird,
identified by its numbered band, was trapped on
March 7 and 19, 1917, on several occasions from
February 25 to March 22, 1920, and on March 27,
1 92 1, in each case within one hundred yards of the
spot where it was first secured. Since this was its
winter home, we must assume that on each of the
years from 191 6 to 1921 this bird had migrated

NOCTURNAL MIGRATION 6;^

north to breed, and had subsequently returned to
spend the winter in one particular area of thicket,
brush-pile, and open glade in southern Georgia.
Such precision of movement impresses one as truly
remarkable.

The regularity with which birds move, appear,
and disappear during migration has naturally oc-
casioned much comment, and has resulted in various
theories that attempt to explain it. Thus a peculiar
magnetic sense whereby birds are attracted by the
magnetic pole; a special nasal sense that enables
identification of air-currents and other phenomena;
the direction of regular winds; the angle or direction
of the sun, and of light rays; a reflex attraction,
masked by one author under the caption of tropism;
memory of routes once traversed; telepathy; direct
perception of the point toward which the journey is
directed; and hereditary memory of the route to be
traversed, all have been put forward as hypotheses
to explain the facility with which birds reach distant
points. All have had their champions, and with all
this divergence of opinion, it must be admitted that
the matter is as yet far from definitely settled.

Mr. A. H. Clark ^ has presented a clear statement
of what he considers to be the method of pathfinding
employed by the golden plover in its journey south
to South America. This he attributes to a course

» Juk, 1905, pp. 134-140.

64 THE MIGRATIONS OF BIRDS

laid in accordance with prevailing winds, as he con-
siders, from observations made in the West Indies,
that the birds tend to travel across the wind, which
thus shapes their line of direction. On this basis he
considers that, on leaving the coast from Labrador
south to Nova Scotia, the birds travel southeast
across prevailing southwesterly winds. This would
change to a southwest course when the northeast
trades were encountered at a point east of the
Bahamas, and so carry the birds to the northern
coast of South America.

Some have considered that birds are sufficiently
observant to be able to guide a course by the sun by
day, or by the moon and the stars by night, a propo-
sition with certain merits, that has been set forth
recently by Mr. William Brewster in his posthumous
work on the Birds of the Lake Umbagog region of
Maine.^ Mr. Brewster considers it possible that
birds make note of the heavenly bodies and direct
their courses accordingly. This may be wholly
probable in some instances, but fails as a final, com-
plete explanation when we consider the regular
flights that are carried on during cloudy or rainy
weather, when the sun or the stars are obscured,
or the apparently marvellous way in which some
species travel without hesitation through dense fogs.
Though many become lost at such times, particu-

^ Bull. Mus. Comp. Zobl. (June, 1924), Ixvi, 32, 2^.

NOCTURNAL MIGRATION 65

larly where puzzled by lights, others move without
difficulty. Mr. Brewster cites the ease with which
common terns return to their nesting-ground on
Muskegat Island through the densest fog, and such
phenomena are of common occurrence with the auk-
lets and murres of Alaskan waters, as these birds
drive directly for their island rookeries, without any
apparent hesitation, through the thickest weather
imaginable. In fact, the courses that they take are
often serviceable to sailors bewildered by fogs as
they indicate the direction of land.

As a basis for consideration of the problem of how
birds find their way, it will be profitable first to con-
sider the case of the homing pigeon, and the little
that is definitely known of the method of its homing
activity aside from the fact that it is capable of re-
turning to its cote without great loss of time from
distances up to 1,000 miles. Those interested in the
sport of racing pigeons recognize individual ability
among their birds, and develop strains rated high
for the number of birds produced that are able to
compete successfully in distance flights. Birds that
are to be used in races each year are put through a
regular course of training that involves flights, first
of a few miles, and then others of increasingly
greater distance. One fancier thus regularly flew his
birds over courses of 9, 18, ;^;^, 45 and 66 miles, after
which the distance was increased to 100, 200, 400,

66 THE MIGRATIONS OF BIRDS

60O5 and finally, in some instances, to 1,000 miles, all
in more or less the same direction. The percentage
of returns and the short periods required for the
journey in case of some of the longer flights are
truly marvellous.

Two factors seem to enter, first, some peculiar
attribute that for lack of a better name we may
term a sense of direction, which drives the flier on
the proper course, and, second, a memory of place
that enables the pigeon to recognize landmarks in
the vicinity of its home when it has arrived.

It must be admitted that, though recognition of
landmarks that guide the bird on its journey are of
assistance in travelling air-lanes crossed on previous
occasions, this cannot wholly explain the ability that
enables a bird successfully to drive across unfamihar
areas a hundred, or several hundred, miles in extent.
In most instances there can be no dependence upon
sight recognition of distant landmarks, as many ex-
periments, in fact the main ones that have been re-
ported in this country, have been carried out in
regions of low relief, where landmarks would not be
visible beyond 25 to 50 miles even from a point a
thousand feet or more above the earth. Further-
more, experiment has shown that in good strains of
homing pigeons it is possible for a fair proportion of
young birds to return to their homes from a distance
of 15 to 20 miles, when they have not had the ad-

NOCTURNAL MIGRATION 67

vantage of special training for racing, and even
where their previous flights have been limited to
short distances. A faculty of perceptive orientation,
in which the bird makes conscious or unconscious
note of the direction travelled, may however figure,
as in experiments by Hodge some years ago, pigeons
carried in an open cage to a point some distance
from their cote started for home without great de-
lay, while others whose cage during transit was cov-
ered closely by a black shawl seemed bewildered for
a time.

The case of the migratory small bird is the more
complex since it performs much of its migratory
flight at night, indifferently in the light or dark of
the moon, at times under weather conditions when
landmarks cannot be visible for any considerable
distance. Also many of these flights carry the voy-
agers across broad stretches of open sea where there
are no lines of guidance of any description, if we
except certain steady winds that prevail in some
latitudes, or the possibility of following the lines of
ocean currents.

Some have considered that birds that have pre-
viously made the southward journey serve as guides
for the young and inexperienced, which may be true
in a few cases but cannot be accepted as the full and
final explanation, since frequently old and young
birds migrate at different times. Adult cuckoos are

68 THE MIGRATIONS OF BIRDS

said to leave England several weeks before the
young essay migratory flight. The young cowbird
of the United States, reared by a foster-parent,
flocks with other young of its kind when grown, and
in many instances can hardly have adult guidance
in migration. Nor can we fall back upon guidance
through leadership of experienced birds of other
species, since all birds do not follow the same route.
It is difficult to explain under the guise of leadership
the diff'erence in line of flight between the Baird's
sparrow, which passes to the southwest from the
prairies of Dakota, and the Leconte's and Nelson's
sparrows, which fly directly south or southeast from
the same point. Under these circumstances one
must think that under leadership of other forms
there would be constant sad confusion among young
birds, which does not happen.

The movements of many seabirds are still more in
point. Two species of albatross, the wedge-tailed
shearwater, and the white-breasted petrel, nest on
certain islands in the Hawaiian Bird Reservation.
During part of the year these birds travel to distant
points on the open sea, yet return to the same low
sand islands each year to nest. The reflection of the
green water inside the coral reefs, thrown on the sky,
perceptible to those accustomed to it when the
atolls are below the line of vision, might explain the
return to islands within 20 or 30 miles, but will not

NOCTURNAL MIGRATION 69

serve as an explanation of the instinct that guides
these birds in their return to the general region from
a distance of hundreds of miles.

Still more remarkable is the case of the Mother
Carey's chicken, and other petrels and shearwaters
that nest near or in Antarctic regions, and after the
breeding season spread northward until they cross
the Equator. As these birds may spend most of the
resting cycle between periods of reproduction out of
sight of land, no one can allege that any recognition
of a route once traversed guides them on their re-
turn to their nesting grounds.

Penguins, birds with wings developed as paddles
that have entirely lost the power of flight, nest on
various islands, mainly in Antarctic regions. Some
species at least perform wandering migrations which
carry them for considerable distances across open
seas during seasons when they are not breeding. As
the birds have not been thoroughly studied these
movements are not well understood, so that much
remains to be learned of the distances that they
wander. It is known that the Magellanic penguin,
which breeds on islands in the Straits of Magellan
and elsewhere in the south, comes north regularly in
winter to the coasts of the Province of Buenos Aires
and eastern Uruguay, and even to Rio Grande do
Sul in Southern Brazil. I have seen dead bodies of
many which had perished from some cause, cast on

70 THE MIGRATIONS OF BIRDS

the beach at La Paloma in eastern Uruguay. The
regress of these wandering individuals to their
proper breeding ground can hardly be attributed to
any use of landmarks, since they swim at sea. Yet
they return regularly to their homes. At the Falk-
land Islands penguins, though present throughout
the year, come in abundance for the breeding season.
The return of these voyagers seems wholly mysteri-
ous unless we assume that they have some instinct of
direction to guide them.

As further instances of the homing habit we may
cite the case of the frigate-bird, which in the Tua-
motu, Gilbert, and Marshall Islands, and probably
elsewhere in the tropical Pacific, has been utilized by
natives as a carrier of messages between islands far
distant from one another as regularly as pigeons were
utilized for a similar purpose in the Middle Ages, in
Persia, Serbia, and Egypt. In fact, the frigate-bird
may be termed the carrier pigeon of the Pacific. The
great birds are reared from the nest, tamed, and
accustomed to certain perches. Carried to other
islands, they are released with messages which in a
few hours they carry to their proper home. Mr.
W. G. Anderson of Honolulu, tells me that formerly
he tamed frigate-birds on Fanning Island near the
Equator, and that when he crossed to Washington
Island, eighty miles distant, he regularly took one of
these birds and released it on his arrival with a mes-

NOCTURNAL MIGRATION 71

sage which it carried to his family on Fanning, out of
sight below the horizon.

Certain experiments in the homing instinct made
by Dr. J. B. Watson on noddy and sooty terns at
the Dry Tortugas Islands, off the southwest coast of
Florida, are highly pertinent in this connection. It
may be noted by way of introduction that these two
terns are tropical species that here occupy their
most northern breeding point in these seas. They
come to these islands from the south, and are not
known to wander any appreciable distance beyond
them to the north.

In one case twelve sooty and twelve noddy terns
captured on the Tortugas, and marked to enable
subsequent identification, were conveyed on a ship
en route to Galveston, and released at distances
varying from 400 to 800 miles from their nesting
colony. Thirteen of these birds returned to their
nests on the Tortugas, three of them from the great-
est distance mentioned. These experiments differ
from the observations given for homing pigeons, and
it is concluded that these two species of terns may
return from a distance of 1,000 miles to their nesting
site, over an open sea that is supposed to be wholly
unfamiliar to them. Watson is unwilling to hazard
a statement as to the actual cause of this homing
ability, but it may appear that it comes from what
may be termed a sense of direction. It is significant

72 THE MIGRATIONS OF BIRDS

that, though these birds were kept below decks,
where they had no opportunity to orient themselves,
on release they started flight to the east, in the
proper direction to carry them toward their home.
If we are willing to attribute a sense of direction
to some mammals, including man in certain in-
stances, I see no reason why we should deny its de-
velopment in a high degree in migratory birds. Most
of us are familiar with incidents of homing in domes-
tic cats and dogs, and may apply the same principle
to birds. Certainly an instinct for direction should
excite no more astonishment than the instinct for
nest-building or the care and rearing of young,
found among all birds, or the ability to swim and dive
inherent in young grebes, ducks, and sandpipers,
when they have burst the shell and are strong
enough to move. A young great blue heron that I
reared from a tiny chick grew up in a laboratory and
its vicinity wholly removed from the influence of
others of its species. The fact that, when nearly
grown, it evinced an instinctive interest in fish, and
for hours at a time remained motionless watching
the movements of chubs swimming below a bridge,
seems more remarkable to me than the fact that
it ultimately left me and wandered as do other
herons in autumn. The entire problem of orienta-
tion is one that may be cleared eventually by experi-
ment, but up to date has no lucid explanation.

CHAPTER III
Regularity of Migration

THE regularity of travel when birds are on mi-
gration constitutes one of the most interesting
facts in connection with this phenomenon and is one
familiar to all ornithologists. Through years of ob-
servation average dates of spring arrival and autumn
departure have been estabHshed for many localities,
and birds come and go with surprising regularity on
their appointed dates. Arrival in spring is particu-
larly punctual with the majority, and unusual is the
season when the first of the travellers fail to put in
their appearance within a few days of the average
date. Observations on dates of migration over a
considerable period of years are now available for
the United States and Canada, and similar data
have been recorded abundantly for western Europe.
At Washington, D. C, the barn swallow, on the
average, arrives April 12, the least flycatcher May 2,
the chipping sparrow March 22, and the house wren
April 18. On or near these dates one is always sure
to find them. Individuals which breed about our
homes, which arrive often with the bulk of the flight
following a few days after the earliest arrivals, come

74 THE MIGRATIONS OF BIRDS

with particular promptness on their appointed days.
Severe indeed is the weather that delays them for
any length of time.

Departure for the south in autumn is prompt, but
has greater range of variation, particularly in middle
latitudes, as prolonged mild weather may induce
birds to remain beyond their custom. Many late
fall records are based on individuals that have been
injured, have not moulted properly, or for other simi-
lar reason have delayed their departure. Many of
these are unable to migrate, and may linger along
until winter, or may possibly endure through the
cold weather. Ducks with broken wings, or other
injuries from the hunting season, often winter where
they can find open water, and instances of winter
occurrence of unusual birds are frequently recorded.
Catbirds, gnatcatchers, and tanagers have all been
found in the north in midwinter, and in December,
when the ground was covered with snow, the Cape
May warbler has come to the window-sills of the
National Museum. The red-headed woodpecker is a
bird that may or may not retire southward, appar-
ently more or less through whim. When it remains
to winter in the north, it does so when acorns are
abundant; on other years, when mast is equally
available, it retires southward.

As a general rule, among small birds the seed-
eaters compose the early migrants in spring as they

REGULARITY OF MIGRATION 75

may subsist on seeds from the previous season. In-
sect-feeders of necessity come later, when the
weather has moderated to permit the development
of plant growth that may shelter and feed insects.
In autumn the process is reversed, as the insect-
feeders leave for the south early and others linger.
The phoebe is one insect-eater that arrives early in
spring, but usually its arrival comes shortly after
swarms of hardy stone-flies begin to emerge from
the larval state in which they have lived through the
winter beneath waters of streams, and fly about, or
gather on shrubs, trees, and stones near the water,
where they furnish a food-supply. Some other
birds, as the myrtle warbler, may turn to a vege-
tarian diet of dried berries, and so eke out the insect
food that they take in summer. A few, as the brown
creeper and golden-crowned kinglet, have specialized
methods of search for spiders and insects in a state
of hibernation. The Carolina wren is a strictly resi-
dent form that feeds mainly on animal matter,
which it secures in winter by search under fallen
leaves and other vegetation, and in crevices about
logs, sticks and stones. Cold seems to have little
effect upon it; but when heavy snows come and re-
main for several weeks, these wrens are in hard
straits and many are killed. Those that survive may
be seen searching the eaves of buildings, curls of
birch bark, or drift left by heavy floods in the limbs

76 THE MIGRATIONS OF BIRDS

of trees, for what food they may find. Near the
northern limit of their range deep snows periodically
reduce them almost to extinction, yet they do not
attempt a southward flight to escape.

Abundance of birds during migration is also a
point of considerable interest. Observers record two
distinct stages in the movements of migratory birds
on their return north in spring, the date of first ar-
rival, when possibly a single individual may be seen
in some particularly favored haunt, and the date
when the species becomes common, which represents
a period when seasonal conditions become generally
favorable. Some birds arrive in numbers when first
noted, but usually the date of bulk arrival is deferred
for a few days or a week, or, rarely, for as long as a
month after the first have been seen. With birds
that do not nest at the point of observation the
period of bulk arrival is followed by a time during
which the species is seen regularly; and then sud-
denly the majority disappear and only stragglers
may be found until finally the last of these are gone.
Counting early and late stragglers, the migration
thus may extend over a period of two, or even three
months, but its main part is usually crowded within
ten to twenty days at the time when conditions are
most favorable. The length of time of possible oc-
currence, of course, decreases steadily in species of
late average arrival.

REGULARITY OF MIGRATION 77

In general in spring migration there are two main
periods of abundance in the central portions of the
United States, the first of which is in early spring
as soon as snow leaves the ground. Crowds of hardy
migrants arrive, and hordes of species uncommon
in winter pass from more southern regions. In in-
land areas the period is one of abundance for finches
and sparrows. As spring opens in full, and the
weather moderates at more northern points, the
crest of this early wave passes, leaving summer resi-
dents to seek their breeding grounds and later ar-
rivals to straggle through. The first week or two of
April often represents a slack period, when bird-life
seems scant after the previous abundance, though
arrivals of new species are noted constantly. These
later migrants increase steadily until about the
middle of May, when the great seasonal rush of the
year is noted, with the passing of warblers, fly-
catchers, vireos, and many others; and it is then that
we hope to make our largest lists of species, since
early laggards and late arrivals mingle in the great-
est abundance of the year. By May 20 this rush is
abated, and by the end of May birds are on their
breeding grounds and belated migrants are few in
number.

The autumn migration pursues a more even
course. The earliest arrivals among northern shore-
birds are noted on mud-bars or sandy beaches dur-

78 THE MIGRATIONS OF BIRDS

ing the first week in July, hardly more than a month
after the last of their kind were recorded in north-
ward flight. The yellow warbler completes its breed-
ing and starts south during the latter part of this
month. Other wood warblers begin to travel in
August, and in mid-September pass in abundance,
with vireos, flycatchers, and similar tree-haunting
birds. October, particularly in the Middle West, is
preeminently the month of migrant sparrows, which
form a wave of migration equalled only by the gath-
erings of wild ducks on some of the northern
marshes. In eastern Kansas near the tenth of Oc-
tober I have found sparrows in mixed bands con-
taining thousands of individuals, scattered through
hedges, marshes, and weed patches. On such occa-
sions I have in the course of a day recorded five
hundred or more LeConte's sparrows, with many
hundreds of song, Lincoln, white-crowned, and
Harris sparrows, and juncos, and smaller numbers of
more unusual species. From the close of this month
the number of migrants steadily decreases, until the
flood of movement is almost stilled by the arrival of
winter. Irruptions of northern species, as pine and
evening grosbeaks, redpolls, siskins, snow buntings,
and longspurs, may continue, however, until the
opening of spring.

There is cessation of migration in fact only during
the period of nesting, and even at that time there

REGULARITY OF MIGRATION 79

may be casual wandering among Individuals that for
some reason are not breeding. Observations on
migration may thus be made throughout most of the
year.

Segregation during Migration

Many birds are distinctly segregated from others
of their kind during their migrations by certain in-
dividual peculiarities. Nighthawks fly in separate
companies because of their erratic flight. A similar
restriction is found in swifts, whose rapid move-
ments through the air and habit of roosting in hol-
low trees or chimneys cause them to travel apart
from any other birds. Glossy ibises, crows, king-
birds, crossbills, waxwings, and bobolinks, for rea-
sons some of which may not be easily apparent, usu-
ally are found gathered with others of their kind
during their travels.

Flocks of swallows, on the other hand, often travel
in mixed companies composed of several species, as
do blackbirds and grackles, shearwaters, and wood
warblers. Similarities of size, form, and method of
search for food draw them together. It is probable
that many sparrows migrate in mixed companies as
they are associated thus by day; but there is no
means of observing definitely their nocturnal pas-
sages except through the medium of their call-notes,

8o THE MIGRATIONS OF BIRDS

which seem to indicate that they travel in flocks
composed of several species.

Some birds in migration maintain a close flock-
formation, as is seen in shore-birds, blackbirds, wax-
wings, longspurs, and snow buntings. Others travel
in loose order, as turkey vultures, bluejays, warblers,
pipits, horned larks, and bluebirds. Still others, like
great horned owls, winter wrens, shrikes, grebes, and
kingfishers, travel alone in ordinary circumstances,
and appear in a close proximity that might indicate
flocking only where abundant food or other unusual
condition draws them together. There is some geo-
graphic variation in this regard, as red-tailed and
rough-legged hawks in eastern North America
travel singly, but in the middle west, may be found
in large flocks.

Migrations among males and females of the same
species may take place simultaneously, or the two
sexes may move separately. In many species in
spring migration the males are the first arrivals on
the nesting ground, as under the territorial theory
each one is under necessity of selecting a site for
summer occupancy. Early migrant robins are usu-
ally males, the first song sparrows to arrive in spring
greet us with cheerful songs that betray their sex,
the first tanagers and rose-breasted grosbeaks are
usually males; in the two last-mentioned I have seen
whole flocks made up of these bright-colored indi-

SEGREGATION DURING MIGRATION 8i

viduals. In a few species male and female seem to
arrive together and proceed at once to the business
of preparing a home. This is especially true of some
shore-birds, that go to the far northern tundras,
where mating may take place almost on the day of
arrival.

In late summer, after the nesting season, males
frequently flock by themselves and remain in bands
until autumn. Yellow-headed blackbirds elect such
segregation, as do most of the surface feeding ducks,
in which males desert the females before the eggs are
hatched. Such bands tend to hold their coherence
until time for departure for the south, and so the
sexes may in part travel in separate bands. Especial
attention has been paid to ducks in this regard, and
it has been found that often males will pass in flight
at certain times to the exclusion of females; again
the flocks will mix, or bands of females will out-
number the males. Once they are near the winter
home, all this changes and the sexes intermingle. In
fact, some of the preliminaries of pairing, or actual
mating itself, are carried on in the south. Black
ducks are frequently found in pairs as early as Janu-
ary, with female leading and the male following as
they take flight, a certain indication that the birds
are paired. These paired individuals naturally mi-
grate north in spring together, though among other
ducks of the same species that are not mated the
sexes may fly separately.

82 THE MIGRATIONS OF BIRDS

Among northern shore-birds the earliest arrivals in
autumn are quite likely to be females, who press
southward immediately when eggs have been de-
posited. I have suspected that these early migrants
may be those whose nests have been destroyed in
some way, though certain observations hint that a
number of shore-birds share in part at least the habits
of phalaropeSj a group in which the female leaves the
care of eggs and young wholly to the male.

