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OCCURRENCE OF APTOSOCHROMATISM
IN PASSERINA CYANEA,

BY

F. J. BIRTWELL.

[Reprinted from ScrEncE, N. S., Vol. XI., No. 269, Pages 292-299, February 23, 1900.]

656
Pate 66/9
Birds

[Reprinted from Science, N. S., Vol. XI., No. 269,
Pages 292-299, February 28, 1900.)

Fyanus 3, Birtwe

THE OCCURRENCE OF APTOSOCHROMATISM
IN PASSERINA CYANEA.*

TuE following remarks upon the Aptoso-
chromatism of Passerina cyanea, although
of insufficient importance to establish the
phenomenon of color change without moult
as a constant occurrence in the species, are
conclusive enough, I am convinced, to
prove the possibility of such a change, and
are merely offered as such for what they
may be worth.

Individual error and dogmatism have
greatly retarded honest effort in this most
important branch of ornithological science.
It is a singular fact that certain individuals
have conceived the idea that a feather once
having passed its premature condition is
utterly disconnected with the vital system
of the bird, and such individuals cling to
this belief with a tenacity wonderful to be-
hold. They do not tell us, by the way,
how it is that certain species of birds lack-
ing external sebaceous glands manage to
present as bright plumage as their allies so
provided. Doubtless they may attribute
the presence of oily matters upon the sur-
face of the feathers of those species in
which thése glands are wanting to osmotic
action ; but-admitting this, why not admit
Aptosochromatism x

In his article on alleged changes of color
in feathers (Bull. Am. Museum Nat. Hist.
1896), Dr. Allen compares a feather to a
green leaf, which when once formed, can-
not extend its growth to repair any injuries
which may arise from insects, etc. This

* Read before the Nuttall Ornithological Club of
Cambridge, Mass., June 5, 1899, with exhibition of
the bird worked upon.

2

simile might well be carried yet farther and
to better advantage. When the later sum-
mer or early fall approaches, certain leaves
undergo a complete change in color, result-
ing in the beautiful colors of our Septem-
ber and October woods. The history of the
underlying phenomena of autumnal col-
oration in leaves is very obscure, yet no one
doubts the occurrence of the change for an
instant. Soit is with Aptosochromatism—
the individual feathers undergo in many
cases complete color changes, and although
the underlying processes of these changes
may be obscure, the fact of their presence is
to my mind undeniable.

At the present time Aptosochromatism
has not progressed far enough to encourage
one to take up in detail the systematic oc-
currence of the color change in our species
of native birds. It seems evident that for
the present, attention should rather be de-
voted to endeavoring to demonstrate its
fundamental principles, without which no
science is firm, plainly evident as may be
its happening.

Passerina cyanea, apart from its seasonal
fall moult by which the plumage acquired
in the spring is changed for the duller garb
of the fall, doubtless exhibts two forms of
Dichromatism, a term whose proper place,
I hope, is now recognized as the funda-
mental term for the complex phenomena of
double coloration. As I shall direct my at-
tention toward proving that Aptosochroma-
tism is concurrent in the species, and Ptoso-
chromatism in the present paper will play
an inconspicuous part. Both are compre-
hensive terms, by the way, coined by Dr.
Coues. The latter term may be defined for
convenience, as the occurrence of Dichroma-
tism depending entirely upon the loss of old

