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Full text of "Migration of birds"

MIGRATION OF BIRDS 




Circular 16 ^ Revised Edition - 1979 

FISH & WILDLIFE SERVICE / UNITED STATES DEPARTMENT OF THE INTERIOR 



From the collection of 




International 

Bird Rescue 

Research Center 

Cordelia, California 



in association with 
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o PreTinger 

i a 

Uibrary 

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San Francisco, California 
2006 



MIGRATION OF BIRDS 



By Frederick C. Lincoln 



Revised By Steven R. Peterson 



Associate Editor Peter A. Anastasi 



Illustrated By Bob Hines 




Circular 16 Revised Edition - 1979 

FISH & WILDLIFE SERVICE / UNITED STATES DEPARTMENT OF THE INTERIOR 



TABLE OF CONTENTS 



Page 
PREFACE 1 

INTRODUCTION 2 

THE HISTORY AND SCOPE OF MIGRATION 4 

TECHNIQUES FOR STUDYING MIGRATION 7 

Direct Observation 7 

Aural 8 

Preserved Specimens 8 

Marking 8 

Bands, Collars, Streamers 8 

Radio Tracking 10 

Radar Observation 10 

Laboratory 11 

Orientation and Navigation 11 

Physiology of Migration 11 

ADVANTAGES OF MIGRATION 13 

STIMULUS FOR MIGRATION 15 

WHEN BIRDS MIGRATE 17 

Time of Year 17 

Time of Day 20 

SPEED OF FLIGHT AND MIGRATION 25 

ALTITUDE OF FLIGHT AND MIGRATION 32 

SEGREGATION DURING MIGRATION 35 

By Individuals or Groups of Species 35 

By Age 36 

By Sex 38 

By Kinds of Flocks 40 

WHERE BIRDS MIGRATE 41 

Migration by Populations Within Species 41 

Fall Flights Not Far South of Breeding Range 42 

Long Distance Migration 44 

ORIENTATION AND NAVIGATION 47 

INFLUENCE OF WEATHER 51 

INFLUENCE OF TOPOGRAPHY 56 

iii 



PERILS OF MIGRATION 58 

Storms 58 

Aerial Obstructions 58 

Exhaustion 59 

ROUTES OF MIGRATION 61 

General Considerations 61 

Flyways and Corridors 62 

Narrow Routes 65 

Converging Routes 65 

Principal Routes From North America 69 

Atlantic Oceanic Route 69 

Atlantic Coast Route and Tributaries 70 

Mackenzie Valley-Great Lakes-Mississippi Valley Route 

and Tributaries 73 

Great Plains-Rocky Mountain Routes 75 

Pacific Coast Route 76 

Pacific Oceanic Route 80 

Arctic Routes 80 

PATTERNS OF MIGRATION 82 

Loops 82 

Dog-legs 87 

Pelagic Wandering 90 

Leap-frogging 90 

Vertical Migration 91 

Pre-migratory Movements 91 

Vagrant Migration 92 

ORIGIN AND EVOLUTION OF MIGRATION 95 

WHERE WE STAND 100 

BIBLIOGRAPHY 102 

LIST OF BIRD SPECIES MENTIONED IN TEXT . , . 115 



IV 



PREFACE 



Frederick C. Lincoln's classic work on the "Migration of Birds" 
first appeared in 1935. It was revised in 1950 and has been out of print 
for several years, after selling over 140,000 copies. Unfilled requests 
by many individuals, clubs, and institutions prompted the Office of 
Conservation Education (now the Office of Public Affairs) in the U.S. 
Fish and Wildlife Service to petition another update for reissue. This 
publication incorporates the results gathered by research biologists 
in the U.S. Fish and Wildlife Service to meet these requests. 

Lincoln's original intent was to present to the American public a 
summary of the facts on bird migration as they existed in the early 
1930's. He wrote with a style that made the topic fascinating to the 
young and old, to the educated and uninformed, and to the ardent 
observer as well as the backyard watcher. An attempt has been made 
to retain this style, while incorporating material from often highly 
technical research efforts. Much of the content and organization of 
the original publication has been maintained, but new sections were 
added to incorporate recent concepts and techniques. Other concepts, 
known to be inconsistent with present knowledge, have been deleted. 
Because graphics are of utmost importance in this type of 
publication, most of the original figures were preserved and, where 
appropriate, new illustrations have been added. 

Since the previous edition, tremendous progress has been made in 
researching and understanding bird migration; along with this 
increased effort has come a substantial increase in the literature 
devoted to the subject. Emphasis was given to reviewing literature 
pertaining to migration studies conducted in North America after 
1950, but a number of examples from the European literature have 
been included to emphasize similarities and differences in migration 
throughout the world. Because extensive author citations tend to 
disrupt the flow of thought, they were kept to a minimum in the text. 
However, this publication is essentially a review of the literature on 
the subject as it existed in the early 1970's, and a rather extensive 
bibliography has been included to cover all the papers quoted in the 
text as well as the many used but not specifically cited. The 
bibliography, then, is primarily intended for those interested in 
pursuing the subject further. 



INTRODUCTION 



The changing picture of bird populations throughout the year 
intrigues those who are observant and who wish to know the source 
and destination of these birds. Birds are the most mobile creatures on 
Earth. Even man with his many vehicles of locomotion does not equal 
some birds in mobility. No human population moves each year as far 
as from the Arctic to the Antarctic and return. Yet the Arctic terns 
do and without the aid of aircraft or compass. 

Birds are adapted in their body structure, as no other creatures, to 
life in the air. Their wings, tails, hollow bones, and internal air sacs 
all contribute to this great faculty. These adaptations make it 
possible for birds to seek out environments most favorable to their 
needs at different times of the year. This results in the marvelous 
phenomenon we know as migration the regular, seasonal 
movement of entire populations of birds from one geographic 
location to another. 

Throughout the ages, migratory birds have been important as a 
source of food after a lean winter and as the harbinger of a change in 
season. The arrival of certain species has been heralded with 
appropriate ceremonies in many lands; among the Eskimos and 
other tribes, the phenomenon to this day is the accepted sign of the 
imminence of spring, of warmer weather, and a change from winter 
food shortages. The pioneer fur traders in Alaska and Canada offered 
rewards to the Indian or Eskimo who saw the first flight of geese in 
the spring, and all joined in jubilant welcome to the newcomers. 

As the North American Continent became more thickly settled, the 
large flocks of ducks and geese, rails, doves, and woodcock that 
always had been hunted for food became objects of the enthusiastic 
attention of an increasing army of sportsmen. Most of the nongame 
species were found to be valuable also as allies of the farmer in his 
never-ending warfare against insect pests. All species have been of 
ever-increasing recreational and esthetic value for untold numbers 
of people who enjoy watching birds. We began to realize our 
migratory bird resource was an international legacy (that cannot be 
managed alone by one state or country) and all nations were 
responsible for its well-being. The need for laws protecting game and 
nongame birds, as well as the necessity to regulate the hunting of 
diminishing game species, followed as a natural course. In the 
management of this wildlife resource, it has become obvious that 
continuous studies must be made of the species' habits, environ- 
mental needs, and travels. In the United States, the Department of 
the Interior recognizes the value of this resource and is devoted to 
programs that will ensure its preservation and wise use. Hence bird 



investigations are made by the U.S. Fish and Wildlife Service, an 
arm of the Interior Department, charged by Congress under the 
Migratory Bird Treaty Act, with the duty of protecting those species 
that in their yearly journeys, pass back and forth between the United 
States and other countries. 

For more than three-quarters of a century the Fish and Wildlife 
Service and its predecessor, the Biological Survey, have been 
collecting data on the important details of bird migration. Scientists 
have gathered information concerning the distribution and seasonal 
movements of many species throughout the New World, from the 
Canadian archipelago south to the Argentine pampas. Supplement- 
ing these investigations is the work of hundreds of U.S. and 
Canadian university personnel and volunteer birdwatchers, who 
report on the migrations and status of birds as observed in their 
respective localities; while others place numbered bands on the legs 
of birds to determine their movements from one place to another. 
These data, stored in field notes, computer cards, scientific journals, 
and on magnetic tape constitute an enormous reservoir of 
information pertaining to the distribution and movements of North 
American birds. It is the purpose of this publication to summarize 
these data and present the more important facts about that little 
understood but universally fascinating subject of bird migration. 
The U.S. Fish and Wildlife Service is grateful to the many persons 
who have contributed their knowledge so that other people, be they 
bird study classes, conservation organizations, or just individuals 
interested in the welfare of the birds, may understand and enjoy this 
precious resource as well as preserve it for generations to come. 



THE HISTORY AND SCOPE OF MIGRATION 



The migrations of birds were probably among the first natural 
phenomena to attract the attention and arouse the imagination of 
man. Recorded observations on the subject date back nearly 3,000 
years, to the times of Hesiod , Homer, Herodotus, Aristotle, and 
others. In the Bible there are several references to the periodic 
movements of birds, as in the Book of Job (39:26), where the inquiry is 
made: "Doth the hawk fly by Thy wisdom and stretch her wings 
toward the south?" The author of Jeremiah (8:7) wrote: "The stork in 
the heavens knoweth her appointed time; and the turtledove, and the 
crane, and the swallow, observe the time of their coming." The flight 
of quail that saved the Israelites from starvation in their wanderings 
through the Sinai wilderness is now recognized as a vast migration 
between their breeding grounds in eastern Europe and western Asia 
and their winter home in Africa. 

Of observers whose writings are extant, Aristotle, naturalist and 
philosopher of ancient Greece, was one of the first to discuss the 
subject of bird migration. He noted cranes traveled from the steppes 
of Scythia to the marshes at the headwaters of the Nile, and pelicans, 
geese, swans, rails, doves, and many other birds likewise passed to 
warmer regions to spend the winter. In the earliest years of the 
Christian era, Pliny the Elder, Roman naturalist, in his "Historia 
Naturalis," repeated much of what Aristotle had said on migration 
and added comments of his own concerning the movements of 
starlings, thrushes, and European blackbirds. 

Aristotle also must be credited with the origin of some 
superstitious beliefs that persisted for several centuries. One of these, 
that birds hibernated, became so firmly rooted, Dr. Elliott Coues 
(1878), * an eminent American ornithologist, listed the titles of no less 
than 182 papers dealing with the hibernation of swallows. In fact the 
hibernation theory survived for more than 2,000 years, and it was not 
until early in the nineteenth century that its acceptance as an 
explanation for the winter disappearance of birds was almost 
completely abandoned. Even after this, a few credulous persons 
suggested this idea as an explanation for the disappearance of 
chimney swifts in the fall before bands from wintering swifts were 
finally reported as taken by Indians in Peru (Coffey 1944). 

The followers of Aristotle believed the disappearance of many 
species of birds in the fall was accounted for by their passing into a 
torpid state where they remained during the cold season, hidden in 

'Publications referred to parenthetically by date are listed in the Bibliography, p. 102 



hollow trees, caves, or in the mud of marshes. Aristotle ascribed 
hibernation not only to swallows, but also to storks, kites, doves, and 
others. Some early naturalists wrote fantastic accounts of the flocks 
of swallows allegedly seen congregating in marshes until their 
accumulated weight bent into the water the reeds on which they 
clung and thus submerged the birds. It was even recorded that when 
fishermen in northern waters drew up their nets they sometimes had 
a mixed "catch" of fish and hibernating swallows. Clarke (1912) 
quotes Olaus Magnus, Archbishop of Upsala, who in 1555 published a 
work entitled "Historia de Gentibus Septentrionalis et Natura," 
wherein he observed that if swallows so caught were taken into a 
warm room they would soon begin to fly about but would live only a 
short time. 

Although the idea of hibernation as a regular method of spending 
the winter is no longer accepted for any species of bird, certain 
hummingbirds, swifts, and poorwills have been known to go into an 
extremely torpid condition in cold weather (Jaeger 1948, 1949). Thus 
Aristotle was at least partially vindicated. 

Aristotle also was the originator of the theory of transmutation, or 
the seasonal change of one species into another. Frequently one 
species would arrive from the north just as another species departed 
for more southerly latitudes. From this he reasoned the two different 
species were actually one and assumed different plumages to 
correspond to the summer and winter seasons. 

Probably the most remarkable theory advanced to account for 
migration is contained in a pamphlet, "An Essay toward the Probable 
Solution of this Question: Whence come the Stork and the Turtledove, 
the Crane, and the Swallow, when they Know and Observe the 
Appointed Time of their Coming," mentioned by Clarke (1912: v. 1, 
9-11) published in 1703. It is written "By a Person of Learning and 
Piety," whose "probable solution" stated migratory birds flew to the 
moon and there spent the winter. Astronauts have so far failed to 
verify this. 

Some people, who easily accepted the migratory travels of larger 
birds, were unable to understand how smaller species, some of them 
notoriously poor fliers, could make similar journeys. They 
accordingly conceived the idea that larger species (e.g., storks and 
cranes) carried their smaller companions as living freight. In some 
southern European countries, it is still believed these broad-pinioned 
birds serve as aerial transports for hosts of small birds that 
congregate upon the Mediterranean shore awaiting the opportunity 
for passage to winter homes in Africa. Similar beliefs, such as 
hummingbirds riding on the backs of geese, have been found among 
some tribes of North American Indians. 

Today we realize that birds do not migrate by "hitching" rides with 
other birds and that the scope of the migration phenomenon is 
worldwide, not simply limited to the United States, the Northern 
Hemisphere, or the world's land masses. The migration heritage is 
developed just as extensively in Old World warblers migrating to and 



from Europe and Africa as in our wood warblers traveling from 
Canada and the United States to South America and back. One of the 
fundamental differences in migration patterns of the Northern and 
Southern Hemispheres is that no land species nesting in the South 
Temperate Zone migrates into the North Temperate Zone, but a few 
seabirds, such as the sooty shearwater, Wilson's storm-petrel, and 
others, migrate north across the Equator over the vast ocean 
expanses after nesting in the South. 



TECHNIQUES FOR STUDYING MIGRATION 



Before we discuss the many intricacies of how, when, and where 
birds migrate, one should have a general idea of how migration data 
are collected and what methods are currently being used to increase 
our knowledge. Since this publication first appeared in 1935, many 
new procedures have been used in the study of bird migration. One of 
these, radar, has been an invaluable adaptation of a technique 
developed for a quite different, but related, purpose. 

Direct Observation 

The oldest, simplest, and most frequently used method of studying 
migration is by direct observation. Size, color, song, and flight of 
different species all aid the amateur as well as the professional in 
determining when birds are migrating. Studies begun by Wells W. 
Cooke and his collaborators (Cooke 1888-1915) and continued by his 
successors in the U.S. Bureau of Biological Survey (later U.S. Fish 
and Wildlife Service) were of particular importance in the earlier 
years of these investigations in North America. Some of the largest 
and most interesting routes and patterns were sorted out by tediously 
compiling and comparing literally thousands of oberservations on 
whether a species was or was not seen in a given locality at a 
particular time of the year. More recently, "The Changing Seasons" 
reports by many amateur bird observers in Audubon Field Notes 
(now American Birds) have been a most important source of 
information on direct observation of migration. In the agregate, 
direct observation has contributed much to our knowledge of 
migration, but, as will be pointed out in other sections, until a few 
years ago, observers were not aware of some of the biases in this 
technique. 

The "moon watch" is a modification of the direct observation 
method. It has long been known that many species of birds migrate at 
night. Until recently, it was not apparent just how important 
nocturnal migration really is. Significant information has been 
derived from watching, through telescopes, the passage of migrating 
birds across the face of a full moon. Since the actual percent of the 
sky observed by looking through a telescope at the moon is extremely 
small (approximately one-hundred thousandth of the observable 
sky), the volume of birds recorded is small. On a night of heavy 
migration, about 30 birds per hour can be seen. The fact that any 
birds are observed at all is testimony to the tremendous numbers 
passing overhead. Large-scale, cooperative moon-watching studies 
have been organized and interpreted by George H. Lowery, Jr. (1951; 
Lowery and Newman 1966). 



Another specialized direct observation approach which has yielded 
important information on the spatial and altitudinal distribution of 
night migrating birds has been the use of small aircraft equipped 
with auxiliary landing lights (Bellrose 1971). Major disadvantages of 
night observation are that species cannot be identified and that birds 
continue to migrate without a full moon. However, these techniques 
do give information on the nocturnal migration movements that 
could not be obtained by other methods. 

Aural 

An adjunct to the previously described nocturnal observation 
methods, which has potential for species identification, is the use of a 
parabolic reflector with attached microphone to amplify call (chip) 
notes (Ball 1952; Graber and Cochrane 1959). This device, when 
equipped with a tape recorder, can record night migrants up to 
11,000 feet on nights with or without a full moon. A primary 
disadvantage is that one cannot tell the direction a bird is traveling 
and there is considerable difficulty in identifying the chip notes made 
by night migrants. In addition, the bird may not call when it is 
directly over the reflector and consequently it would not be recorded. 
These calls are quite different from the notes we hear given by 
familiar birds during the daytime while they are scolding an 
intruder or advertising their territory. 

Preserved Specimens 

Reference material consisting of preserved bird skins with data on 
time and place of collection exist in many natural history museums. 
The essential ingredient in studying migration by this method is to 
have an adequate series of specimens taken during the breeding 
season so differences in appearance between geographically 
separated breeding populations of the same species can be 
determined. Such properly identified breeding specimens may be 
used for comparison with individuals collected during migration to 
associate them with their breeding areas (Aldrich 1952; Aldrich, 
Duvall, and Geis 1958). This supplies a convenient way of recognizing 
and referring to individuals representative of known populations 
wherever they may be encountered. 

Marking 

If birds can be captured, marked, and released unharmed, a great 
deal of information can be learned about their movements. Many 
different marking methods have been developed to identify 
particular individuals when they are observed or recaptured at a 
later date. A few of the general methods are summarized in this 
section. 

Bands, Collars, Streamers 

Since 1920, the marking of birds with numbered leg bands in 
North America has been under the direction of the U.S. Fish and 

8 



Wildlife Service in cooperation with the Canadian Wildlife Service. 
Every year professional biologists and voluntary cooperators, 
working under permit, place bands on thousands of birds, game and 
nongame, large and small, migratory and nonmigratory, with each 
band carrying a serial number and the legend, NOTIFY FISH AND 
WILDLIFE SERVICE, WASHINGTON, D.C., or on the smaller 
sizes, an abbreviation. When a banded bird is reported from a second 
locality, a definite fact relative to its movements becomes known, and 
a study of many such cases develops more and more complete 
knowledge of the details of migration. 

The records of banded birds are also yielding other pertinent 
information relative to their migrations such as arrival and 
departure dates, the length of time different birds pause on their 
migratory journeys to feed and rest, the relation between weather 
conditions and starting times for migration, the rates of travel for 
individual birds, the degree of regularity with which individual 
birds return to the summer or winter quarters used in former years, 
and many other details. Many banding stations are operated 
systematically throughout the year and supply much information 
concerning the movements of migratory birds that heretofore could 
only be surmised. The most informative banding studies are those 
where particular populations of birds are purposely banded to 
produce certain types of information when they are recovered. 
Examples of such planned banding are the extensive marking of 
specific populations of ducks and geese on their breeding grounds by 
the U.S. Fish and Wildlife Service and the Canadian Wildlife 
Service, as well as in "Operation Recovery," the cooperative program 
of banding small landbirds along the Atlantic Coast (Baird et al. 
1958). When these banded birds are recovered, information 
concerning movements of specific populations or the vulnerability to 
hunting is gained. Colored leg bands, neck collars, or streamers can 
be used to identify populations or specific individuals, and birds 
marked with easily observed tags can be studied without having to 
kill or recapture individuals, thus making it a particularly useful 
technique. 

We have learned about the migratory habits of some species 
through banding, but the method does have shortcomings. If one 
wishes to study the migration of a particular species through 
banding, the band must be encountered again at some later date. If 
the species is hunted, such as ducks or geese, the number of returns 
per 100 birds banded is considerably greater than if one must rely on 
a bird being retrapped, found dead, etc. For example, in mallards 
banded throughout North America the average number of bands 
returned the first year is about 12 percent. In most species that are 
not hunted, less than 1 percent of the bands are ever seen again. 

In 1935, Lincoln commented that, with enough banding, some of 
the winter ranges and migration routes of more poorly understood 
species would become better known. A case in point is the chimney 
swift, a common bird in the eastern United States. This is a 



nonhunted species that winters in South America. Over 500,000 
chimney swifts have been banded, but only 21 have been recovered 
outside the United States (13 from Peru, 1 from Haiti, and the rest 
from Mexico). The conclusion is simply this: Whereas banding is very 
useful for securing certain information, the volume of birds that need 
to be banded to obtain a meaningful number of recoveries for 
determining migratory pathways or unknown breeding or wintering 
areas may be prohibitive. One problem in interpretation of all 
banding results is the fact that recoveries often reflect the 
distribution of people rather than migration pathways of the birds. 
Other methods used to mark individuals in migration studies 
include clipping the tip end off a feather (not a major flight feather) 
with a fingernail clipper or touching the feather with colored paint or 
dye. This marking technique is obviously good for only as long as the 
bird retains the feather (usually less than one year), but allows the 
investigator to recognize whether the bird has been handled 
previously or not. 

Radio Tracking 

One of the most promising methods of tracking the movements of 
individual birds in migration has been developed in recent years. It is 
called radio tracking, or telemetry, and consists of attaching to a 
migrating bird a small radio transmitter that gives off periodic 
signals or "beeps". With a radio receiving set mounted on a truck or 
airplane, it is possible to follow these radio signals and trace the 
progress of the migrating bird. One of the most dramatic examples of 
this technique was reported by Graber in 1965. He captured a 
grey-cheeked thrush on the University of Illinois campus and 
attached a 2.5-gram transmitter to it (a penny weighs 3 grams). The 
bird was followed successfully for over 8 hours on a course straight 
across Chicago and up Lake Michigan on a continuous flight of nearly 
400 miles at an average speed of 50 mph (there was a 27 mph tail 
wind aiding the bird). It is interesting to note that while the little 
thrush flew up the middle of Lake Michigan, the pursuing aircraft 
skirted the edge of the lake and terminated tracking at the northern 
end after running low on fuel while the bird flew on. The limitations 
of radio telemetry, of course, are the size of the transmitter that can 
be placed on birds without interfering with flight and the ability of 
the receiving vehicle to keep close enough to the flying bird to detect 
the signals. Despite this difficulty there has been considerable 
development in the technology, and encouraging results to date give 
promise for the future, particularly when receivers can be mounted 
on orbiting satellites (Graber 1965; Bray and Corner 1972; Southern 
1965). 

Radar Observation 

One of the developments of our modern age of electronics has been 
the discovery that migrating birds show up on radar screens used in 
monitoring aircraft. At first, the screen images caused by flying 

10 



birds were a mystery to radar operators, and they designated the dots 
"angels." Later when their nature was understood, students of bird 
migration seized on the unique opportunity to obtain information on 
movements of birds over extensive areas (Sutter 1957; Drury 1960; 
Lacke 1963a, b; Bellrose 1967; Graber 1968; and Gauthreaux 1972a, 
b). 

Three types of radar have been used for studing birds: 1) general 
surveillance radar, similar to ones located at airports, that scans a 
large area and indicates the general time and direction of broad 
movements of birds; 2) a tracking radar that records the path of an 
airplane (or bird) across the sky by "locking on" to a designated 
"target" and continuously following only that object; and 3) a Doppler 
radar similar to those operated by law enforcement agencies for 
measuring the speed of a passing automobile. The latter radar set is 
useful in determining the speed of flying birds. 

The use of radar in migration studies has been invaluable in 
determining direction of mass movement, dates and times of 
departure, height of travel, and general volume, especially at night. 
One interesting fact to come out of current radar work is the 
discovery of relatively large movements of warblers and other land 
birds migrating over the seas rather than along the coastlines and in 
directions observers were completely unaware of a few years ago. 

Laboratory 

Orientation and Navigation __ 

Studies on how migrating birds orient (travel in one compass 
direction) or navigate (travel toward a specific goal) have received 
increasing emphasis in the past 20 years. These studies have focused 
on the ability of birds to orient themselves by the position of the sun 
and stars. Outstanding in this facet of research have been the works 
of Matthews (1951, 1955), Kramer (1952, 1959, and 1961), Sauer and 
Sauer (1960), Mewaldt and Rose (1960), Sauer (1961), Hamilton 
(1962a, b), Schmidt-Koenig (1963, 1964), and Emlen (1969). The basic 
method used in the experiments is to observe the direction in which 
confined birds attempt to move during the period of migratory 
restlessness. The birds are not permitted to have any view of the 
landscape but only the sky above them. In some cases the positions of 
the celestial bodies are changed by the use of mirrors to see the effect 
on the orientation of the experimental birds. In other cases the 
experiments are performed in plantetariums so positions of the stars 
in the artificial heavens can be manipulated and the effect observed. 

Physiology of Migration 

The physiological basis for bird migration has received 
considerable attention, particularly the effects of seasonal increases 
and decreases in daylight and the seasonal rhythms occurring within 
animals and referred to as "biological clocks." Investigations in this 
field include the pioneering work on the relationship of photoperiod 

11 



(daylength) to migration by Rowan (1925, 1926) and many 
subsequent studies (Wolfson 1940, 1945; Marshall 1961; King, 
Barker and Farner 1963; King and Earner 1963; King 1963; Farner 
1955, 1960; and Farner and Mewaldt 1953). These studies have 
become ever more deeply involved in the intricate relationships 
between photoperiod, endocrine interactions, gonad development, 
fat deposition, and migratory unrest. They add to our knowledge of 
the mechanisms that regulate the migratory behavior we observe. 



12 



ADVANTAGES OF MIGRATION 



Why should a bird subject itself to the rigors of a long migratory 
journey twice a year if it can find all the requirements suitable for 
existence in one locality? It seems well to consider briefly the ends 
that are served by this annual round trip between breeding grounds 
and winter quarters. Obviously, the migratory habit enables a 
species to enjoy the summer of northern latitudes and to avoid the 
severity of winter. In other words, migration makes it possible for 
some species to inhabit two different areas during the seasons when 
each presents favorable conditions. If it was not advantageous to 
make the trip twice a year, natural selection would have eliminated 
the tendency, but bird migration has become the rule over much of 
the world rather than the exception. 

By withdrawing in the spring to regions uninhabitable earlier in 
the year, migrant species are generally assured of adequate space 
and ample food upon their arrival in the winter-freed North, and 
those nonmigratory kinds, which stay behind to nest, are also assured 
of ample space for these activities. 

Every pair of birds requires a certain amount of territory for the 
performance of its reproductive duties, the extent of which varies 
greatly between different species. This territory must be large 
enough to provide adequate food, not only for the parent birds but 
also for the lusty appetites of their young. In the Arctic summer, 24 
hours of daylight allow the young to feed or be fed almost con- 
tinuously and rapid growth is apparent. The short breeding season in 
northern latitudes exposes the vulnerable young to predation for a 
brief period and prevents a build up of predator populations. 

It cannot be said that the winter or summer area of every species is 
entirely unsuited to the requirements of all of its members at other 
seasons, because some individuals pass the winter season in areas 
that are frequented only in summer by other individuals of their 
species. Such species may have extensive breeding ranges with wide 
climatic variations so that some individuals may actually be 
permanently resident in a region where others of their kind are 
present only in winter. Also, some individual song sparrows and blue 
jays, for example, have been known to change their migratory status 
(e.g., a particular bird may migrate one year and not the next or vice 
versa). Thus, different individuals or populations within these 
species appear to have different tolerances for climatic conditions. 