Where there is segregation of the sexes, the young
often accompany the female. In fact, we may ex-
plain the flockings of such ducks as mallards if we
consider that the autumn flocks of males are mainly
the old drakes that have remained banded together
since the breeding season, while the mixed flocks of
early fall are females accompanied by young of both
sexes.

When young are grown, in many cases the parents
drive them away to avoid their ceaseless calls for
food, and so force them to shift for themselves.
Many times bands of juvenile individuals are built
up, which must retain some coherence in subsequent
migrations. In Alaska, in August, I have found
young Alaskan longspurs banding in flocks in the
vegetation back of the beaches, with hardly any
adults among them. Young cowbirds may forsake
their foster parents to flock together in bands that
travel south in company, though perhaps joining

SEGREGATION DURING MIGRATION 83

adults later. It is said that in England adult cuckoos
depart early for the Continent, leaving their young
to follow as best they may. As a contrast to this in-
difference, we may look to the Canada goose, in
which families remain together through the summer,
adults shedding their feathers and undergoing the
wing moult that renders them flightless during the
period of growth in their offspring, so that old and
young emerge strong on the wing at the same time.

Abundance of individuals of a species during
migration depends upon a number of factors. Kirt-
land's warblers are seldom seen, because they are
few in number and have a restricted range. Phila-
delphia vireos and Cape May warblers cover a wide
area, but are so scattered that it is unusual to see
more than two or three in a day under the most fa-
vorable circumstances. An abundance of food may
draw together short-eared owls, bitterns, or great
blue herons, species normally of solitary habit, until
many are assembled in a small area. This same
factor may assemble birds of true fleck habit in tre-
mendous numbers. On Great Salt Lake I have seen
northern phalaropes in bands of well over one hun-
dred thousand, drawn together by an abundance of
brine shrimp and alkali fly larvae. The same food
attractions cause assemblages of eared grebes in
that locality.

In species of restricted range abundance is ob-

84 THE MIGRATIONS OF BIRDS

viously to be sought near the center of the migration
path, and individuals will become increasingly rare
as the borders of the range are approached. In the
Plains region aquatic birds are abundant in autumn
migration if autumn rains fill ponds and marshes so
that suitable feeding grounds are available. In dry
seasons few or none are seen, as there is nothing to
attract them. The assumption is that in dry seasons
they pass overhead but, as there are no feeding
grounds do not descend. In this same region in
spring these water-birds abound, since the winter
snows and rains have provided a suitable habitat.

Migration among supposedly
Resident Birds

There are in all temperate regions certain birds
which, as a species, are resident, but yet among
whose individuals there is a certain amount of mi-
gratory movement. Bluejays and woodpeckers, nut-
hatches and chickadees, may be present constantly
through the year, yet the individuals seen in winter
are not always the same as those observed during
summer.

The white-breasted nuthatch is an excellent illus-
tration of slight migratory movement among indi-
vidual birds of resident species. In the vicinity of
Washington the land shows two major topographic

MIGRATION AMONG RESIDENT BIRDS 85

features — the edge of the Piedmont plateau with
its line of falls, and below it the coastal plain,
stretching out toward distant arms of the ocean.
The nuthatch nests regularly in the higher region,
and may be resident there in part, since* the same
nuthatches (marked by bands) come to my window
feeding- shelf summer and winter. In the coastal
plain the nuthatch is absent during summer, except
rarely, but in late autumn appears in fair abundance
in wooded bottoms, and remains until the following
March or April. Even as far up the Potomac as
Plummer's Island, which is within the break of the
fall line, there is noted an increase in its numbers in
winter. In fact it is usually absent there in summer.
Obviously in this species there is a spread or migra-
tion outside the breeding range. The source of the
winter immigrants may be determined only through
banded individuals.

The black-capped chickadee in winter on occasion
invades the ranges of the more southern Carolina
chickadee, as the blackcap has been recorded at
Chevy Chase, Maryland, a suburb of Washington,
though it is not known to breed at any point nearby.

The bluejay is a species of secretive disposition
but showy form that is present in most of its range
throughout the year. Yet at Washington, with the
coming of cool weather, at the end of September, or
in October, there begins a steady southward flight of

86 THE MIGRATIONS OF BIRDS

blue] ays that is unquestionably a migration to some
winter range. Similar flights have been recorded at
other points, and it is hoped that eventually records
from banded birds may throw some light on its
extent. So far as observed this movement is diurnal,
and I have seen no indication of night flight in this
species. The course pursued at Washington is to-
ward the south and southwest, and the steady pas-
sage of birds, flying from 50 to 150 yards from the
earth, is as noticeable as the migration of sharp-
shinned hawks that often takes place at the same
time.

Washington also marks a point near the northern
extension of the southern subspecies of the common
crow (Corvus brachyrhynchos paulus) , a form marked
by small size, that ranges from Alabama north to
southeastern Kansas, Maryland, and Virginia. In
winter we have an influx of the larger northern bird,
which arrives in flocks, and which, until disturbed
by building operations in suburban development,
formed great roosts within the limits of the District
of Columbia itself. With the opening of spring
weather in March the resident birds begin the aerial
gyrations and the peculiar calls that mark their
pairing and mating. I have watched these mating
evolutions among birds circling over low hills near
the Potomac River, while on the tide-flats below I
had before me scattered flocks of the northern birds

MIGRATION AMONG RESIDENT BIRDS 87

working soberly across the mud-bars in prosaic
search for food, unaffected as yet by the warming
weather, since their own nesting grounds in the
north were still covered with inhospitable ice and
snow. It is of interest in this connection to record a
crow banded in January near Stillwater, Oklahoma,
and recovered April 15 near Woodstock, Minne-
sota, as indicating the extent of the migrations in
this species.

In eastern Kansas, where the downy woodpecker
is a common resident, it has on occasion been almost
exterminated by protracted ice storms, which for
weeks at a time covered all trees and shrubbery with
a coating of ice that sheathed food-supplies for these
woodpeckers as if beneath a coat of steel. In the
summer season following such a severe winter, these
woodpeckers may be very rare; but after the first
week in November, when winter conditions come in
states to the northward, downy woodpeckers be-
come fairly common, indicating migration among
them from some region to the northward. The ac-
tual journey of such birds again may be determined
only through banding operations.

Species like the bobwhite, mockingbird, and
Carolina wren appear truly sedentary, except for a
certain amount of post-breeding wandering in the
wren and mocker, and some casual flying in early
autumn on the part of the quail, during which ran-

88 THE MIGRATIONS OF BIRDS

dom individuals may be found in cities^ towns, or
other untoward neighborhoods. With others that
seem equally sedentary it appears that there may be
true migration in greater or less extent. What move-
ment there may be in central latitudes among such
species as meadowlarks, song sparrows, flickers,
robins, and many others that are present through
the year, is as yet purely a matter of speculation.

Many insular birds appear wholly sedentary, in
that there is no interchange of individuals between
islands which often lie within sight of one another
and are easily reached by moderate flights. In east-
ern Porto Rico a species of crow {Corvus leucogna-
phalus) is found in forested areas, but makes no
attempt to cross to the island of Vieques, in plain
sight only fourteen miles away. Bones of this species
are known from St. Croix, indicating that it was
found there in ancient times, but it has never been
reported there as a living bird by modern natural-
ists. Still more strange is the case of a land-rail
(Hypotaenidia wakensis) found on the isolated island
of Wake in the Pacific Ocean between Guam and
Honolulu. The atoll at Wake has three islands,
arranged in the form of a horseshoe surrounding a
broad lagoon, separated from one another by nar-
row channels not more than loo yards wide. The
rail is found on the northern and eastern islands but
does not occur on the one to the southwest. That

MIGRATION AMONG RESIDENT BIRDS 89

the bird is flightless is not an adequate explanation
of this curious distribution, since the channel sepa-
rating this island from the one on the east, where the
bird is common, is practically dry at low tide, twice
in the course of every period of twenty-four hours.
Food and shelter conditions are identical on all three
islands, so that there is no apparent reason for the
anomaly.

The curious hoatzin {Opisthocomus hoatzin) of
northern South America is an excellent example of
sedentary habit in a species with continental range.
The bird is one with very weak powers of flight, so
that it progresses mainly by clambering about
through the branches of the thickets in which it
feeds. It is said in certain instances to move less
than a mile during the entire period of its life, merely
coming out in the open in morning and evening, and
seeking shelter under leafy branches in the heat of
the day.

Irregular or Vagrant Migration

Irregular movements among birds may begin, as
has been indicated, in wandering of adults or young
from the vicinity of the nest site, and may vary in
extent from a few hundred yards to many miles.
During late summer species that have regular bi-
annual migrations may wander in search of food, or
young birds may stray from their accustomed range.

90 THE MIGRATIONS OF BIRDS

As a feature of local migration movement there
may be noticed the interesting summer flights of
herons. In the southeastern United States the little
blue heron {Florida caeruled) is common near the
coasts, and nests in colonies, sometimes with or
near the snowy heron and the American egret. The
immature little blues (which are often pure white
except for more or less slaty wash on the tips of
the primaries, so that they may be mistaken for
egrets) wander regularly after they are grown, and,
strangely enough, at this season many of them pene-
trate to the north far beyond their breeding range.
At the end of July scattered birds begin to appear
along the Potomac, the Patuxent, and the Susque-
•hanna rivers, tributary to Chesapeake Bay, and in
many years the birds become common in August.
With them come snowy herons and egrets in casual
company, and all three travel north on occasion as
far as New England. In the Mississippi Valley they
are found regularly north to southeastern Kansas
and Illinois. In September most of these birds dis-
appear, and it is presumed that they return to the
south.

Similar vagrant wanderings are recorded for
white herons in Europe and Asia, and apparently
hold true in the reef heron {Demigretta sacra) of
Australian coasts and a broad range among islands
in the South Pacific, which is recorded as a wanderer
at many points.

IRREGULAR MIGRATION 91

Others of the larger herons seem to have similar
wandering habits, as they nest in retired colonies,
and after the breeding season the young in particu-
lar range far and wide wherever they find feeding
grounds. The yellow-crowned night heron, also a
form with southern breeding range, comes north
casually, while in the case of the black-crowned night
heron, northward wandering has been proved to be
the usual course from records obtained by marking
the young. Thus young birds marked by Dr. Paul
Bartsch near Washington, D. C, have been taken in
Maryland and New Jersey, while others banded by
different observers in the colony at Barnstable,
Massachusetts, have wandered north into southern
Maine. The distances covered in these instances
are not particularly great.

It is probable that great blue herons also range
northward, since a specimen of the subspecies that
breeds in the Great Basin {Ardea herodias treganzai)^
which I banded near the northern end of Great Salt
Lake, Utah, was killed subsequently near Billings,
Montana. From available evidence it appears that
the post-breeding movements of these herons is ex-
plosive, that is, the birds spread in all directions
from their breeding grounds, regardless of direction.
It may be considered as migration governed only by
the availability of food and safety from enemies,
which is counteracted in autumn by a directive

92 THE MIGRATIONS OF BIRDS

migratory impulse that carries these birds that have
attained northern latitudes to a winter home some-
where in the south.

At the beginning of August, 1925, a Bewick's
wren appeared for a day in one of the courts of the
United States National Museum. The species does
not now nest within forty or fifty miles of Washing-
ton so far as known, so that this individual must be
considered merely a vagrant. On one occasion, at
the same season of the year, I found a canyon wren
in a barn standing on a broad plain in northern
Utah, fifteen miles from the nearest mountain haunt
of the species — also an instance of a wanderer de-
tected perhaps in a journey between the mountain
ranges on either side of a wide basin.

Such examples, however, are merely casual and
are not to be compared to the irruptions of certain
northern birds that sweep down over the south at
irregular intervals. Crossbills furnish classic ex-
amples of such flights, as the curious bills of these
birds invariably attract attention. In ancient
chronicles in England we find flights of crossbills
recorded in the years 1251, 1593, 1757, 179I) 1821,
1829, 1846, 1853, and at numerous other dates from
the year last mentioned to the present. On many
occasions they established themselves, bred for
several years in succession, and then disappeared.
Matthew Paris, Monk of St. Albans, already men-

IRREGULAR MIGRATION 93

tioned, has chronicled the invasion of crossbills in
the year 1251, his attention being attracted to them
by their attacks on apples, a fruit which in the thir-
teenth century had attained a certain importance in
the western counties of England. " In the course of
this year," he writes, "about the fruit season, there
appeared, in the orchards chiefly, some remarkable
birds which had never before been seen in England,
somewhat larger than larks, which ate the kernel of
the fruit and nothing else, whereby the trees were
fruitless, to the loss of many. The beaks of these
birds were crossed." On a subsequent visitation in
1593 they are also reported to feed upon apple-
seeds, a habit so common in England that at one
time the crossbill was often called "shell-apple." In
the record of this occurrence, couched in the quaint
phrases of ancient English, it is said that "it seemed
they came out of some country not inhabited; for
that they at the first would abide shooting at them
either with pellet, bowe or other engine, and not
remove until they were stricken down. . . . They
were very good meate." Crossbill years have been
recorded regularly in modern times in the United
States, and have frequently carried the birds well
south into the Carolinian life-zone. In the Middle
West, in Kansas, where the birds are rarer than in
the east, flights have included the subspecies known
as Bendire's crossbill, which breeds in the Rocky

94 THE MIGRATIONS OF BIRDS

Mountain region, as well as the ordinary form from
the north, indicating a migration from the moun-
tains out across the plains. From this it appears that
these movements may be true wandering without
definite direction. In the winter of 191 6 there oc-
curred an irruption of the white-winged crossbill
that brought these birds south as far as the city of
Washington, where the species, though rare, has
been found occasionally in the summer season.

At irregular intervals too come great flights of
goshawks that spread across the entire northern
half of the United States, and penetrate south to
California and New Mexico. During a recent irrup-
tion the eastern form of this bird was recorded west
across the Rocky Mountains into California, thus
covering the usual range of the western form. The
coming of hordes of this predatory bird is fraught
with danger to the ruffed grouse of Michigan, Wis-
consin, and the New England States, as the hawks
hunt the grouse relentlessly, and have on occasion
reduced these game birds almost to extinction. With
the goshawks often there arrive many snowy owls
and unusual numbers of great horned owls.

As irregular movement in a northern direction I
may cite the case of the thick-billed parrot {Rhyn-
chopsitta pachyrhyncha) ^ resident regularly in the
mountains bordering the Mexican Tableland, which
at intervals of a number of years comes north across

IRREGULAR MIGRATION 95

the border and invades the isolated mountain chains
of southern Arizona, where it has been reported on
several occasions from the Chiricahua Mountains,
and more recently, in 1917, from the Huachuca,
Dragoon, Graham, and Galiuro ranges. The birds
appear in late summer in roving bands that may
include several hundred individuals.

In July, 1917, such an invasion came in the south-
ern Chiricahua Mountains, and by August had pene-
trated to Pinery Canyon at the north end of the
range. Mr. Frank Hands, a close observer, informed
me that he was certain from the condition of their
plumage that many were young which had been
hatched that year. The birds remained here through
the winter, feeding early in the season on cones of
the Chihuahua pine {Pinus chihuahuana) ^ and when
these were gone, on the acorns of various species of
oaks. By November they had decreased in abun-
dance, but a few remained until March, 191 8; in
May of that year a few appeared in the Galiuro
Mountains farther north, and remained until early
autumn.

The flights of birds that have been mentioned
have been a puzzle to naturalists from the irregular-
ity of their occurrence, and have been explained on
the hypothesis of failure of food supply, increase in
numbers beyond the capacity for support of the nor-
mal range, and severe cold. Failure of food seems

96 THE MIGRATIONS OF BIRDS

the most potent cause that may be given, and has
certainly been the active factor in many cases. It
may be mentioned particularly in connection with
the periodic invasions of unusual numbers of the
goshawk and snowy owl, as these seem to come dur-
ing years when disease has destroyed the northern
hares that form their usual food supply. On these
occasions, Indians, lynxes, and other hunting mam-
mals are often hard put for food, while the hunting
birds exercise their powers of flight to carry them to
other regions where food may be procured.

Less certainly has the coming of crossbills been
attributed to failure of their normal food supply of
cones in the north — a factor that may perhaps
operate with the thick-billed parrot, which also feeds
on the seeds of pines as well as on acorns.

Of interest in this connection are the movements
of the sand-grouse of Eurasia, curious birds with
many attributes of grouse and shore-birds, that
seem anatomically most closely allied to the pigeons.
Sand-grouse are regular inhabitants of the high
plateaus or steppes of central Asia, but may range in
great flocks through the surrounding territory.
Henke found them in 1876 breeding in numbers on
the Kirghiz steppes, where nomadic tribes told him
they had been unknown before. In the spring and
summer of 1863 a flight of these birds spread across
western Europe, reaching the coast of Donegal in

IRREGULAR MIGRATION 97

Ireland, the Adriatic Sea, northern Italy, across
France, and north into Sweden. By February, 1864,
the unusual visitors had disappeared. Though a few
pairs were known to breed, the majority in the
European invasion seem to have been merely
vagrant.

In 1888 there occurred another irruption of the
Pallas's sand-grouse that was even more important.
Flocks spread throughout western Europe, and the
birds became so firmly established in the British
Islands that a special act of Parliament was put into
effect to protect them during an adequate closed
season. Subsequently, however, they disappeared.
Except to a few Russian naturalists who had ob-
served it in its Asiatic haunts, the species was prac-
tically unknown, until 1848, when it was found in
south Russia, and 1859, when it spread into western
Europe. It seems, therefore, to have been in a state
of unrest for the past seventy-five years or more,
but has not succeeded in establishing itself per-
manently in the new territory to which it spread.
Without interference by man it might possibly
have been more successful. It has been supposed
that the movements of sand-grouse, like those of
lemmings, are due to surplus production of individ-
uals, leading to undue congestion in the native
haunt.

Other birds are subject to similar movements, as

98 THE MIGRATIONS OF BIRDS

Gatke at Heligoland has recorded incredible num-
bers of the European jay in passage for three days in
October, 1882, while in subsequent years only one
individual was seen.

It is probably true that many vagrant individuals
are carried so far beyond the usual range that they
fail to make any attempt to return, and many others
perish through unfamiliarity with the dangers of the
new environment into which they have come. It is
probable from the records available that most of the
sand-grouse in the invasion mentioned in 1863 and
1864 perished, since everywhere the strange birds
were hunted and killed.

Wastage of individuals among migrants is exten-
sive, and affects vagrants as well as those regular in
travel. It would seem to operate with greater sever-
ity among those of irregular movement, as such have
established no regular annual margin of safety. We
may look then upon these periods of vagrancy to cut
down the number of individuals among the species
concerned. These erratic spreads have probably
served to extend the -range of some species, and may
still do so, though since the rise of man this has be-
come difficult except in the case of inconspicuous
forms.

Flights of snow buntings, longspurs, pine siskins,
redpolls, and many others that penetrate irregularly
to the southward during severe winters may hardly

IRREGULAR MIGRATION 99

be considered in this category of vagrants, since
they are regularly migratory toward the south, and
on occasion merely extend the length of their jour-
neys. Part of their journey is regular, though its
extent may be subject to variation.

Casual Records

The student of local avifaunas, intent on main-
taining a complete list of the birds of his region, with
notes on their abundance and occurrence, is al-
ways elated to detect the unusual visitor. Some un-
expected stranger well repays hours or days passed
in careful scanning of abundant birds of usual oc-
currence, whose habits and movements are wholly
familiar. A glance through any state list or compre-
hensive check-list reveals frequent instances of this
sort, and almost every number of the current maga-
zines dealing with ornithology records others. The
steady increase of record of such unusual occur-
rences is due to the steadily increasing number of
persons interested in observing birds — a factor that
submits the avian population to close scrutiny and
offers more frequent chance of detection of the
unusual.

Casual or accidental records are, roughly, of two
kinds: first, birds recorded just beyond the margins
of their normal ranges, and second, birds from dis-
tant areas whose occurrence is wholly fortuitous. It

loo THE MIGRATIONS OF BIRDS

is perhaps trite to state that the majority of acci-
dental visitors appear during the seasons when they
are in migration. The first group — those found
casually a short distance beyond their normal range
— may represent attempts at extension beyond pres-
ent boundaries, which, if successful, may result in
final establishment of a species in a new area. Dr.
J. Grinnell ^ has discussed this matter rather fully as
regards the State of California, and considers these
accidental occurrences as representing a trial and
error method whereby a part of the surplus of
the stock of any particular species pushes out into
new territory where it may be lost or may survive.
Wastage is severe, but is of small moment in the
working of the laws which through the ages control
distribution of millions of individuals. Again, these
accidental records may represent sporadic attempts
of a species to reestablish itself in regions from which
it has been forced to retreat.

Of another kind are records of birds at points far
from their normal range, which are assumed to rep-
resent individuals that have wandered uninten-
tionally from accustomed paths through the agency
of storms or other untoward circumstances that they
have encountered. These may include strange visi-
tors of every description, sea-birds found far in-
land, land-birds blown at sea, or tropical and sub-

^ /f«^,l922, pp. 373-380.

CASUAL RECORDS loi

tropical species encountered in temperate regions.
Though conceivably such birds may occasionally
have established themselves in new ranges, this
would happen far less frequently than with birds
working out short distances beyond the edge of the
normal range. To this agency, however, we must
look to explain the presence of small land birds on
oceanic islands, where there has never been conti-
nental connection, as in the Leeward Islands of the
Hawaiian group, where a finchlike bird of the family
Drepanididae, another smaller species of the same
group, and an Old World warbler, are found on the
island of Laysan, an isolated bit of sand built up
through filling in an atoll, with less than two square
miles of land surface. (The warbler, Conopoderas
familiarisy and one of the Drepanidids, Himatione
fraithii^ are now extinct.)

Dr. Grinnell ^ has stated that of the 576 forms of
birds recorded for the State of California to 1922,
there are 2S that have been found on only one occa-
sion. These represent mainly casual visitants far
from their usual range. A few more — ten, to be
exact — have been detected twice, while for six
there are three records of occurrence. On the basis
of observations extending over thirty-five years, he
finds that new additions to the list for the state have
come at the average rate of if per year. Since these

^ Auk, 1922, pp. 373-375.