3

feathers which are replaced by others of a
different color. Both processes subserve
the same general purpose and result in a
seasonal change of color, in the present
example, from that of the fall to the nuptial
of the spring. The Ptosochromatic change
of the spring will not farther be considered
here—let it suffice to say that beyond doubt
some indigo birds change color in the spring
by completely, or nearly so, shedding their
feathers. The change not due to such
feather loss is what interests us at the pres-
ent, and will necessarily be presented far
from exhaustively. My remarks are based
chiefly upon observations conducted during
the fall, winter, and early spring of 1898-
99, upon a captive male bird. In view of
the color of the plumage of my bird, at the
time I took possession of it, it must have
been in the adult condition, and as such
birds are commonly captured while in the
adult state, the difficulty in adapting my
bird to his captive condition and the heavy
feather loss undoubtedly resulting from this
may consequently, be explained. I secured
it October 13th, while it was nearing the
completion of its fall moult, which by Octo-
ber 28th was finished. From that date every
cast-off feather was carefully collected and
labelled. In order to be sure of obtaining
all, a fender was placed about the cage and
the room carefully swept at frequent inter-
vals. In addition to this I made many ex-
aminations of the bird and secured such
specimen feathers in a fresh state as I
wished for microscopic examination.
Briefly, the bird was fed mostly upon
millet and canary seed, appeared healthy,
bathed regularly, and during bright days
sang frequently. On March 26th, how-
ever, he died after an illness of three

4

days, before which he was as lively as ever.
Examination showed constipation to be the
probable cause of his untimely death. The
color change had progressed excellently
however, and but little additional informa-
tion could have been gained had he lived,
excepting the period of time occupied by
the entire change. Data is present in suf-
ficient quantity, nevertheless, to enable me
to state the time occupied by the change in
certain portions of the plumage.

The appearance of my bird as regards
color, October 28th, was as follows: Feathers
of the head and breast slightly tinged with
cobalt, the chief color of the feathers being
dull rusty. The breast thus was somewhat
mottled in appearance. Back rusty, the
concealed centers bluish. Primaries and
rectrices blackish with blue edges. Second-
aries and coverts broadly edged with rust
color. Lower abdomen buffy, ventral area
whitish.

From October 28th till January 28th I
observed no marked color change, but from
February until the bird’s death, it was very
noticeable. A curious and undoubtedly un-
normal process intervened however, and in
order to understand this comprehensively I
will tabulate the feather loss beginning with
the first feather shed after October 28th,
when it will be recollected that the bird
had completed its moult.

Nov. 1, 1 contour
tc 7, 1 (a3
(73 12, 1 be

Nov. 21, 2 contours
oh 20. 1 contour
are 2 contours
ES NOO: 1 contour
‘¢ 30-Dec. 5, 4 contours

Dec. 5-11, 4 «

“11-24, 20 «

5

Dec, 24-31, 12 contours

Dec. 31-Jan. 7, 11 a

Jan. 7-23, 5 es daily
‘6 94 12 “c
i 95, Hey 166
66 26, 13 as

‘¢ 27 and 28, 61 be
Jan. 28-Feb. 11, 34 ss

From February 11th to February 28th
an average of 50 contours was lost daily.
By March 5th the loss had abruptly ceased,
and until his death on March 29th the bird
lost but one or two feathers daily. The
loss of down feathers was very small, not
exceeding twenty specimens—a fact of pos-
sible importance to be dwelt upon later on.
The total summary of the contour feathers
lost, carefully estimated at 1350 feathers,
appeared to comprise about three-fifths
of my bird’s entire plumage. They were
shed from all parts of the plumage, and in
view of the heavy loss I was quite prepared
to ultimately conclude that any color
change resulting in my bird would ensue
from extensive feather loss. I was thus
quite unprepared for what eventually fol-
lowed. Microscopically, the cast-off feath-
ers were broken, abraded and apparently
in the worst condition. The barbules were
broken or wanting, the barbs in many
places worn down, and the rhachis of the
larger feathers was split. This is also of
importance as will directly be seen. To
many observers my bird by March 5th
would have been pronounced to be com-
pletely moulting. Immature feathers were
in prominence especially upon the head and
were scattered all about the remaining
feathers of the plumage, which, as has been
before remarked, amounted to about two-
fifths of the entire plumage. The color of
a discarded feather, compared with a freshly