The tendency of some birds to move southward at the approach of 
winter is not always due to seasonal low temperatures. Experiments 
have demonstrated many of our summer insect feeders, when 
confined in outdoor aviaries, comfortably withstand temperatures 

13 



far below zero as long as abundant food is provided. The main 
consideration then, is depletion of the food supply, caused by either 
the disappearance or hibernation of insects or the mantle of snow or 
ice that prevents access to seeds and other food found on or close to the 
ground or submerged in water. Also, shortened hours of daylight 
may restrict the ability of birds to obtain sufficient food at a time 
when low temperatures require increased energy to maintain body 
heat. It is noteworthy that some of our smaller birds, such as the 
chickadees, can withstand a cold winter because their food supplies 
are always available above ground on trees. When there is a good 
supply of pine and spruce seeds, red-breasted nuthatches and 
crossbills will remain through the winter in Canadian woods, but 
when these birds appear abundantly in winter at southern latitudes, 
it may be concluded there is a shortage of these foods in the North. 



11 



STIMULUS FOR MIGRATION 



Modern views based on studies of bird behavior and physiology 
indicate migration is a regular, annually induced movement, 
modified by local weather conditions, but largely independent of 
them. Migration is a phenomenon far too regular to be created anew 
each season merely under stress of circumstances, such as need for 
food; and it begins before the necessity for a change in latitude 
becomes at all pressing. Swallows, nighthawks, shorebirds, and 
others may start their southward movement while the summer food 
supply in the North is at peak abundance. American robins and 
bluebirds may leave abundant food in the South and press northward 
when food supplies there are almost entirely lacking and severe cold 
and storms are likely to cause their wholesale destruction. Regularity 
of arrival and departure is one of the most impressive features of 
migration, and since birds travel in a rather strict accordance with 
the calendar, we might ask: "What phenomena, other than the 
regular changes in length of day, occur with sufficient precision to 
act as a stimulus for migration?" 

Experimental work has abundantly demonstrated the effect of 
increased light upon the growth, flowering, and fruiting of plants. 
Similarly, Rowan's (1925) experiments with slate-colored juncos and 
the work of numerous subsequent investigators showed, at least in 
some temperate zone species of migratory birds, increasing periods 
of daylight triggered sex organs to develop, fat to be deposited, and 
migration restlessness to begin (King and Farner, 1963). When these 
conditions develop to a certain level, the bird enters a "disposition to 
migrate" and takes off for its breeding or wintering grounds. There is 
reason to believe certain weather conditions influence the actual time 
of departure and especially the rate of progress to the breeding area. 

This explanation of the stimulus for migration may apply very 
broadly to birds that winter in temperate parts of the world and nest 
in the same hemisphere but fails in those birds wintering in the 
tropics, where little change in length of day occurs and even 
decreases during the spring in regions south of the Equator. It might 
be asked: "If the lengthening day is the stimulating factor, why 
should our summer birds, wintering in the tropics, ever start north?" 
In addition, if daylength influences when birds are stimulated to 
migrate, why should they not all leave the same locality at the same 
time? Or, if weather controls the departure of birds from a given 
area, should not all the migrants leave when conditions are optimal 
and refrain from departing when conditions are not so? Actually, the 
conditions that place a bird in a disposition to migrate are probably 
the result of a combination of factors affecting different species 

15 



differently. Thus not all birds arrive at this condition at the same 
time. 

It has been demonstrated experimentally that Andean sparrows, 
resident in equatorial regions, come into breeding condition twice 
annually entirely independent of changing light periods (Miller 
1963); evidently the breeding cycle is controlled by periodic internal 
stimuli. Probably northern migrants that winter in equatorial 
regions and beyond have their migratory urges controlled by similar 
rhythms or biological clocks. Also, no evidence suggests that the 
southward migration of birds is controlled by changing periods of 
light even among species such as white-crowned sparrows, for which 
this is a controlling factor in the spring. The fall stimulus is probably 
an innate cyclic occurrence brought on by a biological mechanism of 
unknown nature (King, Barker, and Farner 1963). 

It is pertinent to point out that the migratory instinct appears to be 
more or less transitory and not persistent over an extended period. 
Migratory birds may be delayed en route, either by natural 
conditions such as unusually abundant food supplies or forcibly by 
man. If detained until the end of the migratory season, migrants may 
not attempt to finish the journey because they apparently lose the 
migratory impulse. In the fall and early winter of 1929, abundant 
food and open water caused an unusual number of mallards to arrest 
their migration and remain in western Montana and northern Idaho. 
Later, however, when a heavy snowfall with subzero temperatures 
suddenly cut off the food supply, great numbers of the birds 
subsequently starved to death; a flight of a few hours could have 
carried them to a region of open water and abundant food. 



16 



WHEN BIRDS MIGRATE 



One ordinarily thinks of the world of birds as sedentary during two 
periods each year, at nesting time, and in winter. For individuals this 
is obviously the case, but when the entire avifauna of North America 
or the world is considered, it is found that at almost all periods there 
are some latitudinal movements of birds. A few of these movements 
reoccur year after year with calendar-like regularity. Each species, 
or group of species, migrates at a particular time of the year and some 
at a particular time of the day. In this section some of the interesting 
differences will be discussed as to when birds migrate. 

Time of Year 

Some species begin their fall migrations early in July, and in other 
species distinct southward movements can be detected late into the 
winter. While some migrants are still traveling south, some early 
spring migrants can be observed returning north through the same 
locality. For example, many shorebirds start south in the early part 
of July, while the goshawks, snowy owls, redpolls, and Bohemian 
waxwings do not leave the North until forced to do so by the advent of 
severe winter weather or a lack of customary food. Thus an observer 
in the northern part of the United States may record an almost 
unbroken southward procession of birds from midsummer to winter 
and note some of the returning migrants as early as the middle of 
February. While on their way north, purple martins have been 
known to arrive in Florida late in January, and, among late 
migrants, the northern movement may continue well into June. In 
some species the migration is so prolonged that the first arrivals in 
the southern part of the breeding range will have performed their 
parental duties and may actually start south while others of the 
species are still on their way north. 

A study of these facts indicates the existence of northern and 
southern populations of the same species that have quite different 
migration schedules. In fall, migratory populations that nest farthest 
south migrate first to the winter range because they finish nesting 
first. For example, the breeding range of the black-and-white 
warbler covers much of the eastern United States and southern 
Canada northwest through the prairies to Great Bear Lake in 
Canada (Fig. 1). It spends the winter in southern Florida, the West 
Indies, southern and eastern Mexico, Central America, and 
northwestern South America. In the southern part of its breeding 
range, it nests in April, but those summering in New Brunswick do 
not reach their nesting grounds before the middle of May. (Lines that 
connect points where birds arrive at the same line are called 

17 



isochronal lines. Fig. 2) Therefore, if 50 days are required to cross the 
breeding range, and if 60 days are allowed for reproductive activities 
and molting, they would not be ready to start southward before the 
middle of July. Then with a return 50-day trip south, the earliest 
migrants from the northern areas would reach the Gulf Coast in 
September. Since adults and young have been observed on the 
northern coast of South America by August 21, it is very likely that 
they must have come from the southern part of the nesting area. 




Figure 1. Summer and winter homes of the black-and-white warbler. A very slow 
migrant, these birds nesting in the northern part of the country take 50 days to cross 
the breeding range. The speed of migration is shown in Fig. 2. 

18 



Many smiliar cases might be mentioned, such as the black- 
throated blue warblers still observed in the mountains of Haiti during 
the middle of May when others of this species are en route through North 
Carolina to New England breeding grounds. Redstarts and yellow 
warblers, evidently the more southern breeders, are seen returning 
southward on the northern coast of South America just about the 
time the earliest of those breeding in the North reach Florida on their 
way to winter quarters. Examples of the Alaska race of the yellow 




Figure 2. Isochronal migration lines of the black-and-white warbler, showing a very 
slow and uniform migration. The solid lines connect places at which these birds arrive 
at the same time. These birds apparently advance only about 20 miles per day in 
crossing the United States. 

19 



warbler have been collected in Mississippi, Florida, and the District 
of Columbia as late as October. 

Students of migration know that birds generally travel in waves, 
the magnitude of which varies with populations, species, weather, 
and time of year. Characteristically, one will observe a few early 
individuals come into an area followed by a much larger volume of 
migrants. This peak will then gradually taper off to a few lingering 
stragglers. If we plot numbers observed against time, the rising and 
receding curve takes the form of a bell. In the northern part of the 
United States there are two general migration waves. The first one in 
early spring consists of "hardy" birds including many of our common 
seed eaters like the finches, sparrows, and others. The second wave 
occurs about a month later and consists primarily of insect-eating 
birds, such as flycatchers, vireos, warblers, and the like. Each of 
these species in turn has its own "curve" of migration in the major 
wave. 

Time of Day 

Because most birds appear to be creatures of daylight, it seems 
remarkable that many should select the night for extended travel. 
Among the many nocturnal migrants are the smaller birds such as 
rails, flycatchers, orioles, most of the sparrows, the warblers, vireos, 
thrushes, and shorebirds. It is common to find woods and fields on one 
day almost barren of bird life and on the following day filled with 
sparrows, warblers, and thrushes, which indicates the arrival of 
migrants during the night. Waterfowl hunters sitting in their 
"blinds" frequently observe the passage of flocks of ducks and geese, 
but great numbers of these birds also pass through at night; the calls 
of Canada geese or the conversational gabbling of a flock of ducks are 
common night sounds in spring and fall in many parts of the country. 
Observations made with telescopes focused on the full moon have 
shown processions of birds, and one observer estimated their passage 
over his area at the rate of 9,000 per hour. This gives some indication 
of the numbers of birds in the air at night during peaks of migration. 
At such times radar observations have shown that nocturnal 
migration begins about an hour after sundown, reaches a peak 
shortly before midnight, and then gradually tapers off until 
daybreak. Unless special curcuits are installed in radar sets, bird 
echoes during peak migration periods may cover a radar screen. 

It has been suggested that small birds migrate by night to avoid 
their enemies. To a certain extent this may be true because the 
group includes not only weak fliers, such as the rails, but also the 
small song and insectivorous birds, such as wrens, small woodland 
flycatchers, and other species that habitually live more or less in 
concealment. These birds are probably much safer making their 
flights under the protecting cloak of darkness. Nevertheless, it must 
be remembered that night migrants include also the snipe, 
sandpipers, and plovers. Most shorebirds are usually found in the 
open and are among the more powerful fliers, as some of them make 

20 



annual migratory flights over 2,000 miles nonstop across the ocean. 

Night travel is probably best for the majority of birds chiefly from 
the standpoint of feeding. Digestion is very rapid in birds and yet the 
stomach of one killed during the day almost always contains food. To 
replace the energy required for long flight, it is essential that either 
food be obtained at comparatively short intervals or stores of fat be 
laid on prior to migration. If the smaller migrants were to make 
protracted flights by day they would arrive at their destination at 
nightfall almost exhausted, but since they are entirely daylight 
feeders, they would be unable to obtain food until the following 
morning. Unless reserve energy was carried in the form of fat, the 
inability to feed would delay further flights and result in great 
exhaustion or possibly even death should their evening arrival 
coincide with cold or stormy weather. By traveling at night, they can 
pause at daybreak and devote the entire period of daylight to 
alternate feeding and resting. This schedule permits complete 
recuperation and resumption of the journey on a subsequent evening 
after sufficient energy has been restored. 

The day migrants include, in addition to some of the ducks and 
geese, the loons, cranes, gulls, pelicans, hawks, swallows, 
nighthawks, and swifts. Soaring birds, including broad-winged 
hawks, storks, and vultures, can only migrate during the day because 
their mode of flight makes them dependent on up-drafts created by 
heat from the sun for their long distance travels. On the other hand, 
swifts and swallows feed entirely on diurnal flying insects. The 
circling flocks are frequently seen in late summer feeding as they 
travel while working gradually southward. Formerly, great flocks of 
red-tailed, Swainson's, and rough-legged hawks could be seen 
wheeling majestically across the sky in the Plains States. In the East, 
good flights of broad-winged, Cooper's, and sharp-shinned hawks are 
still often seen, particularly along the Appalachian ridges. 

Because many species of wading and swimming birds are able to 
feed at all hours, they migrate either by day or night and are not 
accustomed to seek safety in concealment. Some diving birds, 
including ducks that submerge when in danger, often travel over 
water by day and over land at night. Strong flyers like the snow geese 
can make the entire trip from their staging area in James Bay, 
Canada, to the wintering grounds on the Louisiana Gulf coast in one 
continuous flight. These birds are seldom shot by hunters enroute 
between these two points but are often observed, when migrating, by 
aircraft pilots. Graham Cooch of the Canadian Wildlife Service 
tracked a flight of the blue phase of this species in 1955. The birds left 
James Bay on October 17 and arrived on the Gulf coast 60 hours later 
after an apparent continuous flight over the 1,700-mile route at an 
average speed of 28 miles per hour. Golden plovers, likewise, 
probably make the southward flight from the Arctic to the South 
American coast in one giant leap. Other Arctic species on their 
northward flight in the spring might prefer to fly at night in lower 
altitudes, but must necessarily fly during the day at higher altitudes 

21 



because of the length of the days. Many warblers that normally fly at 
night may find themselves over water at daybreak and be forced to 
keep flying during the day until landfall is made. 

An interesting comparison of the flights of day and night migrants 
may be made through a consideration of the spring migrations of the 
blackpoll warbler and the cliff swallow. Both spend the winter as 
neighbors in South America, but when the impulse comes to start 
northward toward their respective breeding grounds, the warblers 



Isochronal Migration 
Migration Route 




Figure 3. Migration of the blackpoll warbler. As the birds move northward, the iso- 
chronal lines become farther apart, which indicates that the warblers move faster irith 
the advance of spring. From April 30 to May 1 the average speed is about 30 miles per 
day, while from May 25 to May 30 it increases to more than 200 miles. 

22 



strike straight across the Caribbean Sea to Florida (Fig. 3), while the 
swallows begin their journey by a westward flight of several hundred 
miles to Panama (Fig. 4). From there they move leisurely along the 
western shore of the Caribbean Sea to Mexico, and, continuing to 
avoid a long trip over water, go completely around the western end of 
the Gulf of Mexico. This circuitous route adds more than 2,000 miles 
to the journey of the swallows that nest in Nova Scotia. The question 
may be asked: "Why should the swallow select a route so much longer 




Cliff Swallow 




_ Isochronal Migration Lines 
Migration Route 



Figure 4. Migration of the cliff swallow. A day migrant that, instead of flying across 
the Caribbean Sea as does the black-poll warbler (see Fig. 3), follows the coast 
of Central America, where food is readily obtained. 

23 



and more roundabout than that taken by the blackpoll warbler?" The 
explanation is simple. The swallow is a day migrant while the 
warbler travels at night. The migration of the warbler is made up of a 
series of long nocturnal flights alternated with days of rest and 
feeding in favorable localities. The swallow, on the other hand, starts 
its migration several weeks earlier and catches each day's ration of 
flying insects during its aerial evolutions, while slowly migrating. 
The 2,000 extra miles flown along the insect-teeming shores of the 
Gulf of Mexico are exceeded by the great distances covered by these 
birds in normal pursuit of food. 

Although most of our smaller birds make their longest flights at 
night, close observation shows travel is continued to some extent by 
day. During the latter half of a migratory season birds may show 
evidence of an overpowering desire to hasten to their breeding 
grounds. At this time flocks of birds maintain a movement in the 
general direction of the seasonal journey while feeding on or near the 
ground. Sometimes they travel hurriedly, and while their flights 
may be short, they can cover an appreciable distance in the course of a 
day. 



24 



SPEED OF FLIGHT AND MIGRATION 



There is a widespread misconception among people concerning the 
speed at which birds can fly. One often hears stories of birds fly ing "a 
mile a minute." While undoubtedly some birds can and do attain this 
speed, such cases are exceptional, and it is safe to say that, even when 
pressed, few can develop an air speed of 60 miles per hour. Birds 
generally have two greatly differing speeds, one being the normal 
rate for ordinary purposes, and an accelerated speed for escape or 
pursuit. All birds, except the heavy-bodied, small-winged species 
such as auks, grebes, and other divers, have a reserve speed that may 
be double the normal rate. 

Although it was thought for a long time that migratory flights 
were made at normal cruising speeds, Harrison (1931) and 
Meinertzhagen (1955) showed that migration speeds were in between 
cruising speeds and escape speeds. The theory that migrating birds 
attain high speeds received encouragement from the German 
ornithologist Gatke (1895) who, for many years, observed birds at the 
island of Heligoland. He postulated that the bluethroat, a species of 
thrush smaller than the American hermit thrush, could leave 
African winter quarters at dusk and reach Heligoland at dawn; this 
flight would mean a sustained speed of 200 miles per hour! He also 
thought the American golden plover flew from the coast of Labrador 
to Brazil in 15 hours at the tremendous speed of 250 miles per hour. 
Most ornithologists now consider these conclusions to be unwarrant- 
ed. 

Reliable data on the speed of birds are accumulating slowly. 
Accurate measurements are difficult to obtain unless the bird travels 
over a measured course and wind conditions at the level of flight are 
known. Several subtle factors, besides wind and pursuit, can 
influence the speed of a flying bird. For instance, species that have a 
courtship flight often reach their maximum speeds then. Small 
woodland birds often fly faster across an open area where they might 
be attacked by a bird of prey than under cover where there is less 
danger. Birds in flocks generally fly faster than when flying alone. A 
thermal draft may induce an almost imperceptible air movement at 
the Earth's surface, but a good glider with motionless wings may 
make 35 miles per hour on a current of air that is rising vertically at 
less than 2 miles per hour. If the bird coasts downhill at a slight angle 
in still air, it can attain a similar speed. 

For sustained flight, it may be generally concluded that larger 
birds fly faster than smaller birds. A common flying speed of ducks 
and geese is between 40 and 50 miles per hour, but among the smaller 
birds it is much less. Herons, hawks, horned larks, ravens, and 

25 



shrikes, timed with the speedometer of an automobile, have been 
found to fly 22 to 28 miles per hour, whereas some of the flycatchers 
fly at only 10 to 17 miles per hour. Even such fast-flying birds as the 
mourning dove rarely exceed 35 miles per hour. A peregrine falcon 
will have difficulty catching a pigeon during a level chase at 60 miles 
per hour, but this predator can probably exceed 200 miles per hour 
during a swoop from a greater height onto its prey. 

The speed of migration is quite different from that attained in 
forced flights for short distances. A sustained flight of 10 hours per 
day would carry herons, hawks, crows, and smaller birds from 100 to 
250 miles, while ducks and geese might travel as much as 400 to 500 
miles in the same period (without the aid of a tail wind). Measured as 
straight line distances, these journeys are impressive and indicate 
birds could travel from the northern United States or even from 
northern Canada to winter quarters in the West Indies, Central, or 
South America in a relatively short time. It is probable that 
individual birds do make flights of the length indicated and that barn 
swallows seen in May on Beata Island, off the southern coast of the 
Dominican Republic, may have reached that point after a nonstop 
flight of 350 miles across the Caribbean Sea from the coast of 
Venezuela. 

Radar has given us some of our best estimates of ground speeds for 
migrating flocks, especially at night. Radar echoes, identified as 
shorebirds migrating off the New England coast, moved steadily 
about 45 miles per hour for several hours; songbird echoes typically 
traveled around 30 miles per hour (Drury 1960). Some birds appear 
to reduce flight speed in proportion to the degree of assistance or 
resistance. The literature is in some disagreement on the flight speed 
of birds and the influence of wind, but good radar observations 
coupled with accurate measurements of winds aloft will help give us 
a more accurate estimate of migrating speeds for different species 
under varying wind conditions. 

The intensity of migration depends on circumstances including the 
need for haste. In fall the flights are more likely to be performed in a 
leisurely manner, so that after a flight of a few hours the birds often 
pause to feed and rest for one or several days, particularly if they find 
themselves in congenial surroundings. Some indication of this is 
found in the recoveries of banded birds, particularly waterfowl. If we 
consider only the shortest intervals between banding in the North 
and subsequent recovery in the South, it is found that usually a month 
or more is taken to cover straight-line distance of a thousand miles. 
For example, a black duck banded at Lake Scugog, Ontario, was 
killed 12 days later at Vicksburg, Mississippi. If the bird was taken 
shortly after its arrival, the record would indicate an average daily 
flight of 83 miles, a distance that could have been covered in about 2 
hours' flying time. Among the thousands of banding records of ducks 
and geese, evidences of rapid migrations are decidedly scarce, for 
with few exceptions, all thousand-mile flights have required 2 to 4 
weeks or more. Among sportsmen, the blue-winged teal is well 

26 



known as a fast-flying duck and quite a few of these banded on 
Canadian breeding grounds have covered 2,300 to 3,000 miles in a 
30day period. Nevertheless, the majority of those that have traveled 
to South America were not recovered in that region until 2 or 3 
months after they were banded. Probably the fastest flight over a 
long distance for one of these little ducks was one made by a young 
male that traveled 3,800 miles from the delta of the Athabaska River, 
northern Alberta, Canada, to Maracaibo, Venezuela, in exactly 1 
month. This flight was at an average speed of 125 miles per day. A 
very rapid migration speed was maintained by a lesser yellowlegs 
banded at North Eastham, Cape Cod, Massachusetts, on 28 August 
1935 and killed 6 days later, 1,900 miles away, at Lamentin, 
Martinique, French West Indies. This bird traveled an average daily 
distance of more than 316 miles. 

It seems probable that most migratory journeys are performed at 
little more than the normal, unforced rate of flight, as this would best 
conserve the strength of the birds. Migrating birds passing 
lightships and lighthouses or crossing the face of the moon have been 
observed to fly without hurry or evidence of straining to attain high 
speed. The speed or rate of migration would therefore depend chiefly 
on the duration of flights and tail wind velocity. 

The speed of migration is demonstrated by the dates of arrival, 
particularly during the spring movement. The Canada goose affords 
a typical example of regular but slow migration. Its advance 
northward is at the same rate as the advance of the season (Fig. 5). In 
fact, the isotherm of 35 F appears to be a governing factor in the 
speed at which these geese move north. (An isotherm is a line that 
connects points that have the same temperature at the same time.) 
From an evolutionary viewpoint we might expect this. If the geese 
continually advanced ahead of the 32 F isotherm, they would always 
find food and water frozen and unavailable. By migrating north just 
behind the advance of this isotherm, birds that breed in the far north 
will find food and open water available and have as long a breeding 
season as the climate will allow. 

Few species perform such leisurely migrations; many wait in their 
winter homes until spring is well advanced, then move rapidly to 
their breeding grounds. Sometimes this advance is so rapid, late 
migrants actually catch up with species that may have been pressing 
slowly but steadily northward for a month or more. The following 
several examples of well-known migrants illustrate this. 

The grey-cheeked thrush, which winters in the Colombia- 
Ecuador-Peru-Venezuela-British Guiana area, does not start its 
northward journey until many other species are well on their way. It 
does not appear in the United States until the last of April 25 April 
near the mouth of the Mississippi and 30 April in northern Florida 
(Fig. 6). A month later, or by the last week in May, the bird is seen in 
northwestern Alaska. Therefore, the 4,000-mile trip from Louisiana 
was made at an average distance of about 130 miles per day. 

Another example of rapid migration is furnished by the yellow 

27 



Isotherm of 35F 
Isochronal Migration Lines 




Figure 5. Migration of the Canada goose. The northward movement keeps pace with the 
progress of spring, because the advance of the isotherm of 35 F agrees with that of the 
birds. 

28 




Figure 6. Isochronal migration lines of the gray-cheeked thrush, an example of rapid 
migration. The distance from Louisiana to A laska is about 4, 000 miles and is covered 
at an average speed of about 130 miles per day. The last part of the journey is covered 
at a speed several times what it is in the Mississippi Valley. 

29 



warbler. This species winters in the Tropics and reaches New 
Orleans about April 5, when the average temperature is 65 F. By 
traveling north much faster than the spring season progresses, this 
warbler reaches its breeding grounds in Manitoba the latter part of 
May, when the average temperature is only 47 F. They encounter 
progressively colder weather over their entire route and cross a strip 
of country in the 15 days from May 1 1 to 25 that spring temperatures 
normally take 35 days to cross. This "catching up" with spring is 
habitual in species that winter south of the United States as well as in 
most northern species that winter in the Gulf States. There appears 
to be only six exceptions to this rule: the Canada goose, the mallard, 
the pintail, the common crow, the red-winged blackbird, and the 
robin. 

The snow goose presents a striking example of a late but very rapid 
spring migration. Most all of these geese winter in the great coastal 
marshes of Louisiana, where every year over 400,000 spend the 
winter and congregations of 50,000 or more may be seen grazing in 
the "pastures" or flying overhead in flocks of various sizes. Their 
breeding grounds are chiefly on Baffin and Southampton Islands in 
the northern part of Hudson Bay where conditions of severe cold 
prevail except for a few weeks each year. The birds are not 
stimulated to migrate even though the season in their winter 
quarters is advancing rapidly while their nesting grounds are still 
covered with a heavy blanket of ice and snow. This suggests the 
stimulus for spring departure is regulated by an internal 
mechanism, such as development of the gonads. Accordingly, blue 
geese remain in the coastal marshes until the last of March or the first 
of April, when the local birds are already busily engaged in 
reproduction. The flight northward is rapid, almost nonstop so far as 
the United States is concerned; although the birds are sometimes 
recorded in large numbers in the Mississippi Valley, eastern South 
Dakota, and southeastern Manitoba, there are few records anywhere 
along the route of the great flocks that winter in Louisiana. When the 
birds arrive in the James Bay region, they apparently enjoy a 
prolonged period of rest because they are not seen in the vicinity of 
their breeding grounds until the first of June. During the first 2 
weeks of that month, they pour onto the Arctic tundra by the 
thousands, and each pair immediately sets about the business of 
rearing a brood. 

The American robin has been mentioned as a slow migrant, and, as 
a species, it takes 78 days to make the 3,000-mile trip from Iowa to 
Alaska, a stretch of country that is crossed by advancing spring in 68 
days. In this case, however, it does not necessarily mean that 
individual robins are slow. The northward movement of the species 
probably depends upon the continual advance of birds from the rear, 
so that the first individuals arriving in a suitable locality are the ones 
that nest in that area, while the northward movement of the species is 
continued by those still to come. 

There is great variation in the speed of migration at different 

30 



latitudes of the broad region between the Gulf of Mexico and the 
Arctic Ocean. The blackpoll warbler again furnishes an excellent 
example (Fig. 3). This species winters in northwestern South 
America and starts to migrate north in April. When the birds reach 
the southern United States, some individuals fly northwest to the 
Mississippi Valley, north to Manitoba, northwest to the Mackenzie 
River, and then almost due west to western Alaska. A fairly uniform 
average distance of 30 to 35 miles per day is maintained from the Gulf 
to Minnesota, but a week later this species has reached the central 
part of the Mackenzie Valley, and by the following week it is observed 
in northwestern Alaska. During the latter part of the journey, 
therefore, many individuals must average more than 200 miles per 
day. Thirty days are spent traveling from Florida to southern 
Minnesota, a distance of about 1,000 miles, but scarcely half that time 
is used to cover the remaining 2,500 miles to Alaska. Increased speed 
across western Canada to Alaska is also shown by many other birds 
(Figs. 2,4,6). A study of all species traveling up the Mississippi Valley 
indicates an average speed of about 23 miles per day. From southern 
Minnesota to southern Manitoba 16 species maintain an average 
speed of about 40 miles per day. From that point to Lake Athabaska, 
12 species travel at an average speed of 72 miles per day, while 5 
others travel to Great Slave Lake at 116 miles per day, and another 5 
species cover 150 miles per day to reach Alaska. This change is in 
correlation with a corresponding variation in the isothermal lines, 
which turn northwestward west of the Great Lakes. 

