seen two specimens of the Short-eared Owl that were taken within the
limits of the Adirondack Region, in Lewis County. They were both killed
east of the Black River Valley—one in the town of Greig, and the other
in Lyonsdale.
181. =Nyctiardea grisea nævia= (_Bodd._) _Allen_. NIGHT HERON.—I have
seen a Night Heron that was shot at Crown Point (in Essex Co.) on Lake
Champlain. There were two of them together, and both were killed.
182. =Calidris arenaria= (_Linn._) _Illig._ SANDERLING.—On the 5th of
October, 1881 Mr. O. B. Lockhart killed, from a flock, four Sanderlings
at Lake George, in Warren Co. (Dr. A. K. Fisher.)
183. =Chen hyperboreus= (_Pallas_) _Boie_. SNOW GOOSE.—Dr. A. K. Fisher
writes me that he saw a flock of one hundred and fifty or two hundred
Snow Geese on Lake George (in Warren County) Nov. 19, 1881. In company
with Mr. O. B. Lockhart he rowed out to within a hundred yards of them,
when they were frightened by another boat and took flight, showing
plainly the black tips of their primaries as they left.
184. =Phalacrocorax dilophus= (_Sw. and Rich._) _Nuttall_.
DOUBLE-CRESTED CORMORANT.—Mr. F. H. Knowlton, from Brandon, Vermont,
writes me: “I shot, on September 24, 1879, at St. Regis’ Lake [Franklin
County], two miles from Paul Smith’s, a young female example of
_Graculus dilophus_. The bird was not wild and was easily shot from the
shore.”
185. =Dytes auritus= (_Linn._) _Ridgway_. HORNED GREBE.—On Little
Tuppers Lake (Hamilton Co.), Oct. 22, 1881. Dr. A. K. Fisher and I saw
about eight Horned Grebes and I killed one of them. While crossing
Raquette Lake, the same day, Dr. Fisher shot another. At Big Moose Lake
(in Hamilton and Herkimer Counties) we saw this species every day from
Oct. 26 to Nov. 8, 1881. Nov. 5 I shot one out of a flock of nine. They
were all in the plain fall dress, so that the size alone enabled us to
distinguish young from old. In all the iris was of a bright orange red.
They are excellent divers and can remain under water an astonishingly
long period.—C. HART MERRIAM, M.D., _Locust Grove, N. Y._
ERRATA.
In Vol. VII, page 26, line 6, for “An indistinct, dusky” read “A black.”
Same page, foot note, for “οὐκέω” read “οἰκέω.”
[Illustration:
BULL. NUTT. ORNITH. CLUB., VOL. VII., NO. 3. PLATE 7.
Jeffries & Blake, del. _The Heliotype Printing Co. 211 Tremont
St. Boston_
]
BULLETIN
OF THE
NUTTALL ORNITHOLOGICAL CLUB.
VOL. VII. JULY, 1882. No. 3.
THE COLORS OF FEATHERS.
BY J. AMORY JEFFRIES.
Feathers have been studied from the earliest days of the microscope,
indeed long before the modern microscope came into existence. Malpighei,
Hooke and Leeuwenhoek all wrote on the subject, and not a little of our
knowledge dates from their time. Since then authors have constantly
written on feathers and their colors, until the papers on the subject
may be counted by hundreds. Accordingly little that is new can be
expected from this short article, nor even a history of the literature
of the subject. My only object is to give an idea, so far as is known,
how the colors of feathers are produced, the literature of the subject
being out of the track of most American ornithologists.
Color may be the result of any one or more of the following causes: a
pigment, interference and diffraction of light in their various phases,
fluorescence, and phosphorescence. Of these causes only three have been
called upon to explain the colors of feathers, the last two apparently
playing no part. The fluorescence noted by Dr. Krukenberg in solutions
of certain feather-pigments probably plays no part, or at most an
insignificant one, in the colors of feathers. Pigments act by absorbing
all rays of light but those which enter into their color, that is turn
them into heat.
Interference acts in several different ways, all of which are based on
the same principle, and so films may be taken as an example. If a beam
of light, _xy_ (figure 1), is allowed to fall on any thin plate, or
film, part of the rays will be reflected in the direction _yz_, the
angles _byx_ and _ayz_ being equal. The rest of the rays will pass
through the film to the other surface, being slightly refracted in their
course. Here part will be reflected, and being again refracted at the
first surface, will emerge in a line _wz′_ nearly coincident with _yz_,
the balance passing out into the air. Now the waves composing the white
light of two beams _yz_ and _wz′_ will run together and partially
obliterate each other, after the manner of ripples on water. Accordingly
certain waves will be obliterated, and since white light is due to the
blending of waves of the different colors, the light reflected from the
film will be that of the colors not interfered with, the waves thus
obliterated depending upon their length and the thickness of the film
traversed. So as we look at the film from different points the
conditions vary, and with them the resultant color.