6

plucked one from the body, showed in most
cases a decided contrast. Not only were
the blue portions dull but their superstruc-
tures were gone in many cases, the feathers
then being dull brownish. A probable, and,
as I am convinced, the truthful source of
my bird’s extensive loss is found indirectly
in the temperament of the bird. From the
very first it was fretful and timid, flutter-
ing wildly when uncovered in the morning
or when the cage was cleaned out. Evenan
approach in his direction while hanging in
the room caused a wild fluttering. Upon
such occasions many feathers would be
shed, and those remaining were more or less
injured. Thus when such a vital process
as Aptosochromatism begins to work, these
decrepit feathers necessarily would have to
be renewed in order to take part in the
general plan. The head upon which many
pin feathers appeared, naturally received a
considerable share of the injury as regards
its feathers, and the tail was in a very bad
state.

Tt will be noticed in the table how gradu-
ally the loss began, due doubtless to the
gradual approach of activity towards color
change in the feathers. It must be ad-
mitted that this explanation is purely hy-
pothetical, but such a hypothesis, although
not of fundamental importance, ofttimes
prepares the way for a clearer understand-
ing of the problem under consideration.
The small loss of down feathers points in
two ways to the truth of this assumption.
Firstly, being more or less under the con-
tour feathers they received less of the wear
caused to the others, and secondly, having
no color change in themselves, their part in
the color-changing process was inconspicu-
ous. It is not probable that the bird could

7

have swallowed many down feathers with-
out it being observed in the excrement.

As I frequently examined the bird closely
I noticed at once that the developing feath-
ers which were supplying the places of the
cast-off ones, far from appearing to change
the color of the bird to blue, were actually
coming true to the colors in which they
were shed, %. ¢., in the colors of the fall
plumage. To be positive I collected and
examined extensively and in every case
verified this most interesting principle. It
will be recollected that in my observations
upon the Aptosochromatism of Chrysotis
Levaillanti (see Osprey, III., No. 8, April,
99), similar results were noticed. In later
dates a few parti-changed feathers were
found in the embryonic condition, but these
may be readily accounted for in two ways,
for in no cases were fully changed feathers
so detected. (1) Where a partially changed
feather had been pulled out or shed and
was being renewed, and (2) where a feather
had begun to change before it was matured
(this being noticed in my parrot investiga-
tion). Many of the contradictory and con-
fusing remarks of dealers in birds may per-
haps be explained by these most important
observations, and it may readily be true
that more than a few instances of so-called
color changes depending upon spring moults
in cage birds, may be due to extensive
feather losses precedent to an Aptosochro-
matic change.

It seems unnecessary to dwell upon the
fact that no vital process can readily take
place in a greatly injured organic structure,
and the renewal of my bird’s feathers con-
current with the approach of the macro-
scopic activity of the color change is, I
think, an incident of no little value.

8

The first appearances of a color change
were noticed in some of the old feathers
of the crown during the first week of
February. Here a brightening of the blue
area of the feather was noticed but no per-
ceptible change of color at the tips where
the russet was. From this date till the
death of the bird a slow but constant change
occurred, chiefly noticeable on the rump,
throat, and breast. The first indication of
the approach of the change externally was
the brightening of the blue portion of the
feather, beginning evenly on each vane
from the bottom. When the band of tawny
was reached, it appeared slowly to be ab-
sorbed until but faint tips of this color
could be seen upon the ends of the larger
barbs. In no cases were the barbs or bar-
bules broken off sufficiently to account for
the change. A loss of one-third of the
length of the feathers in many cases would
have been the result, and close observation
did not sustain this in the least. I was en-
abled to notice the change in certain breast
feathers, which was much more rapid than
that of the parrot before referred to. Yet
in the latter case the change which gradu-
ally causes the yellow plumage is a slow
one of life duration, and but few feathers
are involved atatime. That of Passerina
cyanea is one of comparatively short dura-
tion and involves the greater part of the
entire plumage.