As has been previously indicated, the advance of spring in the 
northern interior is much more rapid than in the Mississippi Valley 
and on the Gulf coast. In other words, in the North spring comes with 
a rush, and, during the height of migration season in Saskatchewan, 
the temperature in the southern part of the Mackenzie Valley just 
about equals that in the Lake Superior area, 700 miles farther south. 
Such conditions, coupled with the diagonal course of the birds across 
this region of fast-moving spring, exert a great influence on 
migration and are probably factors in the acceleration of travel 
speed. However, it should be remembered that the birds are getting 
closer to the breeding season and may be stimulated to travel faster 
for this reason. 

Thus it has been shown that the rate of migration varies greatly 
under varying circumstances. Radar investigations along the 
eastern coasts of the United States and England indicate spring 
migration is several miles per hour faster than in the fall. Also, 
directions of migrations in spring were much less diverse than in the 
fall, which suggests less time lost in passage (Tedd and Lack 1958; 
Nisbet and Drury 1967a). King and Farner (1963) found the same 
species put on more fat preparatory to migration in the spring. This 
would give the migrants greater energy reserves for longer flights at 
that season. 



31 



ALTITUDE OF FLIGHT AND MIGRATION 



The factors regulating the heights of bird migration are not clear. 
High-altitude flight may be used to locate familiar landmarks, fly 
over fog or clouds, surmount physical barriers, gain advantage of a 
following wind, or maintain a better physiological balance. 
Meteorological conditions probably account for most of the high- 
altitude records. Wind conditions at ground level are usually quite 
different in direction and velocity than at points higher up. 

In general, human estimates of bird heights are quite unreliable 
except under special conditions, and these estimates will vary with 
the eyesight of the observer. Lucanus (1911) found a European 
sparrow hawk could be distinguished at 800 feet but disappeared 
from sight at 2,800 feet. A rook (a European member of the crow 
family) could be recognized at 1,000 feet but disappeared from sight 
at 3,300 feet. Meinertzhagen (1955) did an interesting experiment 
with an inflated model of a vulture painted black; it had a wing 
expanse of 7 feet 10 inches. When released from an airplane at 4,700 
feet, it was barely visible and invisible without binoculars at 5,800 
feet. At 7,000 feet it was not picked up even when x!2 binoculars were 
used. 

At one time students of bird migration believed normal migratory 
movements took place at heights above 15,000 feet. They reasoned, 
somewhat uncertainly, that flying became easier as altitude was 
gained. It has now been shown, through comprehensive radar 
studies, that 95 percent of the migratory movements occur at less 
than 10,000 feet, and the bulk of the movements occur under 3,000 
feet. However, birds can and do fly well over 15,000 feet without 
apparent ill effects. The physiology of long-distance flight at high 
altitudes is of great interest but can only be touched on briefly in this 
discussion. 

Bird flight at 20,000 feet, where less than half the oxygen is present 
than at sea level, is impressive if only because the work is achieved by 
living muscle tissue. A Himalayan mountain climber at 16,000 feet 
was rather amazed when a flock of geese flew north 2 miles over his 
head honking as they went (Swan 1970). At 20,000 feet a man has a 
hard time talking and running or other rapid movements are out of 
the question; but those geese were probably flying at 27,000 feet and 
even calling while they traveled at this tremendous height. 

Accurate observations on the altitude of migratory flights is 
scanty, although altimeter observations from airplanes and radar 
are becoming more frequent in the literature. An example is the 
report of a mallard struck by a commercial airliner at 21,000 feet 
over the Nevada desert (Manville 1963). It is, of course, obvious that 

32 



some birds must cross mountain ranges during migration and attain 
great altitudes. Numerous observations have come from the 
Himalayas (Geroudet 1954; Swan 1970). Observers at 14,000 feet 
recorded storks and cranes flying so high that they could be seen only 
through field glasses. In the same area large vultures were seen 
soaring at 25,000 feet and an eagle carcass was found at 26,000 feet. 
The expedition to Mt. Everest in 1952 found skeletons of a pintail and 
a black-tailed godwit at 16,400 feet on Khumbu Glacier (Geroudet 
1954). Bar-headed geese have been observed flying over the highest 
peaks (29,000+ feet) even though a 10,000-foot pass was nearby. 
Probably 30 or more species regularly cross these high passes (Swan 
1970). 

Except to fly over high mountain ranges, birds rarely fly as high as 
those traveling down the western Atlantic (Richardson 1972). Many 
of these birds are making long-distance flights to eastern South 
America and beyond. Therefore, flight at high altitudes in this region 
is probably advantageous for them. Richardson postulated stronger 
advantageous tail winds were found higher up and the cooler air 
minimized evaporative water losses. This investigator found air 
temperatures averaged 35 F at 10,000 feet over Nova Scotia in 
September. The lower the ambient temperature, the more heat can 
be lost by convection and the less water is required for cooling. Also, a 
bird flying high can achieve the same range as one flying at sea level 
but must cruise at a higher speed with a corresponding increase in 
power output and oxygen consumption. But the increased cruising 
speed results in shorter flight time and less interference from wind 
(Pennycuick 1969). 

Another postulate favoring the high-altitude flying theory was 
that the wonderful vision of birds was their sole guidance during 
migratory flights. To keep landmarks in view, birds were obliged to 
fly high, particularly when crossing wide areas of water. This will be 
considered in greater detail in the section, "Orientation and 
Navigation," so here it will be sufficient to say that birds rely only in 
part upon landmarks to guide them on migration. Also, it must be 
remembered that definite physical limitations to the range of 
visibility exist even under perfect atmospheric conditions. Chief of 
these is the curvature of the earth's surface. Thus, if birds crossing 
the Gulf of Mexico to Louisiana and Florida flew at a height of 5 
miles, they would still be unable to see a third of the way across 
(during daylight hours). And yet this trip is made twice each year, 
much of the distance probably at night, by thousands of thrushes, 
warblers, and others. 

The altitude of migration depends upon the species of bird, 
weather, time of day or year, and geographical features. Nocturnal 
migrants, studied by radar, appear to fly at different altitudes at 
different times during the night. Birds generally take off shortly 
after sundown and rapidly gain maximum altitude. This peak is 
maintained until around midnight, then the travelers gradually 
descend until daylight. For most small birds the favored altitude 

33 



appears to be between 500 and 1,000 feet (Bellrose 1971), but radar 
studies have found some nocturnal migrants (probably shorebirds) 
over the ocean were at 15,000 or even 20,000 feet (Lack 1960b; Nisbet 
1963b; Richardson 1972). Observations made from lighthouses and 
other vantage points indicate that certain migrants commonly travel 
at altitudes of a very few feet to a few hundred feet above sea or land. 
Sandpipers, northern phalaropes, and various sea ducks have been 
seen flying so low they were visible only as they topped a wave. 
Observers stationed at lighthouses and lightships off the English 
coast have similarly recorded the passage of landbirds flying just 
above the surface of the water and rarely above 200 feet. During the 
World Wars, broad areas in the air were under constant surveillance, 
and many airplane pilots and observers took more than a casual 
interest in birds. Of the several hundred records resulting from their 
observations, only 36 were of birds flying above 5,000 feet and only 7 
above 8,500 feet. Cranes were once recorded at an altitude of 15,000 
feet, while the lapwing was the bird most frequently seen at high 
levels, 8,500 feet being its greatest recorded altitude. Records of the 
U.S. Civil Aeronautics Administration show that over two-thirds of 
all the bird-aircraft collisions occur below 2,000 feet and practically 
none occur above 6,000 feet (Williams 1950). 

Recently, radar has aided greatly in determining differences in the 
altitude of bird flight. Nocturnal migrants appear to fly slightly 
higher, on the average, than diurnal migrants, but daytime flights 
may be influenced more by cloud cover (Lack 1960a; Eastwood and 
Rider 1965). Bellrose (1971) found little difference in the altitudinal 
distribution of small nocturnal migrants under clear or overcast 
skies. Many night migrating birds are killed each year by striking 
lighthouses, television towers or other man-made illuminated 
obstructions, but this does not furnish proof that low altitudes are 
generally used during nocturnal flight because these accidents occur 
chiefly in foggy weather. Under such conditions, migrating birds 
seem to be attracted to and confused by lights. Seabirds, such as 
loons, eiders, and scoters, generally fly very low over the water but 
gain altitude when land is crossed. The reverse is true for landbirds 
(Dorst 1963; Bergman and Donner 1964; Eastwood and Rider 1965). 
There may be a seasonal difference in the altitude of migration, but 
the evidence is conflicting. Radar echoes studied by Bellrose and 
Graber in Illinois (1963) showed fall migrants flew higher than 
spring migrants. They speculated this difference was related to the 
winds during the fall being more favorable for southerly migration 
at higher altitudes, while winds at these altitudes in the spring would 
be less favorable for northerly migration. Eastwood and Rider (1965) 
studied seasonal migration patterns in England and found the 
reverse to be true. They suggested one reason for this seasonal 
difference was that flocks of fall migrants included many young 
birds whose flight capabilities are inferior to adults and 
consequently are unable to achieve the higher altitudes in the fall. 



34 



SEGREGATION DURING MIGRATION 



By Individuals or Groups of Species 

During the height of northward movement in spring, the woods 
and thickets may suddenly be filled with several species of wood 
warblers, thrushes, sparrows, flycatchers, and other birds. It is 
natural to conclude they traveled together and arrived simultaneous- 
ly. Probably they did, but such combined migration is by no means 
the rule for all species. 

As a group, the wood warblers probably travel more in mixed 
companies than do any other single family of North American birds. 
In spring and fall, the flocks are likely to be made up of the adults and 
young of several species. Sometimes swallows, sparrows, blackbirds, 
and some of the shorebirds also migrate in mixed flocks. In the fall, 
great flocks of blackbirds frequently sweep south across the Plains 
States, with common grackles, red-winged blackbirds, yellow- 
headed blackbirds, and Brewer's blackbirds included in the same 
flock. 

On the other hand many species keep strictly to themselves. It 
would be difficult for any other kind of bird to keep company with the 
rapid movements of the chimney swift. Besides flight speed, feeding 
habits or roosting preferences can be so individual as to make 
traveling with other species incompatible. Nighthawks also fly in 
separate companies, as do crows, waxwings, crossbills, bobolinks, and 
kingbirds. Occasionally, a flock of ducks will be observed to contain 
several species, but generally when they are actually migrating, 
individuals of each species separate and travel with others of their 
own kind. 

Although different species generally do not migrate together, we 
often find many species passing through an area at the same time. If 
the different kinds of birds observed in a specific area are counted 
every day throughout the entire migration season, this count often 
rises and falls much like the bell-shaped curve exhibited when the 
number of individuals of a given species are counted through the 
same time period. Figure 7 shows two peaks in the number of species 
passing through the desert at the north end of the Gulf of Eilat 
(=Akaba) in the Red Sea. These two peaks happen to coincide with 
peaks in the numbers of individuals (mostly from the order of 
perching birds) traveling through the area. Therefore, in the latter 
part of March and again in April, one notices not only more birds in 
the area but also more different kinds. 

Closely related species or species that eat the same food organisms 
are not often found migrating through the same area at the same 
time. Ornithologists call this species replacement. In North America, 

35 



peaks in the migration of the five kinds of spotted thrushes generally 
do not coincide. Dates of departure in these species have evolved so all 
the individuals of these closely related birds do not converge on one 
area at the same time and subsequently exhaust the food supply. By 
selection of staggered peak migration dates, evolution has distrib- 
uted the members of this family more or less evenly throughout the 
entire season. Likewise, in the eastern Mediterranean area, we find a 
similar situtation in spring migration for three closely related 
buntings; Cretzschmar's bunting comes through first, followed a few 
weeks later by the Ortolan bunting and, at the tail end of the 
migration period, the blackheaded bunting appears (Fig. 8). 

By Age 

The adults of most birds leave the young when they are grown. This 
gives the parents an opportunity to rest and renew their plumage 
before starting for winter quarters. The young are likely to move 
south together ahead of their parents. This has been documented in a 
number of species including our mourning dove, the common swift of 
Europe, and storks. Mueller and Berger (1967) found an age-specific 
migration pattern in sharp-shinned hawks passing through 
Wisconsin. The immatures were much in evidence during 
mid-September while the adults came through a month later. Far to 

Species Captured 




March April 



Figure 7. Average number of species captured daily in mist nets during spring migra- 
tion at Eilat, Israel, in 1968. The number of species passing through an area on 
migration will rise and fall similar to the number of birds counted in the area. In this 
case two major movements came through about 1 month apart. 

36 



the south in the Antarctic, young Adelie penguins depart for 
northern wintering grounds much earlier than adults. 

In a few species, adults depart south before the young. Adult 
golden plovers, Hudsonian godwits, and probably most of the Arctic 
breeding shorebirds leave the young as soon as they are capable of 
caring for themselves and set out for South America ahead of the 
juveniles. Likewise, data for the least flycatcher indicate adults 
migrate before the young, but Johnson (1963) did not find this 
segregation in the Hammond's flycatcher. In Europe, adult 

Cretzschmar's Bunting 
Ortolan Bunting 
Black-headed Bunting 




\ 



Average Number Captured Daily 



Cretzschmans Bunting 
Ortolan Bunting 
Black-headed Buntin 




March 



April 



May 



Figure 8. Average number of three species of buntings captured daily in mist nets 
during spring migration atEilat, Israel, in 1968. Closely related species that migrate 
through the same area often appear at different times. Thus species that may eat the 
same foods do not compete with each other. 

37 



red-backed shrikes are known to migrate ahead of their young. 

In contrast to this loss of parental concern, geese, swans, and cranes 
remain in family groups throughout migration. The parent birds 
undergo a wing molt that renders them flightless during the period 
of growth of their young so that both the adults and immatures 
acquire their flight capabilities at the same time and are able to start 
south together. Large flocks of Canada geese, for example, are 
composed of many families banded together. When these flocks 
separate into small V-shaped units it is probably correct to assume an 
old goose or gander is leading the family. After female ducks start to 
incubate their eggs, the males of most species of ducks flock by 
themselves and remain together until fall. When segregation of the 
sexes such as this occurs the young birds often accompany their 
mothers south. Murray and Jehl (1964) concluded from mist-netting 
many thousands of migrant passerines at Island Beach, New Jersey, 
that adults and juveniles travel at approximately the same time. 

By Sex 

Males and females of some species may migrate either 
simultaneously or separately. In the latter case it is usually the males, 
rarely the females, that arrive first. Sometimes great flocks of male 
red-winged blackbirds reach a locality several days before any 
females; this is particularly the rule in spring. The first robins are 
usually found to be males, as are also the first song sparrows, 
rose-breasted grosbeaks, and scarlet tanagers. In Europe, the three 
buntings mentioned previously are also segregated as to sex during 
migration. Figure 8 shows two prominant peaks for both the 
Cretzschmar's and Ortolan buntings; during passage the first peak 
was primarily males while the second peak consisted mostly of 
females. This early arrival of males on the breeding grounds is 
associated with territorial possession whereby the male selects the 
area where it intends to breed and each individual attempts to 
protect a definite territory from trespass by other males of his own 
kind, while announcing his presence to rival males and later arriving 
females by song or other display. The female then selects the site 
where she wishes to nest. The long-billed marsh wren is a noteworthy 
example; the males may enthusiastically build several nests before 
the females arrive. In the fall, common and king eiders are sexually 
segregated during migration. During July, flocks crossing Point 
Barrow are composed almost entirely of males, while after the 
middle of August the flocks are almost all females (Thompson and 
Person 1963). In the Chicago area, Annan (1962) reported that some 
males, such as the hermit thrush, Swainson's thrush, gray-cheeked 
thrush, and veery, arrive before any females and predominate 
during the first week of occurrence. 

In a few species the males and females apparently arrive at the 
breeding grounds together and proceed at once to nest building. In 
fact, among shorebirds, ducks, and geese, courtship and mating 
often takes place in whole or in part while the birds are in the South or 

38 



on their way north, so that when they arrive at the northern nesting 
grounds they are paired and ready to proceed at once with raising 
their families. Mallards and black ducks may be observed in pairs as 
early as December, the female leading and the male following when 
they take flight. Naturally, these mated pairs migrate north in 
company, and it was largely to protect such pairings that duck 
shooting in spring was abolished by Federal law. 

In the coastal subspecies of the western flycatcher, the sexes 
appear to migrate in synchrony during the spring in contrast to 
migration of Hammond's flycatcher in which the adult males usually 
precede the females (Johnson 1973). Both sexes of the common 
blackcap of Europe appear to migrate together at least across the 
eastern end of the Mediterranean during the spring (Fig. 9). 

Blackcap 




Numbers captured 
300 



250 



200 



150 



Correlation 0.99 




100 



Figure 9. Numbers of male and female blackcaps captured daily in mist nets during 
spring migration at Eilat, Israel, in 1968. At this point in their migration the sexes 
are passing through the area at the same time. In other species (e.g., the buntings in 
Fig. 8), the males often preceed the females. 

39 



By Kinds of Flocks 

Migratory flights are frequently accomplished in close flock 
formation, as with shorebirds, blackbirds, waxwings, and especially 
some of the buntings, longspurs, juncos, and tree sparrows. Other 
species maintain a very loose flock formation; examples are turkey 
vultures, hawks, swifts, blue jays, swallows, warblers, and bluebirds. 
Still others, the grebes, snowy owls, winter wrens, shrikes, and belted 
kingfishers, ordinarily travel alone, and when several are found in 
close proximity it is an indication they have been drawn together by 
unusual conditions, such as abundant food. 

Just as flocking among resident birds provides group protection 
against predation, flocking in migration greatly facilitates the 
attainment of destination (Pettingill 1970). The V-shaped flocks often 
associated with Canada geese have a definite energy conserving 
function by creating favorable air currents for every member of the 
flock but the leader; when the leader becomes tired, it will often 
change places with a member behind. Night migrating flocks 
generally fly in looser formations than do day migrating flocks. 



40 



WHERE BIRDS MIGRATE 



Migration by Populations Within Species 

Both length and duration of migratory journeys vary greatly 
between families, species, or populations within a species. Bobwhite, 
western quails, cardinals, Carolina wrens, and probably some of the 
titmice and woodpeckers are apparently almost or entirely 
nonmigratory. These species may live out their entire existence 
without going more than 10 miles from the nest where they were 
hatched. 

Many song sparrows, meadowlarks, blue jays, and other species 
make such short migrations that the movement is difficult to detect 
because individuals, possibly not the same ones, may be found in one 
area throughout the year while other individuals that move south 
may be replaced by individuals from the north. Information on 
different movements of this type, within a species, can be gained by 
observing birds marked with numbered bands, colored materials, or 
identification of racially distinct museum specimens. 

The American robin is a good example of this type of movement. 
This species occurs in the southern United States throughout the 
year, but in Canada and Alaska only during the summer. Its 
movements are readily ascertained from study specimens. The 
breeding robin of the southeastern states is the southern race. In 
autumn most of its more northern nesters, such as those from 
Maryland and Virginia move into the southern part of the breeding 
range or slightly farther south. At about the same time the northern 
American robin moves south and winters throughout the breeding 
and wintering range of its smaller and paler southern relative. Thus 
there is complete overlap of wintering ranges of northern and 
southern American robin populations, although some individuals of 
the northern race winter in areas vacated earlier by the southern 
race. 

Among many migratory species there is considerable variation 
among individuals and populations with respect to distances moved. 
Certain populations may be quite sedentary while others are strongly 
migratory, and certain individuals of the same population can be 
more migratory than others. For example, red-winged blackbirds 
nesting on the Gulf Coast are practically sedentary, but in winter 
they are joined by other subspecies that nest as far north as the 
Mackenzie Valley. In certain populations of the song sparrow and 
other species, males remain all year on their northern breeding 
grounds while the females and young migrate south. 

Several species containing more than one distinguishable 

41 



population exhibit "leap-frog" migration patterns. The familiar 
eastern fox sparrow breeds from northeastern Manitoba to 
Labrador, but during the winter it is found concentrated in the 
southeastern part of the United States. On the west coast of the 
continent, however, a study of museum specimens by Swarth (1920), 
indicated six subspecies of this bird breeding in rather sharply 
delimited ranges extending from Puget Sound and Vancouver Island 
to Unimak Island, at the end of the Alaskan Peninsula. One of these 
subspecies, known as the sooty fox sparrow, breeds from the Puget 
Sound-Vancouver Island area northward along part of the coast of 
British Columbia. It hardly migrates at all, while the other races, 
nesting on the coast of Alaska, are found in winter far to the south in 
Oregon and California. Although much overlap exists, the races 
breeding farthest north generally tend to winter farthest south. This 
illustrates a tendency for those populations forced to migrate to pass 
over those subspecies so favorably located as to be almost sedentary. 
If the northern birds settled for the winter along with the sedentary 
population, winter requirements may not be as sufficient as in the 
unoccupied areas farther south (Fig. 10). Therefore, natural selection 
has insured the different populations will survive the winter by 
separating the subspecies into different wintering areas. 

Another example of this "leap-frog" migration is illustrated by the 
common yellowthroat of the Atlantic coast. Birds occupying the most 
southern part of the general range are almost nonmigratory and 
reside throughout the year in Florida, whereas the population that 
breeds as far north as Newfoundland goes to the West Indies for the 
winter. Thus the northern population literally "jumps" over the home 
of the southern relatives during migratory journeys. 

The palm warbler breeds from Nova Scotia and Maine west and 
northwest to southern Mackenzie. The species has been separated 
into two subspecies: those breeding in the interior of Canada and 
those breeding in northeastern United States and Canada. The 
northwestern subspecies makes a 3,000-mile journey from Great 
Slave Lake to Cuba and passes through the Gulf States early in 
October. After the bulk of these birds have passed, the eastern 
subspecies, whose migratory journey is about half as long, drifts 
slowly into the Gulf Coast region and remains for the winter. 

Fall Flights Not Far South of Breeding Range 

Some species have extensive summer ranges (e.g., the pine 
warbler, rock wren, field sparrow, loggerhead shrike, and 
blackheaded grosbeak) and concentrate during the winter season in 
the southern part of the breeding range or occupy additional 
territory only a short distance farther south. The entire species may 
thus be confined within a restricted area during winter, but with the 
return of warmer weather, the species spreads out to reoccupy the 
much larger summer range. 

Many species, including the tree sparrow, snow bunting, and 
Lapland longspur, nest in the far north and winter in the eastern 

42 



/ 



/ 




Breeding Range 

Winter and Breeding Range 

Winter Range 




V 






1 2 3 



Fox Sparrow 



Figure 10. Migration of Pacific coast forms of the fox sparrow. The breeding ranges of 
the different races are encircled by solid lines, while the winter ranges are dotted. The 
numbers indicate the areas used by the different subspecies as follows: L Shumagin 
fox sparrow; 2. Kodiakfox sparrow; 3. Valdezfox sparrow; 4. Yakutatfox sparrow; 
5. Townsendfox sparrow; 6. sooty fox sparrow (After Swarth 1920). 



43 



United States, while others, including the vesper and chipping 
sparrows, common grackle, red-winged blackbird, eastern bluebird, 
American woodcock, and several species of ducks, nest much farther 
south in the United States and Canada and move south a relatively 
short distance for the winter to areas along the Gulf of Mexico. In a 
few of the more hardy species, individuals may linger in protected 
places well within reach of severe cold. The common snipe, for 
example, is frequently found during subzero weather in parts of the 
Rocky Mountain region where warm springs assure a food supply. 
More than 100 summer birds leave the United States entirely and 
spend the winter in the West Indies, Central America, or South 
America. For example, the Cape May warbler breeds from northern 
New England, northern Michigan, and northern Minnesota, north to 
New Brunswick, Nova Scotia, and nearly to Great Slave Lake. In 
winter it is concentrated chiefly in the West Indies on the island of 
Hispaniola. 

Long Distance Migration 

Some of the common summer residents of North America are not 
content with a trip to northern tropical areas of the West Indies and 
Central America, but push on across the Equator and finally come to 
rest for the winter in Patagonia or the pampas of Argentina. Species 
such as nighthawks, some barn swallows, cliff swallows, and a few 
thrushes may occupy the same general winter quarters in Brazil, but 
other nighthawks and barn swallows go farther south. Of all North 
American landbirds these species probably travel the farthest; they 
are found north in summer to the Yukon Territory and Alaska, and 
south in winter to Argentina, 7,000 miles away. Such seasonal flights 
are exceeded in length, however, by the remarkable journeys of 
several species of shorebirds including white-rumped and Baird's 
sandpipers, greater yellowlegs, turnstones, red knots, and sander- 
lings. In this group, 19 species breed north of the Arctic Circle and 
winter in South America; six of these go as far south as Patagonia, a 
distance of over 8,000 miles. 

The Arctic tern is the champion "globe trotter" and long-distance 
flier (Fig. 11). Its name "Arctic" is well earned, as its breeding range 
is circumpolar and it nests as far north as the land extends in North 
America. The first nest found in this region was only 7-1/2 (518 
miles) from the North Pole and contained a downy chick surrounded 
by a wall of newly fallen snow scooped out by the parent. In North 
America the Arctic tern breeds south in the interior to Great Slave 
Lake, and on the Atlantic coast to Massachusetts. After the young are 
grown, the Arctic terns disappear from their North American 
breeding grounds and turn up a few months later in the Antarctic 
region, 1 1 ,000 miles away. For a long time the route followed by these 
hardy fliers was a complete mystery; although a few scattered 
individuals have been noted south as far as Long Island in the United 
States, the species is otherwise practically unknown along the 
Atlantic coasts of North America and northern South America. It is, 

44 



Breeding Areas 
Winter Areas 
Recovery Points 

Migration Points 




Figure 11. Distribution and migration of arctic terns. The route indicated for this bird 
is unique, because no other species is known to breed abundantly in North America 
and to cross the Atlantic Ocean to and from the Old World. The extreme summer and 
winter homes are 11,000 miles apart. 

45 



however, known as a migrant on the west coast of Europe and Africa. 
By means of numbered bands, a picture disclosed what is apparently 
not only the longest, but also one of the most remarkable migratory 
journeys (Austin 1928). 

Few other animals in the world enjoy as many hours of daylight as 
the Arctic tern. For these birds, the sun never sets during the nesting 
season in the northern part of the range, and during their winter 
sojourn to the south, daylight is continuous as well. In other months of 
the year considerably more daylight than darkness is encountered. 



46 



ORIENTATION AND NAVIGATION 



There probably is no single aspect of the entire subject of bird 
migration that increases our admiration so much as the unerring 
certainty with which birds cover thousands of miles of land and 
water to come to rest in exactly the same spot where they spent the 
previous summer or winter. Records from birds marked with 
numbered bands offer abundant proof that the same individuals of 
many species will return again and again to identical nesting or 
winter feeding sites. 

This ability to travel with precision over seemingly featureless 
stretches of land or water is not limited to birds but is likewise 
possessed by certain mammals, reptiles, fishes, and insects; the well- 
known migrations of salmon and eels are notable examples. 

For an animal to return to a specific spot after a lengthy migration, 
it must use true navigation to get there. That is, it needs to not only 
travel in a given compass heading and know where it is at any given 
time so the course may be altered when necessary but also be able to 
recognize its goal when it has arrived. It is dangerous to generalize on 
the means of orientation and navigation in migration; different 
groups of birds with different modes of existence have evolved 
different means of finding their way from one place to another 
(Pettingill 1970). We are only beginning to realize the complexities 
involved in the many modes of bird orientation and navigation. All 
we can do in this section is present a brief summary of some of the 
more important principles involved and the studies that have 
enhanced our knowledge in the area. 