Interference may also produce colored light by means of fine particles
diffused through another substance, as milk in water, the particles in
the air, and the like. Colored light produced in this way is known as
opalescent, the transmitted light tending to the red end of the
spectrum, and the reflected to the other portions. This result can be
obtained by mixing black and white grains, an experiment which all have
tried as school boys, by soaking chalk in ink, the result being a bluish
color.
Diffraction acts apparently by bending the light rays different amounts,
and thus spreading out the spectrum. Explanations of the various
phenomena of this sort are difficult, and need not be entered into here.
Feathers are classed, according to their appearance, into ordinary,
metallic and iridescent, the peculiarities of which are well known and
so need not delay us.
The ordinary feathers are colored by simple pigments, by contrast of
light and darkness and mechanically, as in the case of the Bluebird
(_Sialia sialis_). Pigments of various colors are known to occur in
feathers, and have received special names, as turacin, zoönerythrin,
zoöfulvin, zoöxanthin, zoöchlorin, zoömelanin. These evenly distributed,
as turacin, zoönerythrin, and zoöfulvin, or in patches, as zoömelanin,
impart their respective colors to the feather parts in which they
exist.[67] The color of the mass of the feather may, however, owing to
various colors in the small feather parts, be different from that of any
part.
Of these pigments none seem to be peculiar except turacin. This pigment
is altered by wetting the feathers, and comes from the feathers into the
water in which the birds bathe, a fact of considerable interest, since
the birds maintain their normal color, thus necessitating a new supply
of pigment.
White feathers are the result of the light being reflected as a whole
from the finely divided feather parts. Some grays are the result of
small black nodes in the barbules, which nodes are of considerable size,
and do not disperse the light, being distributed along the barbules.
Other grays are the result of a small quantity of black pigment.
Yellow feathers colored with zoöfulvin receive their hue from this
pigment, which is pretty evenly distributed through the texture like a
dye.
Red feathers, as those of the Flamingo, Cardinal Bird, and the like, are
so colored by a red pigment similar to the yellow one. Brown feathers
are colored by a brown pigment in the feathers, which is for the most
part collected in patches within the cells of the feather.
Violet pigments are said by some to exist, while others have never been
able to extract them, so the causes of this color still remain in doubt.
Green feathers owe their color to various causes. In some it is due to a
green pigment, as Turacoverdin or zoöchlorin, in others it is said to be
due to a mixture of yellow and blue dots. The olive-greens are sometimes
produced by a yellow pigment overlying a dark brown or black.
All the above pigments seem to be blended and used in gaudily colored
birds much after the manner of paints by artists. So that a great
variety of colors may be produced from a few pigments by the skilful
hand of nature.
Metallic feathers, properly speaking, are those which partake of the
characters shown by the red crests of the Woodpeckers. The metallic
appearance is limited to the barbs, the barbules not showing this
peculiarity, and being quickly shed. If a feather from the crest of a
Woodpecker, say _Picus pubescens_, be examined, it will at once be
noticed that the red barbs have few if any barbules, and that the barbs
themselves are enlarged. Such barbules as are present, are not red but
black, and only serve to diminish the effects of the red parts. They
would seem accordingly to be properly classed among useless hereditary
organs. That the red color is due to a pigment is proved by dissolving
it out and by its persistence when examined by transmitted light. But
what causes the brilliancy which has led to their being called metallic?
This is due to the extreme smoothness of the barbs, the horn-cells of
which they are composed being fused together and solid. Thus the
unabsorbed rays of the beam of light which strikes them are reflected as
a whole, instead of being sent in every direction by the walls of the
cells as in most cases. The metallic feathers differ from ordinary
feathers in the same way that window or glass paintings differ from
ordinary pictures. They simply give off much more light, and thus
produce more marked effects on our eyes.
The colors of metallic feathers seem to be limited to the red end of the
spectrum, the colors varying from yellow or orange to red; blue, green
or purple feathers constructed on this principle do not seem to abound.
So far we have only had to deal with pigments, and all has been plain
sailing, but the various accidental colors shown by feathers are far
more difficult of explanation. Not only are the parts extremely small,
but the entire subject of accidental colors as regards organic
structures has been in large part dealt with from a theoretical point of
view. The question has not been how is the feather part made, but what
kinds of structures will produce such color effects. Accordingly divers
opinions have been expressed on the subject, the most probable of these
we shall now endeavor to sketch out.