Upon his death the bird presented the
following appearance as regards color. An
irregular area of brilliant cobalt blue ex-
tended from the throat to the belly down
the center of the breast, the feathers upon
each side graduating gradually to the sides,
where but little change had occurred. Head
partially changed in parts, inter-scapulars

9

not perceptibly changed at all (a place
where many pin feathers formed). Back
altered slightly, rump and scapulars 4
changed to bright greenish blue, the long
russet tips almost entirely changed in some
feathers, wings and tail unaltered with the
exception of the secondaries and coverts,
which had slightly changed on the edges.
Throat slightly blackish, lower ventral re-
gion as with the rump. Assuming, as we
safely may, that the first of February
marked the beginning of the macroscopic
change, we may attribute the total length
of time occupied in the change of some of
the breast feathers, from the fall to the
spring colors, to a period of about fifty
days, which for some of the feathers is an
over-estimate.

It is not a little curious that the feathers
should act so independently and especially
80 when it is considered that each feather
comes true in color.

While skins of birds may serve highly
important purposes, it appears essential
that for good results in investigations upon
color change, one should operate rather upon
live birds in confinement. It is quite ab-
surd to suppose that a single generation in
confinement would so alter the natural laws
of the organism as to obscure Aptosochrom-
atism or Ptosochromatism, if one process
or the other be a natural tendency. It is
objectively certain that the phenomenon
of Aptosochromatism occurs widely, but
whether of individual or specific occurrence
is not yet clearly shown. While my bird
threw out no hint whatever as to the con-
stant occurrence of the color change, it did
prove that the ‘impossibility’ is possible.*

* Dr. Chadbourne has informed me, since the above
was written, that of three confined male indigo birds

10

It is certain that the heavy feather loss of
my bird but indirectly helped the change;
Ist, we have seen that many feathers.
changed which were not renewed by moult ;
2d, we saw that those feathers which were
renewed by direct gain and loss were col-
ored similarly to those which preceded
them, but that later on they changed Apto-
sochromatically, and 3d, no purely blue, 7. e.,
changed feathers, were found in an embry-
onic condition at any time, although fre-
quent careful examinations of the bird were
made.

Although it is of no positive certainty
whether, in the new feathers, the vascular
connection with the body was severed, it
was found that their complete form was at-
tained in most cases a week or more before
a change set in; and in those unshed
feathers carried over from the fall, it is
quite reasonable to suppose that all con-
nections with the body of the bird were as
normal as in other feathers of a similar age.
Before the change of color had begun, in
December or January, in specimens ex-
amined carefully under the microscope, I
could detect no presence of carrier pigment
cells and found the calamus of each feather

observed by him, two changed color ptosochromatic-
ally and the third ‘ without any feather loss to speak
of,’ i. e., aptosochromatically ; and still later on, I
was delighted to learn during a conversation with
Mr. C. J. Maynard that he too had followed a male
Passerina through its entire spring change of color.
The bird involved, belonged to a friend of Mr. May-
nard, who informed him that the bird had changed
its colors during the season just passed without moult-
ing itsfeathers. Determined to follow out the change
exactly, Mr. Maynard examined the bird frequently
the next season, throughout the entire time occupied
by the change, and perfectly satisfied himself that it
was totally unassisted by a moult or any considerable
loss of feathers.

1¥

to be in the expected dried up condition.
The change would thus seem to be confined
to activity in the feathers alone.

In a brief summary of the principal points
already discussed in connection with my
bird we may conclude (1) that Aptosochrom-
atism in my Passerina cyanea occurred
beyond doubt, (2) that although present
with severe feather loss it does not follow
that the gain of color was directly responsi-
ble to it, as proved by careful examination
of the newly acquired feathers, and (3) that
although the feather loss was objectively
independent of the Aptosochromatic change,
it might subjectively be so, inasmuch as old
and imperfect feathers were renewed for
active and healthy ones, in which such a
color change subsequently occurred.