Ability to follow a more or less definite course to a definite goal is 
evidently part of an inherited faculty. Both the direction and the goal 
must have been implanted in the bird's genetic code when the 
particular population became established at its present location. The 
theory is sometimes advanced that older and more experienced birds 
lead the way and thereby show the route to their younger 
companions. This explanation may be acceptable for some species 
such as geese, swans, and cranes because they stay in family groups, 
but not for species in which adults and young are known to migrate at 
different times, especially when young migrate ahead of the adults. 
As indicated in a previous section on segregation, many North 
American shorebirds as well as the cuckoos of New Zealand do this. 
An inherited response to its surroundings, with a definite sense of the 
goal to be reached and the direction to be followed, must be attributed 
to these latter birds. 

It is well known that birds possess wonderful vision. If they also 
have retentive memories subsequent trips over the route may well be 

47 



steered in part by recognizable landmarks. Arguments against the 
theory of landmark memory are chiefly that unescorted young birds, 
without previous experience, can find their way to the winter 
quarters of their species, even if the wintering area has a radically 
different landscape and vegetation than the breeding grounds. 
Experimental findings and field observations indicate landmarks 
are used in navigation by certain birds, but the degree of use varies 
considerably among the species (Bellrose 1972a). 

To a land-dweller traveling the ocean, the vast expanse may seem 
featureless but the reverse may be true for a seabird blown over land 
by a storm. In the latter situation the differences in vegetation and 
topography "obvious" to land-dwellers are completely foreign to a 
seabird as it has had little previous experience to help interpret these 
"strange objects." Griffin and Hock (1949) observed the flight 
behavior of gannets displaced far inland away from their nests. The 
bird appeared to search randomly until the coastline was met, then 
the fliers pursued a much more direct course home. Herring gulls, 
displaced about 250 miles from their nest in 2 consecutive years, 
returned the second year in one-sixth the time required the first year 
(Griffin 1943). To birds such as gannets, albatrosses, and 
shearwaters, which spend almost their entire lives traveling 
thousands of miles at sea and return to very specific nesting areas, the 
"featureless ocean expanses" are probably very rich in visual cues. It 
is difficult to believe a bird dependent on the sea for its livelihood 
cannot help but be aware of wave direction, islands, reefs, atolls, 
concentrations of floating flotsam, organisms, currents, clouds over 
islands, fog belts, etc. 

Much migration takes place at night and great stretches of the 
open sea are crossed to reach destinations. Nights are rarely so dark 
that all terrestrial objects are totally obscured, and features such as 
coastlines and rivers are just those that are most likely to be seen in 
the faintest light, particularly by the acute vision of birds from their 
aerial points of observation. Even if terrestrial objects are completely 
obscured on a very dark night, the migrants are still able to assess 
their surroundings during the day before starting out again. 

Some birds, especially colonial seabirds, seem to be able to fly 
unerringly through the densest fog, particularly in the vicinity of 
their nest site. Members of the Biological Survey, proceeding by 
steamer through a dense fog from the island of Unalaska to Bogoslof 
Island in the Bering Sea, recorded flocks of murres, returning to 
Bogoslof after quests for food. The birds broke through the wall of fog 
astern, flew by the vessel, and disappeared into the mists ahead on the 
same course as the ship. On the other hand, radar observations of 
migrating birds have indicated strong directional movements on 
clear nights but often completely random movements in heavily 
overcast or stormy weather. Possibly some birds can perceive the 
position of the sun through an overcast as honey bees are known to do. 
It is less likely the stars could be detected through overcast at night. 

Careful studies have been made on the homing instinct in various 

48 



seabirds such as Laysan albatrosses, Manx shearwaters, and several 
tropical species of terns. Sooty and noddy terns reach their most 
northern breeding point on the Dry Tortugas, off the southwest coast 
of Florida. They are not known to wander any appreciable distance 
farther north. Displaced breeding birds returned to their nests on the 
Dry Tortugas after they had been taken on board ship, confined in 
cages below decks, and carried northward 400 to 800 miles before 
being released in a region where they had had no previous 
experience. Likewise, Laysan albatrosses and Manx shearwaters 
have returned over 3,000 miles in similar homing experiments. 

Possibly the "homing instinct," as shown by pigeons, terns, 
shearwaters, albatrosses, and by the frigatebirds trained as message 
carriers in the South Pacific, may not be identical with the sense of 
perceptive orientation that figures in the flights of migratory birds. 
Nevertheless, it seems closely akin and is probably governed by the 
same mechanisms. There are good reasons to assume that once we 
know the processes governing displaced homing we will know, in 
general, how birds navigate; this question is still far from being 
answered (Wallraff 1967). 

Some students have leaned toward the possible existence of a 
"magnetic sense" as being the important factor in the power of 
geographical orientation. The theory was conceived as early as 1855 
and reported in 1882 by Viguier. Investigations of this have been 
conducted by Yeagley (1947) and Gordon (1948) with contradictory 
results. In 1951, Yeagley incorporated the idea that sensitivity to the 
effect of the earth's rotary motion through the vertical component of 
the magnetic field is the means of orientation. The basic question 
asked of the theory is: "Can birds detect such minute differences in 
the earth's magnetic field and can these forces affect bird behavior?" 

Attempts to demonstrate the effect of radio waves on the 
navigational ability of birds have produced contradictory results. In 
some of these tests, homing pigeons released near broadcasting 
stations have appeared to be hopelessly confused, whereas in others, 
apparently conducted in the same manner, no effects could be 
discerned. Before sensitivity of birds to electromagnetic stimuli of 
any kind can be accepted or rejected, much additional experimental 
work is necessary. 

Human navigators have used the heavenly bodies in determining 
their course and position for centuries. It would not be surprising 
then to find other long-distance travelers using the same method. One 
of the most constant visual cues a migrating bird could use would be 
the sun's or moon's path and the location of the stars. 

Some of the more recent experimental work on bird navigation has 
been with astronomical (sun) and celestial (star) directional clues. 
Studies by Kramer, Sauer, and others have indicated a phenomenal 
inherited ability in birds to use the position of the sun by day and the 
stars by night to chart their courses. This involves an intricate 
compensation for daily, seasonal, and geographical changes in the 
positions of these heavenly bodies. Kramer (1957, 1961) placed 

49 



diurnal migrants in circular cages and "changed" the position of the 
sun with mirrors. The birds shifted their position to compensate for 
these changes. Sauer (1957, 1958), in a fascinating study with 
nocturnal migrant warblers, placed birds in a round cage open to the 
sky. These birds oriented in the normal direction for that locality and 
time of year. He next placed the cage and birds in a planetarium and 
projected overhead the night sky star patterns for different seasons 
and localities. The familiar star pattern produced a normal 
orientation but an unfamiliar sky caused confusion and complete 
disorientation. These experiments, begun in Germany, are still 
continuing in other countries with other species. Emlen (1969) used 
photoperiod manipulation to change the physiological states of 
spring and fall migratory readiness in indigo buntings. Half the 
sample of birds were in breeding condition whereas the other half 
were already past the reproductive stage even though it was spring 
"outside." When these birds were subjected to a spring star pattern in 
a planetarium, the birds in spring condition oriented northward but 
those in autumnal condition oriented southward. Although some 
results have been negative, by and large the evidence supports the 
original findings that the sun and stars are visual "landmarks" used 
by at least some birds as well as bees and probably many other 
creatures in finding their way home as well as to their winter and 
summer quarters. 

In conclusion, then, we can say this about bird orientation and 
navigation: 1) many cues are available to birds for migratory 
guidance and one or several of these may be used by any migrant; 2) 
different species and groups of birds use different cues, depending on 
their migration traits; 3) visual cues probably play a predominant 
role in migration (radar studies have indicated that some birds can 
maintain their orientation even under completely overcast nights, 
although they usually become disoriented under such conditions); 
and 4) long-distance migrants and pelagic species have a much 
higher developed sense of orientation than those species that migrate 
only short distances or not at all. 



50 



INFLUENCE OF WEATHER 



It is thought by some that the weather has little to do with the time 
of arrival of migratory birds. It is assumed that if the bird is 
physiologically prepared for migration it departs, irrespective of the 
weather. Even if this were the case, weather can influence the 
progress of migration by not only controlling the advance of the 
seasons but also by helping, hindering, or even stopping bird flight 
(Welty 1962). 

Some scientists believe that birds not only avoid bad weather at the 
start of a journey but usually finish the journey in good weather 
(Nesbit and Drury 1967b). Contrary to what many observers believe, 
the arrival of birds in an area, whether they stop or continue on, is 
more often controlled by the weather at the point of departure than at 
the point of arrival. During the peak of migration, suitable weather 
may occur at an observation site, but strong migratory movements 
may be arrested before the birds arrive there because the weather 
was not suitable at the point of departure or somewhere in between. 
In addition, if there is good weather at the point of departure as well 
as farther down the migration route, the migrants, once air-borne in 
a favorable weather pattern, may continue on right over an expectant 
observer and the whole flight will be missed. Nesbet and Drury's 
(1967b) radar study on air-gound comparisons found, with few 
exceptions, ground observers missed the largest movements observed 
on radar. Observation of a large wave of arrivals indicated migrants 
had been stopped by a meteorological barrier, and people were 
actually not reporting maximum migration but an interruption to 
migration. Therefore, when migration is proceeding normally under 
safe conditions, very little movement is visible to the ground observer 
but a large arrival of birds on the ground often indicates something is 
not in order and the migrants have been forced to stop for one reason 
or another. 

The question is frequently asked: "How can I identify weather 
conditions suitable or unsuitable for migration?" It is almost 
impossible to discuss separately the effects of different weather 
factors on migration because barometric pressure, temperature, 
wind, and other meteorological phenomena are very closely related. 

On the North American continent, air masses generally proceed 
about 600 miles per day from the west to the east. These air masses 
vary in pressure, temperature, humidity, and wind. The wind within 
these masses travels in either a clockwise (anticyclonic) or 
counterclockwise (cyclonic) direction. Cyclonic air masses contain 
relatively moist warm air with low barometric pressure centers and 
are designated "lows"; anticyclonic air masses are characterized by 

51 



dry cool air with high barometric pressure areas and are called 
"highs." Where these air masses meet, a "front" is formed, and the 
rapidity with which this front moves through an area depends on the 
temperature and pressure gradient on either side of the front. 

An understanding of frontal systems, with their associated wind, 
temperature and humidity, is one of the keys to understanding when 
birds migrate. You must not only watch the fronts in your area but 
the progress of nearby air masses as well because the birds migrating 
through your area have started their journey to the north or south of 
you depending on the season. The weather conditions at point of 
departure will dictate if and when birds will be passing through your 
area in the near future. 

During fall migration, the best passage of migrants usually occurs 
2 days after a cold front has gone through. That is, the low has passed 
and it is being followed by a high characterized by dropping 
temperatures, a rising barometer, and clearing skies. The 24 hours 
just after a low has passed are not always conducive to a good passage 
of birds because winds are often too strong and turbulent in the 
trough between the two air masses. Hochbaum (1955) correlated 
mass movements of ducks through the prairies with weather systems 




Figure 12. A hypothetical weather system that could be ideal for mass migrations of 
waterfowl in the fall. The strong southerly flow of air created by counter-clockwise 
winds about the lows and the clockwise rotation of air about the highs, aids the rapid 
movement of waterfowl from their breeding grounds in the Canadian prairies to 
wintering areas in southern United States. 

52 



and noted the combination of weather conditions described above 
was ideal for mass migrations of ducks during November. During 
this period, observers at Delta, Manitoba, south to Louisiana 
recorded a tremendous flight of ducks as the proper conditions of 
barometric pressure, temperature, wind, and cloud cover passed 
across the central United States and Canada. An example of the type 
of weather system that is often associated with mass movements is 
illustrated in Fig. 12. 

Records of lapwings on Newfoundland and the Gulf of St. 
Lawrence appear to be the result of a particular series of 
meteorological events (Bagg 1967). The lapwing is a European 
species rarely found in the New World. If cold air moves into western 
Europe from the east, lapwings move westward into England, Wales, 
and Ireland. Occasionally, the development of an anomalous weather 
pattern over the North Atlantic including an elongated low from 
Europe to eastern Canada causes some birds to be literally "blown" in 
the counter-clockwise airstream across the Atlantic to the Gulf of St. 
Lawrence. 

During spring migration, weather conditions conducive to strong 
movements of birds are somewhat the opposite from those in the fall. 
Migrants will move north on the warm sector of an incoming low. 
When a high pressure area has just passed, the influx of warm moist 
tropical air is extended and intensified (Bagg et al. 1950). However, 
during this time, cloudiness and rain associated with the low may 
curtail migration or squeeze it into a narrow period proceeding along 
the warm front. If a fast moving cold front approaches from the 
northwest, the rapid movement of migrants will be sharply curtailed 
or even grounded until more favorable conditions occur. 

The incessant crescendo note of the ovenbird is ordinarily 
associated with the full verdure of May woods, but this bird has been 
known to reach its breeding grounds in a snowstorm, and the records 
of its arrival in southern Minnesota show a temperature variation 
from near freezing to full summer warmth. Temperatures at arrival 
of several other common birds vary from 14 between highest and 
lowest temperatures to 37, the average variation being about 24. 
North American species spending the winter months in tropical 
latitudes experience no marked changes in temperature conditions 
from November to March or April, yet frequently they will start the 
northward movement in January or February. This is in obedience to 
physiological promptings and has no relation to the prevailing 
weather conditions. For migratory birds the winter season is a period 
of rest, a time when they have no cares other than those associated 
with the daily search for food or escape from their natural enemies. 
Their migrations, however, are a vital part of their life cycles, which 
have become so well adjusted that the seasons of travel correspond in 
general with the major seasonal changes on their breeding grounds. 
With the approach of spring, therefore, the reproductive impulse 
awakens, and each individual bird is irresistibly impelled to start the 
journey that ends in its summer home. 

53 



In other words, the evidence indicates the urge to migrate is so 
innate within a species or population that the individuals move north 
in spring when the average weather is not unendurable. The word 
"average" must be emphasized since it appears the migrations of 
birds have evolved in synchrony with average climatic conditions. 
More northern nesting populations of species such as American 
robins and savannah sparrows, timed to arrive on their breeding 
ground when the weather is suitable, pass through areas where their 
more southern kin are already nesting. The hardy species travel 
early, fearless of the blasts of retreating winter, while the more 
delicate kinds come later when there is less danger of encountering 
prolonged periods of inclement weather. Some of the hardy birds 
pause in favorable areas and allow the spring season to advance. 
Then, by rapid travel they again overtake it, or, as sometimes 
happens, they actually outstrip it. Occasionally this results in some 
hardship, but rarely in the destruction of large numbers of 
individuals after arrival. Cases are known where early migrating 
bluebirds have been overwhelmed by late winter storms. 
Nevertheless, if such unfavorable conditions are not prolonged, no 
serious effect on the species is noted. The soundness of the bird's 
instincts is evidenced by the fact that natural catastrophes, great 
though they may be, do not permanently diminish the avian 
populations. 

The spring flight of migrants, if interrupted by cold north winds, is 
resumed when weather conditions again become favorable, and it is 
probable that all instances of arrival in stormy weather can be 
explained on the theory that the flight was begun while the weather 
was auspicious. Even though major movements of migrants in spring 
generally coincide with periods of warm weather and southerly 
winds, observations on the beginning of nocturnal spring flights 
from the coast of Louisiana failed to note any inhibiting factor other 
than hard rain (Gauthreaux 1971). 

Radar studies have indicated that migrant birds possess an 
amazing understanding of wind patterns (Bellrose 1967). Birds can 
recognize many characteristics and select for favorable patterns. 
Head winds are as unfavorable to migration as is rain or snow 
because they greatly increase the labor of flight and cut down the 
speed of cross-country travel. If such winds have a particularly high 
velocity, they may force down the weaker travelers, and when this 
happens over water, large numbers of birds are lost. Moderate tail winds 
and cross or quartering breezes appear to offer the best conditions for the 
flight of migrants. Richardson (1971) found migrants traveling in 
different directions at different altitudes, but each group of birds 
was aided by a following wind. Thus we might expect natural 
selection to operate in favor of those birds that could recognize and 
respond to favorable wind patterns because it would reduce energy 
consumption and flight time on long-distance flights (Hassler et al. 
1963). 

Soaring birds such as hawks, vultures, and storks are very 

54 



dependent on proper wind conditions for migration. In the fall, often 
the best day to observe hawk migration in the eastern United States 
is on the second day after a cold front has passed providing there are 
steady northwest to west winds and a sunny day for production of 
thermals (Pettingill 1962). Considerable drifting may be observed in 
this group of birds because they are literally carried along by the 
wind or glide from one thermal to the next. Haugh and Cade (1966) 
found most hawks migrated around Lake Ontario when winds were 
10 to 25 miles per hour, but, if the wind exceeded 35 miles per hour, 
most hawk migration stopped. 

In conclusion then, we can say that the weather may be the impetus 
for migration for many species, but it cannot stimulate a bird to 
migrate unless it is physiologically prepared. Arrivals on the ground 
are not necessarily indicative of the number of birds passing 
overhead. During the fall, peak migrations usually follow the 
passage of a cold front when the temperature is falling, the 
barometer is rising, winds are from the west or northwest, and the 
sky is clearing. In the spring, most migrants proceed north in the 
warm sector of a low when winds are southerly, warm, and moist, but 
rain, fog, or snow will often curtail the passage of migrants or 
prevent the initiation of a migration. Evolution of migratory 
behavior has probably resulted from the survival of birds capable of 
selecting those wind conditions, which reduce flight time and energy 
consumption, during their passage. 



55 



INFLUENCE OF TOPOGRAPHY 



The relation of the world's land masses to each other and the 
distribution and association of biotypes within these land masses 
influence the direction birds migrate. Topography may aid, hinder, 
or prevent the progress of a migrant depending on the bird's particular 
requirements. Old World migrants must contend with east-west 
tending mountain ranges and deserts, whereas New World travelers 
can proceed north and south across a landscape with its major 
mountain ranges and river systems oriented in the same direction as 
the birds migrate. 

When a distinct feature in the landscape, such as borders between 
fields and forests, rivers, mountain ridges, desert rims, or 
peninsulas, appears to influence migratory travel, we call these 
formations "guiding lines," "diversion-lines," "leading lines," or in 
German, "Leitlinie." It is an observed fact that some birds in a 
migratory movement alter their course to travel along a leading line, 
but whether this feature in the landscape caused the migrants to 
change their course is only theory (Thomson 1960). Besides 
topography, many other factors can influence this type of flight 
behavior including weather, wind speed and direction, time of day, 
species, age, and experience of the bird (Murray 1964). 

Large bodies of water constitute real barriers to soaring birds 
dependent on thermals and air currents. Good examples of these 
barriers include the Mediterranean Sea between Europe and Africa 
and the Great Lakes in North America. Because these water areas do 
not create good thermals (generally a warm surface, such as a large 
field on a sunny day, is needed to create the necessary rising air 
currents for thermals to form) for birds to soar on, migrants are 
forced to travel around them on updrafts created where land and 
water meet. The shoreline, then, may appear to be the guiding line, 
but more than likely the birds are simply following air currents 
created by onshore winds replacing the rising air from the 
surrounding warmer land surface and being deflected upward by 
the shoreline. These conditions often concentrate our buteos (broad- 
winged, rough-legged, red-shouldered, and red-tailed hawks) into 
restricted areas where, on good days, numbers observed can be 
spectacular. Similar conditions exist over the Bosphorus at the 
eastern end of the Mediterranean Sea where literally thousands of 
storks, eagles, and buzzards can be observed on a good day. 

While extensive water areas may alter the migratory path of 
soaring birds, mountain ridges, especially if parallel to the line of 
flight, are often very conducive to migratory travel. Systematic 
coverage of the Appalachian ridges indicates all of them aid the 

56 



migration of soaring birds. Apparently the highest and longest 
ridges deflect the horizontal winds upward better than the shorter 
ridges less than 1,000 feet high, and more birds are seen, on the 
average, along the higher ridges (Robbins 1956). 

In general, nocturnal migrants are not influenced by topography 
as much as diurnal travellers. Radar observations have played an 
important role in establishing this difference. Bellrose (1967) found 
that waterfowl migrating at night through the Midwest were not 
influenced by major river systems, but in the evening or after 
daybreak ducks and geese tended to alter their course along the 
rivers. Drury et al. (1961) recorded massive fall and spring 
movements from the New England area out over the Atlantic Ocean 
without any apparent regard for the coastline. Until nocturnal 
migration could be "watched" on a radar screen, many bird observers 
assumed the guiding effect of the coastline on migratory travel was 
more restrictive than it really is. 

In summary, topography may help or deter a migrant in its 
passage. It affects different birds in different ways. In North 
America, migratory movements are continent wide, and no evidence 
has indicated any particular part of the landscape influences all 
birds in the same manner. Certain bird populations may use general 
areas in migration, but they are usually not rigidly restricted to them 
because of topography. 



57 



PERILS OF MIGRATION 



The migration season is full of peril for birds. Untold thousands of 
smaller migrants are destroyed each year by storms and attacks by 
predatory animals. These mortality factors, and others, help keep 
bird populations in check. Perils of migration are among these 
causes. 

Storms 

Of all the hazards confronting birds in migration, particularly the 
smaller species, storms are the most dangerous. Birds that cross 
broad stretches of water can be blown off course by a storm, become 
exhausted, and fall into the waves. Such a catastrophe was once seen 
from the deck of a vessel in the Gulf of Mexico, 30 miles off the mouth 
of the Mississippi River. Great numbers of migrating birds, chiefly 
warblers, were nearing land after having accomplished nearly 95 
percent of their long flight when, caught by a "norther" against 
which they were unable to make headway, hundreds were forced into 
the waters of the Gulf and drowned. A sudden drop in temperature 
accompanied by a snowfall can cause a similar affect. 

Aerial Obstructions 

Lighthouses, tall buildings, monuments, television towers, and 
other aerial obstructions have been responsible for destruction of 
migratory birds. Bright beams of lights on buildings and airport 
ceilometers have a powerful attraction for nocturnal air travelers 
that may be likened to the fascination for lights exhibited by many 
insects, particularly night-flying moths. The attraction is most 
noticeable on foggy nights when the rays have a dazzling effect that 
not only lures the birds but confuses them and causes their death by 
collision against high structures. The fixed, white, stationary light 
located 180 feet above sea level at Ponce de Leon Inlet (formerly 
Mosquito Inlet), Florida, has caused great destruction of bird life even 
though the lens is shielded by wire netting. Two other lighthouses at 
the southern end of Florida, Sombrero Key and Fowey Rocks, have 
been the cause of a great number of bird tragedies, while heavy 
mortality has been noted also at some of the lights on the Great Lakes 
and on the coast of Quebec. Fixed white lights seem to be most 
attractive to birds; lighthouses equipped with flashing or red lights 
do not have the same attraction. 

For many years in Washington, B.C., the illuminated Washington 
Monument, towering more than 555 feet into the air, caused 
destruction of large numbers of small birds. Batteries of brilliant 
floodlights grouped on all four sides about the base illuminate the 

58 



Monument so brilliantly, airplane pilots noticed that it could be seen 
for 40 miles on a clear night. It is certain there is an extensive area of 
illumination, and on dark nights with gusty, northerly winds, 
nocturnal migrants seem to fly at lower altitudes and are attacted to 
the Monument. As they mill about the shaft, they are dashed against 
it by eddies of wind, and hundreds have been killed in a single night. 

In September 1948, bird students were startled by news of the 
wholesale destruction of common yellowthroats, American redstarts, 
ovenbirds, and others against the 1,250-foot-high Empire State 
Building in New York City, the 491-foot-high Philadelphia Saving 
Fund Society Building in Philadelphia, and the 450-foot-high WB AL 
radio tower in Baltimore. In New York, the birds continued to crash 
into the Empire State Building for 6 hours. 

More recently, the television tower has become the chief hazard. 
These structures are so tall, sometimes over 1,000 feet, they present 
more of a menace than buildings or lighthouses. Their blinking lights 
cause passing migrants to blunder into guy wires or the tower itself 
while milling around like moths about a flame. Numerous instances 
(e.g. Stoddard and Norris 1967) throughout the U.S. indicate this 
peril to migration is widespread. The lethal qualities of airport 
ceilometers have been effectively modified by conversion to 
intermittent or rotating beams. 

Exhaustion 

Both soaring and sailing birds are so proficient in aerial 
transportation that only recently have the principles been 
understood and imitated by aircraft pilots. The use of ascending air 
currents, employed by all soaring birds and easily demonstrated by 
observing gulls glide hour after hour along the windward side of a 
ship, are now utilized by man in his operation of gliders. Moreover, 
the whole structure of a bird makes it the most perfect machine for 
extensive flight the world has ever known. Hollow, air-filled bones, 
together with feathers, the lightest and toughest material known for 
flight, have evolved in combination to produce a perfect flying 
machine. 

Mere consideration of a bird's economy of fuel or energy also is 
enlightening. The golden plover probably travels over a 2,400-mile 
oceanic route from Nova Scotia to South America in about 48 hours of 
continous flight. This is accomplished with the consumption of less 
than 2 ounces of body fat (fuel). In contrast, to be just as efficient in 
operation, a 1 ,000-pound airplane would consume only a single pint of 
fuel in a 20-mile flight rather than the gallon usually required. 
Similarly, the tiny ruby- throated hummingbird weighing approx- 
imately 4 grams, crosses the Gulf of Mexico in a single flight of more 
than 500 miles while consuming less than 1 gram of fat. 

One might expect the exertion incident to long migratory flights 
would result in arrival of migrants at their destination near a state of 
exhaustion. This is usually not the case. Birds that have recently 
arrived from a protracted flight over land or sea sometimes show 

59 



evidences of being tired, but their condition is far from being in a 
state of emaciation or exhaustion. The popular notion birds find long 
ocean flights so excessively wearisome that they sink exhausted when 
terra firma is reached generally does not coincide with the facts. 

The truth is, even small landbirds are so little exhausted by ocean 
voyages, they not only cross the Gulf of Mexico at its widest point but 
may even proceed without pause many miles inland before stopping. 
The sora, considered such a weak flyer that at least one writer was led 
to infer most of its migration was made on foot, has one of the longest 
migration routes of any member of the rail family and even crosses 
the wide reaches of the Caribbean Sea. Observations indicate that 
under favorable conditions birds can fly when and where they please 
and the distance covered in a single flight is governed chiefly by the 
amount of stored fat. Exhaustion, except as the result of unusual 
factors such as strong adverse winds, cannot be said to be an 
important peril of migration. 



60 



ROUTES OF MIGRATION 



General Considerations 

While it is beyond question that certain general directions of flight 
are consistently followed by migratory birds, it is well to remember 
the term "migration route" is to some extent a theoretical concept 
referring to the lines of general advance or retreat of a species, rather 
than the exact course followed by individual birds or a path followed 
by a species with specific geographic or ecological boundaries. Even 
the records of banded birds usually show no more than the place of 
banding and recovery. One ought to have recourse to intermediate 
records and reasoning based on probabilities to fill in details of the 
route actually traversed between the two points. In determining 
migration routes, one must constantly guard against the false 
assumption that localities with many grounded migrants are on the 
main path of migration and localities where no grounded migrants 
are observed are off the main path. 