102 THE MIGRATIONS OF BIRDS

casual visitants may come from anywhere on the
continent, he estimates on the basis of these figures
that there is a possibility of record of occurrence for
the entire group of birds known from North America
north of Mexico in the course of a little more than
400 years.

Casual records of straying birds in continental
areas are subject to considerable chance, since the
area suited for them is broad. Species of striking
appearance are more liable to be noticed than those
of ordinary character, since the latter merge with the
ordinary avian population. The frigate bird of sub-
tropical and tropical seas has been found in the in-
terior in Kansas, Iowa, Wisconsin, Ohio, and Nova
Scotia, the fork-tailed flycatcher in Mississippi,
Kentucky, Maine, and Bermuda, and a form of
kingbird {T^yr annus melancholicus satrapd) of the
tropics has been taken recently at Scarboro,
Maine. These are all single instances. Occasionally
flocks of sea birds appear inland as, for example, the
dovekie, Wilson's petrel, and others.

Detection of straying migrants in insular areas is
more usual perhaps than on continents, since in
limited land space strangers become more conspicu-
ous. The list of birds known for the British Isles in
191 5 numbered 475, of which 149 had been recorded
as accidental visitors. In this list, in addition to
forms from near-by continental areas, there are

CASUAL RECORDS 103

included the American pipit, the yellow-billed and
black-billed cuckoo, the American duck-hawk, the
blue-winged teal, the green-winged teal, American
widgeon, ring-necked duck, bufflehead, hooded mer-
ganser, American bittern, and a long list of shore-
birds from North America.

Small islands are even more productive, since they
offer havens to birds blown to sea. In 191 1 I found
three individuals of an Asiatic bunting {Hypocentor
rustled) on the island of Kiska in the outer Aleutian
chain, two of them dead and the third flitting about
in the grass. The Pribilof Islands in Bering Sea have
yielded a considerable number of birds that have
come as strays, since of the total list of 137 forms
recorded up to 1923, there are 80 which are of
purely casual occurrence. These include a consider-
able number of Asiatic birds that have been found
nowhere else in the area included in the limits of the
list of North America. The majority of these strays
are birds that breed in northeastern Asia, which
have wandered from their usual track toward the
south. Among them may be mentioned the widgeon,
falcated teal. Old World forms of the golden-eye and
pintail, a cuckoo, the brambling, swift, Japanese
hawfinch, and sea eagle. These islands lie in a belt
where they are usually surrounded by fogs during
the period of migration, so that, though visible for a
long distance when the weather is clear, this occurs

I04 THE MIGRATIONS OF BIRDS

so seldom during the season of migration that we
may wonder how wandering birds come to them.
E. A. Preble has called attention to the fact that,
during the seasons when most of the small birds are
migrating, the beaches of the Pribilofs are crowded
with thousands of fur seals and sea lions, gathered
in noisy herds whose roaring and bellowing in com-
bined chorus produces a clamor that is audible dis-
tinctly at a distance of several miles. There is no
question, he states, that many feathered wanderers
are guided by these uncouth sounds to a haven
where they may rest and recuperate. Casual visi-
tants among land birds found here must be consid-
ered as true strays, since these lonely islands do not
lie in any regular migration path except for some
groups of sea fowl. All land birds found, therefore,
are storm blown or lost from some other cause. Even
the yellow wagtail and willow warbler, which cross
each year from Asia to nest in Alaska, travel by
some other route, since they have not as yet been
recorded from the Pribilofs.

Birds of strong flight often appear at points far
distant from their customary haunts. The ruff of
Europe has been recorded on several occasions
from Barbadoes, Trudeau's tern of Argentina and
Uruguay has been found in New Jersey, and the
Bartramian sandpiper has been taken in New
Zealand.

CASUAL RECORDS 105

The facts outlined will give some idea of the
manner in which birds may wander when out of
their accustomed courses, and of the difficulties that
beset them during their travels. It is safe to say that
more than 90 per cent of casual records represent
strays during periods of migration.

CHAPTER IV
Altitudinal or Vertical Migration

SOME species of birds fly hundreds of miles across
more or less level land to reach a summer or a
winter home, while others attain the same objective
by moving through a space of a few miles which car-
ries them up or down the sides of mountains. A few
hundred feet of altitude in these instances corre-
sponds to hundreds of miles of latitude. Wherever
large mountain ranges are found in temperate
regions we find regular migration taking place up
and down their slopes.

Such migration may be noted in India, where bird
migrants from Siberia mingle on the plains with
others that have merely descended the near-by
Himalayas. Species of rosy finches, other finches,
and the snow partridges, from the higher altitudes,
migrate in winter into the foothill region, and then
with the coming of spring move back into the higher
country to breed. With them come woodcock, jack-
daws, and the sprightly whistling thrushes.^ Borders
of streams are frequented by flocks of wagtails from

^ Hingston, R. W. G., A Naturalist in Himalaya^ p. 258.

ALTITUDINAL MIGRATION 107

the north, while bands of snipe and duck, bred in
Arctic regions, swarm in the marshes.

Similar movements occur in the Andes of Argen-
tina, where grebes and coots nest in mountain lakes
and winter in alkaline marshes on the plains, or in
the Rocky Mountains of our own country, where
the rosy finches, juncos, pine grosbeaks, and siskins
descend the mountain slopes in autumn and ascend
them in spring. In the Great Basin I have seen the
violet-green swallows leave their lowland haunts in
May for their breeding grounds in the hills, and
then during a late storm, which covered the moun-
tains with snow but in the valleys fell as cold rain,
return again to the lowlands. Such interchanges
meant only a few miles of flight and were accom-
plished with ease.

In species of birds that inhabit or frequent both
hills and plains it has been noted in spring that first
arrivals may be seen near the foothills and from
there work upward. In autumn early migration may
be observed on the slopes of mountains or at their
bases, depending upon the species. There is, how-
ever, much variation in this, depending largely on
local conditions. In field work in the foothills of the
Front Range in Colorado, R. B. Rockwell and I
found that spring migration in the same species was
approximately a week later in the hills than on the
plains east of Denver, indicating apparently that

io8 THE MIGRATIONS OF BIRDS

many birds came north along the plains and then
spread back into the mountains. Certain species, as
some of the j uncos, which had wintered in the foot-
hill region, in spring moved down toward the level
country and then migrated northward toward their
summer home. There were evident thus two lines of
movement, one that carried incoming migrants up
the gulches into the mountains, and one that
brought winter residents down the gulches toward
the plains. In August in this same region, such
species as the Williamson's sapsucker and western
wood pewee, which had nested in higher mountains
to the west, moved down to lower regions, and at
the same time broad-tailed hummingbirds, western
chipping sparrows, and mountain bluebirds in-
creased in number, apparently from influx from the
same higher regions. There was a distinct tendency
among young of the mountain-breeding birds to
work down the mountain slopes as soon as the
breeding season had closed — a movement that be-
came intensified with the beginning of migration
from the north in September.

Similar movements among different species of
birds have been observed in many localities. Espe-
cially noticeable in autumn are the sudden increases
among birds in the edges of the foothills when cold
spells occur that spread frost or snow in the higher
regions.

ALTITUDINAL MIGRATION 109

In some cases we find altitudinal migration affect-
ing birds of limited range, which nest in the higher
zones of mountains and winter near their bases, or
perhaps pass farther south. With some species, as
the pipit of this country, a suitable breeding range
for some is found in the Arctic-Alpine zone of the
Rocky Mountains, from Colorado northward, while
others seek a similar zone in the tundras of Alaska or
British America.

After the breeding season some species of birds
regularly work upward, to spend the late summer on
the higher slopes of the mountains. Such move-
ment has been recorded in the western house wren,
and has been observed in western kingbirds and in
other species. In the foothills of the California
mountains, where the late summer and early autumn
are extremely dry, T. I. Storer ^ has recorded that
such supposed permanent residents as the spurred
towhee, wren-tit, bush-tit, and Vigor's wren, regu-
larly perform an altitudinal migration, as in late
summer, after the breeding season, they move up
the slopes into the higher zones of the mountains,
where they remain until the coming of autumn rains
breaks the drought at the lower levels and so makes
conditions of life there easier. A fascinating account
of altitudinal migration remains to be written when
the late summer movements of hummingbirds in the

^ Univ. Calif. Publ. Zool. (1925) xxvii, 3.

no THE MIGRATIONS OF BIRDS

mountains of the southwest are better understood.
In July and August, when flowers bloom in abun-
dance in mountain parks at altitudes of 7cxx) to 9000
feet in the Chiricahua, Huachuca, and near-by
mountain ranges, hummingbirds of several species
fairly swarm. Many do not breed here but come
from near-by, though as yet the exact status of such
species as the white-eared hummer is uncertain.

Rapidity of Migration Movement

The rapidity with which migration progresses
when birds are passing to the north in spring seems
to depend to a considerable extent, among small
species at least, upon whether migration begins
early or late in the season. Professor W. W. Cooke,
in his studies on bird migration, gathered and pub-
lished numerous data on this point from records
furnished by a large corps of observers scattered
through the country, who made careful record of
dates of first arrival in their vicinity. Professor
Cooke found that the average rate for the month of
March, when early migrants were retarded by fre-
quent periods of bad weather, was considerably less
than that for April, while in May all migrants
seemed to travel at a much more rapid pace. From
this it is deduced as a general rule that those species
that start their migration late in spring travel to
their breeding grounds at a much more rapid rate

RAPIDITY OF MIGRATION MOVEMENT in

than those that leave their winter quarters earlier in
the year.

Part of our black and white warblers (Mniotilta
varia) winter in Florida and southern Texas, but the
majority pass on to the West Indies, Mexico, and
northern South America. Migrants on their way
north are recorded at the lighthouses of southern
Florida about March 4, but migration does not ex-
tend beyond the northern limit of the winter range
into southern Georgia until about March 24, so that
these early migrants travel at an average rate of
only 20 miles per day through this area. Between
southern Texas and northern North Dakota, this
bird averages about 22 miles per day, but from that
point north to the limit of the breeding range the
rate of speed is almost doubled.

The gray-cheeked thrush, on the other hand,
which does not reach the southern United States
from its winter home in South America until late in
April, arrives a month later in extreme northwestern
Alaska, so that it covers a 4000-mile journey on this
continent at an average rate of 130 miles per day.

Professor Cooke has figured the average speed for
small birds in general in passing up the Mississippi
Valley at 23 miles per day. In addition to the species
that have been mentioned he gives some interesting
figures for a few others. The black-poll warbler, in
its northern flight from South America, arrives on

112 THE MIGRATIONS OF BIRDS

our southern coasts in April. In travelling north to
the northern boundary of the United States the
birds move at a rate of 30 to 35 miles per day, but
from that point north the speed increases tremen-
dously, as black-polls appear in a week's time in the
central Mackenzie Valley, and in another week
arrive in northwestern Alaska. It appears that some
at least must average 200 miles per day for the
latter part of the journey. The species requires 30
days to cross the thousand-mile interval from the
Gulf coast to southern Minnesota, and only a little
more than half that time to traverse the 2,500 miles
that separate that point from the extreme limit of
its range in Alaska.

From the same source may be taken some inter-
esting data on the spring movements of the robin.
In the east, migrant robins come north at a leisurely
rate, travelling through New England with the slow
advance of spring, so that to their northern breeding
limit in Newfoundland they average only 17 miles
per day. In the west, the western form of the robin
winters north into British Columbia and has to per-
form only a short migration to pass into Alberta and
Saskatchewan, to which it moves at an average
advance of only 8 miles per day. In the interior, the
eastern subspecies moves from its winter range
north to central Minnesota at the rate of 13 miles
per day, a rate that is doubled in the course to south-

RAPIDITY OF MIGRATION MOVEMENT 113

ern Canada. Here a part of the birds turn to the
northwest and move at an average rate of 50 miles
per day, and finally accelerate to a rush that carries
them across a space of 70 miles in twenty-four hours,
and at this increased speed arrive at their limit in
Alaska. Professor Cooke finds that their northward
movement coincides closely with the passage of the
isotherm of 35 degrees Fahrenheit, which brings
spring throughout the country. The differences
noted in average speed through our continent are
thus correlated with the average advance of spring,
so that the robin merits its reputation as the herald
who announces the close of winter.

In connection with rapidity of migration it may
be well to note that there is often a distinction be-
tween the rapidity of movement in the bulk of the
species as a whole and of single individuals. At the
opening of migration a few birds of a species may
appear, but it may be a week or a month before the
bulk begins movement and the bird becomes com-
mon. Thus a few blackbirds reach our marshes early
in spring, but the return of cold weather may retard
the flights of their fellows for some time. Practically
nothing is known as yet of the manner in which
single birds travel, since our observations to date
have been restricted mainly to group identification.
Early stragglers form the vanguard in most of our
birds. It is apparent thus in many cases that cou-

114 THE MIGRATIONS OF BIRDS

riers of migration advance rapidly and cover a con-
siderable extent of country, perhaps reaching well
through the range long before the main army begins
to move. This is often true in fall flights where there
is no climatic bar to progress. Juncos appear in
middle latitudes in September, but do not become
abundant until the middle of October or the first
part of November. Yellow-legs start south in July,
and by the end of that month may reach South
America, though the main flight does not appear in
the extreme south until September or October.
Travel into the northern zones in spring, early in the
season, is retarded of course by the continuance of
cold in the north, so that the earlier movements
must await thaws.

In early migration, there is much lingering along
the way to feed and rest, particularly among those
birds that travel long distances. In Argentina and
Uruguay I found migration northward among shore-
birds beginning at the end of January and well under
way in March, though the final rush did not come
until April. As this final flight coincides with the
initiation of migration among these birds in the
United States it will be seen that those who re-
sponded early to the migration impulse were slower
in progress than those that started later.

Definite data for the rate at which birds travel
south in autumn are lacking, as at that season birds

RAPIDITY OF MIGRATION MOVEMENT 115

are quieter than in spring and more difficult to ob-
serve. The journey in many cases also is irregular
and prolonged. We may look to data secured from
bird banding to give more definite information as to
the rapidity of migratory movement in individual
birds, and we shall turn to that source especially for
the movements of autumn migrants when sufficient
records have been amassed.

Distances travelled by Migrants

The length of the migration route is a highly vari-
able factor, depending upon local conditions and the
species of bird concerned. In the mountains of Him-
alaya, as winter approaches, the snow partridge may
descend a few hundred feet in altitude, to a winter
ground, merely by travelling a mile or two, or, in
this country, the long-tailed chickadees of the Rocky
Mountains may drop down from the aspen groves at
8,000 feet, where they have nested, to creek bottoms
a few miles distant in the foothills. Flights that may
be covered in a few minutes place these birds in
regions where they find conditions suitable to their
needs for winter. We may contrast these flights
with that of the Arctic tern, which nests in the most
northern land known (the first nest discovered is
said to have been only 450 miles from the North
Pole) and which spends the winter in seas skirting
the Antarctic continent, with an air line 1 1,000 miles

Ii6 THE MIGRATIONS OF BIRDS

in length between its summer and its winter resi-
dence. (See Fig. 3.) It has been truly remarked that
this tern probably experiences more daylight than
any other living creature, since it lives in regions
where the midnight sun is its constant companion in
both north and south, and only in travelling does it
encounter any extended periods of darkness.

Many birds nest in the northern United States
and Canada and pass south toward the Gulf of
Mexico to winter. As well-known examples may
be cited such winter residents as the white-throated,
white-crowned, and tree sparrows, j uncos, brown
creepers, golden-crowned kinglets and robins, with
hordes of grackles, redwings, and cowbirds among
our smaller birds, and various species of ducks, the
woodcock, and many others, among larger ones.
Such migrants include the hardier species, some of
whose individuals may linger in protected places
well within the reach of severe cold.

Many of our small birds travel much greater dis-
tances for no apparent reason. Many species of
wood warblers nest in the northern United States
and Canada, and fly in winter to the West Indies,
leaving perhaps a few of their individuals to linger
in the southern states. Black and white warblers
range in winter season from extreme southern
Georgia southward into the West Indies; some, un-
dismayed by broad waters, cross to Venezuela and

Figure 3

Map to show migration range of the arctic tern {Sterna paradisaea).
(Courtesy of Bureau of Biological Survey.)

DISTANCES TRAVELLED 117

penetrate even as far as Ecuador. Part of the yellow
warblers travel even farther, as they range south
into Brazil. The last species mentioned is one of the
earliest to begin its migratory movements south, as
it is recorded in southward flight in Florida at the
end of July.

The nighthawk that nests on the upper Yukon
may winter in Argentina, while the marsh wren of
the upper Mississippi Valley, with wings apparently
weak, may fly south in autumn as far as central
Mexico. The migration routes of some of the wag-
tails, the common swallow, the willow warbler, and
the spotted flycatcher, which pass from northern or
central Europe to South Africa, may be cited as
among the longest journeys for small land birds of
which we have knowledge. Some of these long
flights must be performed without great delay en
route \ for I found the North American barn swallow
in western Paraguay shortly after the twentieth of
September, when no doubt a part of the species had
not yet left the United States.

A number of birds that have extended breeding
ranges withdraw in autumn to the south, to concen-
trate in the southern portion of the breeding area, or
spread only a short distance farther south. This is
true of the rock wren, the black-capped chickadee,
the black-headed grosbeak, the field sparrow, and
the migrant shrike. In such forms the entire group

ii8 THE MIGRATIONS OF BIRDS

is confined within a limited area for the period of
winter, and then spreads to reoccupy the full range
with return of warmer weather.

The difference between subspecies has made pos-
sible the discovery of interesting facts indicative of
length of migration in a number of species. As an
example may be cited the yellow-throat of Florida
{Geothlypis trichas ignotd)^ marked from other forms
by a more rounded wing, which is strictly sedentary,
but in winter has as its companions yellow-throats
from the north, some of which cross to the Bahamas
and Cuba. In England, an insular area where such
matters are readily detected, resident forms of the
greater spotted woodpecker, the dipper, the robin
red-breast, the song-thrush, the great titmouse, and
others, are joined in winter by individuals of con-
tinental subspecies from the north, which return to
their proper haunts at the opening of the breeding
season. Similar instances may be found in many
areas in the temperate zones both north and south
of the Equator.

Very often individuals of a widely distributed
species from the northern part of the range tend to
migrate farther south than those from intermediate
regions, instead of there being a uniform shift of
northern birds to the central portion of the range, to
replace others that have gone on southward. In
other words there is a tendency for birds living

DISTANCES TRAVELLED 119

under fair conditions to migrate only a short dis-
tance, while others which are forced, or choose, to
migrate, pass on to distant unoccupied areas for
winter. Mr. H. S. Swarth has shown an excellent
example of this in his discussion of the races of the
fox sparrow, of which there are sixteen forms rec-
ognized at present. Our familiar eastern bird nests
from northwestern Alaska to Labrador, and con-
centrates in winter in the southeastern portion of
the United States, so that it travels a long route
each year. On the west coast of North America
there are six subspecies of this bird which in summer
are established in definite breeding ranges from
Unimak Island, at the end of the Alaska Peninsula,
south to the region of Puget Sound. Beginning at
the north these forms are known as Passerella iliaca
unalaschcensiSy insularisy sinuosuy annectens^ town-
sendi andfuliginosa. (See Fig. 4.) The three north-
ern races, unalaschcensis^ insularis^ and sinuosa^
which occupy complementary ranges extending
from the Alaska Peninsula east to the region of
Prince William Sound, migrate to a common
wintering ground in southern California. The
next form, annectens^ breeds in the Yakutat Bay
region of Alaska and winters almost entirely in the
coastal region of central California. The form known
as townsendiy which nests in the coast region of
southern Alaska, winters in the coast region of

I20 THE MIGRATIONS OF BIRDS

northern California, being found only casually
south to the region of San Francisco Bay; while the
last of the forms under consideration, Juliginosa^
from Vancouver Island and the Puget Sound region,
may perform a vertical migration down mountain-
slopes, but aside from that wanders only a com-
paratively few miles beyond its breeding range. The
northern forms thus pass completely over those in
intermediate regions in veritable leapfrog fashion.

We can readily understand why birds might wish
to leave the inhospitable north with the coming of
winter, but why many individuals press on across
the equatorial region to south temperate lands can
be explained only by ease in accomplishment of
flight, and an instinct to wander. Any one who has
worked among the diversified faunas of the tropics
will agree that in the region of the Equator may be
found areas suitable to almost any species of bird,
where there is no question of crowding or shortage
of food supply. Insects swarm, and vegetable food,
in form of seeds and fruits, is abundant. A climate
that varies from humid to arid fosters heavy for-
ests, dry, open scrubs, broad savannas with high
growths of grasses, or areas of plain with herbage in
tufts or clumps. Sandy beaches, or broad mudflats
with low growths of mangroves, are found on the
coasts, and lakes and streams are common. Where a
local dry season is encountered, it is necessary only

Figure 4

Map to show migration of western forms of the fox sparrow {Passer-
ella iliaca). Breeding range in solid lines and winter range in dotted
lines. Numbers represent subspecies as follows: i,unalaschcensis; 2,
insularis; 3, sinuosa; 4, annectens; 5, townsendi; Sfuliginosa. Taken
from Swarth. (Courtesy of Museum of Vertebrate Zoology, Univer-
sity of California.)

DISTANCES TRAVELLED 121

to shift a short distance to an area where rains are
prevalent, if such change is desired. It would seem
that any bird could choose among these diversified
haunts one suited to its needs, and in fact many do
linger in such regions. That others press on into the
summer weather of the south temperate region may
be explained only by belief that flight is not labori-
ous, and that they delight to wander. It is possibly
merely an outgrowth, or, better, a continuation of
the wandering instinct that has carried them to
breeding grounds in areas where for part of the year
the season is inhospitable.