The results quoted of Dr. Chadbourne
and Mr. Maynard appear to me to be con-
elusive in themselves and require no further
comment. Microscopically, the color change
was not of as much prominence as might
have been expected at first thought, but it
will be recollected that blue and violet
colored feathers depend, in a large measure,
for their effects, upon involved objective
superstructures, which act in combination
with some underlying pigment or pigments.
These pigments produce chemical objective
effects, due to the absorption of all light
rays not depending upon the characteristic
color of the pigments. ;

Chemically and microscopically, the
feathers of my Passerina cyanea appeared
to contain two pigments, one, a diffused
non-granular tawny colored stain, the other,
a granular blackish substance. The yel-
lowish stain was confined to the transparent
sheath of the barbs and to the barbules,
while the granular matter varied in place-
ment with the color of the feathers.

12

An unchanged, 7. e., fall-colored feather,
examined in a fresh state, exhibited the fol-
lowing appearance under the microscope.
The rhachis appeared, centrally, to be cellu-
lar in construction with an enveloping
sheath thickly supplied with the black pig-
ment matter, the granules arranged in an
order suggestive of a streaming movement
toward the tip of the feather. At the junc-
tion with each barb a small portion of the
main system curved upward into the central
portion of that member. Proximally this
column ended in the modification of the
rachis into barbs. The center of each barb
of the colored parts of the feathers con-
tained a prismatic column, resembling to
my eye, a number of bodies set together so
as to resemble the nodes and internodes of
a bamboo cane. At the distal end of each
barb these bodies tapered, and in many
eases the extreme joints were separated
from the main column. About the blue
portions of the feathers, these columns were
massed thickly with black matter, the por-
tions giving the rusty effects being much
less plentifully supplied, and surrounding
this central column a transparent envelope
of the yellowish stain was present. The
barbules of the non-blue area were the color
of this sheath but became well supplied
with the dark pigment when the blue-pro-
ducing area was met with, completely ob-
scuring the presence of the stain. The tips
of the prismatic columns showed a pale
brownish orange color, but gradually as the
microscope slide was passed across the stage
the color became deeper until when one-
half of the length of the barbs had passed
before the objective, it appeared deep black.

The blue area of such a feather gave a
good reaction for Zoomelanin (black), for

13

by boiling the feather in KOH, 0.5% and
then heating with chlorine, the dark matter
was completely broken up, and the feather
appeared colored as with the rusty-colored
tip which was apparently unaltered by the
test.

When compared to a feather wholly
changed to blue by the Aptosochromatic
process, a valuable suggestion is at once
thrown out, as to the nature of the change
of color. Ina microscopic examination of
such a feather it is noticed that the lower
parts of the central barb colums were as in
the bicolored-fall feathers excepting that
the massing of the black appeared to be
denser. The upper parts however which
were deep orange brown before, varying to
lighter tints as the tips of the barbs were
approached, now appear thickly massed
with the black also, and the yellowish
barbules are likewise colored. The stream-
ing movement of the color granules is now
esvecially prominent in an actively chang-
ing feather, and it readily appears that the
rhachis gives up a part of its matter to the
barbs, which in turn supply it to the bar-
bules. A positive change of pigment is man-
ifested macroscopically, for a fall feather
held to the light or crushed, remains yel-
lowish in its yellow-colored parts, while a
spring feather, appearing entirely blue, so
treated, shows darkly, due to the addition
of black pigment.

Undoubtedly the blue effects are pro-
duced by the prismatic column in coopera-
tion with the dark involved pigment, the
sheath enveloping these parts playing its
part with the barbules in producing the fall-
colored feather. A cross section of the blue-
producing barb sustains this view. When
placed under the microscope with all light

14

obstructed, but that descending to the stage
from above, the sheath became invisible
but the central column showed up like
phosphorus as a pale glimmering blue which
became opalescent with the varying quan-
tities of light admitted. Unsectioned feath-
ers so treated acted quite similarly, but the
parts of the column appearing in the tips of
the fall feathers, instead of betraying blue,
showed gleaming white effects. Under trans-
mitted light, as in ordinary examinations,
the effects of the pigments alone were seen.