There is also infinite variety in the routes covered during 
migration by different species. In fact, the choice of migration 
highways is so wide that is seems as if the routes of no two species 
coincide. Differences in distance traveled, time of starting, speed of 
flight, geographical position, latitudes of breeding and wintering 
grounds, and other factors contribute to this great variation of 
migration routes. Nevertheless, there are certain factors that serve to 
guide individuals or groups of individuals along more or less definite 
lines, and it is possible to define such lines of migration for many 
species. 

Except in a few species, individuals probably do not follow 
precisely the same route twice. This is especially true in the group of 
soaring birds that utilize thermals. Mueller and Berger (1967b) 
recaptured only three migrants in subsequent years at Cedar Grove, 
Wisconsin, after banding over 50,000 birds there. In general, those 
populations of species with very discernible breeding or wintering 
grounds have readily discernible migration routes. However, even 
the whole migration process of certain species may show great yearly 
fluctuations (Rudebeck 1950). 

Aldrich et al. (1949) showed from banding data great variation in 
migration patterns between species of waterfowl. In some species 
there was considerable diversity in direction of movement, not only of 
different breeding populations within a species but also for different 
individuals of the same breeding population. The impression is 
inescapable; waterfowl migration is even more complicated than 
originally supposed, and it is difficult to make generalizations with 

61 



regard to migration pathways for even a single species let alone 
waterfowl in general. 

Flyways and Corridors 

Through plotting accumulated banding data in the 1930's, 
investigators became impressed by what appeared to be four broad, 
relatively exclusive flyway belts in North America. This concept, 
based upon analyses of the several thousand records of migratory 
waterfowls recoveries then available, was described by Lincoln 
(1935a). In this paper (p. 10), Lincoln concluded that: 

. . . because of the great attachment of migratory birds for 
their ancestral flyways, it would be possible practically to 
exterminate the ducks of the West without seriously interfer- 
ing with the supply of birds of the same species in the Altantic 
and Mississippi flyways, and that the birds of these species 
using the eastern flyways would be slow to overflow and re- 
populate the devasted areas of the West, even though environ- 
mental conditions might be so altered as to be entirely 
favorable. 

Since 1948, this concept served as the basis for administrative action 
by the Fish and Wildlife Service in setting annual migratory water- 
fowl hunting regulations. 

The concept of bird populations being confined to four fairly 
definite and distinct migration "flyways" is probably most applicable 
to those birds that migrate in family groups, namely geese, swans, 
and cranes, but does not appear to be very helpful in understanding 
the movements of the more widely dispersing ducks. The "pioneering 
spirit" in Canada geese, for example, is limited by their social 
structure the young travel to and from specific breeding and 
wintering areas with their parents. These young later in life usually 
breed in the same areas as did their parents. If a goose population is 
decimated in one flyway, either by hunting or natural calamities, 
other goose populations in other flyways are not seriously 
endangered, but also these populations are very slow to repopulate an 
area where the previous goose population had been decimated. This is 
not the case with ducks because these birds are not always bound by 
their intrinsic behavior to return to specific breeding areas. Con- 
sequently, vacant breeding areas are more rapidly repopulated by 
ducks than by geese. 

Although Lincoln's analysis was confined to ducks and geese, some 
thought that it applied to other groups of birds as well. Everyone 
now realizes that the concept of four flyways, designated as the 
Atlantic, Mississippi, Central, and Pacific Flyways, was an 
oversimplification of an extremely complex situation involving 
crisscrossing of migration routes, varying from species to species. It 
can be considered meaningful only in a very general way, even for 
waterfowl, and not applicable generally to other groups of birds. 
Nevertheless the four "Flyway" areas have been useful in 

62 



regionalizing the harvest of waterfowl for areas of different 
vulnerability of hunting pressure. 

Bellrose (1968) identified corridors of southward migrating 
waterfowl east of the Rocky Mountains and determined, through 
statistical analyses, the relative abundance of birds in each. He 
showed major corridors of dabbling duck movements down the Great 
Plains and Missouri-Mississippi river valleys with minor off shoots at 
various points from these corridors eastward to the Atlantic coast 
where they joined equally minor eastern movements from the North 
(Fig. 13). Bellrose's map of migration corridors for the diving ducks 





Dabbling Ducks East of Rockies 

1,500,000-3,000,000 

750,000-1,500,000 

I 

350,000-750,000 
100,000-350,000 
30,000-100,000 
1,000-30,000 



Figure 13. Migration corridors used by dabbling ducks east of the Rocky Mountains 
during their fall migration (After Bellrose 1968). 

63 



showed heavy traffic similar to that of dabbling species down the 
Great Plains and relatively heavily used corridors from these central 
arteries eastward across the Great Lakes area to the Atlantic coast, 
terminating particularly in the vicinity of Chesapeake Bay. A fairly 
well-used corridor extends along the Atlantic coast. 



Breeding Range 
Winter Range 
Lightly Traveled Routes 
Heavily Traveled Routes 




Figure 14- Distribution and migration of Harris' sparrow. This is an example of a 
narrow migration route through the interior of the country. 

64 



With our present knowledge of bird migration it is difficult at best 
to recognize distinct broad belts of migration down the North 
American continent encompassing groups of distinct populations or 
species. It seems that so much intermingling of populations occurs 
that distinctions between broad "flyway" belts are not discernible. 
About all we can say for sure now is that birds travel between certain 
breeding areas in the North and certain wintering areas in the South 
and that a few heavily traveled corridors used by certain species, and 
more generalized routes followed by one or more species, have 
become obvious. 

Narrow Routes 

Some species exhibit extremely narrow routes of travel. The red 
knot and purple sandpiper, for example, are normally found only 
along the coasts because they are limited on one side by the broad 
waters of the ocean, and on the other by land and fresh water; neither 
of these habitats furnish conditions attractive to these species. 

The Ipswich race of the savannah sparrow likewise has a very 
restricted migration range. It is known to breed only on tiny Sable 
Island, Nova Scotia, and it winters from that island south along the 
Atlantic coast to Georgia. It is rarely more than a quarter of a mile 
from the outer beach and is entirely at home among the sand dunes 
with their sparse covering of coarse grass. 

The Harris' sparrow supplies an interesting example of a 
moderately narrow migration route in the interior of the country 
(Fig. 14). This fine, large sparrow is known to breed only in the 
narrow belt of stunted timber and brush at or near the limit of trees 
from the vicinity of Churchill, Manitoba, on the west shore of Hudson 
Bay, to the Mackenzie Delta 1,600 miles to the northwest. When this 
sparrow reaches the United States on its southward migration, it is 
most numerous in a belt about 500 miles wide, between Montana 
and central Minnesota and continues south through a relatively 
narrow path in the central part of the continent. Knowledge of 
habitat preference by Harris' sparrows suggests the narrow 
migration range is restricted to the transition between woodland and 
prairie, a type of habitat approaching the woodland-tundra 
transition of its breeding area. Development of this migration route, 
of course, preceded destruction of the heavy eastern forests by 
colonists from Europe. Its winter range lies primarily in similar 
country extending from southeastern Nebraska and northwestern 
Missouri, across eastern Kansas and Oklahoma and through a 
narrow section of eastern Texas, at places hardly more than 150 miles 
wide. 

Converging Routes 

When birds start their southward migration the movement 
necessarily involves the full width of the breeding range. Later, in the 
case of landbirds with extensive breeding ranges, there is a 
convergence of the lines of flight taken by individual birds owing, in 

65 



part, to the conformation of the land mass and in part to the east-west 
restriction of habitats suitable to certain species. An example of this 
is provided by the eastern kingbird, which breeds in a summer 
range 2,800 miles wide from Newfoundland to British Columbia. On 
migration, however, the area traversed by the species becomes 
constricted until in the southern part of the United States the 
occupied area extends from Florida to the mouth of the Rio Grande, a 
distance of only 900 miles. Still farther south the migration path 
continues to converge, and, at the latitude of Yucatan, it is not more 
than 400 miles wide. The great bulk of the species probably moves in 
a belt less than half this width. 

The scarlet tanager presents another extreme case of a narrowly 
converging migration route starting from its 1,900-mile-wide 
breeding range in the eastern deciduous forest between New 
Brunswick and Saskatchewan (Fig. 15). As the birds move 




Figure 15. Distribution and migration of the scarlet tanager. During the breeding sea- 
son individual scarlet tanagers may be 1,500 miles apart in an east-and-west line 
across the breeding range. In migration, however, the lines gradually converge until in 
South America they are about 500 miles apart. 

66 



southward in the fall, their path of migration becomes more and 
more constricted, until, at the time they leave the United States, all 
are included in the 600-mile belt from eastern Texas to the Florida 
peninsula. The boundaries continue to converge through Honduras 
and Costa Rica where they are not more than 100 miles apart. The 
species winters in the heavily forested areas of northwestern South 
America including parts of Colombia, Ecuador, and Peru. 

The rose-breasted grosbeak also leaves the United States through 
the 600-mile stretch from eastern Texas to Apalachicola Bay, but 




16. Distribution and migration of the rose-breasted grosbeak. Though the width 
of the breeding range is about 2,500 miles, the migratory lines converge until the 
boundaries are only about 1,000 miles apart when the birds leave the United States. 

67 



thereafter as this grosbeak crosses the Gulf of Mexico and enters the 
northern part of its winter quarters in southern Mexico the lines do 
not further converge. However, the pathway of those individuals that 
continue on to South America is considerably constricted by the 
narrowing of the land through Central America to Panama (Fig. 16). 

Although the cases cited represent extremes of convergence, a 
narrowing of the migratory path is the rule to a greater or lesser 
degree for the majority of North American birds. Both the shape of 
the continent and major habitat belts tend to constrict southward 
movement so that the width of the migration route in the latitude of 
the Gulf of Mexico is usually much less than in the breeding territory. 

The American redstart represents a case of a wide migration route, 
but even in the southern United States, this is still much narrower 
than the breeding range (Fig. 17). These birds, however, cross all of 
the Gulf of Mexico and pass from Florida to Cuba and Haiti by way of 
the Bahamas, so here their route is about 2,500 miles wide. 




Figure 1 7. Distribution and migration of the redstart. An example of a wide migration 
route, birds of this species cross all parts of the Gulf of Mexico, or may travel from 
Florida to Cuba and through the Bahamas. Their route has an east-and-west width of 
more than 2,000 miles. 

68 



Principal Routes From North America 

W. W. Cook presented seven of the more important generalized 
routes for birds leaving the United States on their way to various 
wintering grounds (1915a; Fig. 18). When migrants return 
northward in the spring, they may follow these same routes, but it is 
not known for certain whether they do. These routes are discussed in 
the following sections. 

Atlantic Oceanic Route 

Route No. 1 (Fig. 18) is almost entirely oceanic and passes directly 
over the Atlantic Ocean from Labrador and Nova Scotia to the Lesser 
Antilles, then through this group of small islands to the mainland of 
South America. Most of the adult eastern golden plovers and some 
other shorebirds use this as their fall route. As we mentioned 
previously, radar has indicated strong fall movements of warblers 
from the New England coast out over the Atlantic to points south 
along this route. Since it lies almost entirely over the sea, this route is 
definitely known only at its terminals and from occasional 
observations made on Bermuda and other islands in its course. Some 
of the shorebirds that breed on the Arctic tundra of the District of 
Mackenzie (Northwest Territories) and Alaska fly southeastward 
across Canada to the Atlantic coast and finally follow this oceanic 



-J. 




Principal Western Routes 
Most Extensively Used Routes 
Atlantic Coast Routes 
Atlantic Oceanic Route 



Figure 18. Principal migration routes used by birds in passing from North America to 
winter quarters in the West Indies, Central America, and South America. Route 4 is 
the one used most extensively while only a few species make the 2,400 mile flight down 
Route 1 from Nova Scotia to South America. 



route to the mainland of South America. The golden plover may 
accomplish the whole 2,400 miles without pause or rest, and in fair 
weather the flocks pass Bermuda and sometimes even the islands of 
the Antilles without stopping. Although most birds make their 
migratory flights either by day or by night, the golden plover in this 
remarkable journey flies both day and night. Since this plover swims 
lightly and easily, it may make a few short stops along the way. 

The Arctic tern follows the Atlantic Ocean route chiefly along the 
eastern side of the ocean. Likewise, vast numbers of seabirds such as 
auks, murres, guillemots, phalaropes, jaegers, petrels, and 
shearwaters follow this over-water route from breeding coasts and 
islands in the Northern and Southern Hemispheres. 

Atlantic Coast Route and Tributaries 

The Atlantic coast is a regular avenue of travel, and along it are 
many famous points for observing both land and water birds. About 
50 different kinds of landbirds that breed in New England follow the 
coast southward to Florida and travel thence by island and mainland 
to South America (Fig. 18, route 2). The map indicates a natural and 
convenient highway through the Bahamas, Cuba, Hispaniola, Puerto 
Rico, and the Lesser Antilles to the South American coast. Resting 
places are affored at convenient intervals, and at no time need the 
aerial travelers be out of sight of land. It is not, however, the favored 
highway; only about 25 species of birds go beyond Cuba to Puerto 
Rico along this route to their winter quarters, while only six species 
are known to reach South America by way of the Lesser Antilles. 
Many thousands of American coots and wigeons, pintails, blue- 
winged teal, and other waterfowl as well as shorebirds, regularly 
spend the winter season in the coastal marshes, inland lakes, and 
ponds of Cuba, Hispaniola, and Puerto Rico. 

Route No. 3 (Fig. 18) is a direct line of travel for Atlantic coast 
migrants en route to South America, although it involves much 
longer flights. It is used almost entirely by landbirds. After taking off 
from the coast of Florida there are only two intermediate land masses 
where the migrants may pause for rest and food. Nevertheless, tens of 
thousands of birds of about 60 species cross the 150 miles from 
Florida to Cuba where many elect to remain for the winter months. 
The others negotiate the 90 miles between Cuba and Jamaica, but, 
from that point to the South American coast, there is a stretch of 
islandless ocean 500 miles across. Relatively few North American 
migrants on this route go beyond Jamaica. The bobolink so far 
outnumbers all other birds using this route that it may be designated 
the "bobolink route" (Fig. 19). As traveling companions along this 
route, the bobolink may meet vireos, kingbirds, and nighthawks 
from Florida, Chuck-will's-widows from the Southeastern States, 
black-billed and yellow-billed cuckoos from New England, gray- 
cheeked thrushes from Quebec, bank swallows from Labrador, and 
blackpoll warblers from Alaska. Sometimes this scattered 
assemblage will be joined by a tanager or a wood thrush, but the 

70 




Bobolink 




Bobolink 



Breeding Range 
Winter Range 
Migration Routes 




Figure 19. Distribution and migration of the bobolink. In crossing to South America, 
most of the bobolinks use route 3 (Fig. 18), showing no hesitation in making the 
flight from Jamaica across an islandless stretch of ocean. It u-ill be noted that colonies 
of these birds have established themselves in western areas, but in migration they 
adhere to the ancestral flyways and show no tendency to take the short cut across 
Arizona, New Mexico, and Texas. 



71 



"bobolink route" is not popular with the greater number of migrants. 

Formerly, it was thought most North America landbirds 
migrated to Central America via the Florida coast, then crossed to 
Cuba, and finally made the short flight from the western tip of Cuba 
to Yucatan. A glance at the map would suggest this as a most natural 
route, but, as a matter of fact, it is practically deserted except for a 
few swallows and shorebirds or an occasional landbird storm-driven 
from its normal course. What actually happens in the fall is that 
many of the birds breeding east of the Appalachian Mountains travel 
parallel to the seacoast in a more or less southwesterly direction and, 
apparently maintaining this same general course from northwestern 
Florida, cross the Gulf of Mexico to the coastal regions of eastern 
Mexico. They thus join migrants from farther inland in using route 
No. 4 (Fig. 18). 

Routes used by the Atlantic brant merit some detail because their 
flight paths were long misunderstood. These birds winter on the 
Atlantic coast, chiefly at Barnegat Bay, New Jersey, but depending 
upon the severity of the season and the food available, south also to 
North Carolina. Their breeding grounds are in the Canadian arctic 
archipelago and on the coasts of Greenland. According to the careful 
studies of Lewis (1937), the main body travels northward in spring 
along the coast to the Bay of Fundy, overland to Northumberland 
Strait, which separates Prince Edward Island from mainland New 
Brunswick and Nova Scotia. A minor route appears to lead 
northward from Long Island Sound by way of the Housatonic and 
Connecticut River Valleys to the St. Lawrence River. 

After spending the entire month of May feeding and resting in the 
Gulf of St. Lawrence, the eastern segment of the brant population 
resumes its journey by departing overland from the Bay of Seven 
Island area. The eastern and larger segment of the population 
appears to fly almost due north to Ungava Bay and from there to 
nesting grounds, probably on Baffin Island and Greenland. The 
smaller segment travels a route slightly north of west to the 
southeastern shores of James Bay, although east of that area some of 
the flocks take a more northwesterly course by descending the Fort 
George River to reach the eastern shore of James Bay. Upon their 
arrival at either of these two points on James Bay, the brants of this 
western segment turn northward and proceed along eastern Hudson 
Bay to their breeding grounds in the Canadian Arctic. 

In general, the fall migration of the brant follows the routes 
utilized in the spring. At this season, the eastern population appears 
only on the western and southern shores of Ungava Bay before 
continuing their southward journey to the Gulf of St. Lawrence and 
beyond. Also, it appears that most of the birds of the western 
segment, instead of following the eastern shores of Hudson and 
James bays, turn southwestward across the former, by way of the 
Belcher Islands, to Cape Henrietta Maria, and from there south 
along the western shores of James Bay by way of Akimiski and 
Charlton Islands. At the southern end of James Bay, they are joined 

72 



by those that have taken the more direct route along the east coasts of 
the bays and all then fly overland 570 miles to the estuary of the St. 
Lawrence River. 

The Atlantic coast wintering area receives accretions of waterfowl 
from three or four interior migration paths, one of which is of first 
importance, as it includes great flocks of canvasbacks, redheads, 
scaup, Canada geese, and many black ducks that winter in the 
waters and marshes of the coastal region south of Delaware Bay. The 
canvasbacks, redheads, and scaup coming from breeding grounds on 
the great northern plains of central Canada follow the general 
southeasterly trend of the Great Lakes, cross Pennsylvania over the 
mountains, and reach the Atlantic coast in the vicinity of Delaware 
and Chesapeake Bays. Black ducks, mallards, and blue-winged teals 
that have gathered in southern Ontario during the fall leave these 
feeding grounds and proceed southwest over a course that is 
apparently headed for the Mississippi Valley. Many do continue this 
route down the Ohio Valley, but others, upon reaching the vicinity of 
the St. Clair Flats between Michigan and Ontario, swing abruptly to 
the southeast and cross the mountains to reach the Atlantic coast 
south of New Jersey. This route, with its Mississippi Valley branch, 
has been fully documented by the recovery records of ducks banded 
at Lake Scugog, Ontario. 

Canvasbacks migrate from the prairie pothole country of the 
central United States and Canada to many wintering areas in the 
United States. This duck has been the subject of a particular study 
(Stewart, Geis, and Evans 1958), and its principle migration routes, 
based on recovery of banded birds, are shown to follow an important 
trunk route from the major breeding area in the prairie provinces of 
Canada and the northern prairies of the United States southeast- 
ward through the southern Great Lakes area to Chesapeake Bay, the 
chief wintering area (Fig. 20). Relatively few canvasbacks proceed 
southward along the Atlantic seaboard. A less important route 
branches off from the main trunk in the southern Minnesota region 
and extends south along the Mississippi Valley to points along the 
river. Other individuals of the prairie breeding population fly 
southward on a broad front to the gulf coast of Texas and the interior 
of Mexico, while some proceed southwestward on a relatively broad 
path to the northern Pacific coast. 

Mackenzie Valley-Great Lakes-Mississippi Valley 
Route and Tributaries 

The route extending from the Mackenzie Valley past the Great 
Lakes and down the Mississippi Valley is easily the longest of any in 
the Western Hemisphere. Its northern terminus is on the Arctic 
coast in the regions of Kotzebue Sound, Alaska, and the mouth of the 
Mackenzie River, while its southern end lies in Argentina. 
Nighthawks, barn swallows, blackpoll warblers, and individuals of 
several other species that breed northward to the Yukon Territory 
and Alaska must cover the larger part of the route twice each year. 

73 



For more than 3,000 miles from the mouth of the Mackenzie to 
the delta of the Mississippi this route is uninterrupted by 
mountains. In fact, the greatest elevation above sea level is less than 
2,000 feet. Because it is well timbered and watered, the entire region 
affords ideal conditions for its great hosts of migrating birds. It is 



Density Line 

Representing Approximately 

3.000 Birds 




Figure 20. Principal migratory routes of the canvasback. The major route of travel 
extends from breeding areas in central Canada southeast across the Great Lakes and 
either south down the Mississippi River or east to Chesapeake Bay (After Stewart 
et al 1958). 

74 



followed by such vast numbers of ducks, geese, shorebirds, 
blackbirds, sparrows, warblers, and thrushes that observers 
stationed at favorable points in the Mississippi Valley during the 
height of migration can see a greater number of migrants than can 
be noted anywhere else in the world. 

When many of these species, including ducks, geese, robins, and 
yellow-rumped warblers, arrive at the Gulf coast, they spread out 
east and west for their winter sojourn. Others, despite the perils of a 
trip involving a flight of several hundred miles across the Gulf of 
Mexico, fly straight for Central and South America. This part of the 
route is a broad "boulevard" extending from northwestern Florida to 
eastern Texas and southward across the Gulf of Mexico to Yucatan 
and the Isthmus of Tehuantepec (Fig. 18, route 4). This route appears 
to have preference over the safer but more circuitous land or island 
routes by way of Texas or Florida. During the height of migration 
some of the islands off the coast of Louisiana are wonderful 
observation points for the student of birds, as the feathered travelers 
literally swarm over them. 

Present detailed knowledge of the chief tributaries to the 
Mackenzie-Great Lakes-Mississippi Valley route relates primarily 
to waterfowl. Reference has been made already to the flight of black 
ducks that reach the Mississippi Valley from southern Ontario. 
Some individuals of this species banded at Lake Scugog, Ontario, 
have been recaptured in succeeding seasons in Wisconsin and 
Manitoba, but the majority was retaken at points south of the 
junction of the Ohio River with the Mississippi indicating their main 
route of travel from southern Ontario. 

A second route that joins the main artery on its eastern side is the 
one used by eastern populations of lesser snow geese, including both 
blue and white phases, that breed mainly on Southampton Island 
and in the Fox Basin of Baffin Island. In the fall these geese work 
southward along the shores of Hudson Bay and, upon reaching the 
southern extremity of James Bay, take off on their flight to the great 
coastal marshes of Louisiana and Texas west of the Mississippi River 
delta. 

Great Plains Rocky Mountain Routes 

This route also has its origin in the Mackenzie River delta and 
Alaska. The lesser sandhill cranes, white-fronted geese, and smaller 
races of the Canada goose follow this route through the Great Plains 
from breeding areas in Alaska and western Canada. It is used chiefly 
by the pintails and American wigeons that fly southward through 
eastern Alberta to western Montana. Some localities in this area, as 
for example, the National Bison Range at Moiese, Montana, 
normally furnish food in such abundance that these birds are induced 
to pause in their migratory movement. Some flocks of pintails and 
wigeons move from this area almost directly west across Idaho to the 
valley of the Columbia River, then south to the interior valleys of 
California. Others leave Montana by traveling southeastward across 

75 



Wyoming and Colorado to join other flocks moving southward 
through the Great Plains. 

Observations made in the vicinity of Corpus Christi, Texas, have 
shown one of the short cuts (Fig. 18, route 5) that is part of the great 
artery of migration. Thousands of birds pass along the coast to the 
northern part of the State of Veracruz, Mexico. Coastal areas along 
the State of Tamaulipas to the north are arid and so entirely unsuited 
for frequenters of moist woodlands that it is probable that much, or 
all, of this part of the route for these species is a short distance off 
shore. It is used by such woodland species as the golden-winged 
warbler, the worm-eating warbler, and the Kentucky warbler. 

Pacific Coast Route 

Although it does present features of unusual interest, the Pacific 
coast route is not as important as some of the others described. 
Because of the equable conditions that prevail, many species of birds 
along the coast from the northwestern states to southeastern Alaska 
either do not migrate or else make relatively short journeys. This 
route has its origin chiefly in western Alaska, around the Yukon 
River delta. Some of the scoters and other sea ducks of the north 
Pacific region as well as the diminutive cackling Canada goose of the 
Yukon River Delta use the coastal sea route for all or most of their 
southward flight. The journey of the cackling goose, as shown by 
return records from birds banded at Hooper Bay, Alaska, has been 
traced southward across the Alaskan Peninsula and apparently 
across the Gulf of Alaska to the Queen Charlotte Islands. The birds 
then follow the coast line south to near the mouth of the Columbia 
River, where the route swings toward the interior for a short 
distance before continuing south by way of the Willamette River 
Valley. The winter quarters of the cackling goose are chiefly in the 
vicinity of Tule Lake, on the Oregon-California line, and in the 
Sacramento Valley of California, although a few push on to the San 
Joaquin Valley. 

A tributary of this "flyway" is followed by Ross' goose, which 
breeds in the Perry River district south of Queen Maud Gulf and 
other areas farther east on the central Arctic coast of Canada (Fig. 
21). Its fall migration is southwest and south across the barren 
grounds to Great Slave and Athabaska Lakes, where it joins 
thousands of other waterfowl bound for winter homes along the 
eastern coast of the United States and the Gulf of Mexico. But when 
Ross' geese have traveled south approximately to the northern 
boundary of Montana, most of them separate from their companions 
and turn southwest across the Rocky Mountains to winter in 
California. In recent years a few Ross' geese have been found 
wintering east of the Rocky Mountains along with flocks of lesser 
snow geese and may be correlated with an eastward extension of 
their breeding range. 

The southward route of those migratory landbirds of the Pacific 
area that leave the United States in winter extends chiefly through 

76 



the interior of California to the mouth of the Colorado River and on to 
winter quarters in western Mexico (Fig. 18, routes 6 and 7). 

The movements of the western tanager show a migration route that 
is in some ways remarkable. The species breeds in the mountains 
from the northern part of Baja California and western Texas north to 
northern British Columbia and southwestern Mackenzie. Its winter 
range is in two discontinuous areas southern Baja California and 



P 6' 



& 







r-L r ' ^r 'WM>r 

i T S v--< T \ r 
i i } \ IH^ 

' -f- -rl -V-'-^ 7 " 




Figure 21. The breeding range, wintering range, and main migration route of Ross' 
geese. This is the only species of which practically all members breed in the Arctic, 
migrate south through the Canadian prairie, and upon reaching the United States, 
turn to the southwest rather than the southeast. The southern part of this route, how- 
ever, is followed by some mallards, pintails, wigeons, and other ducks. 



77 



eastern and southwestern Mexico south to Guatemala (Fig. 22). 
During spring migration the birds appear first in western Texas and 
the southern parts of New Mexico and Arizona about April 20 (Fig. 
23). By April 30 the vanguard has advanced evenly to an 
approximate east-west line across central New Mexico, Arizona, and 




Figure 22. Breeding and wintering ranges of the western tanager. See Fig. 23 for the 
spring route taken by the birds breeding in the northern part of the range. 

78 



southern California. By May 10 the easternmost birds have advanced 
only to southern Colorado, while those in the far west have reached 
northern Washington. Ten days later the northward advance of the 
species is shown as a great curve, extending northeastward from 
Vancouver Island to central Alberta and thence southeastward to 



r--r -MM3 



Isochronal Migration Lines 
Migratbn Route 




Figure 23. Migration of the western tanager. The birds that arrive in eastern A Iberta by 
May 20 do not travel northward along the eastern base of the Rocky Mountains, 
because the vanguard has then only reached northern Colorado. Instead the isochronal 
lines indicate that they migrate north through California, Oregon, and Washington 
and then cross the Rockies in British Columbia. 