Mortality Among Migrant Birds

Without great reflection it is obvious that the
migrant bird, in traversing hundreds, perhaps thou-
sands, of miles of land and water, is subject to many
more perils and dangers than if the same indi-
vidual were able to remain in one locality. Storms,
unfamiliar coverts, and exposure to the attacks of
winged and four-footed enemies, to say nothing of
the possibility of becoming lost while crossing broad
stretches of water, annually destroy our smaller
migrants in untold thousands. To enable mainte-
nance of a species at the necessary maximum to pre-
vent its disappearance from the earth, it is required
that each pair shall produce a sufficient number of

122 THE MIGRATIONS OF BIRDS

offspring to permit the annual toll of death and to
leave a pair to begin the next breeding season, with
a certain ratio of additional individuals to fill the
gaps left among breeding birds that chance to be
killed before they have accomplished the act of
reproduction.

It has been noted that many birds of continental
areas in the Tropics are sedentary, or that, where
there is wandering among them, the distance cov-
ered is comparatively slight and is traversed more or
less in the shelter of their usual cover. Storms and
the crossing of broad waters do not figure in the
migratory movements of these, nor are they in dan-
ger of becoming lost. As a corollary, we find the rate
of reproduction low; from two to four eggs consti-
tute a set, with two or three as the usual number.
Broods may come at irregular seasons, but appar-
ently it is normal for them to have but one breeding
period each year. Among exceptions to this rule
may be recorded honey-creepers of the genus
Coereba^ which in the West Indies rear brood after
brood throughout the year, and are in consequence
overwhelmingly abundant in comparison with other
species. This, however, is unusual among tropical
birds.

The case of the small migrant perching bird of the
northern hemisphere is far different. Families of
three to six are the rule, with four or five as the aver-

MORTALITY AMONG MIGRANT BIRDS 123

age. Some are restricted to one annual family,
many species rear two, and a few of the more com-
mon ones three broods a season. In spite of their
apparent prolificness, these birds do not increase
appreciably in numbers unless there is some change
in conditions that affect them. The family in the
song sparrow, for example, which begins the season
with two individuals, by August, if there has been
no summer mortality, with an average family of
four to the brood has increased to ten or to four-
teen, depending upon whether two or three families
have been produced. In other words, unless deaths
begin early, the summer season closes with the origi-
nal pair of adults augmented by from eight to twelve
young. This increase represents the margin of safety
in this particular species, and illustrates the tremen-
dous annual mortality among song sparrows as a
group. Ducks rear a single brood, with six to twelve
or more young, but maintain themselves in spite of
the vicissitudes of travel and the slaughter of the
hunting season. Most shore-birds, with four young
or less as the annual addition, are unable to with-
stand destruction by man in addition to the other
perils that they encounter, and have to be carefully
protected to avoid actual extermination. The slow
production to offset death in the passenger pigeon,
which laid but a single egg, was unquestionably the
cause of extinction of this species, as excessive hunt-

124 THE MIGRATIONS OF BIRDS

ing, in addition to the usual dangers it encountered,
destroyed the delicate balance that controlled its
existence as a species, leaving man as the ultimate
cause of its destruction, much as shamefaced hu-
mans would like to attribute the ruthless extermina-
tion of this fine bird to some catastrophe of nature.

When birds have become accustomed to toll by
man, protection has at times brought a prompt re-
action, as may be seen in the case of the eastern
robin. For generations the winter flocks of this door-
yard intimate of the north were sought by hunters in
their southern migrations as basis for delectable pot-
pies. Unfamiliar with the confiding habits of the
birds on their breeding grounds, men had no scruples
in shooting them for sport and food. With the opera-
tion of the Federal Migratory Bird Treaty Act the
robin, considered under the law as a beneficial song
bird, has been afforded protection throughout its
range, so that it has increased in many regions, with
the result that now serious complaints are made of
its depredations on small fruits in the north. It is
even stated that farmers in some sections of New
Jersey have given up the culture of strawberries, as
they have been unable to cope with the appetite of
the robin for that excellent product.

Natural agencies at intervals take tremendous
toll of bird-life, as is shown by the casual instances in
which this destruction comes under the observation

MORTALITY AMONG MIGRANT BIRDS 125

of man. Sudden storms overtake hurrying clouds of
migrants, and batter them by the thousands into
lakes or seas where they drown miserably, leaving
windrows of bodies cast on lonely beaches as mute
witnesses of tragedy. Unseasonable cold may attack
birds in or near their winter homes and destroy
them in countless numbers. Such accidents have
beset our eastern bluebird, and on one occasion re-
duced its numbers appreciably for a period of years.
Cold, with consequent lack of food, has been re-
corded as the cause of death of myriads of swallows
in the Chaco of Paraguay, where most of the vic-
tims were species migrant from south temperate
regions, but among them were undoubtedly individ-
uals of our own barn swallow.

W. E. Saunders ^ has recorded a catastrophe that
overtook bands of fall migrants passing across Lake
Huron in October, 1906. A sudden drop in tempera-
ture, followed by a fall of snow ranging from two to
eighteen inches according to the locality, apparently
caught a heavy rush of migration across the lake.
Thousands of birds fell into the water and were
drowned, to be cast up subsequently along the
beaches, where their bodies in places were said to lie
piled one on another. At one point the dead were
estimated at 1,000 to the mile, and at another place
at 5,000 to the same distance. The bulk of the birds

^ Auk, 1907, pp. 108-110.

126 THE MIGRATIONS OF BIRDS

were juncos, tree sparrows, white-throated sparrows,
swamp sparrows, winter wrens, and golden-crowned
kinglets, with scattering rusty grackles, saw-whet
owls, brown creepers, hermit thrushes, and miscel-
laneous warblers, vireos, finches, and others. Their
total number was not computed, but must have
been tremendous.

Of maximum extent for one species are the catas-
trophes that have beset migrant Lapland longspurs
in the Middle West on their northern flights in very
early spring. In the plains regions this species con-
gregates in enormous numbers where food is obtain-
able. I have seen more than one hundred thousand
gathered in a single field, to feed on various weed
seeds. In their northward flight on occasion these
birds have encountered blinding storms of wet,
clinging snow, which at night bewildered the travel-
lers until they flew into various obstructions, or sank
to the ground and there perished. In such a catas-
trophe in Minnesota, in March, 1907, Dr. T. S.
Roberts has estimated that 750,000 of these birds
lay dead on the ice of two lakes, each a mile in ex-
tent. The area where dead birds were reported in
greater or less abundance on this occasion covered
over 1,500 square miles. It is astonishing to note
that in the second winter following I found long-
spurs on the prairies of eastern Kansas in even
greater numbers than usual. Similar catastrophes

MORTALITY AMONG MIGRANT BIRDS 127

have been reported recently from eastern Colorado
and Nebraska, so that the destruction of individuals
in this one species has been almost inconceivable,
running to many hundreds of thousands in these
known instances. It is of interest to observe that
among these longspurs and in the instance noted for
other birds on Lake Huron, destruction took place
during a fall of snow. It may be suggested that the
snow was the active factor rather than the cold, and
that the steady fall of flakes, more or less visible,
brought such confusion and uncertainty that the
birds flew downward rather than directly ahead and
so came to their death.

Ducks in various places in the west have perished
in multitudes from poisonous alkalis concentrated in
or about lakes or ponds in which on other years the
birds have fed with impunity. In part this has been
due to the agency of man in withdrawing water from
streams for irrigation thus lessening the supply of
fresh water that had formerly washed alkaline flats.
Such has been the case around Great Salt Lake in
Utah, where ducks and waders have died in tens of
thousands since 1910. Similar conditions occur reg-
ularly from the natural desiccation of alkaline
lakes at scattered points throughout the Great
Basin, a condition that has probably continued
since long before the advent of civilized man. Al-
though these conditions operate against resident

128 THE MIGRATIONS OF BIRDS

birds, they are most serious in connection with mi-
grants, as migration carries thousands of individuals
through these regions and augments the number
affected many fold.

Destruction of migrants through striking light-
houses has been tremendous. Clarke has described
graphically such experiences at the Eddystone Light
on the coast of England, when hour after hour be-
wildered birds by scores hovered mothlike about the
light, eventually to fall exhausted and perish. At the
Kentish Knock Lightship conditions were similar.
During heavy migrations losses were appalling, as
birds continued to strike the lantern and fall into
the water for hours; on one occasion, in mid-Octo-
ber, such destruction continued for ten and one-half
hours. The following quotation from his observa-
tions at this lightship is of interest:

Seen from the deck the three beams from the lantern
appeared to be thrown towards the surface of the sur-
rounding waters at an angle of 45.° The birds — brilliant
glistening objects — seemed to ascend, as it were,
these streams of light by a series of short jerky flaps
performed by wings which appeared to be only half
spread for flight. Some of them paused when within a
short distance of the lantern, remaining almost station-
ary, as if to sun themselves in the radiance of the slowly
passing beam. Others were bolder and approached the
light more closely, but ere they reached it spread their
tails like fans, in order to check at the last moment their

MORTALITY AMONG MIGRANT BIRDS 129

perilous onward course, and then sheered off, returning
in a moment or two to repeat the performance. . . .
Others, again, approached the light gently, and either
fluttered against the glass, or, as was particularly the
case with the starling, perched on the iron frame work of
the lantern windows and seemed to revel in the light. In
this respect the starling differed from the rest, and when
one brilliant beam had passed, the bird craned its neck
and appeared to gaze longingly toward the next, which
was slowly approaching. Indeed, the actions of the star-
ling in particular showed the birds under the spell of
some overpowering fascination. A number of the visitors
made their debut with a wild dash for the light, and
these, if they struck the glass direct, were killed out-
right; while if the contact were made obliquely, they
glanced off stunned, and, slightly injured, descended
with a curious zigzag flight which sometimes carried
them some little distance ere they were lost amid the
waves. . . . To complete the scene there was the sin-
gular effect produced by its central feature — namely,
the great lantern, which, placed high up on the mast,
swung slowly to and fro among the glittering hosts that
danced attendance upon its mystic charms. On occa-
sions when the rays were not particularly conspicuous,
the migrants flew aimlessly around, passing from ray to
ray, sometimes for many hours. It is extraordinary how
long some birds will fly round a light without resting.
As a good example may be mentioned the case of a
Kestrel, which appeared at 8.00 P.M. . . . and careered
around without a break or rest of any kind until 1.30

I30 THE MIGRATIONS OF BIRDS

A.M. . . . This bird often came close up to the light, but
checked itself by spreading its tail; and it also frequently
flew to windward, and then dashed back over the lantern
at a tremendous pace. It paid no attention to the few
birds which were sometimes present during its pro-
longed visit.^

Mr. William Brewster, in an article on bird migra-
tion published by the Nuttall Ornithological Club,^
has given a graphic account of observation at a light-
house on Point Lepreaux in the Bay of Fundy, in
August and September, 1885. Many birds struck
the light during the first week in September, when
wood warblers, red-eyed vireos, and gray-cheeked
thrushes were in migration. Mr. Brewster describes
his observations on the night of September 4 in the
following words :

Above, the inky black sky; on all sides, dense wreaths
of fog scudding swiftly past and completely enveloping
the sea which moaned dismally at the base of the cliffs;
about the top of the tower, a belt of light projected some
thirty yards into the mist by the powerful reflectors; and
in this belt swarms of birds, circling, floating, soaring,
now advancing, next retreating, but never quite able
.... to throw off the spell of the fatal lantern. Their
rapidly vibrating wings made a haze about their forms
which in the strong light looked semitransparent. At a
distance all appeared of a pale, silvery gray color, nearer,

' Clarke, Studies in Bird Migration (1912), li, 22, 23.
2 Mem. Nuttall Ornith. Club, No. i, 1886, pp. 7-8.

MORTALITY AMONG MIGRANT BIRDS 131

of a rich yellow. They reminded me in turn of meteors,
gigantic moths, swallows with the sunlight streaming
through their wings. I could not watch them for any
length of time without becoming dizzy and bewildered.
When the wind blew strongly they circled around to
leeward, breasting it in a dense throng, which drifted
backward and forward, up and down, like a swarm of
gnats dancing in the sunshine. Dozens were continually
leaving this throng and skimming toward the lantern.
As they approached they invariably soared upward, and
those which started on a level with the platform usually
passed above the roof. Others sheared off at the last
moment, and shot by with arrow-like swiftness, while
more rarely one would stop abruptly and, poising a few
feet from the glass, inspect the lighted space within.
Often for a minute or more not a bird would strike.
Then, as if seized by a panic, they would come against
the glass so rapidly, and in such numbers, that the sound
of their blows resembled the pattering of hail. ... At
times it fairly rained birds, and the platform, wet and
shining, was strewn with the dead and dying.

Birds are attracted to lights in greatest numbers
on dark nights when the air contains quantities of
moisture, not necessarily in the form of fog or mist,
but often when it is suspended invisibly. The great
destruction at lighthouses and lightships has aroused
considerable interest, especially since it was found
that many birds were not actually injured but
merely fluttered down to fall into the water beneath.

132 THE MIGRATIONS OF BIRDS

In England and elsewhere in Europe shelves and
perches in some cases have been placed below the
lights, to afford resting places for birds, on which
they can remain until they have overcome their be-
wilderment. These have been of great service in the
conservation of life, and at a number of points where
birds in former years were killed by thousands now
few dead are found. Many modern lighthouses have
lights of an intermittent type, arranged to flash at
regular intervals, and often alternate colored rays
with the usual beams of white light. These intermit-
tent flashes, particularly where they are not white,
are not so attractive, so that at many lights the
danger has been largely eliminated.

It would appear, too, that birds may learn to
avoid such dangers. The Washington Monument, a
square pillar rising to a height of 555 feet, was noted
for years for the destruction that it caused to small
migrants, particularly in autumn, and thirty or
forty years ago it was not unusual to find seventy-
five or one hundred dead warblers, sparrows, and
other small species about its base following a rainy
or foggy night. Since 1910 this destruction has prac-
tically ceased, and it is now unusual for even a few
birds to strike under the conditions mentioned. I
have watched this monument in recent years during
the time of migration, and have made many visits to
it to look for birds, but have seen very few.

MORTALITY AMONG MIGRANT BIRDS 133

All of the dangers that have been discussed are
those that regularly beset birds in their travels, and
many of them may not be eliminated, since our
feathered friends are not amenable to traffic regula-
tions which might promote the safety of their jour-
neys.

CHAPTER V

General Observations on Lines of
Migratory Flight

FROM previous statements it will be realized
that there is infinite variety in the distances
travelled by various birds in migration, and in the
choice of the routes that are followed. In fact, the
variety is so great that it almost seems as if the
methods employed in migration by no two species
exactly coincide. One species travels farther than
another, one passes south and another southwest,
one begins migratory movement early and another
procrastinates, and so on in a highly varied assort-
ment of differences. There are factors, however,
that tend to throw floods of migration along certain
lines and to leave other areas occupied to a less de-
gree, so that there are certain general lines of migra-
tion that may be traced.

Much has been written about these paths of mi-
gration, and it is generally recognized that birds in
migratory flight tend to follow lines of major topo-
graphic relief on the earth's surface when these
trend in the proper direction. Lanes of migration

LINES OF MIGRATORY FLIGHT 135

may be relatively narrow, depending upon the habi-
tat chosen by birds as a place to live, as exemplified
by the knot, the purple sandpiper, the surf-bird, and
others which, except when on their breeding
grounds, normally are found along sea-coasts, where
their chosen home is bounded on one side by broad
reaches of salt water and on the other by land or
fresh water, both equally unsuited to furnish the
food and haunt desired by these species and neces-
sary to their well-being. The knot ventures some-
what casually inland, but the bulk of its flight is
coastal. The others are strictly maritime in distri-
bution except in their northern homes. These birds
travel in narrow lanes from which there is no pro-
nounced deviation.

In those species that migrate habitually overland
the case is quite different, since here the migration
path is broad and diffuse, with indefinite boundaries.
Throughout the entire northern hemisphere, with
the exception perhaps of such tremendous altitudes
as are encountered on Mount Everest, there is in all
probability no point at which migrants do not pass.
In or over prairies or forested areas, mountains or
valleys, deserts or marshes, lakes or plains, we find
migrant birds at some time during the year, or under
proper conditions hear their calls as they pass over-
head at night. It is true that there are lines of pro-
nounced concentration in migration marked by some

136 THE MIGRATIONS OF BIRDS

river valley, mountain range, or other feature, but
such flight lines must not be visualized as narrow
paths or arterial traffic lanes, similar to the high-
ways of humans, designed especially to carry avian
travellers north and south; they are merely favored
passageways in one broad fly line that is continent
wide in extent. It is only at such places as Point
Pelee in Lake Erie, or Whitefish Point in Lake
Superior, that there is any true semblance to a
narrow lane.

It must be borne in mind, then, in subsequent dis-
cussion that the lines of flight suggested are merely
broad lanes in which migration tends to concentrate,
or general tracts through which flight is particularly
abundant. Quite often we find that early arrivals
among birds are noted first at points in the concen-
trated lanes, and that only with the rush that marks
the passage of the mass of individuals of a species
do they appear at stations at the side. In some forms
the first bird will be seen in the course of some broad
north and south river valley, and it may be several
days before there is a spread to points at either side.
In other species movement may come on a broad
front extending indifferently across the land, so that
arrivals are noted simultaneously across the line of
advance.

The accompanying diagram (see Fig. 5) to illus-
trate the author's conception of the main migration

Figure 5

Main migration routes in North America, from present knowledge.
Broken lines indicate the course of broad flight lines that extend at
either side. Certain minor channels not as yet perfectly understood
are purposely omitted to avoid confusion.

LINES OF MIGRATORY FLIGHT 137

lines of North America has been made with careful
consideration of known facts. Professor Cooke, in
his studies, plotted seven main lines of flight in
which more modern knowledge has suggested modi-
fications, and has added several minor or subsidiary-
lanes.

It must be emphasized that the dotted lines on the
accompanying diagram represent direction of flight.
They must not be construed as narrow pathways.
Migration movement is continent wide, so that the
flow of migrants resembles a tremendous stream in
which currents tend in different directions, with the
difference that with birds we may see distinct cross-
ing of lines of flight. To avoid confusion as few
lines have been used in the diagram as has been
found practicable. Thus the line paralleling the
eastern coast represents southward flight along the
coast and in the interior, and lines in the interior are
intended to convey the idea of movement through
broad adjacent areas.

In following paragraphs the discussion is directed
mainly to the southward flight in autumn. North-
ward migrations, except as elsewhere noted, flow in
general through the same channels.

To begin in the east, the first of the major north
and south lines is one that leads directly south across
the Atlantic Ocean from the coasts of Nova Scotia
and Labrador through or past Bermuda, perhaps

138 THE MIGRATIONS OF BIRDS

extending in part through the Bahamas and the
larger West Indian Islands, to the Lesser Antilles,
and then down the course of these small islands to
the mainland of South America. No land birds are
known to make the long sea flight that this journey-
entails, but it is a regular route in autumn lor thou-
sands of water-birds, of which the golden plover is
the best example. The route seems to be used by-
many other shore-birds, which pass directly south
without troubling to follow the eastern coast line of
the United States, as distance means little to these
strong flyers. It is also the passage taken in part by
such sea-birds as jaegers, and perhaps by the Arctic
tern. As it lies at sea, it is known definitely only at
the terminals or at the intermediate lands that offer
points of observation. Some shore-birds that nest
on the Arctic tundras of northwestern North
America in autumn fly southeast to follow finally
the sea road that has just been outlined.

Another regular lane extends down the eastern
coast of the United States, restricted for some
species to the immediate vicinity of salt water, while
for others there is available inland a broad stretch of
land along which minor routes of travel may be es-
tablished. Many coastal points in this line are
famous as points of observation both for land and
water-birds as they offer a considerable diversity of
natural conditions. The shore-birds that have been

LINES OF MIGRATORY FLIGHT 139

mentioned, so far as known, return north in spring
by routes that carry them along or over the land, so
that the outer sea lane is used apparently by few
individuals in returning to the north.

From the interior basin that drains into Hudson
Bay and the Arctic Ocean many birds converge in
southward flight on the Great Lakes, and then pass
directly south, as is the case with the blue goose,
which travels from its breeding grounds somewhere
in western Keewatin to this point and then drives
south to the Gulf coast of Louisiana and Texas.
Others from this same point, including many ducks
and geese, pass directly southeast toward the head of
Delaware and Chesapeake bays and ultimately
reach Currituck Sound and the coast of South Caro-
lina. There is also migration, not indicated on the
map since it is only partly understood, among a few
birds from the interior plains region to the southeast
that brings such species as LeConte's sparrow to the
coast of South Carolina.

Migrants that continue to wintering grounds
beyond Florida and the Gulf Coast have now a
choice of three travel lanes. One of these leads
through Florida, Cuba, the Bahamas, Santo Do-
mingo, Porto Rico, and the Lesser Antilles, to South
America. Though a considerable number of migrant
land birds embark on this passage the majority are
content to linger in Antillean islands, and few seem

140 THE MIGRATIONS OF BIRDS

to traverse the entire route. Many wood warblers
pursue this course in both spring and autumn, and
are found abundantly in passage. More popular is
the direct line from Florida to Cuba and Jamaica,
with a long stretch of five hundred miles which
reaches across the Caribbean Sea to the coasts of
Colombia and Venezuela. Our bobolink, trans-
formed in fall into a dull-colored, sparrowlike reed-
bird or rice-bird, seeks this line of flight and seldom
varies far from it, as only once has it been recorded
east as far as Vieques Island east of Porto Rico. The
chuck-wills-widow, a whippoorwill-like bird of the
southeastern states, in part crosses this route,
though some individuals remain to winter in the
West Indies. Yellow-billed and black-billed cuckoos,
the gray-cheeked thrush, the bank swallow, and
the black-poll warbler, may traverse this road, but
on the whole it is not popular except with the bobo-
link.