Blue colors seem to be accidental, that is, the result of other causes
than pigments. Not only have all efforts to extract the pigments failed,
but blue feathers appear gray when examined by transmitted light. Again,
no blue can be found in transverse sections of blue feather parts. This
method of studying the colors of feathers is worthy of more extended use
than it has yet had. By this means all physical effects of the outer
coat are avoided, and the exact position of the pigments can be seen.
Sections are quickly prepared by fastening the feather on to a piece of
pith with collodion, and mounting sections pith and all. The pith keeps
the sections on end, a result otherwise difficult to obtain.
Gray-blues, such as those seen in _Dendrœca cœrulescens_, are due to
opalescence. The feather is full of fine granules of black or darkish
pigment, which in a manner already described produces a blue color.
Brilliant blues, as those shown by _Sialia sialis_, _Cyanospiza cyanea_,
_Cœreba lucida_, and the like, do not seem to be susceptible of a like
explanation. The color is too intense and pure to be produced in such a
small space by opalescence. So most authors have simply ascribed it to
some other form of interference, as a thin outer plate, which would seem
on examination to be the true cause. Figure 2, drawn from a section of a
Bluebird’s barb enlarged about one thousand diameters, will give an idea
of the structure found in such cases. The central cells are full of some
dark pigment, probably zoömelanin, while the surface is bounded by a
transparent layer of horn varying from ¹⁄₃₀₀₀₀ to ¹⁄₁₀₀₀₀ of an inch in
thickness. Thus we have a contrivance not ill adapted to the production
of interference colors, the black pigment absorbing all rays which are
not reflected by the horn coat on the outside. Yet there are decided
difficulties in this view. Thin as it is, the outer horn coat is thick
compared to the length of light waves, and again the blue color is
constant. However, in spite of these objections, the color must be
ascribed to the action of the outer coat of cells. The structure of
other bright blue feathers is much the same, though differences in
minutiae exist. Thus the outer layer of cells, the external walls of
which form the outer coat of the barb, are devoid of pigment in the Blue
Jay. (Fig. 3.)
Here it is of interest to note that the barbs of the brown female Indigo
bird differ but slightly from the bright blue barbs of the male. In the
female the pigment is more diffuse, and the outer horny coat is thicker
and less dense and lustrous.
The above feathers with their smooth outer coat are connected with true
iridescent feathers by an intermediate group. I refer to the
highly-colored blue and green feathers of such birds as _Chlorophanes
atrocristatus_ (Fig. 2) and _Cœreba lucida_. In these the ends of the
barbs are enlarged and the barbules reduced to a minimum, after the
manner of the Woodpeckers; unlike them, however, the surface is rough,
each cell being rounded out. When examined under a microscope such barbs
appear as if covered with a mosaic of gems. Sections show, whatever may
be the shape of the barb, that the walls of the iridescent parts are
extremely thin, so thin that exact measurements cannot be made with the
instruments at my disposal. The thickness got when reduced to fractions
of an inch, is approximately ¹⁄₁₀₀₀₀₀₀ of an inch, a film sufficiently
thin for all purposes of interference. Many of these feathers when
magnified show that the color is not uniform, but that all the colors
contribute their quota to the final color. The figure of a section of a
barb of _Chlorophanes atrocristatus_ will give some idea of such a
feather. In this case the final color seems to be the result of mixing
the light reflected from the dark end with that from the yellow
triangular part.
We now naturally come to the true iridescent feathers, of which the
Peacock may be taken as an example. The iridescent barbules are made up
of flat, wonderfully thin cells, arranged end to end, as shown in figure
5. When examined with transmitted light, they are seen to be films full
of a brownish pigment more or less evenly dispersed through the mass.
When cut in sections and looked at on edge they resemble, even under
quite high powers, the edge of a piece of paper. Here we have the most
admirable contrivance for the production of iridescent light, the plates
being fully thin enough, and all white light which may get through the
walls being taken up by the brown pigment within. All the parts of the
eye are constructed on the same plan, and only provided with brownish
pigments, hence the color must be due to variations in the thickness.
Here it is well to notice that the colors are quite constant.
The brilliant colors of these feathers have often been ascribed to
irregularities of surface, the traces of the cell cavities being
mistaken for pits on the surface. That this is an error is at once shown
by examining a section.