79 



northern Colorado. Since these tanagers do not reach northern 
Colorado until May 20, it is evident those present in Alberta on that 
date, instead of traveling northward through the Rocky Mountains, 
their summer home, actually reached there by a route that carried 
them west of the Rockies to southern British Columbia and thence 
eastward across the still snowy northern Rocky Mountains. 

Pacific Oceanic Route 

The Pacific oceanic route is used by the Pacific golden plover, 
bristle-thighed curlew, ruddy turnstone, wandering tattler and 
other shorebirds. The ruddy turnstone, and probably other 
shorebirds, migrating from the islands of the Bering Sea, have an 
elliptical route that takes them southward via the islands of the 
central Pacific and northward along the Asiatic coast. In addition, 
many seabirds that breed on far northern and southern coasts or 
islands migrate up and down the Pacific well away from land except 
when the breeding season approaches. 

The Pacific golden plover breeds chiefly in the Arctic coast region 
of Siberia and in a more limited area on the Alaskan coast. Some of 
the birds probably migrate south via the continent of Asia to winter 
quarters in Japan, China, India, Australia, New Zealand, and 
Oceania. Others evidently go south by way of the Pacific Ocean to the 
Hawaiian Islands and other islands of the central and southern 
Pacific. Migrating golden plovers have been observed at sea on a line 
that apparently extends from Hawaii to the Aleutian Islands; it 
appears certain some of the Alaskan birds make a nonstop flight 
across the sea from Alaska to Hawaii. While it would seem incredible 
that any birds could lay a course so accurately as to land on these 
small isolated oceanic islands, 2,000 miles south of the Aleutians, 
2,000 miles west of Baja California, and nearly 4,000 miles east of 
Japan, the evidence admits only the conclusion that year after year 
this transoceanic round-trip journey between Alaska and Hawaii is 
made by considerable numbers of golden plovers. 

Arctic Routes 

Some Arctic nesting birds retreat only a short distance south in the 
winter. These species include the red-legged kittiwake, Ross' gull, 
emperor goose, and various eiders. The latter group of ducks winter 
well south of their nesting areas but nevertheless remain farther 
north than do the majority of other species of ducks. The routes 
followed by these birds are chiefly parallel to the coast and may be 
considered as being tributary either to the Atlantic or Pacific coast 
routes. The heavy passage of gulls, ducks, black brants, and other 
water birds at Point Barrow, Alaska, and other points on the Arctic 
coast, has been noted by many observers. The best defined Arctic 
route in North America is the one following the coast of Alaska. 

A migration route, therefore, may be anything from a narrow path 
closely adhering to some definite geographical feature, such as a 
river valley or a coastline, to a broad boulevard that leads in the 



desired direction and follows only the general trend of the land mass. 
Oceanic routes appear to be special cases that are not fully 
understood at the present time. Also it must be remembered that all 
the main routes contain a multitude of tributary and separate minor 
routes. In fact, with the entire continent of North America crossed by 
migratory birds, the different groups or species frequently follow 
lines that may repeatedly intersect those taken by others of their own 
kind or by other species. The arterial or trunk routes, therefore, must 
be considered merely as indicating paths of migration on which the 
tendency to concentrate is particularly noticeable. 



81 



PATTERNS OF MIGRATION 



Band recoveries, netting records, and personal observations help 
us to critically examine migration routes and probe deeper into the 
origin and evolution of these pathways. We are beginning to realize 
certain deviations occur from the "normal" north and south 
movements expected in most species. In the previous section on 
routes, we touched briefly on the fact that some routes are not 
poleward at all, but in some other direction. We know that many 
migrants do not stop at the exact localities year after year but they 
probably do follow the same general course each season. After many 
years of observations a pattern emerges for that population, species, 
or group of species. In this section we would like to take a closer look 
at some of the interesting patterns (or "eccentric routes" as Cook 
(1915a) referred to them) in migration that birds are annually to 
travel from breeding to wintering grounds and back again. In many 
cases, the causative agents are unknown or pure conjecture, but in 
others, sound biological principles can be put forth that may indicate 
why a particular species could have evolved the specific pattern it 
exhibits. 

Loops 

Many species do not return north in the spring over the same route 
they used in the fall; rather, they fly around an enormous loop or 
ellipse. Cook (1915a) considered food as the primary factor in 
determining the course birds took between winter and summer 
ranges. Individuals that returned by the same route and did not find 
sufficient food for their needs at that time were eliminated from the 
population, and only progeny from individuals that took a 
different course with sufficient food lived to build the tradition of a 
loop migration. Other investigators consider prevailing winds a 
major factor in the evolution of loop migration. Whatever the reason 
may be, it has most likely evolved separately in each species to satisfy 
its particular needs, and the fact that this pattern occurs all over the 
world in completely unrelated species is a good illustration of 
convergent evolution. 

The annual flight of adult golden plovers is so unusual, it will be 
given in some detail. The species is observed by hundreds of bird 
watchers every year and it well illustrates loop migration (Fig. 24). 

In the fall, the birds fatten on the multitude of berries along the 
coasts of Labrador and Nova Scotia, then depart south over the 
Atlantic Ocean to South America. After reaching the South 
American coast the birds make a short stop, then continue overland 
to the pampas of Argentina, where they remain from September to 

82 





Breeding Range 
Western Subspecies 

Winter Range 

Western Subspecies 

Breeding Range 

Eastern Subspecies American Golden Plover 

Winter Range 
Eastern Subspecies 



+ Migratory Routes 



Figure 24. Distribution and migration of the American golden plover. Adults of the 
eastern subspecies migrate across northeastern Canada and then by a nonstop flight 
reach South America. In spring they return by way of the Mississippi Valley. Their 
entire route, therefore, is in the form of a great ellipse with a major axis of 8,000 miles 
and a minor axis of about 2,000 miles. The western subspecies migrates across the 
Pacific Ocean to various localities including the Hawaiian and Marquesas islands 
and the Low Archipelago. 

83 



March. When these golden plovers leave their winter quarters they 
cross northwestern South America and the Gulf of Mexico to reach 
the North American mainland on the coasts of Texas and Louisiana. 
Thence they proceed slowly up the Mississippi Valley and, by the 
early part of June, are again on their breeding grounds, having 
performed a round-trip journey in the form of an enormous ellipse 
with the minor axis about 2,000 miles and the major axis 8,000 miles 
stretching from the Arctic tundra to the pampas of Argentina. The 
older birds may be accompanied by some of the young, but most of the 
immature birds leave their natal grounds late in summer and move 
southward through the interior of the country, returning in spring 
over essentially the same course. The oceanic route is therefore used 
chiefly by adult birds. 

A return by the oceanic route in the spring could be fatal. The 
maritime climate in the Northeast results in foggy conditions along 
the coast and the frozen soil would offer few rewards for the weary 
travelers. By traveling up the middle of the continent, a much better 
food supply is assured (Welty 1962). 

Several North American warblers including the Connecticut 
warbler (Fig. 25) and the western race of the palm warbler have been 
found to follow circuitous migration routes. The Connecticut warbler 
is not observed or banded on the East coast in spring, but it is 
recorded farther inland during the season. Thus this warbler 
proceeds down the East coast in the fall and up the interior of the 
continent in the spring. Similarly, the western race of the palm 
warbler moves from its breeding grounds directly east to the 
Appalachian Mountains before turning south along the coast. 
Television tower kills in northern Florida indicate the population is 
very concentrated here at this time of year. In the spring this race 
also proceeds north through the interior. Graber (1968) points out 
that the eastern race of the palm warbler also proceeds south along 
the coast in the fall and poses this question: "does the western popula- 
tion of this species intentionally move toward the ancestral range, or 
is the fall flight direction merely a consequence of the temperate zone 
westerly circulation?" 

Graber concluded from radar observations that the disparity in 
seasonal flight directions of many migrants was a positive response of 
migrants to favorable wind directions at that time of year. The east- 
oriented transgulf migrants followed an elliptical migration because 
postfrontal air flow in the fall at latitude 40 N is northwesterly, and, 
in the spring southerly; whereas winds over the Gulf of Mexico are 
consistently easterly or southeasterly. Therefore, transgulf migrants 
returning north in the spring would be moved westward across the 
Gulf unless they compensated for wind drift. Observers were not 
aware of high-altitude drift before radar (Bellrose and Graber 1963). 

Numerous other loop migrations have been documented through- 
out the world. In the fall, the short-tailed shearwater, is observed off 
the west coast of North America as far south as California. At this 
time the species is on the eastern leg of a tremendous figure-eight 

84 



/ i j 

/ V- _r i 



- 



Fall Migration Route South 
Overlapping Spring and Fall 



Migration Routes 

Spring Migration Route North 




Figure 25. Breeding range and migration routes of the Connecticut warbler. From the 
breeding range in northern United States and southern Canada, it migrates east in 
the fall to New England, then south along the Atlantic coast to Florida and across the 
West Indies to winter in South America. In the spring it does not return by the same 
route but rather completes a loop by migrating northwest across the Allegheny Moun- 
tains and the Mississippi Valley (Adapted from Cooke 1915a). 

85 



circuit around the Pacific Ocean (Fig. 26). The subalpine warbler 
and red-backed shrikes perform loop migrations between Europe 
and Africa. Both pass much farther to the east in the spring than in 
the fall (Moreau 1961). The Arctic loon travels south across inland 
Russia to southern Europe but returns to its Arctic breeding grounds 
via the Gulf Stream on the sea because this water is open much 
earlier in the spring than the inland waterways (Welty 1962). 





Bass Strait Breeding Area 
Migration Route 
Museum Specimen 



Short -Tailed Shearwater 



Figure 26. Migration route of the short-tailed shearwater. An example of an incredi- 
bly large loop migration pattern in a pelagic species. Breeding adults return to two 
islands in Bass Strait during the last part of October after completing a figure-eight 
circuit of the northern Pacific Ocean (From Serventy 1953). 

86 



Dog-legs 

Dog-leg migration patterns are characterized by a prominent bend 
or twist in the route. Studies have shown some of these illogical, out- 
of-the-way means for connecting wintering and breeding areas have 
no biological function, but instead, are the result of tradition much 
like the lineage of crooked streets in Boston can be traced back to old 
cowpaths (Welty 1962). Many species have extended their range in 
recent years, but the pioneers continue to retrace the old route from 
the point of origin even if the new areas are not on the same axis as the 
earlier route. The old pathways have apparently become implanted 
as part of the migratory instinct in all members of particular 
populations even after extending their ranges considerable distances 
from the original. 

Good examples of this crooked traditional path can be seen in the 
routes taken by Old World species extending their ranges into the 
New World from Europe and Asia. The European wheatear has 
extended its range into Greenland and Labrador where the local 
breeding population has become a separate race. When the Labrador 
individuals depart from their breeding grounds, they proceed north 
to Greenland, their ancestral home, then west to Europe and south to 
Africa, the traditional wintering area for all wheatears. Alaskan 
breeding wheatears migrate to Africa in the opposite direction via 
Asia where the Alaskan population presumably originated. Alaskan 
breeding Arctic and willow warblers and bluethroats also migrate 
westward into Siberia and then southward on the Asiatic side. Some 
investigators believe the Arctic tern colonized the New World from 
Europe because when this bird departs for the south it first crosses 
the Atlantic to Europe, then moves down the eastern Atlantic coast to 
Africa and either back across the Atlantic to South America or 
continues south down past South Africa (Fig. 11). To get to South 
America from the eastern Arctic, it would be shorter to follow the 
golden plover's flight path straight down the Atlantic or along the 
east coast of the United States but the fact that no Arctic terns have 
been observed in the Caribbean indicates that they do no follow that 
route. 

In western United States, California gulls nest in various colonies 
around Great Salt Lake and Yellowstone Park. Banding records 
indicate these populations winter along the California coast (Fig. 27). 
Instead of traveling southwest by the shortest distance to the 
wintering grounds, they proceed longitudinally down the Snake and 
Columbia Rivers and reach the coast around Vancouver ( Woodbury 
et al. 1946). Thence they proceed south along the coast to Oregon and 
California. In the spring the adults return over the same course 
rather than taking the shorter flight northeast in April across the 
deserts and mountains; this route would be largely made over a cold 
and inhospitable country (Oldaker 1961). 

Sladen (1973) has mapped the migration routes of whistling swans, 
and several dog-leg patterns are apparent in the eastern and western 

87 



Wintering Ground 
Migratory Route 
Band Recovery 
Yellowstone Area 




Figure 27. Migration route and wintering grounds of California gulls banded in north- 
western Wyoming. During fall migration, the birds proceed west from the breeding 
grounds to the Pacific Ocean before turning south to wintering areas in California. A 
more direct route across Nevada would entail a trip through relatively barren country 
(After Diem and Condon 1967). 



populations (Fig. 28). In the eastern population, a sharp change in 
direction occurs at their major feeding and resting areas in North 
Dakota. After the birds arrive from the Arctic breeding grounds, 
they proceed east-southeast to their wintering grounds on 
Chesapeake Bay. In the western population, thousands of birds 
migrate from the Alaskan breeding grounds to the large marshes 
along Great Salt Lake. Then after a major stopover, this population 
heads west over the mountains to California. 



Fall Migration of 
Western Population 



Fall Migration of 
Eastern Population 




Figure 28. Distribution and migration routes of whistling swans in North America. 
Birds from the central arctic head south to North Dakota before proceeding east to 
Chesapeake Bay, while many Alaskan breeders migrate to Great Salt Lake before 
turning west to winter in California (After Sladen, 1973). 

89 



Pelagic Wandering 

Many of the pelagic birds observed off our coasts or at sea appear to 
be nomadic when they are not breeding. These movements are not 
necessarily at random because there is usually a seasonal shift in the 
population, often for great distances and in specific directions, away 
from the breeding area after completion of the nesting cycle. Also the 
return from the sea to nesting areas is at a definite time of year. This 
may not be true migration in the classical sense (Thomson 1964), 
although it is similar in most respects. 

Because of the extensive and often inhospitable habitat of pelagic 
birds (to human observers at least), observations on their movements 
are difficult at best and accurate records are few. We do know some of 
these species have regular routes (e.g., Arctic terns) and specific 
patterns of migration (e.g., the loop in the short-tailed shearwater). 
As more knowledge is accumulated on the "nomadic" species, we may 
actually find they too have regular migration routes based on 
biological needs. 

Movements of some of the tubenoses (Order Procellariiformes, that 
includes albatrosses, fulmars, shearwaters, and petrels) have been 
correlated with ocean currents, prevailing winds, temperatures, and 
general water fertility (Kuroda 1957; Shuntov 1968; Fisher and 
Fisher 1972). Commercial fishermen have long known ocean 
currents are very important factors in the supply of nutrients, 
plankton, and forage fish for larger fish. These same foodstuffs often 
attract pelagic birds as evidenced by the tremendous concentrations 
that occur off the Peruvian coasts where the upwelling of cold 
nutrient-bearing water is evident. Kuroda (1957) found some fine 
correlations between the route of the short-tailed shearwater and 
ocean currents. Likewise Shuntov (1968) found the migratory routes 
of albatrosses were over temperate marine waters of high biological 
productivity. The Laysan albatross was correlated with cold 
currents, while the black-footed albatross occurred over warm 
currents. Many Southern Hemisphere pelagic species have been 
extremely successful in exploiting rich northern waters during 
the summer; the group is probably the most abundant and 
widespread in the world (Bourne 1956). 

Leap-frogging 

When two or more races of the same species occupy different 
breeding ranges on the same axis as migratory flight, the races 
breeding the farthest north often winter the farthest south. Thus, a 
northern race "leap-frogs" over the breeding and wintering range of 
the southern populations. This has been well documented in the fox 
sparrow discussed previously (Fig. 10) and is exhibited by races of 
Canada geese breeding in central Canada as well. One of the smaller 
races of this goose breeds along the Arctic coast of the Northwest 
Territories and winters on the Gulf coast of Texas and northeastern 
Mexico, while a much larger race breeds in the central United States 
and Canada but winters in the central part of the United States. This 

90 



leaping over occurs in other species as well, including the bluebird 
(Pinkowski 1971). 

Vertical Migration 

In the effort to find winter quarters furnishing satisfactory living 
conditions, many North American birds fly hundreds of miles across 
land and sea. Others, however, are able to attain their objectives 
merely by moving down the sides of a mountain. In such cases a few 
hundred feet of altitude corresponds to hundreds of miles of latitude. 
Movements of this kind, known as "vertical migrations," are found 
worldwide wherever there are large mountain ranges. Aristotle first 
mentions vertical migration: "Weakly birds in winter and in frosty 
weather come down to the plains for warmth, and in summer migrate 
to the hills for coolness . . ."(Dorst 1962). The number of species that 
can perform this type of migration pattern is obviously limited to 
those species adapted to breeding in alpine areas. 

In the Rocky Mountain region vertical migrations are particularly 
notable. Chickadees, rosy finches, juncos, pine grosbeaks, William- 
son's sapsuckers, and western wood pewees nest at high altitudes and 
move down to the lower levels to spend the winter. The dark-eyed 
juncos breeding in the Great Smoky Mountains make a vertical 
migration, but other members of the species, breeding in flatter 
areas, make an annual north-south migration of hundreds of miles 
(Van Tyne and Berger 1959). There is a distinct tendency among the 
young of mountain-breeding birds to work down to the lower levels as 
soon as the nesting season is over. The sudden increases among birds 
in the edges of the foothills are particularly noticeable when cold 
spells with snow or frost occur at the higher altitudes. In the Dead 
Sea area of the Middle East, some birds that breed in this extremely 
hot desert move up into the surrounding cooler hill during the winter 
(Thomson 1964). 

The vertical migrations of some mountain dwelling gallinaceous 
birds (mountain quail and blue grouse) are quite interesting because 
the annual journey from breeding to wintering grounds is made on 
foot. Mountain quail make this downward trek quite early in the fall 
well before any snows can prevent them from reaching their goal. 
Blue grouse perform essentially the same journey in reverse. During 
midwinter, these birds can be found near timberline eating spruce 
buds protruding above the snow. 

These illustrations show that the length and direction of a 
migration route are adapted to the needs for survival and are met in 
some cases by a short vertical movement or great latitudinal travels 
in others. 

Pre-migratory Movements 

Recent banding studies have demonstrated many migrants, 
especially young of the year, have a tendency to disperse after 
fledging. These premigatory movements have also been called "post- 
fledging dispersal," "reverse migration," and "postbreeding north- 

91 



ward migration." Demonstration of this phenomenon is especially 
important as it relates to locality-faithfulness (Ortstreue), range 
extension, and gene mixture between populations. These movements 
cannot be considered as true migrations even though they are 
repeated annually by the species between breeding grounds and 
some other area. These movements are generally repeated by the 
same age class in the population but not the same individuals. 

Nevertheless, these regular northward movements are quite 
striking, especially in herons. The young of some species commonly 
wander late in the summer and fall for several hundred miles north 
of the district in which they were hatched. Young little blue herons as 
well as great and snowy egrets are conspicuous in the East as far 
north as New England and in the Mississippi Valley to southeastern 
Kansas and Illinois. Black-crowned night herons banded in a large 
colony at Barnstable, Massachusetts, have been recaptured the same 
season northward to Maine and Quebec and westward to New York. 
In September most of them return to the south. 

These movements have been noted in several other species as well. 
Broley (1947) nicely illustrated this northward movement of bald 
eagles along the Atlantic coast (Fig. 29). Birds banded as nestlings in 
Florida have been retaken that summer 1,500 miles away in Canada. 
Van Tyne and Berger (1959) surmised the summer heat of Florida 
was too great for this eagle, a northern species that has only recently 
spread into Florida to take advantage of abundant food and nesting 
sites, which it exploits during the cooler season. Postbreeding 
northward movements are also shared by wood ducks, yellow- 
breasted chats, eastern bluebirds, and white pelicans. 

A somewhat different type of postbreeding migration is the so- 
called "molt migration" exhibited by many species of waterfowl 
(Salomonsen 1968). These birds may travel considerable distances 
away from their nesting area to traditional molting sites where they 
spend the flightless period of the eclipse plumage. At such times they 
may move well into the breeding ranges of other geographic races of 
their species. These movements may be governed by the availability 
of food and are counteracted in fall by a directive migratory impulse 
that carries those birds that attained more northern latitudes after 
the nesting period, back to their normal wintering homes in the 
south. 

Vagrant Migration 

The occasional great invasions beyond the limits of their normal 
range of certain birds associated with the far North are quite 
different from migration patterns discussed previously. Classic 
examples of such invasions in the eastern part of the country are the 
periodic flights of crossbills. Sometimes these migrations will extend 
well south into the southern States. 

Snowy owls are noted for occasional invasions that have been 
correlated with periodic declines in lemmings, a primary food 
resource of northern predators. According to Gross (1947), 24 major 

92 



invasions occurred between 1833 and 1945. The interval between 
these varied from 2 to 14 years, but nearly half (11) were at intervals 
of 4 years. A great flight occurred in the winter of 1926-27 when more 
than 1,000 records were received from New England alone, but the 



500 Miles 
Nesting Area 
Northern Recoveries 




Fi(ju re 29. Northern recoveries of young bald eagles banded as nestlings in Florida. The 
birds sometimes "migrate" over 1,500 miles up the coast during their first summer 

before returning south (From Broleij 1947). 

93 



largest on record was in 1945-46 when the "Snowy Owl Committee" of 
the American Ornithologists' Union received reports of 13,502 birds, 
of which 4,443 were reported killed. It extended over the entire width 
of the continent from Washington and British Columbia to the 
Atlantic coast and south to Nebraska, Illinois, Indiana, Pennsyl- 
vania, and Maryland. One was taken as far south as South Carolina. 

In the Rocky Mountain region, great flights of the beautiful 
Bohemian waxwing are occasionally recorded. The greatest invasion 
in the history of Colorado ornithology occurred in February 1917, 
when it was estimated that at least 10,000 were within the corporate 
limits of the city of Denver. The last previous occurrence of the 
species in large numbers in that section was in 1908. 

Evening grosbeaks likewise are given to more or less wandering 
journeys, and, curiously enough, in addition to occasional trips south 
of their regular range, they travel east and west for considerable 
distances. For example, grosbeaks banded at Sault Ste. Marie, 
Michigan, have been recaptured on Cape Cod, Massachusetts, and in 
the following season were back at the banding station. Banding 
records and museum specimen identifications demonstrate that this 
east-and-west trip across the northeastern part of the country is 
sometimes made also by purple finches, red crossbills, and mourning 
doves. 



94 



ORIGIN AND EVOLUTION OF MIGRATION 



The origin and evolution of bird migration has been discussed in 
ornithological literature for centuries. As we have seen from the 
foregoing discussion, migration exists in many forms throughout the 
world and probably arose to satisfy many different needs in different 
orders of birds at the same time. New pattens, traditions, and 
routes are arising today as well as disappearing. Currently, the 
migration patterns we see are a composite result of historic 
influences mixed with present day influences. Even though the 
migration of several different species may be very similar, the 
patterns exhibited today can be the result of quite different 
evolutionary processes. Because it cannot be substantiated by 
experimental facts, any explanation of how a particular pattern or 
route originates is pure conjecture. 

The general anatomical and physiological attributes of birds 
enable them to develop more diverse and spectacular migratory 
behavior than any other group of animals. Their potential for long 
sustained flights is of primary importance in pre-adapting birds to 
successful migrations. Migration has long since become a definite 
hereditary habit of many species of birds that recurs in annual cycles, 
evidently because of physiological changes which prompt a search 
for an environment suitable for reproduction and survival. Like the 
bird's other habits its migratory behavior is just as characteristic as 
the color of its plumage and, like it, evolved through natural selection 
because it was advantageous for the survival of the population. Its 
origin has been thought by some to be a mystery locked in past ages, 
but by study of the history of how birds came to occupy their present 
ranges, information becomes available which suggests theories that 
may be developed and explored. Two that are commonly mentioned 
are termed the "Northern Ancestral Home Theory" and the 
"Southern Ancestral Home Theory." 

According to the former of these hypotheses, in earlier ages when 
conditions of climate, food, and habitat were favorable for existence 
of birds throughout the year much further north than is the case 
today, many species remained in these nothern latitudes as 
permanent residents. Today, such conditions are found only in more 
southern regions where migrations are much shorter or nonexistent. 
Gradually, however, in the Northern Hemisphere the glacial ice 
fields advanced southward, causing a southward movement of 
conditions favorable to northern birds, until finally all bird life was 
confined to southern latitudes. As the ages passed, the ice cap 
gradually retreated, and each spring the birds whose ancestral home 
had been in the North moved in again to fill newly opened breeding 

95 



habitat only to be driven south again at the approach of winter. As the 
size of the ice-covered area diminished, the journeys to the summer 
breeding areas became even longer until eventually the climatic 
conditions of the present age became established, and with them, 
present patterns of the annual advance and retreat we call migration. 

The opposing theory is simpler in some respects and supposes the 
ancenstral home of Northern Hemisphere migratory birds was in the 
Tropics. As all bird life tends to overpopulation, there was a constant 
effort of young individuals to pioneer and seek breeding grounds 
where competition was less severe. Species better adapted to more 
northern latitudes moved in that direction for nesting but were kept 
in check by the glacial ice and forced to return southward with the 
recurrence of winter conditions. Gradually, as the ice retreated, vast 
areas of virgin country became successively suitable for summer 
occupancy, but the winter habitat in the South remained the home to 
which the birds returned after the nesting season. 

The above two theories presume that the Quaternary glaciations, 
which occurred 10,000 to 1 million years ago, have been the 
predominate influence on bird migration in North America and 
Europe as we observe it today. There is no doubt these extreme 
climatic and ecologic barriers played a part in shaping or modifying 
some patterns, but as Moreau (1951) has pointed out, well-developed 
migrations occur in parts of the world, including the Southern 
Hemisphere or even within the tropics, where continental glaciation 
was not a factor. Furthermore, migrations to fit various needs have 
probably been going on ever since birds could fly. The tremendous 
Pleistocene glaciations actually occupied less than a hundreth of the 
time birds have existed on the earth and probably only determined 
the details of migrations as we see them today (Moreau 1951). 

The northern and southern ancestral home theories appear 
diametrically opposed to each other but Dorst (1963) concludes they 
are perfectly compatible. Since the phenomena probably occurred 
simultaneously, northern migrants then originated from two stocks: 
the North Temperate Zone birds sought refuge to the south during 
the glacial periods and the tropical avifauna expanded their range 
during the interglacial periods. Dorst also stated this double origin is 
more prevalent in North America where the tropical element is most 
abundant. Birds representing this element include hummingbirds, 
tyrant flycatchers, orioles, tanagers, and blackbirds. At some 
latitudes, they nest in the same area as the shorebirds which are of 
arctic parental stock. 

These theories assume migration is a genetic, inherited character, 
but we now know in some species it can be modified in the lifetime of 
one individual and the place some individuals return to nest or winter 
is not the ancestral home but a place to which they had been 
transported at an early stage in their development. Traditions that 
have lived for countless generations may die overnight if experienced 
individuals are lost or no longer active (Hochbaum 1955); migration 
patterns remain constant only as long as the factors influencing these 

96 



patterns remain constant. But the landscape and the interacting 
ecological stresses are forever changing, and we would expect the 
adaptive behavior of birds to respond with them. One of these 
responses to an expanding habitat is colonization of new territory and 
expansion of a species' range with accompanying development of a 
migratory habit. The search for favorable conditions under which to 
breed in summer and to feed in winter, as influenced by competition 
for space, has been the principal factor underlying the extension of 
ranges, usually by young, nonconditioned individuals. This is 
exemplified by the northward extension in historic times of a number 
of species. Many of these range extensions have closely followed 
man's settlement of the area and the subsequent changes in habitat 
that man has made. 