Fear of a sea-passage cannot account for the com-
paratively small number of birds that cross the
Caribbean Sea from Cuba, since to the westward
from Florida to Texas the path of the main flight of
birds that passes to Central America leads across the
width of the Gulf of Mexico to Yucatan and Vera
Cruz, a journey necessitating navigation of an open
area of sea as broad as the Caribbean. This route
seems to receive migrants that pass south through

LINES OF MIGRATORY FLIGHT 141

the coastal plain and Piedmont plateau east of the
Alleghany Mountains, those that come down the
broad reach of the Mississippi Valley, and many
that come south through the Plains region. Millions
of birds then cross the stretch of five to seven hun-
dred miles of open water across the Gulf of Mexico,
to reach southern Mexico, where there is land over
which they may continue to Central America or to
South America. The Isthmus of Panama offers a
narrow passage, but apparently many birds scorn
its protection and fly directly across the Bay of
Panama. I have seen barn swallows in such flight,
and have examined in the flesh a Traill's flycatcher
killed by striking a ship crossing this bay at night.
Hosts of warblers and others of our smaller birds
cross the Gulf of Mexico direct, and comparatively
few take the more roundabout channel through
Florida to Cuba and from Cuba to Yucatan, though
for many years this was assumed to be the regular
channel for our eastern birds that winter in eastern
Mexico. It seems simpler for the travellers to at-
tempt the direct journey in spite of the fact that on
the Cuban route it would be necessary to cross
barely one hundred miles of open water.

In the northern portion of the broad central area
of North America there is a distinct trend of migra-
tion lines in spring toward the northwest (and in
autumn to the southeast), which carries many dis-

142 THE MIGRATIONS OF BIRDS

tinctly eastern forms to the Mackenzie River Valley
and even into Alaska.

In western North America we find, in general, a
wide, poorly defined flight line, which carries birds
through the Plains area or the Rocky Mountains
southward into Mexico. The northern portion of
the Great Basin, particularly the region about Great
Salt Lake in Utah, has proved to be an area of con-
centration in autumn migration, particularly for
migrant ducks and shore-birds coming from the
north. Such birds concentrate in these great
marshes, and then in subsequent flight may travel
southeast, south, or southwest. There appear to be
two main flight lines, one that crosses the mountains
to the western border of the Plains and then sweeps
southward, and another that passes to the west and
southwest through areas of desert, to cross the
Sierra Nevada and pour a vast flood of birds into
the trough of the interior valley of California east of
the Coast Range. The return flight in spring, while
abundant, is of somewhat different character, since
many birds that come south through this region
seem to migrate north by other lines. The early
spring flights have not been adequately studied, and
will no doubt with close observation yield unsus-
pected facts. It is possible that a number of northern
water-birds not supposed to pass commonly through
the interior use the Bear River marshes at the north-

LINES OF MIGRATORY FLIGHT 143

ern end of Great Salt Lake as a regular stopping
station in the spring of the year.

Some migrants through the Rocky Mountain
region continue south into Mexico, but few seem to
penetrate far beyond the Mexican tableland. Study
of migration in that part of the Rocky Mountain
region south of the area where severe winters come
to the valleys is complicated by many altitudinal
movements, in which birds merely move up and
down the mountain slopes as the seasons change.
The greater part of the species found are not exten-
sive travellers except for those finches, sparrows,
shrikes, thrushes, and water-birds that nest in the
far north and winter in this region.

West of the Rocky Mountains there is a broad
line of flight down the Sacramento and San Joaquin
valleys in California, which is scarcely separated by
the coast ranges from a coastal line that passes
south to southern California and for some birds con-
tinues down the coast of Mexico. This coastal line is
marked strongly by species of migrant water-birds
which are restricted to the vicinity of salt water in
their search for food. Some of these are truly shore-
birds and follow the beaches. Others are maritime,
among which are included great numbers of shear-
waters and fulmars, and many auklets, that pass at
sea.

Many peculiarities of distribution due to migra-

144 THE MIGRATIONS OF BIRDS

tion lines are found in western North America^ par-
ticularly in Alaska and British Columbia. The east-
ern robin travels north to the headwaters of the
Mackenzie River, then swings over into the valley
of the Yukon and continues to the Kowak River in
northwestern Alaska. The western robin, a sub-
species characterized by somewhat greater size,
paler coloration, and lack of white spots on the tail,
when compared with the eastern bird, though found
in British Columbia and Saskatchewan, in Alaska
covers only the coastal district of southwestern
Alaska and does not penetrate into the interior.

In work on the Stikine River region of northern
British Columbia and southwestern Alaska, Mr. H. S.
Swarth has found that certain migratory forms of
the interior cross the mountains to the valley of the
Stikine (which flows into the Pacific), and penetrate
far down the river into territory that would in most
cases be assigned on geographic grounds to the forms
of birds found in the coast region proper. The north-
ern flicker (Colaptes auratus borealis)^ the eastern
nighthawk (Chordeiles m. minor), Hammond's fly-
catcher {Empidonax hammondi), the Canada jay
{Perisoreus c, canadensis), the rusty blackbird
(Euphagus carolinus), the eastern chipping sparrow
{Spizella p. passerina), the eastern yellow warbler
{Dendroica a. aestiva), and the redstart {Setophaga
ruticilld), here all cross the mountains and establish

LINES OF MIGRATORY FLIGHT 145

breeding stations from twenty to one hundred miles
from the point where the Stikine debouches into the
Pacific. In the valley of the Skeena River, two hun-
dred miles south of the Stikine, the catbird, king-
bird, and red^eyed vireo, all eastern forms, penetrate
to within one hundred and eighty miles of the sea.
In normal migration these retrace their route across
the mountains and move south along the broad in-
terior flight lines.

In considering North America as a whole, we must
mention also two important terminals, one on the
northeast and the other on the northwest, where
a few extralimital birds come to our shores to breed
and then in fall return to Old World wintering
grounds. In Ellesmere Land and Greenland, for
example, we find the wheatear breeding regularly;
and J. C. Phillips, reasoning from the many records
of the European widgeon in the eastern United
States, is inclined to believe that this duck has a
breeding colony in Greenland.

In western Alaska Kennicott's willow warbler and
the Alaskan yellow wagtail nest each summer, and
then return westward, to migrate south through
eastern Asia, while the European teal (Nettion
creccd) crosses to breed in the Aleutian Islands, but
is not known to reach the mainland. The Old World
warbler and the wagtail mentioned have had their
Alaskan colonies so long established that birds from

146 THE MIGRATIONS OF BIRDS

Alaska now differ sufficiently in color from Siberian
stock to enable them to be distinguished as sub-
species. This indicates long residence, yet we find
them following a perilous migration route across the
stormy, often fog-bound waters of Bering Sea to an
Old World winter home, when a safer route to the
south in the New World is open to them. Still more
intriguing and exciting to the imagination are the
birds that nest in Alaska, or in Siberia, and migrate
south across the open sea to winter in the islands of
the Pacific. From the American side these are
mainly water-birds whose movements will be dis-
cussed in another connection later.

Migration routes in Europe have been worked out
in considerable detail, while those of Asia have been
indicated, but are less certainly known. A hasty
review will give some of the interesting points con-
cerning the main channels.

To begin in the west — there is a broad zone of
flight that extends from the Arctic islands of Spitz-
bergen and Nova Zembla south, by way of the Scan-
dinavian peninsula, to the British Isles, a line that
receives certain tributary flight from Greenland and
Iceland. In England lines of flight extend along the
coasts, carrying large numbers of birds, while others
spread back inland throughout the island.

Another broad line is supposed to cross from the
shores of the White Sea in Russia to Holland, or to

LINES OF MIGRATORY FLIGHT 147

pass via the valley of the Rhine to the shores of the
Mediterranean. Of special interest are flights east
and west across the English Channel from the
French and Flemish coasts to England. A compli-
cated line of flight is indicated also south and south-
west through Russia. Many of the migrants from
Europe find congenial winter quarters by flights
across the Mediterranean Sea to Africa, where there
is a vast land area offering them choice of highly
diversified land conditions.

In Siberia the valleys of the Obi, Yenesei, and
Lena are supposed to offer broad pathways south,
which may swing migrants down past the Black Sea
into Egypt, via the Caspian Sea, to the shores of the
Persian Gulf, or through mountain passes into India
or the Malayan countries. The wintering hordes
toward the east are swelled by a flood of birds that
come south from Kamchatka, eastern Siberia, and
Manchuria coastwise into Japan, the Philippine
Islands, Malaysia, and the islands to the south.

The flights indicated are broadly outlined, with-
out reference to many cross lines and minor divi-
sions which are not pertinent in the present work.
They may be dismissed with the statement that
they seem more complicated than those known in
North America.

Winter migrants from the north are abundantly
evident in many of the East Indian Islands at the

148 THE MIGRATIONS OF BIRDS

proper season. In the Philippines hundreds of wag-
tails, pipits, and waders appear during autumn
migration, some to remain for the winter, others to
pass on to points farther south. In the Celebes, in
addition to these northern migrants, there are re-
corded various movements among local birds which
shift to some extent with the seasons. With the
flowering and fruiting of certain trees small parrots
of several species iXrichoglossus ornatus^ Eutelipsitta
meyeri, and Loriculus stigmatus) are abundant in
Manado in March, April, or May, and then disap-
pear, while a weaver-finch congregates in Makassar
during the rice harvest in June and July, and then
disperses. Certain large pigeons, as the nutmeg
pigeon and some of its allies, travel widely through
the East Indies, where they wander with the avail-
ability of food, but resort at the proper season to
restricted areas to nest. The Nicobar pigeon in par-
ticular has this habit, and may spread through an
area of broad extent during its wanderings.

South of the Equator we find few published data
that give definite routes of migration, and those few
are so widely scattered that it is not practicable to
summarize them completely here. Merely a hint
of the main routes followed may be traced in state-
ments in paragraphs that follow.

From North America a number of species of birds
come annually to winter in South America, but com-

LINES OF MIGRATORY FLIGHT 149

paratively few of these pass beyond the tropics.
There are some however that go south regularly to
the South Temperate Zone, and among those that
perform this extended flight are a few birds of com-
paratively small size. The barn swallow migrates in
part to Paraguay and Argentina, and may be found
in the southern spring hawking about with flocks of
native swallows, some of which later may retreat to
Patagonia to breed. The bobolink is more worthy of
mention as, though the barn swallow ranges from
the West Indies southward in winter, the bobolink
withdraws entirely into Brazil and the Chaco.

The cliff" swallow, the olive-backed thrush, the
yellow-billed cuckoo, the nighthawk, and Swainson's
hawk are regular, though not abundant, arrivals as
far as northern i\rgentina, while along the coasts of
the Province of Buenos Aires we may expect para-
sitic and long-tailed jaegers, and Cabot's, royal, and
arctic terns. The bulk of North American migrants
here, however, is composed of shore-birds, of which
some species, as the golden plover, the upland
plover, Baird's, white-rumped, buff-breasted, and
pectoral sandpipers, the Hudsonian godwit, and for-
merly the Eskimo curlew, find in the pampas and in
Patagonia their winter metropolis. A few individuals
of these northern species arrive in the south in
July and August, but the main southward flight
occurs from September to October. In other words

I50 THE MIGRATIONS OF BIRDS

these shore-birds pass south with the coming of
autumn in the northern hemisphere, cross the Equa-
tor, and then follow the advance of the southern
spring to their winter home, where they live amid
summer weather. At the close of the southern sum-
mer, with the coming of colder weather in February
and March, they withdraw northward and again
cross the Equator, to follow the northern spring in
its advance to their breeding grounds in the northern
United States, Canada, and Arctic America. Their
journey thus is timed to take advantage of the shift-
ing seasons of both hemispheres.

In their movements through South America these
northern species have three main routes, one along
the Atlantic Coast, one that skirts the Pacific Coast
line, and a third that follows north and south along
the great interior river system of the Paraguay and
Parana. There is also migration, not well under-
stood, across the high plateaus of the Andes, parti-
cularly in the vicinity of Lake Titicaca.

With regard to the movements of native birds in
South America, there are many observations on
record in the writings of Dabbene, Gibson, Hudson,
and others, while J. L. Peters has given an account
of the spring arrival of a number of species in north-
ern Patagonia.

Migratory movements are as readily evident to
the field observer as in northern regions. Flocks of

LINES OF MIGRATORY FLIGHT 151

various species of ducks, seed-snipe, small flycatch-
ers {Lessonia rufd), that run about on the open
ground, a migrant form of house wren, with other
birds, appear in the Province of Buenos Aires from
more southern regions at the beginning of winter,
and as summer approaches, again withdraw to the
southward. A goatsucker (Xhermochalcis longiros-
tris) is a regular summer migrant from Brazil to
Patagonia. Occasionally one becomes lost in pas-
sage across the pampas and descends in some Ar-
gentine estancia, where it is greeted with amazement
by wondering peons, who seek its feathers as a po-
tent charm by whose force a suitor may hope to gain
favor in the eyes of his inamorata. Near Buenos
Aires the jacana, the sulphur-bellied flycatcher
{Myiodynastes solitarius)^ two species of martins
{Progne elegans and Phaeoprogne t. taper a) ^ and a
small swallow {Jridoprocne albiventris) are summer
visitants, which at the approach of cold retire to the
north, as does the bulk of some other species, a part
of whose individuals are sufficiently hardy to brave
the moderate cold of winter in that latitude.

Even in northern Paraguay, in the edge of the
tropics, the spring migration is easily evident, as
with the advance of September Podager nacunda, a
bird related to the nighthawk, passes in regular
evening flights toward its summer haunt in the
pampas, hawking for food as it travels in rapid zig-

152 THE MIGRATIONS OF BIRDS

zags across openings in the forest; a kingbird {Ty-
rannus m. melancholicus) appears and continues
south into the scantily wooded area of central Ar-
gentina; and a little goatsucker {Setopagis parvulus)
arrives from winter quarters in Bolivia and Brazil,
to utter its tremulous calls at evening.

The low woodland of the level reaches of the in-
terior Chaco, which lies west of the Rios Parana and
Paraguay, from Santa Fe in Argentina to southern
Bolivia, with its dense jungles impervious to cold
winds, and its tangled openings where the rays of
the sun are warm even on frosty mornings, harbors
many winter visitants from the more open country,
or from the mountain slopes to the west. Here
small flycatchers, warblers, and other insect-eating
birds rest in comfort, remaining quiet during brief
spells of cold, and becoming active when the sun
appears. Broad stretches of dense scrub that cover
the low hills east of the mountains from Tucuman
northward, also offer secure coverts where small
birds at times fairly swarm.

Altitudinal migration is easily evident in the
Andean foothills from Bolivia southward, as in
autumn flycatchers and other small birds work down
the mountain slopes in little bands which travel
down to the plains and then pass on northward.
With heavy storms at high altitudes these move-
ments are especiallv marked and may include birds

LINES OF MIGRATORY FLIGHT 153

from the hills, which migrate temporarily to the
warmer lowlands and then return to higher regions
after the stress of weather has passed.

In considering migration among birds of this por-
tion of the southern hemisphere we must not neglect
to examine the remarkable habits of some of the
shearwaters and petrels. The sooty shearwater, for
example, nests on islands in New Zealand seas and in
the vicinity of Cape Horn, and in May, after the
breeding season, migrates northward, to cross the
Equator through both great oceans, and reach the
latitude of southern Greenland and the Kuril and
Aleutian islands. In September, it returns south-
ward. The slender-billed shearwater, at the same
season, from breeding grounds in southern Austra-
lian and New Zealand waters, comes north along the
western side of the Pacific, and in May passes south
along the eastern shores of that ocean. One or the
other of these two species in Alaskan waters, ranges
in flocks numbering tens of thousands. Wilson's
petrel, the little Mother Carey's chicken of the
sailor, also nests in extreme southern latitudes and
passes north in March, April, and May, on erratic
flights that carry it through the oceans of the entire
world with the exception of the North Pacific. These
species and some others penetrate as far north of the
Equator, as some terns, jaegers, and shore-birds
which breed in the Arctic travel south of it.

154 THE MIGRATIONS OF BIRDS

The migrations of birds in Africa are comparable
to those recorded for South America, though, as on
that continent, information available from the tropi-
cal area is meagre, since ornithologists interested in
the subject have seldom been resident for sufficient
time to make prolonged observations. As a winter
resort for migrants from the Northern Hemisphere,
Africa is more popular than South America, prob-
ably because of the comparative ease with which it
is reached by cautious wayfarers. Spain, Italy, and
near-by islands, and Arabia, offer passageways on a
broad front for birds that do not care to attempt
directly a crossing of the comparatively narrow
width of the Mediterranean. If blown aside by
storm, migrants have fair chance of a landing some-
where on the broad land area of either the northern
or southern continent, so that the dangers of crossing
are little more than those incurred in flight over
land. The physical barriers imposed against mi-
grants are thus more favorable than in the New
World, where the Gulf of Mexico and the Caribbean
Sea extend at an angle, with a narrow line of islands,
separated by considerable distances in some cases,
forming the only barrier from the open sea on the
east. It has been said that more migrants cross the
Mediterranean Sea than any other sea in the world
though whether more pass than fly across the Carib-
bean and the Gulf of Mexico combined is perhaps
open to question.

LINES OF MIGRATORY FLIGHT 155

In the Cape region of South Africa W. L. Sclater
has recorded seventy-six migrant species from
Europe and Asia that come for the period of the
northern winter; while J. P. Chapin, working
mainly in the forest belt of equatorial Africa, has
recorded approximately fifty visitors from the Palae-
arctic region. On the face of it one might suppose
that the great desert of the Sahara would interpose a
barrier to flight as perilous to cross as that of some
great sea, but apparently this is hardly true since,
though bird life is scant in areas of shifting sands,
zoological exploration of recent years has yielded a
varied avifauna in many districts in the Sahara.
Hartert has recorded 24 or more Northern Hemi-
sphere migrants in Air in the central Sahara, where
they were associated with many obviously tropical
species; and there are broad areas where desert
mountains and semi-arid valleys offer favorable
conditions. To the eastward the Nile Valley and the
eastern coast-line offer ready fly lines, which lead as
far south as the bird may care to go. The valley of
the Nile in particular is favored by multitudes of
shore-birds, cranes, ducks, and other fowl that nest
in northern Europe and Siberia.

The northern migrants that reach southern Africa
arrive in October and leave for the north in March
and April. Among them are included such well-
known European birds as the golden oriole, four

156 THE MIGRATIONS OF BIRDS

forms of wagtail, the red-backed shrike, the willow
wren, the spotted flycatcher, the swallow, the
Egyptian kite, three marsh harriers, the white
stork, five plovers, and an assortment of other shore-
birds. In southern Africa Sclater finds 21 native
species regularly migrant toward the north at the
close of summer, which return in spring to breed.
They are supposed to winter in central Africa.
Curiously enough, of the entire number of these
migrants no less than nine are cuckoos. These are
accompanied by three native forms of swallows, a
swift, a roller, a wryneck, a falcon, Abdim's stork,
two coursers {Cursorius temminckii and Rhinoptilus
chalcopterus)y and a wattled plover {Afribyx sene-
gallus lateralis).

Local migration is, however, more extensive in
southern Africa than the list just enumerated would
indicate, since there are about fifty additional forms
a part of whose individuals remain in winter when
others travel to the north. Movements among
these are dependent in part upon rains or other
conditions. Some, as the wattled starling and
Nordmann's pratincole, wander, when not nesting,
with the appearance and disappearance of the hordes
of locusts for which these regions are noted. The
white stork, a migrant from Europe, joins them in
their travels during the season that it is present.
Andersson, in studies of the birds of Damaraland,

LINES OF MIGRATORY FLIGHT 157

recorded a number of species which were present
only during the rainy season, a condition that may
hold as well in other parts of Africa.

In the northeastern section of the Congo Basin
Chapin, during observations that covered three
successive years, has recorded nearly forty species
of truly African birds which he considered more or
less migrant. Most interesting among these is the
pennant-winged night-jar (Cosmetornis vexillarius)^
a remarkable species in which the adult male has
two of the inner primaries (the second and third)
greatly elongated, so that they measure two and
one half times the length of the bird from the end
of the bill to the tip of the tail. Though strictly
tropical in its range, this striking species migrates
regularly back and forth across the Equator twice
each year. From September to November it breeds
in the open country south of the equatorial forest,
from Angola and Lake Tanganyika to Damaraland
and the Transvaal. A few birds remain throughout
the season in the northern edge of the breeding zone,
but the majority migrate northward in February to
Uganda and the grass country adjoining the forest
on the north. Its movements correspond with the
seasonal appearance of termites in the two regions
concerned, so that in the activities of these insects,
which form a valuable food, we may see a reason for
the shifting in range on the part of the goatsucker.

158 THE MIGRATIONS OF BIRDS

An allied species, the standard-wing night-jar
(Macrodipteryx longipennis)^ has somewhat similar
habits, and a like migration is suspected in the case
of other birds.

i^i; Before leaving the subject of Africa it may be men-
tioned that thirty-six forms of sea-birds are found
on the southern coasts, most abundantly in the
winter period from March to October, which in the
breeding season leave for islands far distant in the
ocean, where they rear their young. The majority
of these — twenty-nine to be exact — are petrels,
shearwaters, and albatrosses, while the others are
mainly terns.

Perhaps there are fewer data assembled on the
migration of birds in Australia than on this phenom-
enon in any of the other continents, yet a study
of the movement of birds here is highly important,
in the evidence it offers that may throw light on the
possible origin of migratory movement. There are,
as in other southern continents, a small number of
species that come in search of winter quarters.
Thirty of the migrant forms, other than pelagic
wanderers among sea-birds, which seem thus far
to have been recorded at all regularly, are shore-
birds or their relatives, while one of the remaining
three, the white-winged black tern (Chlidonias
leucoptera)^ is found only rarely in North Australia.
This leaves the spine-tailed swift (Chaetura cauda-

LINES OF MIGRATORY FLIGHT 159

cutd) and the Pacific swift {Micropus pacificus) as
the only other species that perform regular flights
to this far-distant land, where they remain during
the northern winter. These two occur regularly
and penetrate to the southern portion of the con-
tinent. There are a few other species as the corn-
crake {Crex crex), a yellow wagtail {Budytes flava
simillima), the parasitic jaeger {Stercorarius para-
siticus) and the upland plover {Bartramia longi-
cauda)y which have occurred in Australia casually,
but cannot be considered regular visitants. Few of
the winter residents go farther than Australia, so
that records of northern migrants for Tasmania and
New Zealand are in the main casual or accidental,
and are based on few occurrences. In New Zealand
the only regular migrant seems to be the Pacific
godwit {Limosa lapponica baueri), though there
are a few records for the knot, curlew sandpiper,
and the Pacific turnstone, which indicate more or
less regular arrival among these birds. The corn-
crake, the two swifts that come to Australia, the
parasitic jaeger, and a long list of shore-birds have
been included in the New Zealand list but only on
basis of from one to three records.