The massing of the granules of pigment
begins evenly upon each vane, from the
bottom of each barb and works towards the
tips, the barbules being filled, from the tips
first, as they are passed. The tips of the
distal barbs usually were the last to com-
pletely undergo this change.

In both fall and spring feathers, the ob-
jective superstructure occupied the same
relative position, being confined to the cen-
ter of the barbs alone for almost their en-
tire lengths.

Dr. Gadow, who has published results of
his investigations upon the nature of the
blue-producing structures in feathers, con-
cludes that the production of blue is, in a
measure, caused by the fine ridges of the
prismatic columns, and thinks that the
bodies of the columns and the transparent
sheaths of the barbs may exert an appreci-
able influence. He adds in consequence
‘the production of blue therefore in a
feather would be the result of a very com-
plicated process.”’

As shown in my feathers, however, the
blue appeared to be largely independent of
the envelope of the barbs, yet this might
concentrate light rays or so modify them
that the consequent would be helpful. One

15

thing appears certain, that to the presence
of quantities of granular black-like matter
is due no small share of the ultimate pro-
duction of blue.

The causes of the differences in the shade
of tbe blue feathers from violet to greenish,
according to their position on the bird, ap-
peared to be very slight microscopically, and
I could detect no constant characters with
the facilities at my disposal.

As tothe causes of the activity necessary
to produce a color change, we may only
infer. As proved by dissection my bird was
not undergoing any prominent sexual
change, and the theory that the temperature
of the atmosphere might be responsible
would not be applicable to most cage birds
which are kept in warmrooms. There can
be no doubt, however, but that the fall
change of plumage is one of protective ten-
dency, and it is highly possible that until
changed in the spring, the feathers, in a
certain sense, are immature. In the case
of the double yellow-headed parrot before
mentioned, the color change was of a retro-
grade nature, but in the present example
the process is synthetic rather than other-
wise.

Numerous theories have been published
which endeavor to account for the dichro-
matic fall change of many birds, but it
would be irrelevant to discuss them here.
One thing appears certain, that the process
is deeply involved in the vital system of
the organism. Professor Beddard cites an
example noticed by Professor Weber of a
chaffinch which was so colored that one-half
of the bird was in the male plumage and
the other portion in the female. Dissection
proved the bird to be a Hermaphrodite, i. e.,
the side sustaining the male plumage was

16

found to contain a testicle,while the opposite
portion of the body possessed an ovary, and
Professor Beddard writes that this curious
abnormality had been noticed before.

As no vascular connection appeared to be
present in the perfect feathers of my bird,
the change appears to be one of internal
activity in the feathers themselves, and the
simile before mentioned, of the autumn leaf,
appears to be still more strongly consistent.
The change is none the less vital, however,
and ceases with the death of the organism.
No tests delicate enough were applied to
determine if new matter was formed di-
rectly in the feather. It appeared prob-
able that none was, but that the striking
change depended upon the massing of the
dark granular matter from the rhachis to
the barbs and their appendages. The ab-
sence of definite data upon the chemistry
of animal pigments makes remarks in a
qualitative direction wholly undesirable.

To conclude our microscopic study, how-
ever, we may affirm: (1) that microscop-
ically as well as macroscopically an appre-
ciable Aptosochromatic change took place
in the individual feathers of my Passerina
cyanea; (2) that this change far from being
analytical or retrograde was inclined to the
nature of constructive synthesis, probably
passive in nature ; (3) that the change was
definite as shown by comparison with the
blue areas of unchanged feathers ; (4) that
it depended chiefly upon the gain of dark
pigment in the vicinity of the prismatic
column, and (5) that there was an appre-
ciable difference in the amounts of blackish
pigment supplied to the barbs and barbules,
before and after the change.

F. J. BIRTWELL.

ALBUQUERQUE, NEW MEXICO.

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