From the previous descriptions of migration patterns and routes, it 
will be observed that the general trend of migration in most northern 
populations of North American birds is northwest and southeast. 
Eastern species tend to extend their ranges by pushing westward, 
particularly in the North. For example, in the Stikine River Valley of 
northern British Columbia and southwestern Alaska the common 
nighthawk, chipping sparrow, rusty blackbird, yellow warbler, 
American redstart, and others have established breeding stations at 
points 20 to 100 miles from the Pacific Ocean. The northern race of 
the American robin, common flickers, dark-eyed juncos, blackpoll 
warblers, yellow-rumped warblers, and ovenbirds, all common 
eastern species, also are established as breeding birds in western 
Alaska. The ovenbird has even been detected on the lower Yukon 
River, and the sandhill crane and gray-cheeked thrush have moved 
across Bering Strait into Siberia. These birds continue to migrate 
through the eastern part of the continent. Instead of taking the 
shortest route south, they retrace the direction of their westward 
expansion and move southward along the same avenues as their more 
eastern relatives. 

The red-eyed vireo is essentially an inhabitant of states east of the 
Great Plains, but an arm of its breeding range extends northwest to 
the Pacific coast in British Columbia (Fig. 30). It seems evident this is 
a range extension that has taken place comparatively recently by a 
westward movement via deciduous woodland corridors, and the 
invaders retrace in spring and fall the general route by which they 
originally entered the country. 

In the case of the bobolink, a new extension of the breeding range 
and a subsequent change in the migration of the species has taken 
place since settlement by European man (Fig. 19). Because the 
bobolink is a bird of damp meadows, it was originally cut off from the 
Western States by the intervening arid regions, but with the advent 
of irrigation and the bringing of large areas under cultivation, small 
colonies of nesting bobolinks appeared at various western points. 
Now the species is established as a regular breeder in the great 
mountain parks and irrigated valleys of Colorado and elsewhere 
almost to the Pacific coast. These western pioneers must fly long 

97 



Breeding Range 
Winter Range 
Migration Limits 




Figure 30. Distribution and migration of the red-eyed vireo. It is evident that the red- 
eyed vireo has only recently invaded Washington by an extension of its breeding range 
almost due west from the upper Missouri Valley. Like the bobolink (Fig. 19), however, 
the western breeders do not take the short cut south or southeast from their nesting 
grounds but migrate spring and fall along the route traveled in making the extension. 

98 



distances east and west to reach the western edge of the route 
followed by the bulk of the bobolinks that breed in the northern 
United States and southern Canada. 

During the past few decades, various populations of Canada geese 
have altered their migration patterns as a result of transplanting 
brood stock, development of refuges or changing agricultural 
practices. These routes will continue tachange in the coming years as 
long as these factors are in a state of flux. It has been shown 
that man can establish breeding colonies of Canada geese with young 
birds almost anywhere. 

Europe also has several good examples of changes in migration 
routes through range extension. One of the best examples is the serin. 
During the past century, this European finch has spread its breeding 
range from around the Mediterranean Sea to include the entire 
continent. While the Mediterranean populations remain sedentary, 
the more northern breeding birds are migratory. Most likely, those 
birds that did not migrate from the North were eliminated by severe 
weather. Similarly, the wheatear, yellow wagtail, and Arctic 
warbler have extended their breeding ranges eastward across the 
Bering Sea into Alaska, but the wheatear, for instance, migrates all 
the way back across Asia to Africa where it winters with other 
wheatears coming from Europe, Iceland, and Greenland. 

As bird populations become more and more migratory, we might 
expect their flight capabilities to be enhanced accordingly. These 
changes in morphology are readily seen in wing shape. Several 
groups of birds have closely related species or populations some of 
which are migratory and others sedentary. The sedentary species or 
populations have more rounded wings because of the relative length 
of the wing quills. On the other hand, populations that migrate great 
distances, such as albatrosses, falcons, swifts, various shorebirds, 
and terns, have more pointed wings. Kipp(1942, 1958) demonstrated 
this using orioles. The sedentary black-headed oriole of India has a 
well-rounded wing whereas the closely related black-naped oriole is 
migratory between India and Siberia and has primaries that are 
much more pointed and well developed. 

Thus it seems the origin and evolution of migration have roots in 
the present that are deep in the past. The important thing to consider 
in the evolution of a migratory trait is whether a population can adapt 
to new conditions by genetic modification of its physiology and 
habits. The migratory habit has evolved in those populations in 
which, on the average, more individuals survive by moving to a 
different area part of the year than if they remained in the same area 
all year. 



99 



WHERE WE STAND 



The migration of birds had its beginning in times so remote its 
origins have been largely obscured and can be interpreted now only 
in terms of present conditions. The causes underlying migration are 
exceedingly complex. The mystery that formerly cloaked the 
periodic travels of birds, however, has been largely dispelled through 
the fairly complete information now available concerning the extent 
and times of seasonal journeys of most species. Many gaps still 
remain in our knowledge of the subject, but present knowledge is 
being placed on record, and the answers to many uncertainties that 
continue to make bird migration one of the most fascinating subjects 
in the science of ornithology must be left for future studies. In some 
areas we are on the threshold of discovery. More and more 
sophisticated approaches including radar, radio telemetry, com- 
puter processing of banding data, and physiological and behavior 
studies are being developed. 

With the widespread use of these new techniques, we are beginning 
to realize the benefits, aside from aesthetic reasons, for studying 
migration. Radar alone has aided tremendously in documenting 
flock size, heights, and speeds of migration as well as the descriptions 
and locations of patterns and routes of specific migrants in relation to 
aircraft flight lanes. Recent studies have indicated local, nonmigra- 
tory populations of various blackbirds cause nearly all of the rice 
damage in southern States and the "hordes from the North" 
contribute very little to the losses. In addition, the transport of 
arborviruses from one continent to another via these long distance 
migrants is being investigated. People have started to uncover the 
secrets of migration and utilize this knowledge for the betterment of 
our society. 

Each kind of bird seems to have its own reaction to the 
environment, so that the character of movement differs widely in the 
various species, and seldom do any two present the same picture. In 
fact, bird migration has been described as a phase of geographic 
distribution wherein there is a more or less regular seasonal shifting 
of the avian population caused by the same factors that determine the 
ranges of the sedentary species. If this view is correct, then it must be 
recognized that the far-reaching works of man in altering the natural 
condition of the Earth's surface can so change the environment 
necessary for the well-being of the birds as to bring about changes in 
their yearly travels. The nature and extent of the changes wrought by 
man on the North American Continent are readily apparent. 
Extensive forests have been burned or cut away, rolling prairies 
turned over with the plow, and wetlands drained or filled. Their 

100 



places have been taken by a variety of human activites. These great 
changes are exerting pressure on native bird populations, and 
various species may be either benefited or adversely affected. 

The Federal Government has recognized its responsibility to 
migratory birds under these changing conditions. Enabling acts 
allow for carrying out migratory bird treaty obligations in 
cooperation with other countries, and now most species have legal 
protection under regulations administered by the U.S. Fish and 
Wildlife Service. The effectiveness of conservation laws, however, is 
increased in the same measure that the people of the country become 
acquainted with the migratory bird resource and interest themselves 
personally in the well-being of the various species. Long before 
European man came to America, the birds had established their 
seasonal patterns of migration throughout the Western Hemisphere. 
The economic, scientific, and esthetic values of these migratory 
species dictate they be permitted to continue their long-accustomed 
and to some extent still-mysterious habits of migration. 



101 



BIBLIOGRAPHY 



Able, K. P. 

1970. A radar study of the altitude of nocturnal passerine migration. Bird-Banding 
41(4): 282-290. 

Aldrich, J. W. 

1949. Migration of some North American waterfowl. U.S. Fish and Wildl. Serv., 
Spec. Sci. Rep. Wildl. 1. 49 p. 

Aldrich, J. W. 

1952. The source of migrant mourning doves in southern Florida. J. Wildl. Manage. 
16:447-456. 

Aldrich, J. W., A. J. Duvall and A. D. Geis. 

1958. Racial determination of origin of mourning doves in hunters' bags. J. Wildl. 
Manage. 22: 71-75. 

Alexander, J. R., and W. T. Keeton. 

1972. The effect of directional training on initial orientation in pigeons. Auk 89: 
280-298. 

Allard, H. A. 

1928. Bird migration from the point of light and length of day changes. Am. Nat. 62: 
385-408. 

American Ornithologists' Union. 

1957. The Check-list of North American birds. 5th edition. American Or- 
nithologists' Union. 691 p. 

Anderson, K. S., E. J. Randall, A. J. Main and R. J. Tonn. 

1967. Recoveries of birds banded by encephalitis field stations, 1957-1965. Bird- 
Banding 38(2): 135-138. 

Annan, 0. 

1962. Sequence of migration by sex, age, and species of thrushes of the genus 
Hylochichla through Chicago. Bird-Banding 33(3): 130-137. 

Anonymous. 

1972. Population ecology of migratory birds. A symposium. Wildl. Res. Rep. 2. 
U.S. Fish and Wildl. Serv. 278 p. 

Austin, 0. L., Jr. 

1928. Migration routes of the Arctic Tern (Sterna paradisaea Brunnich). North- 
east Bird Banding Assoc. 4(4): 121-125. 

1929. Some Labrador banding records. Northeast Bird Banding Assoc. 5(1): 35-36. 
Bagg, A. M. 

1967. Factors affecting the occurrence of the Eurasian Lapwing in eastern North 
America. Living Bird 6: 87-121. 

Bagg, A. M., W. W. H. Gunn, D. S. Miller, J. T. Nichols, W. Smith and F. P. Wolfarth. 

1950. Barometric pressure patterns and spring bird migration. Wilson Bull. 62: 
5-19. 

Baird, J., C. S. Robbins, A. M. Bagg and J. V. Dennis. 

1958. "Operation Recovery" the Atlantic coastal netting project. Bird-Banding 
29(3): 137-168. 

102 



Baird, J., A. M. Bagg, I. C. J. Nisbet and C. S. Robbins. 

1959. Operation Recovery report of mist-netting along the Atlantic coast in 1958. 
Bird-Banding 30: 143-171. 

Ball, S. C. 

1952. Fall bird migration of the Gaspe Peninsula. Peabody Mus. Nat. Hist. Yale 
Univ. Bull. 7. 211p. 

Behle, W. H. 

1958. The bird life of Great Salt Lake. Univ. of Utah Press, Salt Lake City. 203 p. 
Bellrose, F. C. 

1967. Radar in orientation research. Proc. XIX Int. Ornithol. Congr.: 281-309. 

Bellrose, F. C. 

1968. Waterfowl migration corridors east of the Rocky Mountains in the United 
States. Biol. Notes 61, 111. Nat. Hist. Surv., Urbana, 111 24 p. 

1971. The distribution of nocturnal migration in the air space. Auk 88(2): 397-424. 

1972a. Possible steps in the evolutionary development of bird navigation p. 223-257. 
In: Caller, S. R. et al. ed. Animal orientation and navigation symp. N.A.S.A. 
Wash., D.C. 606 p. 

1972b. Mallard migration corridors as revealed by population distribution, band- 
ing, and radar. In: Population ecology of migratory birds: A Symp. Wildl. Res. 
Rep. 2. U.S. Fish and Wildl. Serv. p. 1-26. 

Bellrose, F. C. and R. R. Graber. 

1963. A radar study of the flight directions of nocturnal migrants. Proc. XIII Int. 
Ornithol. Congr: 362-389. 

Bellrose, F. C. and J. G. Sieh. 

1960. Massed waterfowl flights in the Mississippi flyway 1956 and 1957. Wilson 
Bull. 72: 29-59. 

Bennett. H. R. 

1952. Fall migration of birds at Chicago. Wilson Bull. 64: 197-220. 
Bergman, G. and K. 0. Donner. 

1964. An analysis of spring migration of the Common Scoter and Longtailed Duck 
in southern Finland. Acta Zool. Fenn. 105: 1-59. 

Bergtold, W. H. 
1926. Avian gonads and migration. Condor 28: 114-120. 

Bissonette, T. H. 

1936. Normal progressive changes in the ovary of the starling (Stu-rnus vulgaris) 
from December to April. Auk 53: 31-50. 

1939. Sexual photoperiodicity in the blue jay (Cyanocitta cristata). Wilson Bull. 
51: 227-232. 

Bogert. C. 

1937. The distribution and the migration of the Long-tailed Cuckoo (Urodynamis 
taitensis Sparrman). Am. Mus. Novit. 933. pp 1-12. 

Bourne, W. R. P. 
1956. Migrations of the sooty shearwater. Sea Swallow 9: 23-25. 

Bray, 0. E. and G. W. Corner. 

1972. A tail clip for attaching transmitters to birds. J. Wildl. Manage. 36(2): 
640-642. 

Broley. C. L. 
1947. Migration and nesting of Florida bald eagles. Wilson Bull. 59: 3-20. 

103 



Bruderer, B. and P. Steidinger. 

1972. Methods of quantitative and qualitative analysis of bird migration with a 
tracking radar, p. 151-167. In: Caller, S. R., et al ed. Animal orientation and 
navigation symp. N.A.S.A. Wash., D.C. 606 p. 

Clarke, W. E. 
1912. Studies in bird migration. 2 vol. London. 

Coffey, B. B., Jr. 

1944. Winter home of chimney swifts discovered in northeastern Peru. Migrant 
15(3): 37-38. 

Cooch, G. 

1955. Observations on the autumn migration of blue geese. Wilson Bull. 67(3): 

171-174. 
Cooke, M. T. 

1937. Flight speed of birds. U.S. Dept. Agr. Cir. 428. 13 p. 

1945. Transoceanic recoveries of banded birds. Bird-Banding 16(4): 123-129. 
Cooke, W. W. 

1888. Report of bird migration in the Mississippi Valley in the years 1884 and 1885. 

U.S. Dept. Agr. Div. Econ. Ornithol. Bull. 2. 313 p. 
1904a. Distribution and migration of North American warblers. U.S. Dept. Agr. 

Div. Biol. Surv. Bull. 18. 142 p. 

1904b. The effect of altitude on bird migration. Auk 21: 338-341. 
Cooke, W. W. 

1905a. Routes of bird migration. Auk 22: 1-11. 

1905b. The winter ranges of the warblers (Mniotiltidae). Auk 22: 296-299. 
1906. Distribution and migration of North American ducks, geese, and swans. U.S. 

Dept. Agr. Bur. Biol. Surv. Bull. 26. 90 p. 
1908. Averaging migration dates. Auk 25: 485-486. 
1910. Distribution and migration of North American shore birds. U.S. Dept. Agr. 

Bur. Biol. Surv. Bull. 35. 100 p. 

1913a. Distribution and migration of North American herons and their allies. 

U.S. Dept. Agr. Bur. Biol. Surv. Bull. 45. 70 p. 

1913b. The relation of bird migration to the weather. Auk 30: 205-221. 
1914. Distribution and migration of North American rails and their allies. U.S. 

Dept. Agr. Bull. 128. 50 p. 

1915a. Bird migration. U.S. Dept. Agr. Bull. 185. 48 p. 
1915b. Bird migration in the Mackenzie Valley. Auk 32: 442-459. 
1915c. Distribution and migration of North American gulls and their allies. U.S. 

Dept. Agr. Bull. 292. 70 p. 

1915b. The Yellow-billed loon: a problem in migration. Condor 17: 213-214. 
Cortopassi, A. J. and L. R. Mewaldt. 
1965. The circumannual distribution of white-crowned sparrows. Bird-Banding 

36(3): 141-169. 

Coues, E. 

1878. Birds of the Colorado Valley: a repository of scientific and popular informa- 
tion concerning North American ornithology. U.S. Dept. Int. Misc. Pub. 11. 807 p. 
Curtis, S. G. 

1969. Spring migration and weather at Madison, Wisconsin. Wilson Bull. 81(3): 
235-245. 

Delacour, J. 

1947. Birds of Malaysia. Macmillan Co. N.Y. 382 p. 
1963. The waterfowl of the world, 4 vols. Country Life Ltd. London. 

104 



DeLury, R. E. 

1938. Sunspot influences. J. R. Anstron. Soc. of Can. pt. 1, March 1938, pt. 2, April 
1938. 50 p. 

Dennis, J. V. 

1967. Fall departure of the Yellow-breasted Chat (Icteria virens) in eastern North 
America. Bird-banding 38 (2): 130-135. 

De Schauensee, R. M. 

1970. A guide to the birds of South America. Livingston Pub. Co. Wynnewood, 
Penn. 470 p. 

Diem, K. L. and D. D. Condon. 

1967. Banding studies of water birds on the Molly Islands, Yellowstone Lake, 
Wyoming. Yellowstone Lib. and Mus. Assoc., Yellowstone Nat. Park. 41 p. 

Dixon, J. 

1916. Migration of the Yellow-billed Loon. Auk 33 (4): 370-376. 
Dixon, K. L. and J. D. Gilbert. 

1964. Altitudinal migration in the Mountain Chickadee. Condor 66: 61-64. 
Dorst, J. 

1963. The migration of birds. Houghton Mifflin Co. (Am. ed), Boston. 476 p. 

Drury, W. H. Jr. 

1960. Radar and bird migration a second glance. Mass. Audubon 44(4): 173-178. 

Drury, W. H. Jr., I. C. T. Nisbet and R. E. Richardson. 

1961. The migration of angels. Nat. Hist. 70(8): 10-17. 

Eastwood, E. 
1967. Radar ornithology. Methuen, London. 278 p. 

Eastwood, E. and G. C. Rider. 

1965. Some radar measurements of the altitude of bird flight. Br. Birds 58: 393-426. 

Eaton, R. J. 

1933. The migratory movements of certain colonies of Herring Gulls (Larus 
argentatus smithsonianus Coues) in eastern North America. Parti. Bird-Banding 
4(4): 165-176. 

Eaton, R. J. 

1934. The migratory movements of certain colonies of Herring Gulls in eastern 
North America. Part II. Bird-Banding 5(1): 1-19. 

1934. The migratory movements of certain colonies of Herring Gulls in eastern 
North America. Part III. Bird-Banding 5(2): 70-84. 

Emlen, S. T. 

1967. Migratory orientation in the Indigo Bunting (Passerina cyanea). Part II: 
Mechanism of celestial orientation. Auk 84: 463-489. 

1969. Bird migration: influence of physiological state upon celestial orientation. 
Science (Wash., D.C.) 165 (3894): 716-718. 

1970. The influence of magnetic information on the orientation of the Indigo 
Bunting (Passerina cyanea). Anim. Behav. 18(2): 215-224. 

Earner, D. S. 

1945. The return of Robins to their birthplaces. Bird-Banding 16(3): 81-99. 
1950. The annual stimulus for migration. Condor 52(3): 104-122. 
1955. The annual stimulus for migration: experimental and physiologic aspects. In: 

Recent studies in avian biology. Univ. 111. (Urbana) Bull: 198-237. 
1960. Metabolic adaptations in migration. Proc. XII Int. Ornithol. Cong.: 197-208. 

105 



Earner, D. S. and L. R. Mewaldt. 

1953. The relative roles of diurnal periods of activity and diurnal photoperiods in 
gonadal activation in male Zonotrichia leucophrys gambelii. Experimentia 9: 
219-221. 

Fisher, H. I. and J. R. Fisher. 

1972. The oceanic distribution of the Laysan Albatross (Diomedea immutabilis). 
Wilson Bull 84: 7-27. 

Fisher, J. and R. M. Lockley. 

1954. Sea-birds. Houghton Mifflin, Boston. XVI + 320 p. 

Furlong, W. R. 
1933. Land-birds in a gale at sea. Bird Lore 35(5): 263-265. 

Gatke, H. 

1895. Heligoland as an ornithological observatory: the results of fifty years' experi- 
ence (trans, from German by R. Rosenstock). David Douglas Pub., Edinburgh. 
599 p. 

Gauthreaux, S. A. Jr. 

1970. Weather radar quantification of bird migration. Bioscience 20(1): 17-20. 

1971. A radar and direct visual study of passerine spring migration in southern 
Louisiana. Auk 88: 343-365. 

1972a. Flight directions of passerine migrants in daylight and darkness: a radar 
and direct visual study p. 129-137. Galler, S. R., et al. ed. In: Animal orientation 
and navigation symp. N.A.S.A. Wash., D.C. 606 p. 

1972b. Behavioral responses of migrating birds to daylight and darkness: a radar 
and direct visual study. Wilson Bull. 84: 136-148. 

Geroudet, P. 

1954. Des oiseaux migrateurs trouves sur la glacier de Khumbu dans 1'Himalaya. 
Nos Oiseaux 22: 254. 

Godfrey, W. E. 

1966. The birds of Canada. Natl. Mus. Can. Bull. 203, Biol Series No. 73. 428 p. 
Gordon, D. A. 

1948 Some considerations of bird migration: continental drift and bird migration. 
Science (Wash., D.C.) 108: 705-711. 

Graber, R. R. 

1965. Night flight with a thrush. Audubon 67: 368-374. 

1968. Nocturnal migration in Illinois different points of view. Wilson Bull. 80(1): 
36-71. 

Graber, R. R. and W. W. Cochrane. 

1959. An audio technique for the study of nocturnal migration of birds. Wilson 
Bull. 71: 220-236. 

Griffin, Dr. R. 

1940. Homing experiments with Leach's Petrels. Auk 57(1): 61-74. 
1943. Homing experiments with Herring Gulls and Common Terns. Bird-Banding 
14(1 and 2): 7-33. 

Griffin, D. R. 

1958. Listening in the dark. Yale Univ. Press, New Haven. 413 p. 
1964. Bird migration. Nat. Hist. Press. Garden City, N.Y. 180 p. 

Griffin, D. R. and R. J. Hock. 

1948. Experiments on bird navigation. Science (Wash., D.C.) 107(2779): 347-349. 

1949. Airplane observations of homing birds. Ecology 30: 176-198. 

106 



Grinnell, J. 

1931. Some angles in the problem of bird migration. Auk 48: 22-32. 
Gross, A. 0. 

1927. The Snowy Owl migration of 1926-27. Auk 44: 479-493. 

1947. Cyclic invasions of the Snowy Owl and the migration of 1945-46. Auk 64(4): 
584-601. 

Gwynn, A. M. 

1968. The migration of the Arctic Tern. Aust. Bird Bander 6(4): 71-75. 
Haartman, L. von. 

1968. The evolution of resident vs. migratory habit in birds: some considerations. 
Ornis Fenn. 45(1): 1-7. 

Hagar, J. A. 
1966. Nesting of the Hudsonian Godwit at Churchill, Manitoba. Living Bird 5: 5-43. 

Hamilton, W. J. III. 
1962a. Bobolink migratory pathways and their experimental analysis under night 

skies. Auk 79(2): 208-233. 
1962b. Celestial orientation in juvenile waterfowl. Condor 64(1): 19-23. 

Harrisson, T. H. 
1931. On the normal flight speed of birds. Br. Birds 25: 86-96. 

Hassler, S. S., R. R. Graber and F. C. Bellrose. 

1963. Fall migration and weather: a radar study. Wilson Bull. 75: 56-77. 
Haugh, J. R. and T. J. Cade. 

1966. The spring hawk migration around the southeastern shore of Lake Ontario. 
Wilson Bull. 78(1): 88-110. 

Hebrard, J. J. 

1971. The nightly initiation of passerine migration in spring: a direct visual study. 
Ibis 113(1): 8-18. 

Hochbaum, H. A. 

1955. Travels and traditions of waterfowl. Univ. of Minn. Press, Minneapolis. 301 p. 
Hofslund, P. B. 

1965. Hawks above Duluth. In: The bird watcher's America, ed. 0. s. Pettingill, Jr. 
McGraw-Hill Book Co., N. Y. 

1966. Hawk migration over the western tip of Lake Superior. Wilson Bull. 78: 79-87. 
Hussell, D. J. T., T. Davis and R. D. Montgomerie. 

1967. Differential fall migration of adult and immature Least Flycatchers. Bird- 
Banding 38(1): 61-66. 

Jaeger, E. C. 

1948. Does the Poor-will "hibernate"? Condor 50: 45. 

1949. Further observations on the hibernation of the Poor-will. Condor 51: 105-109. 
Johnson, N. K. 

1963. Comparative molt cycles in the Tyrannid genus Empidonax. Proc. XIII Int. 

Ornithol. Congr.: 870-883. 
1973. S pring migration of the Western Flycatcher with notes on seasonal changes in 

sex and age ratios. Bird-Banding 44(3): 205-220. 
Keeton, W. T. 

1969. Orientation by pigeons: is the sun necessary? Science (Wash., D. C.) 165(3896): 
922-928. 

Kenyon. K. W. and D. W. Rice. 
1958. Homing of Laysan Albatrosses. Condor 60: 3-6. 

107 



King, J. R. 

1963. Annual migratory-fat deposition in the White-crowned Sparrow. Proc. XIII 
Int. Ornithol. Congr.: 940-949. 

King, J. R., S. Barker and D. S. Farner. 

1963. A comparison of energy reserves during the autumnal and vernal migratory 
periods in the White-crowned Sparrow (Zonotrichia leucophrys gambelii). Ecol. 
44(3): 513-521. 

King, J. R. and D. S. Farner. 
1963. The relationship of fat deposition to Zugunruhe. Condor 65(3): 200-223. 

Kipp, F. A. 
1942. Ueber Flugelban and Wanderzug der Vogel. Biol. Zbl. 62: 289-299. 

1958. Zur Geschichte des Vogelzuges auf der Grundlage der Flugelanpassungen. 
Vogelwarte 19: 233-242. 

Kramer, G. 

1952. Experiments on bird orientation. Ibis 94: 265-285. 
1957. Experiments on bird orientation and their interpretation. Ibis 99: 196-227. 

1959. Recent experiments on bird orientation. Ibis 101: 399-416. 

1961. Long distance orientation. In: Marshall, A. J. Biology and comparative 
physiology of birds. 2 Vol. Academic Press, N.Y. and London. 

Kuroda, N. 

1957. A brief note on the pelagic migration of the Tubinares. Misc. Rep. of the 
Yamashina Inst. for Ornithol. and Zool. 11: 10-23. 

Lack, D. 

1959. Migrations across the sea. Ibis 101(3-4): 374-399. 

1960a. The influence of weather on passerine migration. Auk 77: 171-209. 
Lack, D. 

1960b. The height of bird migration. Br. Birds 53: 5-10. 

1962. Radar evidence on migratory orientation. Br. Birds 55(4): 139-157. 
1963a. Migration across the southern North Sea studied by radar. Part 4. Autumn. 

Ibis 105 (1): 1-54. 

1963b. Migration across the southern North Sea studied by radar. Part 5. Move- 
ments in August, winter and spring, and conclusion. Ibis 105(4): 461-492. 

Lewis, H. F. 

1937. Migrations of the American Brant (Branta bernicla hrota). Auk 54: 73-95. 
Lincoln, F. C. 

1917. Bohemian Waxwing (Bombycilla garrula) in Colorado. Auk 34: 341. 

1922. Trapping ducks for banding purposes: with an account of the results obtained 
from one waterfowl station. Auk 39: 322-334. 

1924a. Banding notes on the migration of the Pintail. Condor 26: 88-90. 