Among native Australian birds there may be
recognized two groups, a small band that is regu-
larly migrant with the season, and a greater number
that are so irregular in occurrence that they have

i6o THE MIGRATIONS OF BIRDS

well been called nomadic. Among regular migrants
may be noted the dollar-bird (a roller, Eurystomus
pacificus), and the channel-bill {Scythrops novae-
hollandiae)^ a large cuckoo, which, according to
North, arrives in Queensland and New South Wales
in August or September, and departs with the com-
ing of cold weather in April. The sacred kingfisher
{Sauropatis sanctd) in New South Wales comes in
August and September, and, after breeding, departs
in March. A few remain throughout the winter,
and the migration of this species is not far, as it is
said to be resident in northern Queensland. The
spotted harrier (Circus assimilis) reaches New
South Wales in August and departs in February.
The slate-breasted rail {Rallus p. pectoralis) ap-
pears on the Adelaide Plains in August or Septem-
ber and leaves in November. Of greater interest
are the movements of the bee-eater (Cosmaerops
ornatus)^ of which two forms are known, an eastern
and a western, of which the last may be sedentary.
Though a few of the eastern subspecies may remain
throughout the year in the northern portions of
Australia, the majority migrate to New Guinea,
possibly to other islands, as they have been seen in
flight past Thursday Island, and at other points in
Torres Straits. Some are said to make a direct flight
to eastern New Guinea, without troubling to pass
north to the narrow pass at the end of the York
Peninsula.

LINES OF MIGRATORY FLIGHT i6i

There are four species of swallows that reach
South Australia, three of which are certainly mi-
gratory. The welcome swallow {Hirundo neoxena)
a species that received its common name through
the pleasure that its appearance gave early white
settlers, has been recorded by Morgan near Ade-
laide throughout the year, but is less numerous
through the winter period. Some of those that re-
main are not seriously inconvenienced by cold, as
occasionally they breed at that season. However,
it has been stated that after cold nights ten or a
dozen of these swallows have been found dead in
the reed beds to which they resort to roost. The
fairy martin {Lagenoplastes artel) is a strictly mi-
gratory species, while the white-breasted swallow
(Cheramoeca leucosternori) at Laura, 140 miles north
of Adelaide, where at an altitude of 700 feet the
winter is cold, is strictly migratory, though at sea-
level, at Port Augusta, only sixty miles away, where
the winter air is milder, the birds are resident. It is
possible that here they perform only a brief altitudi-
nal flight. The welcome swallow and the white-
breasted swallow cross to the island of Tasmania to
breed but return to the continent to winter.

In New Zealand the Australian avocet, an Aus-
tralian heron {Notophoyx novaehollandiae) ^ a night-
heron {Nycticorax caledonkus)^ the Australian tree-
duck {Leptotarsis eytoni)^ a teal {Nettion castaneum)^

i62 THE MIGRATIONS OF BIRDS

a pochard {Nyroca australis)^ and a darter {Anhinga
novaehollandiae), are noted as irregular visitants,
indicative of slight migratory wanderings among
these species, which carry them beyond their native
continent of Australia. In New Zealand, too, we
find two cuckoos (Lamprococcyx lucidus and Urody-
namis taitensis) which are present only in summer
and disappear in cold weather. The long-tailed
cuckoo migrates through the Pacific Islands to Fiji
and beyond. The winter home of the other species
is not certainly known.

Considerable numbers of birds found on the
Australian continent are so distinctly irregular in
their occurrence that they may be best termed
nomadic, since they wander with climatic changes
and are not seasonal in their occurrence. Many of
these are directly affected by rains in their move-
ments, as failure of water supply in the more arid
sections may drive them to more favored areas,
while conversely an excess of rain recalls them. A
gallinule {T^ribonyx ventralis), according to Captain
S. A. White, visits South Australia every few years,
where it remains from July to November. After
appearing regularly for a time, it may be absent
entirely for a number of years — an erratic habit
that is apparently common to it throughout the
continent. Various lorikeets are said to be governed
in their nomadic forays by the blossoming of the

LINES OF MIGRATORY FLIGHT 163

eucalyptus, on whose flowers they depend for food.
In New South Wales in favorable years T. P. Austin
has found the musk lorikeet {Glossopsitta concinnd)
arriving by thousands with the blossoming of these
trees. At times they soon disappear, though in some
years a part remain to breed. In other seasons very
few are seen. Similar habits are recorded for the
little \or\\Lttt {Glossopsitta pus ilia) in the same region.
The cockatoo parrot {Leptolophus hollandicus)
comes usually to Victoria in summer, while the grass
parrakeet {Melopsittacus undulatus) is found to be
irregularly migrant in many localities. Like the
lorikeets, certain of the honey-eaters (Meliphagidae)
shift about with the flowering of eucalyptus, and
are present or absent in accordance with the status
of these trees.

The arrival of birds in abundance with the com-
ing of rains has been recorded on numerous occa-
sions in the more arid sections, while it is stated
that, if proper conditions continue, these birds breed
and may continue their presence for two or three
years. The condition is highly peculiar, in that
the nomadic habit is not confined to a few species
as in the northern hemisphere, but is widespread
and dominant among non-sedentary forms, so that
it supplants the regular north and south movements
found in other continents except in a comparatively
few forms. It differs from regular migration in that

164 THE MIGRATIONS OF BIRDS

there is no hereditary tendency toward regularity
of movement. It may be considered as one of the
preliminary stages leading to the development of a
regular seasonal movement when it becomes neces-
sary to adjust to regular seasonal cycles.

CHAPTER VI
Migration Among Shore-birds

SANDPIPERS, snipe, and plover, and the other
forms that comprise the group of shore-birds are
renowned among ornithologists for their powers of
flight and the distances that they cover in migration.
Approximately seventy of the two hundred or more
that are known nest in Arctic regions and are forced
to migrate each year. The distances they cover are
marvellous, as a number pass south to winter in the
southern hemisphere. One or two species, as
Peale's sandpiper {Aechmorhynchus parvirostris) of
the Tuamotu Archipelago in the South Pacific and
an allied species {Prosobonia leucoptera) of Tahiti,
— the latter now perhaps extinct — are, so far as
known, entirely sedentary. A few other forms of
sandpipers perform limited migrations, but such
appear unusual in an assemblage of species noted
for the extent of their semi-annual flights. As a
group the shore-birds cover greater distances in the
aggregate in their spring and autumn flights than
any other birds.

The purple sandpiper {Arquatella m. maritima),
breeding in the northern hemisphere, in eastern

i66 THE MIGRATIONS OF BIRDS

North America is found in winter from Greenland
south regularly as far as Long Island. Its western
forms, the Aleutian sandpiper {Arquatella m. couesi)
and the Pribilof sandpiper {A. m. ptilocnemis)^ which
breed on islands in Bering Sea and the Northern
Pacific, come south only into southern Alaska. The
American woodcock (Ruhicola minor) ^ nesting
mainly in northeastern United States, winters in the
southern states largely east of the Mississippi River.
In South America there is a peculiar three-toed
sandpiper {Phegornis mitchelli)^ found at high alti-
tudes in the Andes, which seems to content itself
with a limited migration down into valleys; while
another, the so-called sociable plover {Pluvianellus
sociabilis)^ ranging near the Straits of Magellan is
not known to migrate at all.

Among North American species of shore-birds
there are twenty-three forms which are found in
winter from our southern states south to South
America, four others which fly south through the
Pacific Islands, and ten, in addition to those already
mentioned, which retire wholly to South America
in winter. It is possible that this last number may
be increased to twelve, since the winter range of
the red and northern phalaropes is not certainly
known.

The majority of our shore-birds nest in boreal
regions, and many seem to remain on their breeding

MIGRATION AMONG SHORE-BIRDS 167

grounds a very short time; for the spring migration
does not close until the end of May, while in some
species early migrants begin to arrive from the north
by the first week in July. In the case of the Wilson's
phalarope {Steganopus tricolor) in Utah, I have
definitely established that there are many that do
not breed each year. At the northern end of Great
Salt Lake this species nests in small colonies where
marsh conditions are suitable. During June, in
addition to the breeding colonies, I found large flocks
composed entirely of non-breeding individuals (as
was shewn by examination of the sexual organs in a
considerable number) congregated on the lake front
where food was abundant. On one occasion I esti-
mated that between 20,000 and 30,000 were gath-
ered about shallow pools on one stretch of alkali
barrens, and it was impossible to say how many
more were concealed in the shimmering heat haze
that concealed all low objects beyond a distance of
half a mile. Strangely enough more than ninety
per cent of these birds were females, which leads to
an assumption that there may be a preponderance
of that sex in the species under discussion, as mated
pairs at the time were on their nesting grounds in
nearby marshes.

It is not improbable that some of the early mi-
grants which are recorded among other shore-birds
are also non-breeding individuals, or are perhaps

i68 THE MIGRATIONS OF BIRDS

those whose eggs have been destroyed and their
attempts at rearing a family thus frustrated. With
no further cause to remain in the north, these may
push rapidly southward and form our early mi-
grants. However we may attempt to explain the
phenomenon, the facts remain that many birds of
this group start south very early, so that by the
middle of July in the northern United States mi-
gration is well under way in a number of species.
It is of interest to note that passage southward in
m^any individuals is rapid. In 191 2, in Porto Rico,
the spotted sandpiper arrived from the north on
July 9, and the solitary sandpiper on July 29. In
1920, in southern South America, I noted the be-
ginning of migratory movement from the north
among these birds on July 31, with the arrival of
the lesser yellow-legs on lagoons near Las Palmas,
Chaco. The solitary sandpiper reached the town
of Formosa on the Rio Paraguay on August 23;
while during the first week of September, when I
had penetrated north to Puerto Pinasco in northern
Paraguay, migration began in earnest, and a steady
stream of sandpipers and plover passed southward
through the Chaco throughout the month. This
southward movement was still in force during Octo-
ber when I was in the open pampas of eastern
Buenos Aires, and continued without appreciable
abatement until the close of the first week in No-

MIGRATION AMONG SHORE-BIRDS 169

vember. By the middle of November, arrivals from
the north ceased and birds of this group were settled
on their winter resting grounds.

Changing conditions in this far distant region
have affected many of our North American mi-
grants, which go there to winter, as seriously as the
persecution of guns to which they have been sub-
jected in the North. Broad areas of dry or marshy
pampa, under primitive conditions the winter homes
of myriads of golden plover, upland plover, and
Eskimo curlew, are now devoted to raising wheat or
to the pasturage of great herds of cattle and sheep.
Added to this change in ecological conditions, there
has been persecution by man because certain of
these birds became famed for the delicate flavor
of their flesh. The Eskimo curlew, unable to adapt
itself to changing conditions, is practically, if not
actually, extinct; while the upland plover, greatly
reduced in abundance, at present aided by protec-
tion from gunners in the United States and Canada,
is holding its own though its fate is doubtful, since
in South America it has inherited the name and
epicurean fame that proved the downfall of the
Eskimo curlew. The golden plover is in better
state, since it lives on the broad coastal mudflats
as well as on the open prairies, and in the former
locality is less accessible. It was strange to find the
white-rumped sandpiper, a species known well to

lyo THE MIGRATIONS OF BIRDS

few ornithologists in the United States, the most
abundant of the wintering shore-birds on the
pampas.

On the eastern coast of the province of Buenos
Aires, while living in a lonely herdsman's hut among
sand dunes, far from other habitation, I witnessed
an interesting example of crossing lines of migration
in these birds. Apparently many shore-birds drive
down the broad interior basin of the Rio Paraguay
and continue straight south in their rapid flight,
until they reach the coast in the vicinity of Bahia
Blanca. Here some remain, some pass on south,
and a certain number swing around to follow east
and then north along the coast to wintering grounds
near the mouth of the Rio de la Plata. At the camp
mentioned I noted these birds driving by toward
the north, while at the same time little bands of
sanderlings, occasional knots, and a steady stream
of jaegers came directly south by the coastal route.
Thus I had spread before me the spectacle of two
lines of migration flight, both emanating originally
from the same northern sources, but here, near the
end of their long journeys, meeting and passing in
directions diametrically opposite — one of the most
interesting sights that has come to my attention
during long years spent in field observation.

Once established on their wintering grounds,
these birds become quiet and more or less sedentary.

MIGRATION AMONG SHORE-BIRDS 171

Heavy rains that flood new areas in the pampas may
frequently bring small flocks of shore-birds in search
of new feeding grounds, but such movements are
of slight extent and affect comparatively few indi-
viduals. A period of moult is at hand and the birds
are inactive. Change in behavior is especially
marked in the two species of yellow-legs, which be-
come as quiet in notes and demeanor as small sand-
pipers or plover, quite in contrast to their noisy
greeting of intruders in their flights north of the
Equator. They remain thus during the months
that mark the northern winter.

The impulse toward the return flight to the north
comes early; for at the close of January in 1921 I
noted a slight movement among golden plover on
the eastern coast of Uruguay. On February 7 up-
land plover began passing northward in small
numbers through eastern Uruguay, and on the fol-
lowing day pectoral sandpipers began their flight.
These early individuals must make frequent long
stops, so that their northward flights extend over
a considerable period of time, since their breeding
grounds are not open to them until a much later
date. Slow increase in northward migration was
observed during February, and by the close of the
first week in March the movement was in full swing.
The first week in April marked its culmination, and
by the end of that month decrease in shore-birds

172 THE MIGRATIONS OF BIRDS

was easily apparent. Many northern shore-birds
however linger in the central portion of South
America until May, when they must drive swiftly
northward, with comparatively little rest, to reach
their northern homes by the opening of the brief
period of summer.

There is also evident migration among a few
South American forms that belong to the shore-
bird group. What is known in Spanish as the
Chorlito inviernOy " the little winter plover" {Zonibyx
modes tus)y and the Falkland plover {Charadrius
falklandicus)^ nest regularly from Patagonia south-
ward, and with the approach of cold weather migrate
north in company with foreign species as far as the
pampas, but there linger. With them come a few
individuals of a larger form {Oreopholus r. ruficollis).
These southern species are not known however to
reach the Equator in their northward journeys.
Migratory flight of a similar nature is known in the
Paraguayan jack-snipe (Capella paraguaiae)^ but its
extent has not been definitely ascertained.

Brief mention has been made previously of mi-
gration from Arctic regions into the oceanic islands
of the South Seas, a wintering ground that reaches
to the eastern atolls of Polynesia, far distant from
any continent. The Pacific golden plover and the
turnstone regularly perform this flight, while with
them come the bristle-thighed curlew, the wander-

MIGRATION AMONG SHORE-BIRDS 173

ing and Eastern tattlers (Heteroscelus incanus and
H. brevipes), the sanderling, the Pacific godwit, and
the sharp-tailed sandpiper. These pass to the far
south, the godwit regularly reaching New Zealand,
while some of the others penetrate irregularly or
casually to that group of islands. The Pacific
golden plover is a regular migrant to the islands of
Hawaii, and winters there in some abundance on
grassy uplands; others of the subspecies pass on
far to the southward. In the passage south, if
these birds touch at the Aleutian Islands, they have
a distance of nearly 2800 miles across open seas be-
fore they reach a safe haven of land. As in this great
stretch there are no landmarks, they must revert
to some sense of direction to guide them safely.

Among hunters on the island of Barbadoes in the
British West Indies there is current belief that shore-
birds migrant to that island alight to rest on the
surface of the ocean; and it is the custom when
shooting to taste the axillar feathers of birds killed.
If these have a flavor of salt, it is assumed that the
bird has recently arrived, and the salty taste is
attributed to immersion in the ocean. Though it
is not impossible that shore-birds might alight on
the water to rest and then fly again, there is no ob-
servation known to me to prove that they regularly
do so. The salt taste alluded to could easily arise
from a deposit from vapors blown by the wind, as

174 THE MIGRATIONS OF BIRDS

it is common in walking along sea beaches for lips
and hands to receive a slight deposit of salt — a cir-
cumstance that must operate on the feathers of
birds as well as on the skin of humans.

It has been my fortune to see wayfaring shore-
birds make a landfall after a long trans-ocean flight.
While cruising through the Leeward Islands of
Hawaii in 1923, I observed turnstones coming up
from the south, where the nearest land, in the Gilbert
or Marshall Islands, was a thousand miles away.
The birds usually arrived in early morning. On
one occasion in particular some turnstones came
beating up from the south at daybreak, flying low
in the trough of the waves to escape as far as pos-
sible the force of the wind. They seemed tired and
passed rather slowly toward low islands in the atoll
at Pearl and Hermes Reef a few miles distant.

Africa, like South America, receives many mi-
grant shore-birds, as nineteen species that breed in
the far north come there regularly to winter. Many
others pass south through Asia to wintering grounds
among East Indian islands, or penetrate to distant
Australia. Northern shore-birds are found in
abundance in the Philippines and Celebes, and
Mathews records thirty species of this group that
winter more or less regularly in Australia.

From this review it appears that many plover
and sandpipers that breed in Arctic regions winter

MIGRATION AMONG SHORE-BIRDS 175

south of the Equator in the southern hemisphere,
so that as a group they have longer migration routes
than any other order of birds. Though the south-
ern hemisphere has a number of peculiar forms some
of which are more or less migratory, there are none
that perform the extensive flights common among
their brethren of the north.

In connection with this group, it may be well to
consider claims that have been made that the god-
wits, yellow-legs, and plover found in South America
in winter do not really come from the north, but
that there are two groups in the species concerned,
one that breeds in boreal regions and in winter mi-
grates toward the Equator, and another that nests
somewhere in Patagonia, the islands of Antarctic
Seas, or even on the great Antarctic continent, and
in cold weather flies toward the north to winter in
Argentina. This belief has been based in part upon
the irregular occurrence of these migratory birds
during periods when all should have been on their
northern breeding grounds, and in part upon dis-
belief in the power of flight in creatures apparently
small and weak.

It may be said definitely that there has never
been any proof of the breeding of such species as
the golden plover, the yellow-legs, the godwits, or
other similar species, considered as migrants from
the north, during their sojourn south of the Equator

176 THE MIGRATIONS OF BIRDS

in South America or elsewhere. Eggs of yellow-legs
are said to have been found in Argentina, and Lay-
ard has stated that in New Caledonia he has seen
the golden plover followed by a downy chick; but
in these and similar instances on record supposed
parentage on the part of the shore-birds concerned
has been based solely on assumption and associa-
tion, and authentic instances have never been pro-
duced. Layard, for example, did not collect the
downy young that he supposed to be that of a golden
plover; and eggs have been attributed to the yel-
low-legs in Argentina simply because those birds
were seen near-by.

Double nesting periods have been claimed for the
European bee-eater and some other birds in South
Africa, but as our knowledge has increased, it ap-
pears that, with the possible exception of certain
cuckoos, the birds that breed in Africa are a dif-
ferent set of individuals from those that nest in the
north. In the New World the pied-billed grebe, the
cinnamon teal, and the fulvous tree-duck have
breeding ranges in both North and South America.
In some cases individuals in the two groups differ
slightly from one another, while in others, notably
the cinnamon teal, they appear indistinguishable.
Yet, so far as we know, the colonies are wholly dis-
tinct and have no interchange of individuals.

There are a number of shore-birds that remain in

MIGRATION AMONG SHORE-BIRDS 177

the south during the northern summer, as they have
been recorded in South America, and I have per-
sonally seen golden plover, turnstones, and tattlers
among islands in the Pacific at that season. Scat-
tered individuals that I have examined were found
to be wounded, sterile, or otherwise diseased indi-
viduals that were unable to perform the long flight
to their northern homes, or from their condition
lacked the physiological incentive to so do. In the
Hawaiian islands it appeared to me that most of
these lingerers seemed to feel a desire to travel
northward, but were restrained by their condition
from making the attempt. A number seen were
individuals that had not been successful in carrying
through the winter moult, and in consequence were
in very ragged plumage. Imperfections in the flight
feathers would weigh heavily against chance of
success in prolonged flights to northern lands. We
shall never know how frequently such imperfections
result in slackened flight, which prevents such birds
from reaching the safety of the distant land toward
which they fly, as any that may fail disappear in the
broad seas they are required to cross.

Of classic interest in discussion of the flights of
American shore-birds is the migration route cov-
ered by the golden plover. The eastern form of this
bird, from its breeding stand in Arctic America in
late summer, migrates to the east and southeast

178 THE MIGRATIONS OF BIRDS

to Ungava and Labrador, and from there embarks
in a flight that carries it directly out over the open
sea. It is uncommon ordinarily on the coasts of
New England, and casual and irregular south to
Long Island. From that point south, the bird is al-
most unknown. The migration route carries it past
Bermuda, the Bahamas, and the Lesser Antilles,
apparently in large part over the ocean, as few seem
to alight. Colonel Fielden has recorded early arri-
vals at the island of Barbadoes in July and the first
part of August, but finds that the main flight comes
after the latter part of August. The course in flight
across the island is from northwest to southeast,
and if unfavorable winds prevail, many alight. The
early arrivals are black-breasted birds, which in-
dicates that they are adults. The young begin to
appear about the twelfth of September, and con-
tinue in flight into October or even November.
From here they continue south to the continent of
South America, and finally reach a wintering ground
in the Argentine pampas.

During the fall migration golden plover may be
scattered over a tremendous range. In 1920 I
noted the earliest arrivals at small lagoons in the
Chaco west of Puerto Pinasco, Paraguay, on the
sixth of September. On this same date Dr. Francis
Harper, travelling for the Biological Survey, re-
ported golden plover in small numbers in the vicin-

MIGRATION AMONG SHORE-BIRDS 179

ity of Lake Athabasca in central Canada. In an air
line the species was thus spread across more than
six thousand miles of the earth's surface, while, by
the actual line of flight which these birds pursue,
the separation of northern and southern individuals
was infinitely greater.

The flight of golden plover in spring begins casu-
ally at the end of January but is not fully under way
until March and April, when they pass north with
a rush to the northern coast of South America.
From here, instead of flying north over the sea on
a return journey by the course pursued in autumn,
they cross to the Gulf coast of the United States and
go north through the Mississippi Valley to their
Arctic breeding grounds. Their spring route is thus
over a course where the birds are entirely absent in
autumn.