Before leaving the subject I cannot refrain from calling attention to
the wonderful diversity of means employed, as well as their complexity
in the production of feather colors. Among the Parrots we have the most
skilful painting combined with accidental colors. Yet all ornithologists
base specific differences on slight variations of color, and this in
spite of the fact that birds may change their color according as they
are wet or dry, owing to the nature of their food, or to slight
differences in the quantity of pigment.
In this they are no doubt often right, but when we come to varieties
based on the very faintest distinctions of color and form, we may well
pause till more is known of avian physiology.
EXPLANATION OF PLATE I.
_Fig. 1._ Diagramatic representation of the effect of a film on light.
_Fig. 2._ Transverse section of a barb of _Chlorophanes
atrocristatus_; Hartnack 3–9 im. the light part yellow, the dark part
dark brown.
_Fig. 3._ Transverse section of a barb of _Cyanocitta cristata_. Hart.
3–9 im.
_Fig. 4._ Same of _Cyanospiza cyanea_ ♂.
_Fig. 5._ Two sections of a barbule of a Peacock.
_Fig. 6._ Section of barb of _Sialia sialis_ much magnified.
ON A COLLECTION OF BIRDS LATELY MADE BY MR. F. STEPHENS IN ARIZONA.
BY WILLIAM BREWSTER.
(_Continued from p. 94._)
33. =Peucedramus olivaceus= (_Giraud_) _Coues_. OLIVE-HEADED
WARBLER.—The Olive-headed Warbler, one of Giraud’s famous “sixteen”
Texas species, has found an unquestioned place in our fauna only on the
strength of three Arizona specimens, taken by Mr. Henshaw at Mount
Graham, in September, 1874. Accordingly, the acquisition of the fine
series catalogued below can scarcely fail to be a matter of much
interest. As will appear from the accompanying data, Mr. Stephens met
with the bird in only a single locality in the Chiricahua Mountains
where it was apparently not uncommon in March: but he writes of a
previous specimen (an adult male) taken among the Santa Catarina
Mountains, in February, 1880, a date which seems to imply that the
species winters in the latter range. His observations throw no light on
its still unknown breeding haunts.
The specimens obtained during the past season were found in pine woods
on the mountain sides at an elevation of from ten to twelve thousand
feet. Although individuals often occurred not far from one another, two
were rarely seen in actual companionship. The only exception to this is
noted under date of March 24, when a small flock was met with on a steep
slope near the summit of one of the mountains. In their actions these
Warblers reminded Mr. Stephens of _Dendrœca occidentalis_. They spent
much of their time at the extremities of the pine branches where they
searched among the bunches of needles for insects, with which their
stomachs were usually well filled. Occasionally one was seen to pursue a
falling insect to the ground, where it would alight for a moment before
returning to the tree above. The only song heard consisted of “a few low
notes” which were rarely uttered, but a peculiar “_cheerp_” was repeated
at frequent intervals.
The examples before me illustrate a fact which I do not find mentioned
by previous writers, viz., that during the first year the males wear a
plumage similar to that of the females. I have three in this condition;
two of them, although in unworn dress, are absolutely undistinguishable
from adults of the opposite sex; the third (No. 77), however, has the
throat appreciably tinged with the brownish-saffron of the adult male.
The females show some variation in respect to the dusky patch on the
side of the head. In most of them it is confined to the auriculars, and
even there is much mixed with yellow; but No. 46 has a continuous,
dull-black stripe extending from the bill through the eye, and spreading
over the auriculars in a broad, well-marked patch. Nos. 94 and 101
differ from the others in having the crown so slightly washed with
olive-green that the whole upper surface is nearly uniform, a condition
which I take to be the immature one of this sex. The adult males show
but little individual variation. Both sexes and all ages have the basal
half of the lower mandible light brown.
44. ♂ ad., Morse’s Mill, Chiricahua Mountains, March 14, Length, 5.10;
extent, 9; wing, 3.12; tail, 2.35; culmen, .56; tarsus, .72.
45, ♂ ad., same locality and date. Length, 5.40; extent, 9.20; wing,
3.16; tail, 2.55; culmen, .55; tarsus, .69. Iris dark brown.
72, ♂ ad., Morse’s Mill, March 19. Length, 5.40; extent, 8.90.
91, ♂ ad., Morse’s Mill, March 24. Length, 5.40; extent, 9; wing, 3.08;
tail, 2.50; culmen, .55; tarsus, .75.
92, ♂ ad., same locality and date. Length, 5.20; extent, 8.90.
102, ♂ ad., Morse’s Mill, March 25. Length, 5.30; extent, 8.80; wing,
3.10; tail, 2.44; culmen, .56; tarsus, .75.