1924b. Returns from banded birds, 1920 to 1923. U.S. Dept. Agr. Bull. 1268. 56 p. 

1926. The migration of the Cackling Goose. Condor 28: 153-157. 

1927a. Notes on the migration of young Common Terns. Northeastern Bird- 
Banding Assoc. Bull. 3: 23-28. 

1927b. Returns from banded birds, 1923 to 1926. U.S. Dept. Agr. Tech. Bull. 
32. 95 p. 

1928. The migration of young North American Herring Gulls. Auk 45: 49-59. 

1934. Distribution and migration of the Redhead (Nyroca americana). Trans. 
Twentieth Am. Game Conf.: 280-287. 

1935a. The waterfowl flyways of North America. U.S. Dept. Agr. Cir. 342. 12 p. 

1935b. The migration of North American birds. U.S. Dept. Agr. Cir. 363. 72 p. 

108 



Lincoln, F. C. 

1937. Our greatest travelers. In: The book of birds. Natl. Geog. Mag. 2: 301-350. 
1939a. The migration of American birds. Doubleday, Doran & Co., N.Y. 189 p. 
1939b. The individual vs. the species in migration studies. Auk 56(3): 250-254. 
1941. The waterfowl flyways. Wild ducks. Am. Wildl. Inst. 20-29. 

1945. Flyway regulations. Trans. Tenth North Am. Wildl. Conf.: 50-51. 

1946. Keeping up with the waterfowl. Audubon Mag. 48(3): 194-205. Reprinted as 
U.S. Fish and Wildl. Serv. Leaflet 294. April 1947. 10 p. 

Lowery, G. H. Jr. 

1945. Trans-gulf spring migration of birds and the coastal hiatus. Wilson Bull. 
57(2): 92-121. 

1946. Evidence of trans-gulf migration. Auk 63(2): 175-211. 

1951. A quantitative study of the nocturnal migration of birds. Univ. Kan. Pub. 
Mus. Nat. Hist. 3(2): 361-472. 

Lowery, G. H., Jr. and R. J. Newman. 

1966. A continentwide view of bird migration on four nights in October. 
Auk 83(4): 547-586. 

Lucanus, F. von. 
1911. Ueber die Hohe des vogelzuges. Verh. V Int. Ornithol. Congr. 557-562. 

McMillan, N. T. 

1938. Birds and the wind. Bird Lore 40(6): 397-406. Reprinted Smithson. Rep. 
for 1939: 355-363. 

Magee, M. J. 

1938. Evening Grosbeak recoveries. Northeastern Bird-Banding Assoc. Bull. 4: 
56-59. 

Main, J. S. 
1932. The influence of temperature on migration. Wilson Bull. 44: 10-12. 

Manville, R. H. 
1963. Altitude record for mallard. Wilson Bull. 75: 9 

Marshall, A. J. 

1961. Breeding seasons and migration. Chapter 21: 307-339. In: Biology and 
comparative physiology of birds, Vol. II. A. J. Marshall ed. Academic Press, 
N.Y. and London. 468 p. 

Matthews, G. V. T. 
1951. The experimental investigation of navigation in homing pigeons. J. Exp. 

Biol. 28: 508-536. 
1955. Bird navigation. Univ. Press, Cambridge. 141 p. 

May, J. B. 

1929. Recoveries of Black-crowned Night Herons banded in Massachusetts. North- 
eastern Bird-Banding Assoc. Bull. 5: 7-16. 

Mazzeo, R. 

1953. Homing of the Manx Shearwater. Auk 70: 200-201. 
Meanly, B. 

1971. Blackbirds and the southern rice crop. U.S. Fish and Wildl. Serv. Res. 
Pub. 100. 64 p. 

Meinertzhagen, R. 

1920. Some preliminary remarks on the altitude of the migratory flight of birds 
with special reference to the Paleoarctic region. Ibis, Series 11, 2: 920-936. 

109 



1921. Some preliminary remarks on the velocity of migratory flight among birds 
with special reference to the Paleoarctic region. Ibis, Series 11, 3(2): 228-238. 

1955. The speed and altitude of bird flight (with notes on other animals). 

Ibis 97: 81-117. 
Mewaldt, L. R. and R. G. Rose. 

1960. Orientation of migratory restlessness in the White-crowned Sparrow. 
Science 131: 105-106. 

Miller, A. H. 

1963. Photoregulative and innate factors in the reproductive cycles of an equatorial 
sparrow. Proc. XVI Int. Congr. Zool. 1: 166. 

Moreau, R. E. 

1951. The migration system in perspective. Proc. X Int. Ornithol. Cong. 245-248 
1953. Migration in the Mediterranean area. Ibis 95: 329-364. 

1961. Problems of Mediterranean-Sahara migration, Part 3. Ibis 103a(4): 580-623. 
Mueller, H. C. and D. D. Berger. 

1967a. Fall migration of Sharp-shinned Hawks. Wilson Bull. 79: 397-415. 
1967b. Wind drift, leading lines, and diurnal migration. Wilson Bull. 79(1): 50-63. 
Murphy, R. C. 

1936. Oceanic birds of South America. Am. Mus. Nat. Hist. New York. 2 vol. 
Murray, B. G. Jr. 

1964. A review of Sharp-shinned Hawk migration along the northeastern coast of 
the United States. Wilson Bull. 76: 257-264. 

1965. On the autumn migration of the Blackpoll Warbler. Wilson Bull. 77(2): 
122-133. 

Murray, B. G. Jr. and J. R. Jehl Jr. 

1964. Weights of autumn migrants from coastal New Jersey. Bird-Banding 35: 
253-263. 

Nice, M. M. 

1937. Studies in the life history of the Song Sparrow. I. A population study of 
the Song Sparrow. Trans. Linn. Soc. N.Y. 4: 1-247. 

Nisbet, I. C. T. 

1961. Studying migration by moon-watching. Bird-Migr. 2(1): 38-42. 
1963a. Quantitative study of migration with 23-centimeter radar. Ibis 105(4): 
435-460. 

Nisbet, I. C. T. 

1963b. Measurements with radar of the height of nocturnal migration over Cape 
Cod, Massachusetts. Bird-Banding 34(2): 57-67. 

Nisbet, I. C. T. and W. H. Drury Jr. 

1967a. Scanning the sky/birds on radar. Mass. Audubon 51: 166-174. 
1967b. Weather and migration. Mass. Audubon 52(1): 12-19. 
1968. Short-term effects of weather on bird migration: A field study using 
multivariate statistics. Anim. Behav. 16(4): 496-530. 

Odum, E. P. 

1958. The fat deposition picture in the White-throated Sparrow in comparison 
with that in long-range migrants. Bird-Banding 29(1): 105-108. 

Oldaker, R. F. 

1961. 1960 survey of the California Gull. West. Bird Bander. 36(3): 26-30. 
Orr, R. T. 

1970. Animals in migration. MacMillan Co. Collier-MacMillan Ltd. London. 303 p. 

110 



Packard, F. M. 

1945. The birds of Rocky Mountain National Park, Colorado. Auk 62: 371-394. 
Parslow, J. L. F. 

1969. The migration of passerine night migrants across the English Channel 
studied by radar. Ibis 111 (1): 48-79. 

Pennycuick, D. J. 

1969. The mechanics of bird migration. Ibis 111: 525-556. 
Perdeck. A. C. 

1967. Orientation of starlings after displacement to Spain. Ardea 55(3-4): 194-204. 
Peterson. R. 

1961. The long journey. Audubon Mag. 63(2): 72-75. 
Pettingill, 0. S. Jr. 

1962. Hawk migrations around the Great Lakes. Audubon Mag. 64: 44-45, 49. 

1970. Ornithology in laboratory and field. Fourth ed. Burgess Pub. Co., 
Minneap. 524 p. 

Phillips, J. H. 

1963. The pelagic distribution of the Sooty Shearwater (Puffinus griseus). Ibis 
105: 340-353. 

Pinkowski, B. C. 

1971. An analysis of banding-recovery data on Eastern Bluebirds banded in 
Michigan and three neighboring states. Jack-Pine Warbler 49(2): 33-50. 

Pough. R. H. 

1948. Out of the night sky. Audubon Mag. 50(6): 354-355. 
Ralph. C. J. 

1971. An age differential of migrants in coastal California. Condor 73: 243-246. 
Raynor, G. S. 

1956. Meterological variables and the northward movement of nocturnal land bird 
migrants. Auk 73: 153-175. 

Rense, W. A. 

1946. Astronomy and ornithology. Pop. Astron. 54(2): 1-19. 
Richardson, W. J. 

1971. Spring migration and weather in eastern Canada: a radar study. Am. 
Birds 25(3): 684-690. 

1972. Autumn migration and weather in eastern Canada: a radar study. Am. 
Birds 26: 10-17. 

Richardson, W. J. and M. E. Haight. 
1970. Migration departures from starling roosts. Can. J. Zool. 48(1): 31-39. 

Robbins, C. S. 

1949. Weather and bird migration. Wood Thrush 4(4): 130-144. 
1956. Hawk watch. Atl. Nat. 11: 208-217. 

Robbins, C., D. Bridge and R. Feller. 

1959. Relative abundance of adult male Redstarts at an inland and a coastal 
locality during fall migration. Md. Birdlife 15(1): 23-25. 

Rowan, W. 

1925. Relation of light to bird migration and developmental changes. Nature 
(Lond.) 115: 494-495. 

1926. On photoperiodism, reproductive periodicity, and the annual migrations of 
birds and certain fishes. Boston Soc. Nat. Hist. Proc. 38: 147-189. 

Ill 



1930a. Experiments in bird migration. II. Reversed migration. Nat. Acad. Sci. 

Proc. 16: 520-525. 

1930b. The mechanism of bird migration. Sci. Prog. 25: 70-78. 
1931. The riddle of migration. Williams & Wilkins, Baltimore. 151 p. 

Rudebeck, G. 
1950. Studies on bird migration. Var. Fagelvarld, Supplementum I. 148 p. 

Salmonsen, F. 
1968. The moult migration. Wildfowl 19: 5-24. 

Sauer, F. 

1957. Die Sternenorientierung nachtlich ziehender Grasmucken (Sylvia attri- 
capilla borin and curruca). Z. Tierpsych. 14: 29-70. 

1958. Celestial navigation by birds. Sci. Am. 199(2): 42-47. 

Sauer, E. G. F. 
1961. Further studies on the stellar orientation of nocturnally migrating birds. 

Psychol. Forsch. 26(3): 224-244. 
1963. Migration habits of Golden Plovers. Proc. XIII Int. Ornithol. Cong.: 454-467. 

Sauer, E. G. F., and E. M. Sauer. 

1960. Star navigation of nocturnal migrating birds. Cold Spring Harbor Symp. on 
Quant. Biol. 25: 463-473. 

Schmidt-Koenig, K. 

1963. Sun compass orientation of pigeons upon equatorial and transequatorial 
displacement. Biol. Bull. 124(3): 311-321. 

1964. Sun compass orientation of pigeons upon displacement north of the Arctic 
circle. Biol. Bull. 127(1): 154-158. 

Schnell, G. D. 

1965. Recording the flight speed of birds by Doppler Radar. Living Bird 4: 79-87. 

Schuz, E. 

1963. On the North-Western migration divide of the White Stork. Proc. XIII Int. 
Ornithol. Cong. 475-480. 

Serventy, D. L. 

1953. Movements of pelagic sea-birds in the Indo-Pacific region. Proc. 7th Pacific 
Sci. Cong.: 4: 394-407. 

1958. Recent studies on the Tasmanian mutton-bird. Aust. Mus. Mag. 12: 327-332. 

Sheldon, W. 

1965. Hawk migration in Michigan and the Straits of Mackinac. Jack-Pine 
Warbler 43(2): 79-83. 

Suntov, V. P. 

1968. Some correlations in the dispersal of Albatrosses in the Northern Pacific. 
Z. Zhurn. 47: 1054-1064. (In Russian, Eng. summ.) 

Sladen, W. J. L. 

1973. A continental study of whistling swans using neck collars. Wildfowl 24: 8-14. 
Snyder, L. L. 

1943. The Snowy Owl migration of 1941-42. Wilson Bull. 55(1): 8-10. 
Southern, W. E. 

1959. Homing of Purple Martins. Wilson Bull. 71: 254-261. 

1965. Avian navigation. Article No. 2, Field Studies and Experiments, p. 87-88; 
In. Biotelemetry, Bioscience 15(2): 79-121, 159. 

112 



Stevenson, H. M. 

1957. The relative magnitude of the trans-gulf and circum-gulf spring migrations. 
Wilson Bull. 69(1): 39-77. 

Stewart, R. E., A. D. Geis and C. D. Evans. 

1958. Distribution of populations and hunting kill of the Canvasback. J. Wildl. 
Manage. 22: 333-370. 

Stoddard, H. L. and R. A. Norris. 

1967. Bird casualties at a Leon County, Florida TV tower: an eleven-year study. 
Bull. Tall Timbers Res. Stn. 8. 104 p. 

Storer, J. H. 

1948. The flight of birds. Cranbrook Inst. Sci. Bull. 28: 94 p. 
Storr, G. M. 

1958. Migration routes of the Arctic Tern. Emu 58(1): 59-62. 
Sutter, E. 

1957. Radar-Beobachtungen uber den Verlauf des nachtlichen Vogelzuges. Rev. 
Suisse Zool. 64: 294-303. 

Swan, L. W. 

1970. Goose of the Himalayas. Nat. Hist. 79(10): 68-75. 
Swarth, H. S. 

1920. Revision of the avian genus Passerella, with special reference to the 
distribution and migration of the races in California. Univ. Calif. Pub. Zool. 
21(4): 75-224. 

Swirski, Z. 

1965. Bird migrations (trans, from Pol.). Pol. Sci. Pub. Warsaw, Pol. 106 p. 
Taverner, P. A. 

1935. Continental land masses and their effect upon bird life. Condor 37: 160-162. 
Tedd, J. G. and D. Lack. 

1958. The detection of bird migration by high-power radar. Proc. R. Soc. 
(B) 149: 503-510. 

Thompson. D. Q. and R. A. Person. 

1963. The eider pass at Point Barrow, Alaska. J. Wildl. Manage. 27: 348-356. 
Tomson, A. L. 

1960. Bird-migration terms. Ibis 102: 140. 

1964. A new dictionary of birds. McGraw-Hill Co. N.Y. 928 p. 

1965. The transequatorial migration of the Manx Shearwater (Puffin des anglais). 
Oiseau Rev. Fr. Ornithol. 35: 130-140. 

Van Tyne, J. and A. J. Berger. 

1959. Fundamentals of ornithology. John Wiley & Sons, Inc. New York. 624 p. 
Viguier, C. 

1882. Le sens de 1'orientation et ses organes. Rev. Philos. 14: 1-36. 
Voous. K. H. and J. Wattel. 
1963. Distribution and migration of the Greater Shearwater. Ardea 51: 143-157. 

Walcott, D. and M. Michener. 

1967. Analysis of tracks of single homing pigeons. Proc. XIV Int. Ornithol. 
Cong.: 311-329. 

Walraff, H. G. 

1967. The present status of our knowledge about pigeon homing. Proc. XIV Int. 
Ornithol. Congr.: 331-358. 

113 



Welty, J. C. 
1962. The life of birds. W. B. Saunders Co. Phila. & Lond. 546 p. 

Wetmore, A. 
1926. The migration of birds. Harv. Univ. Press, Camb., Mass. 217 p. 

Williams, G. G. 
1945. Do birds cross the Gulf of Mexico in spring? Auk 62(1): 98-111. 

1947. Lowery on trans-gulf migration. Auk 64(2): 217-237. 

1950. Weather and spring migration. Auk 67: 52-65. 
Williamson, K. 

1958. Bergmann's Rule and obligatory overseas migration. Br. Birds 51(6): 209-232. 

Winkenwerder, H. A. 

1902. The migration of birds with special reference to nocturnal flight. Wis. Nat. 
Hist. Soc. 2: 177-263. 

Wolff, W. J. 

1970. Goal orientation versus one-direction orientation in Teal (Anas c. crecca) 
during autumn migration. Ardea 58: 131-141. 

Wolfson, A. 

1940. A preliminary report on some experiments on bird migration. Condor 42(2): 
93-99. 

1945. The role of the pituitary fat deposition and body weight in bird migration. 
Condor 47(3): 95-127. 

1948. Bird migration and the concept of continental drift. Science (Wash., D. C.) 
108: 23-30. 

Woodbury, A. M. 

1941. Animal migration-periodic response theory. Auk 58: 463-505. 
Woodbury, A. M., W. H. Behle and J. W. Sugden. 

1946. Color-banding California Gulls at Great Salt Lake, Utah. Bull. Univ. Utah, 
37(3): 1-15. 

Yeagley, H. L. 

1947. A preliminary study of physical basis of bird navigation. J. Appl. Physiol. 
18(12): 1035-1063. 

1951. A preliminary study of a physical basis of bird navigation. Part II. J. Appl. 
Physiol. 22(6): 746-760. 



114 



LIST OF BIRD SPIECIES MENTIONED IN TEXT 



COMMON NAME' 



SCIENTIFIC NAME* 



Albatross, Black-footed 

Albatross, Laysan 

Blackbird, Brewer's 

Blackbird, Red-winged 

Blackbird, Rusty 

Blackbird, Yellow-headed 

Blackcap 

Bluebird, Eastern 

Bluethroat 

Bobolink 

Bobwhite 

Brant (Atlantic) 

Brant, Black 

Bunting, Black-headed 

Bunting Cretzchmar's 

Bunting, Indigo 

Bunting, Ortolan 

Bunting, Snow 

Canvasback 

Cardinal 

Chat, Yellow-breasted 

Chuck-will's-widow 

Coot (American) 

Crane, Sandhill 

Creeper, Brown 

Crossbill, Red 

Crow (Common) 

Cuckoo, Black-billed 

Cuckoo, Yellow-billed 

Curlew, Bristle-thighed 

Dove, Mourning 

Dove, Turtle 

Duck, Black 



Diomedea nigripes 
Diomedea immutabilis 
Euphagus cyanocephalus 
Agelaius phoeniceus 
Euphagus carolinus 
Xanthocephalus xanthocephalus 
Sylvia atricapilla 
Sialia sialis 
Luscinia svecica 
Dolichonyx oryzivorus 
Colinus virginianus 
Branta bemicla hreta 
Branta bemicla nigricans 
Emberiza melanocephala 
Emberiza caesia 
Passerina cyanea 
Emberiza hortulana 
Plectrophenax nivalis 
Ay thy a valisineria 
Cardinalis 
Icteria virens 
Caprimulgus carolinensis 
Fulica americana 
Grus canadensis 
Certhia familiaris 
Loxia curvirostra 
Corvus brachyrhynchos 
Coccyzus erythropthalmus 
Coccyzus americanus 
Numenius tahitiensis 
Zenaida macroura 
Streptopelia turtur 
Anas rubripes 



* For all North American species the authors have followed nomenclature in the 1957 edition of the A.O.U. 
Check-list. Also, we have incorporated the new names presented in the April 1973 issue of ThfAuk( volume 90. 
number 2, pages 411-419), the quarterly journal of the A.O.U. For other parts of the world we have used the 
most authoritative sources available. 

115 



Duck, Wood 

Eagle, Bald 

Egret, Great 

Egret, Snowy 

Eider, Common 

Eider, King 

Falcon, Peregrine 

Finch, Purple 

Flicker, Common 

Flycatcher, Hammond's 

Flycatcher, Least 

Flycatcher, Western 

Frigatebird, Magnificent 

Godwit, Black-tailed 

Godwit, Hudsonian 

Goose, Bar-headed 

Goose, Canada 

Goose, Emperor 

Goose, Ross' 

Goose, Snow [Blue] 

Goose, White-fronted 

Goshawk 

Grackle, Common 

Grosbeak, Black-headed 

Grosbeak, Evening 

Grosbeak, Pine 

Grosbeak, Rose-breasted 

Grouse, Blue 

Gull, California 

Gull, Herring 

Gull, Ross' 

Hawk, Broad-winged 

Hawk, Cooper's 

Hawk, Red-shouldered 

Hawk, Red-tailed 

Hawk, Rough-legged 

Hawk, Sharp-shinned 

Hawk, Sparrow (European) 

Hawk, Swainson's 

Heron, Black-crowned Night 

Heron, Little Blue 

Hummingbird, Ruby-throated 



Aix sponsa 

Haliaeetus leucocephalus 
Casmerodius albus 
Egretta thula 
Somateria mollissima 
Somateria spectabilis 
Falco peregrinus 
Carpodacus purpureus 
Colaptes auratus 
Empidonax hammondii 
Empidonax minimus 
Empidonax difficilis 
Fregata magnificens 
Limosa limosa 
Limosa haemastica 
Anser indicus 
Branta canadensis 
Philacte canagica 
Chen rossii 
Chen caerulescens 
Anser albifrons 
Accipter gentilis 
Quiscalus quiscula 
Pheucticus melanocephalus 
Hesperiphona vespertina 
Pinicola enucleator 
Pheucticus ludovicianus 
Dendragapus obscurus 
Larus califomicus 
Larus argentatus 
Rhodostethia rosea 
Buteo platypterus 
Accipter cooperii 
Buteo lineatus 
Buteo jamaicensis 
Buteo lagopus 
Accipter striatus 
Accipter nisus 
Buteo swainsoni 
Nycticorax nycticorax 
Florida caerulea 
Archilochus colubris 



116 



Jay, Blue 

Junco, Dark-eyed 

Kingfisher, Belted 

Kinglet, Golden-crowned 

Kittiwake, Red-legged 

Knot, Red 

Lapwing 

Lark, Horned 

Longspur, Lapland 

Loon, Arctic 

Mallard 

Martin, Purple 

Nighthawk, Common 

Nuthatch, Red-breasted 

Oriole, Black-headed (Indian) 

Oriole, Black-naped 

Ovenbird 

Owl, Great-horned 

Owl, Snowy 

Pelican, White 

Penguin, Adelie 

Petrel, Wilson's Storm 

Pewee, Western Wood 

Phalarope, Northern 

Pigeon (Rock Dove) 

Pintail 

Plover, Golden 

Quail, Mountain 

Redhead 

Redstart, American 

Robin, American 

Rook 

Sanderling 

Sandpiper, Baird's 

Sandpiper, Purple 

Sandpiper, White-rumped 

Sapsucker, Williamson's 

Serin 

Shearwater, Manx 

Shearwater, Short-tailed 

Shearwater, Sooty 

Shrike, Loggerhead 



Cyanocitta cristata 
Junco hyemalis 
Megaceryle alcyon 
Regulus satrapa 
Rissa brevirostris 
Calidris canutus 
Vanellus vanellus 
Eremophila alpestris 
Calcarius lapponicus 
Gavia arctica 
Anas platyrhynchos 
Progne subis 
Chordeiles minor 
Sitta canadensis 
Oriolus xanthornus 
Oriolus chinensis 
Seiurus aurocapillus 
Bubo virginianus 
Nyctea scandiaca 
Pelecanus erythrorhynchos 
Pygoscelis adeliae 
Oceanites oceanicus 
Contopus sordidulus 
Libipes lobatus 
Columba livia 
Anas acuta 
Pluvialis dominica 
Oreortyx pictus 
Ay thy a americana 
Setophaga ruticilla 
Turdus migratorius 
Corvus frugilegus 
Calidris alba 
Calidris bairdii 
Calidris maritima 
Calidris fuscicollis 
Sphyrapicus thyroideus 
Serinus serinus 
Puffinus puffinus 
Puffinus tenuirostris 
Puffinus griseus 
Lanius ludovicianus 



117 



Shrike, Red-backed 

Snipe, Common 

Sora (Rail) 

Sparrow, Andean (Rufous-collared) 

Sparrow, Chipping 

Sparrow, Field 

Sparrow, Fox 

Sparrow, Harris' 

Sparrow, Ipswich 

Sparrow, Savannah 

Sparrow, Song 

Sparrow, Swamp 

Sparrow, Tree 

Sparrow, Vesper 

Sparrow, White- throated 

Swallow, Bank 

Swallow, Barn 

Swallow, Cliff 

Swan, Whistling 

Swift, Chimney 

Swift, Common 

Tanager, Scarlet 

Tanager, Western 

Tattler, Wandering 

Teal, Blue-winged 

Tern, Arctic 

Tern, Noddy 

Tern, Sooty 

Thrush, Gray-cheeked 

Thrush, Hermit 

Thrush, Swainson's 

Thrush, Wood 

Turnstone, Ruddy 

Veery 

Vireo, Red-eyed 

Vulture, Turkey 

Wagtail, Yellow 

Warbler, Arctic 

Warbler, Blackpoll 

Warbler, Black-and-white 

Warbler, Black-throated Blue 



Lanius collurio 
Capella gallinago 
Porzana Carolina 
Zonotrichia capensis 
Spizella passerina 
Spizella pusilla 
Passerella iliaca 
Zonotrichia querula 
Passerculus sandwichensis 

princeps 

Passerculus sandwichensis 
Melospiza melodia 
Melospiza georgiana 
Spizella arborea 
Pooecetes gramineus 
Zonotrichia albicollis 
Riparia riparia 
Hirundo rustica 
Petrochelidon pyrrhonota 
Olor columbianus 
Chaetura pelagica 
Apus apus 
Piranga olivacea 
Piranga ludoviciana 
Heteroscelus incanum 
Anas discors 
Sterna paradisaea 
Anous stolidus 
Sterna fuscata 
Catharus minimus 
Catharus guttatus 
Catharus ustulatus 
Hylocichla mustelina 
Arenaria interpres 
Catharus fuscescens 
Vireo olivaceus 
Cathartes aura 
Motacilla flava 
Phylloscopus borealis 
Dendroica striata 
Mniotilta varia 
Dendroica caerulescens 



118 




irbler, Cape May 
Warbler, Connecticut 
Warbler, Golden-winged 
Warbler, Kentucky 
Warbler, Palm 
Warbler, Pine 
Warbler, Subalpine 
Warbler, Willow 
Warbler, Worm-eating 
Warbler, Yellow 
Warbler, Yellow-rumped 
Waxwing, Bohemian 
Wheatear 
Wigeon, American 
Woodcock, American 
Wren, Carolina 
Wren, Long-billed Marsh 
Wren, Rock 
Wren, Winter 
Yellowlegs, Greater 
Yellowlegs, Lesser 
Yellowthroat, Common 



Dendroica tigrina 
Oporomis agilis 
Vermivora chrysoptera 
Oporomis formosus 
Dendroica palmarum 
Dendroica pinus 
Sylvia cantillans 
Phylloscopus trochilus 
Helmitheros vermivorus 
Dendroica petechia 
Dendroica coronata 
Bombycilla garrulus 
Oenanthe oenanthe 
Anas americana 
Philohela minor 
Thryothorus ludovicianus 
Telmatodytes palustris 
Salpinctes obsoletus 
Troglodytes troglodytes 
Tringa melanoleuca 
Tringa flavipes 
Geothlypis trichas 



119 




Created in 1849, the Department of the Interior America's 
Department of Natural Resources is concerned with the man- 
agement, conservation, and development of the Nation's water, 
fish, wildlife, mineral, forest, and park and recreational 
resources. It also has major responsibilities for Indian and 
Territorial affairs. 

As the Nation's principal conservation agency, the Depart- 
ment works to assure that nonrenewable resources are developed 
and used wisely, that park and recreational resources are con- 
served for the future, and that renewable resources make their 
full contribution to the progress, prosperity, and security of the 
United States now and in the future. 



* U.S. GOVERNMENT PRINTING OFFICE: 1979 O 274-535