The Pacific form of this species, which nests along
the Bering Sea coast of Alaska and in northeastern
Siberia, travels south along the eastern coast of
Asia as far as Australia, Tasmania, and New Zea-
land, and through the Pacific islands from Hawaii
southward. The two groups of birds in this species
thus pursue wholly different courses in their flights.

The turnstone is a species that is almost cosmo-
politan in range as it nests in the far north, to 70
degrees North Latitude and farther, and migrates
south throughout the World, though mainly along

i8o THE MIGRATIONS OF BIRDS

salt waters, extending in winter as far as South
Africa, Australia, New Zealand, and Chile. The
little sanderling covers a similar vast area, as it
nests in the Arctic regions of both hemispheres, and
in winter is found south to Patagonia, southern
Africa, and Australia. These two species have a
greater migration range than any others known, for
they are found at one time or another on almost
every seacoast in the entire world.

The Seasonal Flight of Ducks

With the advent of civilization feathered game
invariably has decreased in abundance, yet our
wild ducks, because of their wariness and the nature
of their haunts, have remained common until to-day,
and as a group probably show the most easily ob-
served examples of the actual process of migration.
Small birds as migrants, appear and disappear with
their movements cloaked by darkness so that their
flight passes unseen, except under the exceptional
circumstances of observation of the face of the moon
by telescope, or as the passage of migrants in the
darkness is detected by their calls. Nearly all ducks
fly regularly by day, travelling at heights where they
are readily visible; and as most of us, if not hunt-
ers, possess traces at least of the hunting instinct,
these flights attract instant attention.

SEASONx^L FLIGHT OF DUCKS i8i

Though ducks fly often by day, they also migrate
by night if conditions require it; northern flights
late in autumn frequently come in during the night,
though I have seen birds arrive from the north by
thousands late in afternoon, when they came swing-
ing down in long straggling flocks, 80 to 100 yards
above the earth, and passed on to the south without
a glance at the decoys set in front of my shooting
blind. These birds had evidently come a consider-
able distance, and were on their way to points still
more remote. Dr. J. C. Phillips has noted that the
ruddy duck flies invariably by night, and says that
he has seen them coming in to resting grounds at
the first sign of dawn. This habit, however, is con-
fined so far as I am aware to this species alone among
our North American ducks. Southward flight of
such species as scoters, which are largely frequenters
of salt water, is mainly by day, and is easily observed,
as during the time of flight the birds pass steadily.

In the northern hemisphere a few ducks nest in
the marshes of middle latitudes, but by far the
greater number breed in the sloughs and ponds
of northern areas. Most species of ducks are hardy
and do not flee from cold so long as food is available.
Their movements, therefore, are governed largely
by the presence of food and by search for areas
where they may hope to escape from their greatest
enemy, man. Though widely scattered for the

1 82 THE MIGRATIONS OF BIRDS

period of breeding, during the remainder of the
year they are concentrated in favorable areas, where
they may assemble in tremendous numbers. In
North America the marshes of Great Salt Lake, the
interior valleys of California, the delta region at the
mouth of the Mississippi River, the estuaries of the
Susquehanna and Potomac rivers, and the region
of Currituck Sound are all famous ducking grounds.
It will be of interest to trace some of the migration
routes by which ducks reach these regions. We
have available for this study a fair amount of in-
formation based on birds that have been banded,
so that some of the routes may be traced in some
detail. It is interesting to find that a number do
not tend in direct north and south Hnes.

The Bear River marshes at the northern end of
Great Salt Lake have been known as one of the
famous shooting grounds in the western states, but
it was not until data became available from banded
ducks that the importance of this region as a
centre of distribution was realized. From 19 14 to
1 91 6 I was occupied during the months of summer
and autumn in studies of the birds of these marshes,
and banded some 1200 birds as an incidental part
of other work in hand. Returns from these have
yielded results of the greatest interest.

As a preliminary statement, it may be noted that
many of the birds captured and banded at this point

SEASONAL FLIGHT OF DUCKS 183

had nested elsewhere. It is a well-known fact that
drakes in most of our species of ducks desert their
mates shortly after incubation of the eggs is begun.
These males, particularly in some of the surface-
feeding ducks, congregate at once in large flocks,
and may at this time migrate to favorable localities
where they pass the remainder of the summer. At
the mouth of Bear River male pintails and mallards
begin to congregate in these post-breeding bands
at the end of the first week in June, and continue
to gather from that time until autumn. By the end
of June it was not unusual to find two thousand
pintails or more in one flock, and their number in-
creased regularly with the advance of the season.
A careful canvass of the vicinity in May showed an
average local breeding stock of only one hundred
pairs of this species, so that the majority of these
recreant benedicts had come from other regions,
how far distant we may not say. It is interesting
to note that observers in central and northern
Canada and in Alaska have commented on summer
flocking in this species with subsequent disappear-
ance of a part, so that some of the Bear River birds
may have come from a long distance. This, how-
ever, for the present is purely speculation.

Summering bands of males moult at once into
dull summer or eclipse plumage, and then shed the
flight feathers, becoming flightless for a period,

184 THE MIGRATIONS OF BIRDS

whence their need of extensive marshes as hiding
places. Females follow the males to the seclusion
of the marshes when the young are old enough to
shift for themselves, but have their moult delayed
until late summer. This early separation of the
sexes persists in part through the autumn, though
mixed flocks of males and females are of frequent
occurrence.

The duck population of the Bear River marshes
continues to grow steadily beyond the normal breed-
ing stock, until the first of September, with a sud-
den increase at the end of August, when hordes of
young begin to arrive from other breeding areas.
Between September i and 10 fully two thirds of the
ducks that have gathered migrate out to other
regions. Cinnamon teal and redheads leave in a
body at this time, and with them go many others.
The sudden disappearance of the host of birds is
easily noted, but others continue to arrive, and by
October i enormous numbers are present. During
the second week in October there is increase in flight
from the north, which continues steadily until the
close of the season. Ice closes the bays in part by
Thanksgiving time, and between December i and
15 the last of these birds are driven to other regions.

Ducks that I banded at this point were killed
subsequently over the entire western United States,
from western Missouri and Kansas to California,

SEASONAL FLIGHT OF DUCKS 185

and from the Mexican border to Saskatchewan.
(See Fig. 6.) Analysis of the records gives a clue to
some of the lines of migratory flight that are pur-
sued. By way of introduction, however, it may be
stated that ducks are birds of strong flight to which
mountain barriers mean little, so that their journeys
from the Salt Lake Valley do not necessarily follow
uniform trails through the sky. Certain general
routes however are indicated. There is one broad
fly line that passes south over the Rocky Mountain
plateau, used by a comparatively small number of
birds, which carries ducks to the scattered lakes
and ponds of central and southern Utah, New Mex-
ico, and Arizona. To digress for a moment, it may
be observed that this line of flight is the one pur-
sued by snowy herons from the colonies at the mouth
of Bear River; birds of that species, as shown by
banded individuals, migrate south through south-
ern Arizona, where one was killed on the San Pedro
River in Cochise County, to a wintering ground on
the west coast of Mexico. Returns from these birds
have been interesting. A peon at Mexcaltitan, Ter-
ritory of Tepic, found a bit of aluminum on the leg
of a heron that he had killed to eat, and brought it
to a Japanese labor contractor. The band had been
preserved from curiosity, as the peon was unable
to read; so that the merest chance brought a return
from one of the snowy herons banded the year pre-

1 86 THE MIGRATIONS OF BIRDS

vious in distant Utah. Another was reported,
through the State Department, by the American con-
sul at Acapulco, from a bird killed on the Papagayo
Lagoon in Guerrero. A third, banded July 3, 191 6,
was killed January 20, 1923, near Escuinapa, in
Sinaloa.

To return to ducks, we find indicated a general
line of flight from the Salt Lake Valley to the west,
which is followed by a large number of birds,
among which may be enumerated green-winged
teal, shovellers, and a part of the pintails and mal-
lards. This flight strikes the broad valley of the
Sacramento, and then spreads southward through
the marshes and sloughs of the interior basin, south
to southern California. Return records from birds
banded near Great Salt Lake include a considerable
number of green-winged teal taken in the region
outlined in California.

Another group of birds passes to the eastward, to
the Great Plains area, and continues south to Texas.
There is indication that some of the ducks that take
this route fly north through Idaho to the head-
waters of the Missouri, and then follow down east
of the foothills of the Rocky Mountains. At least,
I have record of one pintail banded and released at
the mouth of Bear River September 4, 191 6, which
was killed eleven days later near Glasgow, Montana,
and there are three returns of banded redheads from

Figure 6

Map of part of western North America to show return records
from ducks and other birds banded in the Salt Lake Valley,
Utah. Point of release indicated by arrow. Return records
marked by dots. (Courtesy of Bureau of Biological Survey.)

SEASONAL FLIGHT OF DUCKS 187

Idaho. There is no reason to suppose, however,
that a majority of these birds do not cross directly-
through the mountains. This southeastern mi-
gration seems to include many pintails, and the
cinnamon teal and redhead.

Mallards seem to scatter widely from the point
of release. A few remain in Utah through the
winter, where warm springs afford them open feed-
ing grounds, as several banded birds were taken in
December and January in that state. One was
killed in Owens Valley, California, another in south-
eastern New Mexico, one near El Paso, Texas, and
one near Houston, Texas. These few records indi-
cate a wide variation in habit and a wide range for
this species, since some remain in the north, some
cross to California, and some migrate to the plains
regions east of the Rocky Mountains.

Pintails banded at this point have shown a re-
markable distribution having been recovered
throughout a wide range in the west. A few have
lingered in Utah until December and January,
though few ducks of this species can find suitable
range so far north. Many cross to the interior val-
leys of California, where banded birds from Utah
have been taken from the marshes above Suisun
Bay south to the Imperial Valley near Calipatria.
Migration to California may take place early, as
one pintail, released on Bear River August 20, was

1 88 THE MIGRATIONS OF BIRDS

killed near Dos Palos, in Merced County, California,
on October i6. A part of the pintails from Utah
travel to the Plains region east of the Rocky Moun-
tains by routes not easily understood. Evidence at
hand indicates a flight to the northward to the head
waters of the Missouri River, and south over the
Great Plains, since one marked bird was killed in
eastern Montana, one in the sand-hill region of
Nebraska, and another near the Gulf Coast of
Texas. In spring flight several of these banded
birds have been taken in Oklahoma, Kansas, Mis-
souri, and Saskatchewan, indicating a flight north
through the Plains region, in which the birds do not
recfoss the mountains to the Great Basin.

From the evidence presented it seems that ducks
concentrate in the Salt Lake Valley, and from there
spread in migration over the entire western half of
the United States. The region is highly important
in the life of many species, so that it is unfortunate
that, because of man's diversion of water from
streams for purposes of irrigation, the bays inhabited
by waterfowl in certain years become polluted with
alkalis, so that ducks die there by the tens of thou-
sands.

Interesting data on the movements of ducks from
other regions are available through records assem-
bled by F. C. Lincoln from banding operations under
the Biological Survey. Of these, there may be

SEASONAL FLIGHT OF DUCKS 189

mentioned returns from black ducks banded by
H. S. Osier at Lake Scugog in south central Ontario.
These returns divide into two more or less distinct
groups, one from points to the southward in the
drainage of the Mississippi Basin, and the second
from New Jersey, Delaware, Maryland, Virginia,
North and South Carolina — pointing clearly to a
migration line directly to the southeast, which ap-
parently may reach the heads of Delaware and
Chesapeake bays and from there spread southward.
A few returns from mallards indicate apparently
similar lines of flight. It is interesting to compare
these results with those obtained by Lincoln in a
large number of mallards banded near Browning, on
the Illinois River, in west central Illinois. Returns
from these have centred near the Mississippi River,
with extension to the Gulf coast of Texas, and
straggling records from Georgia and Florida. From
Browning it appears that the main flight is south,
with only a few birds passing to the southeast.
Black ducks and mallards banded by J. Pulitzer in
Hancock County, Maine, and F. Thompson at Bar
Harbor, Maine, have been killed in the coastal
region to the south, none as yet having been secured
from the interior. The flight here thus seems to fol-
low the trend of the coast to the south.

Migration of North American ducks southward
beyond the limits of the United States is of uncer-

I90 THE MIGRATIONS OF BIRDS

tain extent. A blue-winged teal banded in Septem-
ber by Osier at Lake Scugog, Ontario, was killed the
following December near Port of Spain, Trinidad.
The species passes regularly south to the West
Indies and to northern South xAmerica, and has been
recorded in Brazil and Chile. Large numbers of
northern ducks travel in winter to suitable points
on the Mexican tableland, so that near the City of
Mexico they are baited to small lakes and killed in
hundreds by armadas — batteries made of a hun-
dred or more gun barrels so arranged that they may
be fired simultaneously. Pintails and scaup ducks
travel into the West Indies, and with casual ducks
of other species range down the eastern coast of
Central America as far as Panama. The extent of
this migratory flight is not, however, definitely
known.

Ducks are capable of flying long distances over
oceans also, as shovellers and pintails are regularly
migrant in the Hawaiian Islands, and go south at
least to the Line Islands near the Equator. They
have also been recorded in the Marshall and Gilbert
Islands.

Northward flights in spring do not necessarily
follow the same lines pursued in autumn, since, as
has been said, pintails banded in the Salt Lake
Valley have been taken in spring in Saskatchewan.
It is assumed that they migrated in autumn, to

SEASONAL FLIGHT OF DUCKS 191

winter in the Mississippi River drainage, and then
flew north in spring through the interior. The
northward flight in spring through the Mississippi
Valley is much more abundant than the southward
movement through the same region, indicating that
birds come in converging lines to favorable winter-
ing grounds, where they concentrate, and then travel
north in company. It is possible that the difference
in spring and fall movement in this area is more ap-
parent than real, since we find in autumn, through
the Plains area in particular, that water is scarce, as
that season of the year is usually dry. This would
force waterbirds to drive on through without stop-
ping, while in spring, after the rains and snows of
winter, every pond and slough is filled with water
and offers attractive feeding grounds. On rare oc-
casions when early autumn rains fill the marshes
which normally at that season are dry, the increase
in ducks in southward flight is very noticeable.
These birds undoubtedly have what may be termed
"weather sense," which draws them to follow shift-
ing seasons that offer conditions in their favor. In
late December, 1920, 1 was engaged in field observa-
tion in the western pampas of Argentina, in a region
where no rain had fallen in months, and where
lagoons and marshes were entirely dry. One even-
ing there came a tremendous downpour of rain, a
veritable flood, and on the following morning I

192 THE MIGRATIONS OF BIRDS

flushed a South American pintail from a pond at
the edge of the village where I was stopping. At
that season males of these ducks were travelling
about to some extent, and this and other individ-
uals, which arrived a day or so later, came to new
country as soon as local conditions had become
favorable to them.

A northward flight through the interior of North
America is indicated in some ducks that come south
along the North Atlantic coast, as certain species
common in that section in autumn are almost ab-
sent in spring.

In Europe, on the whole, it appears that ducks
make shorter flights in migration than in North
America since the extremes of northern climate are
not so great and the birds do not have so far to move
to find suitable wintering range. Records from
western Europe from pintails banded by Professor
H. C. C. Mortensen at the Island of Fano, on the
coast of Denmark, indicate that the birds migrated
south through the valley of the Rhine, and along
the Bay of Biscay south to the northern shores of
the Mediterranean Sea from Spain to Jugoslavia.
From this winter ground these birds passed north
in spring into Lapland, Finland, and northern Rus-
sia in the vicinity of Archangel. Their flights thus
covered almost as extensive a range as those of the
American pintail spreading from a centralized area

SEASONAL FLIGHT OF DUCKS 193

on Great Salt Lake. That sixteen of these banded
birds were recaptured during subsequent autumn
migrations at the point where they were originally-
marked indicates that western Denmark is on a
regular fly line for this species.

The European green-winged teal, in appearance
a close counterpart of our species, has been found
in recent years to be the breeding species of the
Aleutian Islands, but does not range to the main-
land of Alaska. Though common in the Aleutians,
in autumn migration it evidently crosses to the
coast of Asia, as there are no certain records for it
in the states of our western coast. This bird, in
western Europe, migrates south from the Scandi-
navian peninsula, to winter in Ireland, the south of
England, and France, as shown by birds banded in
Denmark, and at two points in England. A few pass
as far as southern Spain and Italy.

The mallard in western Europe has somewhat
different habits from the two ducks just enumerated,
since it is strictly migratory only in the far north.
Large numbers of birds bred in England and Ger-
many either proved to be strictly sedentary or
moved only from fifty to one hundred miles during
winter. The migration of this species in western
Europe is later in autumn and earlier in spring than
in North America. It may be noted that there is a
very large form of wild mallard {Anas platyrhynchos
conboschas) which remains in Greenland.

194 THE MIGRATIONS OF BIRDS

Migratorial movements among some of the native
ducks of southern South America are regular with
the coming of colder weather. Males of some of
these have the habit, which has been noted for other
species, of abandoning the female so that these males
band in large flocks in late summer. Their migra-
tion may come early: during the first week in No-
vember, in 1920, I saw large numbers of South
American pintails come from the south into a region
of marshes and lagoons in the eastern part of the
Province of Buenos Aires, following a tremendous
storm of wind and rain that flooded the country.
This flight continued morning and evening for three
days and included many thousands of birds. The
ducks travelled in small or large flocks, which flew
steadily to the northward only thirty to sixty yards
above the earth. During one forenoon I estimated
the total number that passed my camp at between
15,000 and 20,000, and believed that fully 95 per
cent of them were males. Those that I shot were
still in full breeding condition, indicating that they
had only recently deserted their mates. The main
flight comes later in the year, from March to May,
when the hosts of young bred in the south come up
to winter in the northern lakes. At this season the
birds are found in tremendous numbers in suitable
localities.

THE MIGRATIONS OF OTHER BIRDS 195

The Migrations of Some Other Birds

Common birds that do not seem particularly-
strong in flight in many instances perform wonder-
ful migrations of which we are only now gaining a
true conception. Flight seems so much a matter of
custom and habit, that even small birds are able to
cover great distances without apparent over-fatigue
so long as they can obtain proper food.

The chimney swift, found in summer through-
out the eastern half of North America from Mani-
toba and Quebec south to the Gulf coast, has long
been an anomaly, since, though abundant in num-
bers, its winter home has never been definitely
located. In autumn, toward the close of their stay,
the birds congregate at nightfall in large flocks,
which roost in certain selected chimneys, or occa-
sionally resort to some hollow tree after the fashion
of their ancestors. Such resorts are visited year
after year, and I recall particularly one large hollow
tree that I knew in boyhood, to which these birds
came in tremendous numbers for a few nights each
autumn. Migrant swifts pass south to the Gulf
coast, where for a time they are extremely numerous,
and then disappear, to return at the close of March,
and to work slowly northward during April to their
breeding grounds. For many years they were
wholly unknown south of our limits, but recently a

196 THE MIGRATIONS OF BIRDS

few have been recorded in April in Haiti, apparently
in northward migration. We may suppose that
their winter home is somewhere in the northern part
of South America, though this remains to be defi-
nitely ascertained. Identification of swifts in
regions of tropical forest is difficult, as the birds fly
above the trees, where they are usually beyond gun-
shot. There are in the Tropics in addition, related
swifts, which can not be distinguished from our
northern species except with the birds close at hand,
which still further complicates the case. In the
Tropics there are few chimneys, so that we must
picture the chimney swift in winter returning to
former habits of roosting in hollow trees, as it did
universally before the advent of civilized man. For
six months of each year then it frequents settlements
in the north, where it nests and roosts in chimneys,
or, casually, in barns and outbuildings, while during
the winter season it must revert to the ancient cus-
toms of its race, truly a curious mixture of habit.

Migrations among the strong-winged nighthawks
of North America are of considerable interest, since
these birds show a tendency to follow the general
direction of river valleys more closely than there
would seem to be need. Formerly these birds were
far more abundant than at present, and for many
years it was usual to shoot them in wanton sport,
especially during their autumn flights, a custom

THE MIGRATIONS OF OTHER BIRDS 197

that persisted for many years throughout the greater
part of the eastern United States from Wisconsin
to Florida. The birds were killed by thousands and
became reduced in numbers, since they rear but one
brood with a maximum of two young each season,
and were unable to withstand the excessive drain
upon their number by the constant shooting to
which they were subjected. On the Potomac River
above the city of Washington the scanty autumn
flight that remains passes regularly down-stream
toward the southeast, a direction that seems to be
held until the birds pass beyond the limits of the
Piedmont plateau and reach the level expanses of
the Coastal plain. A number of years ago, while
studying the birds in the plains region of central
Oklahoma in late May, I found nighthawks very
abundant. Most of those secured were of the form
known as Howell's nighthawk {Chordeiles m.howelli)^
which bred locally, but among others I secured three
specimens of the western nighthawk {Chordeiles m.
henryi)y which nests in New Mexico, Arizona, north-
ern Chihuahua and Sonora. As the latter were at
a point farther east than ever previously recorded,
we can only suppose that they were in migration
and were following the course of the South Canadian
River through Oklahoma to its headwaters in the
mountains of New Mexico. One year in the Bighorn
Basin in Wyoming, I saw nighthawks arriving from

198 THE MIGRATIONS OF BIRDS

the north during early June in a line of flight that
carried them up the valley of the Big Horn River.
It would seem that they may have followed west
along the valley of the Yellowstone from the region
of the Plains, and then turned off into the valley of
the Big Horn, which flows to the north, so that the
final portion of their spring migration carried them
directly south to their breeding area.

The migration flights of the bobolink possess
considerable interest, since the actual limits of the
winter home of this species were for some time
uncertain. The birds come north in spring, arriving
in middle latitudes in late April or early May, with
the males in handsome, pied summer plumage.
With the settlement of the west it appears that this
species has greatly increased in numbers in that
section, if it has not actually extended its range, as
in the Gallatin valley and similar areas in north-
western Montana it is now common, though form-
erly it was very local in occurrence. After breeding
in northern meadows and hay-fields, where the
musical songs and handsome appearance of the
males endear them to all, these birds in late summer
resort to marshes and grassy swales, where they pass
through a moult in which the males assume a dull
streaked plumage like that of their mates.