77, ♂ im., Morse’s Mill, March 20. Length, 5.20; extent, 8.90; wing,
3.03; tail, 2.37; culmen, .55; tarsus, .77. In plumage of the ♀.
90, ♂ im., Morse’s Mill, March 24. Length, 5.10; extent, 8.50; wing,
2.85; tail, 2.30; culmen, .56; tarsus, .71. Same remarks.
103, ♂ im., Morse’s Mill, March 25. Length, 5.10; extent, 8.50; wing,
2.90; tail, 2.33; culmen, .57; tarsus, .67. Same remarks.
46, ♀ ad., Morse’s Mill, March 14. Length, 5.20: extent, 8.50; wing,
2.93; tail, 2.35; culmen, .56; tarsus, .73.
47, ♀ ad., same locality and date. Length, 5; extent, 8.30; wing, 2.87;
tail, 2.18; culmen, .58; tarsus, .73.
81, ♂ ad., Morse’s Mill, March 21. Length, 5; extent, 8.50; wing, 2.76;
tail, 2.35; culmen, defective; tarsus, .72.
93, ♀ ad., Morse’s Mill, March 24. Length, 5.20; extent, 8.80.
94, ♀ ad., same locality and date. Length, 5; extent, 8.20: wing, 2.84;
tail, 2.18; culmen, defective; tarsus, .71.
101, ♀ ad., Morse’s Mill, March 25. Length, 5.10; extent, 8.50: wing,
2.87; tail, 2.22; culmen, .58; tarsus, .75.
34. =Dendrœca æstiva= (_Gmel._) _Baird_. YELLOW WARBLER.
210, ♂ ad., Cienega Station, April 16. Length, 5; extent, 7.50; wing,
2.75; tail, 2.20; tarsus, .74. “Iris dark brown; bill dark horn color
above, lighter below; legs pale brown. Common in the migrations.”
35. =Dendrœca coronata= (_Linn._) _Gray_. YELLOW-RUMPED
WARBLER.—Chiricahua Mountains; a single specimen, taken March 26.
From its general dispersion over North America, the Yellow-rumped
Warbler was of course to be expected in Arizona, at least as a visitor,
but I cannot learn that it has been previously detected within the
limits of that Territory. Mr. Stephens, however, sends me an adult
female which must be referred to _coronata_, although it is in some
respects peculiar, if not intermediate between that species and
_auduboni_. The wing-bands are as distinctly separated as in _coronata_
(with females and immature males of both species this character is not
always well-defined), and the throat, generally, is equally white, but
on its left side, adjoining the maxillary line, there is a small patch
of the faintest possible yellow. The light superciliary stripes, which
should be at least indicated in female _coronata_, are also entirely
wanting.
114, ♀ ad., Chiricahua Mountains, March 26. Length, 5.50; extent, 8.70;
wing, 2.98; tail, 2.52. “Iris brown.”
36. =Dendrœca auduboni= (_Towns._) _Baird_. AUDUBON’S WARBLER.
343, ♂ ad., Tucson, May 7. Length, 5.80; extent, 9.52; wing, 3.05;
tail, 2.75. “Iris dark brown; bill and legs black.”
37. =Dendrœca nigrescens= (_Towns._) _Baird_. BLACK-THROATED GRAY
WARBLER.—On April 1, Mr. Stephens secured five males of this species
among the Chiricahua Mountains. The only additional specimens in the
collection are two females taken late in the season (No. 203, ♀ ad.,
Cienega Station, April 15. No. 357, Santa Rita Mountains, May 12.).
38. =Dendrœca townsendi= (_Nutt._) _Baird_. TOWNSEND’S WARBLER.
2.98, ♀ ad., Tucson, April 28. Length, 5.10; extent, 7.70; wing, 2.45.
“Iris dark brown; bill and legs black; soles of the feet yellow. Among
mesquites.”
373, ♂ ad., Santa Rita Mountains, May 13. Length, 5.30; extent, 8.10;
wing, 2.64.
374, ♀ ad., same locality and date. Length, 4.90; extent, 7.40; wing,
2.44. “Iris dark brown; soles of feet yellowish. Water oaks of
foot-hills; very fat.”
Even the most adult males of this species seem to have the
throat-patch slightly sprinkled with yellow. At least I have yet to
see one with the black absolutely pure and unmixed.
39. =Siurus nævius= (_Bodd._) _Coues_ NORTHERN WATER THRUSH.—A single
specimen taken May 4, at Tucson. It was among willows on the borders of
a stream.