Southward migration begins about the middle of
August, with August 1 8 as the average date of arri-

THE MIGRATIONS OF OTHER BIRDS 199

val from the north in the vicinity of Washington.
Though a few straggle south into Colorado and
Kansas, the majority of the birds from the north-
west part of the range travel to the southeast, so
that the main flight passes east of the Mississippi
River, and concentrates especially along the tidal
marshes of the eastern coast. When southward
flight begins, it comes with a rush that distributes
the flocks far southward, so that on the east coast
the birds arrive at suitable points in the region from
Maryland south to Georgia and Florida almost
simultaneously at some date between the middle of
August and the first of September. Bobolinks in
flocks now frequent marshes and weed-grown fields
in the lowlands, and formerly, when rice was ex-
tensively cultivated in the southeast, were very
destructive to that crop. Where the grass known
as wild rice {Zizania palustris) is abundant, the
birds gather in large flocks and, under the name
of reed-bird or rice-bird, are pursued by hunters.
Outside of marshes they are seldom seen except
as their call comes in morning and evening from
flocks passing overhead. A part of the migration
is regularly performed by day in both spring and
autumn, so that the arrival and passage of the
species is easily noted.

From the Gulf coast the bobolink crosses in
autumn to Cuba, and from there continues directly

200 THE MIGRATIONS OF BIRDS

across the Caribbean to northern South America,
and then on southward to its principal wintering
ground in the central portion of that continent.
During winter it continues to frequent swamps and
grass-grown marshes, and seems to have its centre
of abundance in the Chaco, a vast area of poorly
drained, swampy land, with broad grass-grown
savannas, that extends west of the Parana and
Paraguay rivers, from northern Santa Fe in north
central Argentina, north into Bolivia and Brazil.
For untold years the bobolink had been safe in this
winter home, as for human neighbors it had only
scattered groups of Indians of nomadic habit who,
though they probably killed a few of these birds
with throw-sticks or other weapons, did not trouble
to exert themselves particularly after such small
game, and were too few in number to be any serious
menace. Within the past ten years there has begun
a change in this condition, which is bound to affect
the bobolink sooner or later. Soil in the Chaco is
fertile, and white men, who entered it first to obtain
the valuable woods of its forests, have now begun to
divide the land and put it under cultivation. Since
the World War, colonization has been especially
active, and great areas are now settled where a few
years ago the only human inhabitants were a few
Indians. Sadly enough it must be recorded that
the cultivation of rice has begun in this area, and

THE MIGRATIONS OF OTHER BIRDS 201

unquestionably the bobolink will flock to this crop
as it did in former years in the southeastern United
States when the rice industry was at its height in
that section. In 1920 I heard some complaint of
it, and if the rice industry increases, the bobolink
will come in for destruction. It must be noted too
that many of the colonists are from southern Europe
particularly from Italy, and that these peoples, as
usual, have brought with them to their new homes
the custom prevalent in their native land of con-
sidering all small birds as game. Hunters in the
Chaco now kill all manner of sparrows, blackbirds,
and flycatchers for the pot, so that, as the country
settles, the bobolink will be subject to toll from this
source. What the final result may be time alone
can tell, but it is certain that hunting will press
severely on the abundance and continuance of the
species.

The bobolink on reaching South America seems
to delay its southward flight. Todd has recorded
its arrival in the Santa Marta District of Colombia
on September 11 — an indication, by the way, of
the rapidity with which the species travels south,
since that date represents a point of maximum
abundance for the species in Maryland and Virginia
— and finds that it remains until October 14. Early
arrivals come to the Chaco of northern Argentina
(at Ocampo, Santa Fe) about the first of November;

202 THE MIGRATIONS OF BIRDS

but from the little that we know at present, it ap-
pears that flocks wander to a considerable extent,
since Venturi, at the point last mentioned, records
a sudden increase in abundance about the first of
January. In its southern home the bobolink is
known to European settlers as charlatan from the
pied dress of the male in breeding plumage, and
many are captured in northern Argentina by bird-
catchers who sell them throughout the country. I
saw them offered in several Argentine cities and
have known of their shipment across the mountains
to Chile. In 1925 one that had been purchased in
Valparaiso was brought to the National Zoological
Park, in Washington.

Harris's sparrow (Zonotrichia querula), a species
allied to the white-crowned and white-throated
sparrows, but of larger size, with throat marked with
black, is an excellent example of a species with
limited distribution and migration. In summer it
nests in a more or less unknown region in Hud-
sonian Zone, from Fort Churchill on Hudson's Bay
westward, possibly to near Great Bear Lake. In
September and early October it migrates south to a
wintering ground from northern Kansas south to
northern Texas. Migration is almost directly south
and extends only through a comparatively narrow
area along the eastern edge of the Great Plains.
Stragglers come to eastern Colorado on the west

THE MIGRATIONS OF OTHER BIRDS 203

and central Wisconsin and Illinois on the east, but
the full migration centres through a narrow region
comprising eastern Kansas and western Missouri.
Here this fine bird swarms in thickets and hedgerows
during October, and again in April, filling the air
with its rollicking whistled calls. At the height of
the migration thousands may be seen in a single
day, but outside this strip, which is barely 250 miles
wide, the bird is casual or rare. The cause for this
limited distribution is wholly obscure, for areas at
either hand seem equally suited for the needs of the
bird, which has the habits of its congeners. No
other bird has this distribution, which lies along the
lines where forms of the eastern half of the country
begin to disappear and those of the west to appear.
To observers in the eastern states the coming of
the hosts of wood warblers (Mniotiltidae) marks the
height of the spring migration. Trees and thickets
are filled with small birds, flitting among the twigs,
whose bright colors, revealed by field glasses or by
favorable light to the unaided eye, come as a never-
failing and refreshing surprise. The very fact that
more than thirty distinct species may be seen in a
single day adds to the excitement of their identifica-
tion and one never knows what rarity may appear
among their ranks. The tree-hunting forms (mainly
of the genus Dendroica) have the habit of moving
in mixed flocks which may contain a dozen or twenty

V- V,

t>

204 THE MIGRATIONS OF BIRDS

species, so that one must scan each individual to
make sure that some species new to the day's list
of birds is not overlooked. Their identification in
spring is not difficult, save as it necessitates memo-
rizing the characters that distinguish a large num-
ber of forms, as at this season males are in breeding
dress and are marked by many beautiful patterns,
which include combinations and blendings of five
of the colors of the spectrum, blue, green, yellow,
orange, and red. With these as a base the diversity
of shade of markings and mixture of colors is almost
endless. Though well marked in spring, in autumn
these same birds are the despair of the beginner in
field ornithology, as the young wear soft blended
patterns and even the adults have subdued their
brilliant colors or have discarded them for others
of plainer hue. Particularly astonishing is the
change in the chestnut-sided warbler, which in
spring has a chestnut line on the sides and a yellow
crown-cap and in autumn shows us a greenish back
and a white breast, or in the bay-breasted warbler,
which exchanges its handsome plumage for a duller
streaked dress, in which many individuals can be
distinguished from the related black-poll only by
the color of the tarsus and feet. Without these
active sprites, however, much of the thrill of autumn
migration through eastern woodlands would be lack-
ing, as their very elusiveness makes our wood warb
lers the more attractive.

THE MIGRATIONS OF OTHER BIRDS 205

The wood warblers are found only in the New
World, where they have their centre of abundance
in North America. A few are mainly sedentary, as
is the case with the form of orange-crowned warbler
{Vermivora celata sordida), found on the Santa
Barbara Islands in California, which remains in
winter on Santa Catalina, though migrants range
to the mainland opposite, even as far as Haywards
and Palo Alto. The yellow-throat of Florida
{Geothlypis trichas ignotd) so far as known is entirely
sedentary, as are the yellow-throats in the marshes
of the San Diegan district (G. /. scirpicola), and
those of the vicinity of San Francisco Bay (G. /.
sinuosa) in California.

The pine warbler of the east withdraws from the
north to concentrate within the southern limits of
the breeding range, the only one of our species that
has this habit. It breeds north into southern Can-
ada, and in winter is found north to Virginia and
Illinois and, casually, farther. The few that cross
into Tamaulipas in northeastern Mexico are about
the only ones that pass beyond the southern limits
of the breeding range.

The myrtle warbler is the only species that seems
to be unaffected particularly by cold, as, though in
winter it is found south to the Greater Antilles,
Mexico, and even to Panama, it remains common
in the southern United States, and winters regu-

2o6 THE MIGRATIONS OF BIRDS

larly north as far as Mason and Dixon's line or
even farther. Its western representative {Dendroica
coronata hooveri)^ which nests in Alaska, winters from
southern Oregon through the valleys of California.
I have seen the eastern form in eastern Kansas in
January during severely cold weather, and it is
frequently common in the milder winter climate of
Washington.

The two forms of the palm warbler winter
regularly in the Gulf States, and in Florida are found
with black and white, orange-crowned, yellow-
throated, worm-eating, parula, black-throated blue,
and prairie warblers, oven-birds, and northern
water-thrushes. The black and white, Nashville,
orange-crowned, myrtle, and sycamore warblers are
found in winter in southern Texas, and the orange-
crowned, dusky, Alaska myrtle, Audubon's, Town-
send's, and hermit warblers occur at that season in
more or less abundance in the lower portions of
California.

Of our North American species and subspecies, as
enumerated in the A. O. U. Checklist for 1910, there
are 22 that winter in the West Indies, 44 that are
found in winter in Mexico, 37 in Central America,
and 22 that reach South America. Four species
winter almost entirely in South America. The ma-
jority have an extended range, which may cover
the area from the Greater Antilles and Mexico south,

THE MIGRATIONS OF OTHER BIRDS 207

through Central America and northern South Amer-
ica. Swainson's warbler retires in winter to the
Island of Jamaica, while Bachman's warbler is
known at that season only in Cuba. Kirtland's
warbler, which nests in a limited area in the state of
Michigan, goes southeast to concentrate in the
Bahamas.

The Connecticut warbler is peculiar for the eccen-
tric migration route that it follows. This bird breeds
from the northern peninsula of Michigan to Mani-
toba in a decidedly limited area. In autumn mi-
gration it moves southeast or east, to cover the
area from Pennsylvania to New England, and then
follows south, east of the Appalachian Mountains,
through Florida and the West Indies to its winter
home in South America. On its return in spring it
passes again through Florida, but then continues to
the northwest, west of the mountains, through the
eastern portion of the Mississippi drainage, to its
nesting grounds. In the vicinity of Washington, it
is found in small numbers during the autumn in
dense growths of weeds or in thickets, but in spring
it is so rare that it has been seen on few occasions.

The black-poll warbler is of peculiar interest for
the length of its migration route and for the com-
parative rapidity with which it travels. The species
nests mainly in Canada, from the northern border
of tree growth in Labrador to Alaska, and winters

2o8 THE MIGRATIONS OF BIRDS

entirely in South America, from Ecuador and Gui-
ana to eastern Brazil. The migration flight is per-
formed through the West Indies, so that birds from
the northwest and northeast converge toward Cuba
in southward flight. Both spring and autumn move-
ments are comparatively late, and in spring, when
the lazy song of the black-poll is heard, we know
that the close of migration is near at hand. The
rate at which the bird travels is rapid, so that for
its entire course through the United States it ad-
vances at the average rate of about seventy-five
miles per day. Professor Cooke estimates that the
final spring flight through northwestern Canada
proceeds at an average rate of two hundred miles
per day.

Much of the migration of wood warblers is per-
formed by night, but in spring or autumn we often
find mixed flocks feeding along through tree growth
in the general direction in which migration is pro-
ceeding. At times, late in the autumn, this move-
ment is especially noticeable, and often warblers
come flying in from the north, to work hurriedly
through the trees for a few moments and then, with
soft calls, rise and pass on out of sight to the south.
Feeding flocks move rapidly in the same direction,
so that the distance covered in the course of early
morning and late afternoon, when the birds are
particularly active, must be considerable. Flights

THE MIGRATIONS OF OTHER BIRDS 209

of warblers have been seen also crossing ocean
waters during the day. C. J. Maynard, at the close
of April in 1884, while sailing through the Bahamas,
recorded a considerable flight of warblers, most of
them blackpolls, which were passing from the south-
east. The birds were flying low, from six to twenty
feet above the surface, and passed in little bands
containing from two or three to one hundred in-
dividuals. They were flying against a northerly
wind, which increased until it was quite violent,
yet warblers continued to arrive and depart in great
numbers from a small islet of two acres extent. This
flight continued from April 27 to 29, a period of
three days, during which many thousands of warb-
lers passed. Maynard considered his centre of ob-
servation on Leaf Key as a point in a wide area
through which this migration was passing, so that
the total flight during these three days was truly
enormous. Dr. F. M. Chapman has also noted
day-flying flocks in early May, in crossing from
Miami to the Biminis.

Mortality among these sea voyagers must be
tremendous. Maynard speaks of finding several
dead in the water or on shore where they had fallen.
Ships passing through these areas are frequently
used as havens of rest, and I have observed that
many of the small birds that come to them seem
utterly exhausted so that they may be captured in
the hand.

210 THE MIGRATIONS OF BIRDS

The clifF swallow^ whose range covers the greater
part of North America from Mexico north to Canada
and Alaska, from the Atlantic to the Pacific coasts,
has a peculiar line of migration flight, as birds from
the east migrate westward, so that the species
seems to go around the Gulf of Mexico instead of
across it. This line, followed in spring as well as in
autumn, accounts for the belated arrival of the
species on the eastern coast, and may possibly have
some connection with its rarity in recent years in
eastern Maryland and adjacent areas. Its line of
flight is the more peculiar since barn swallows cross
regularly through Cuba and other Antillean islands
to the mainland of South America. The cliff swallow
in its chosen route is not governed by any dislike
of prolonged flight, since after it reaches Panama it
may continue south into Argentina.

Some observations on the spread of the common
starling are of interest. It has been learned through
banded birds that there is pronounced migration in
this species from the Scandinavian Peninsula, Fin-
land, and western Russia, south or sometimes south-
west, since birds from this region, including north-
ern Germany, have been taken in winter in Great
Britain. Birds from Germany have migrated also
into Spain, Italy, and even Tunis in northern Africa.
On the other hand, the breeding starling of England
seems to be rather strictly sedentary, since of a con-

THE MIGRATIONS OF OTHER BIRDS 211

siderable number banded returns have come from
comparatively near to where the birds were marked,
only a few having crossed to Ireland, and one to
the coast of France. Many have been taken in
winter in the same locality where they were banded
as nestlings. It appears then that northern starlings
are migrant, while those of more temperate climate
are usually resident.

In the United States successful introduction of
the starling was made in two importations released
in Central Park in New York City, one of eighty
birds in April, 1890, and one of forty birds in March,
1 891. The point of origin of these is not definitely
known, so that it cannot be said whether they were
of migratory or non-migratory stock. It required
ten years for the starling to establish itself firmly
in New York City in the vicinity of Central Park,
but since 1900 the spread of the species has been
regular (see Fig. 7). In its dispersal the starling
seems to have been largely vagrant, though until
1 914 it remained in the main near the coast, and not
until 1 91 6 was there pronounced inland invasion.
Since that time it has moved rapidly westward,
until it has crossed the mountains with outpost
breeding colonies, and will unquestionably spread
rapidly through the Mississippi Valley. It is inter-
esting to note that until 1920 the distances travelled
north and south from the centre of original dis-

212 THE MIGRATIONS OF BIRDS

persal at New York are almost identical, as in that
year it was breeding north to the coast of central
Maine and south to northeastern North Carolina.
This indicates a concentric dispersal in these two
directions, though one would naturally suppose that
the bird would travel more rapidly toward the south.
There is evident wandering in late autumn and
winter, so that casual occurrences have been re-
corded recently from Wisconsin, Illinois, Tennessee,
and Mississippi. It is usually several years before
breeding colonies are established in new regions. At
Washington, D. C, in November, 1913, a flock of
several hundred arrived preceding a storm from the
north, and spent all one afternoon in whirling in the
wonderful evolutions customary to this species back
and forth over the Mall. Individuals were recorded
all through the winter, but it was several years be-
fore the bird became established commonly as a
breeding species. Now it is nesting all through the
country in near-by Virginia and Maryland. In the
United States the starling does not seem to have
established any regular migratory habits, but seems
to wander at random. It has been believed that a
certain number have been carried southward in
migrant flocks of grackles, cowbirds, or red-winged
blackbirds, as starlings in autumn frequently roost
with these species. This method of dispersal may
be probable in some cases, though it cannot be con-

Figure 7

Breeding range of the European starling in North America to 1922.

The species was originally introduced in New York City.

(Courtesy of Bureau of Biological Survey.)

THE MIGRATIONS OF OTHER BIRDS 213

sidered as usual as has been supposed. The flight of
the starling is so much more rapid than that of the
blackbirds that it would be difficult for it to accom-
pany them for great distances. The blackbirds in
question habitually fly from 22 to 28 miles per hour,
while the starling as regularly travels at a rate of
38 to 49 miles per hour. The two speeds are so in-
compatible that it might be difficult for the species
to keep together in prolonged flight. Furthermore,
if starlings were to begin migration with flocks of
grackles, there would be no incentive for them to
drop out en route, as they would naturally accom-
pany the other birds to the far south. If this method
had been used in their dispersal, it is natural to sup-
pose that they would have appeared early in the
southern winter quarters of the blackbirds under
discussion, which, as has been said, is not the case
since the starling has spread gradually to the south-
ward.

The migratory quail, already mentioned as a
source of food to the starving Israelites during the
exodus, comes south toward Africa in September
in enormous numbers, when immense quantities
are captured in nets for food. The birds are crowded
into low narrow cages often so closely that they can
barely stir, with the crates darkened to prevent
fighting, and are sent alive to market. From the
shoreb of the Mediterranean tens of thousands have

214 THE MIGRATIONS OF BIRDS

been shipped to large cities, and it is said that in
one year five million were shipped to England from
Egypt. The birds often appear very tired on arrival
after migration in their winter home, and at times
descend in large numbers to alight on ships, though
we may hardly credit the tale of an ancient historian
who averred that they fell upon ships until the boats
were swamped and sunk.

Migration among sea-birds is a matter of much
interest. In the outer islands of the Hawaiian chain,
there is found a series of islets given over almost en-
tirely to birds, turtles, and seals; except for a cable
station at the atoll known as Midway, there are
now no permanent human inhabitants. Birds, how-
ever, have occupied these islands for a great many
years, and gather there annually in tremendous
colonies. Laysan Island, 850 miles northwest of
Honolulu, is the most famous of these island rook-
eries, since it became known early through the value
of its deposits of guano. To Laysan at the close of
October and in early November each year come
thousands of Laysan and sooty albatross to mate
and rear their young. The chicks, as woolly as
lambs, one in a family, are slow in development, so
that they do not attain their growth until May or
June. The parents care for them assiduously until
summer, when the young are grown but are still
unable to fly, and then wander off to sea, leaving

THE MIGRATIONS OF OTHER BIRDS 215

the young to their own devices. For several weeks
these immature birds wander about, without food,
living on the fat stored over the body during the
previous period of care, and finally teach themselves
to fly by extending their growing wings in the steady
sweep of the trade winds. When strong on the wing,
they too leave the vicinity, so that after June it is
rare to see an albatross near the breeding station.
All are wandering at sea far from any land. Whether
their migration is regular or nomadic we may only
conjecture. Their return is regular, and we may
marvel at the means by which they are able to find
again the isolated islands on which they breed.
Their migration is similar in its performance to
that of land birds, except that the birds may possibly
not move in any stated direction; but it is performed
under wholly different conditions. The wanderings
of the Laysan albatross are unknown, but the sooty
albatross is seen following ships throughout much of
the North Pacific, north to the Gulf of Alaska and
the Aleutian Islands. It appears that a certain
number do not nest each year, since some of the
birds are found in small numbers in these distant
waters when the majority of the species is in breed-
ing quarters.

We are accustomed to think of autumn migration
in the northern hemisphere as always towards the
south, except for post-breeding wandering in late

2i6 THE MIGRATIONS OF BIRDS

summer in herons and a few others, which is followed
by a retreat south with the coming of cold weather.
The various races of the large-billed sparrow {Pas-
serculus rostratus) follow an unusual course, which
is an exception to the general rule. For many years
they were recorded along the southwestern coast of
California and in Lower California, but their breed-
ing place was unknown. Recently it has been dis-
covered that the species as a whole nests from the
mouth of the Colorado River south to the western
coast of Lower California, and that in autumn, from
this restricted breeding range, it migrates in part
south along the coast of Lower California and Mex-
ico, and in part north along the coast of California^
as it is common on the coastal marshes of Los
Angeles County and comes north regularly as far
as Santa Barbara. A large number of individuals
thus pass the winter a considerable distance north
of their breeding ground. No other perching bird
in the North American avifauna is known to have
this habit.

Heermann's gull of the western coast has a some-
what similar migration, as it breeds on islands in the
Gulf of California and on the western coast of Ja-
lisco, and then migrates north as far as Vancouver
Island in British Columbia.

CONCLUSION 217

Conclusion

In concluding these observations, we may define
migration among birds briefly as advance and retreat
with fluctuation in conditions favorable to the vari-
ous species. Each form has its own reaction to its
environment, so that the movement found in migrant
forms differs widely, and seldom do two present the
same picture. Dr. J. Grinnell ^ has defined migra-
tion as "a phase of distribution wherein more or
less regular seasonal shifting of population takes
place in response to precisely the same factors as
hem in the ranges of sedentary species.'' It appears
that the beginnings of the present instinct for mi-
gration, and the habit of its continuance, are so
ancient that they are wholly obscure and may be
interpreted only in terms of present conditions. The
underlying cause is certainly complex and is due to
multiple factors. We have in the past fifty years
cleared away many uncertainties regarding it, but
must look to the future to explain definitely the
basic reasons for the institution of migration (par-
ticularly in species that seem to have no need for
seasonal movement), the cause of the varying
length of the journey in different forms, and the
method of orientation followed in pursuing flight
over courses which, to young individuals at least,
are unknown.

' Auk, 1922, pp. 379-380.