£>6£ Dwight, Plumages of Gulls. [April
THE PLUMAGES OF GULLS IN RELATION TO AGE AS
ILLUSTRATED BY THE HERRING GULL (LARUS
ARGENTATUS) AND OTHER SPECIES.
BY JONATHAN DWIGHT, M. D.
Plates X-XIV
It is nearly a score of years since I placed on record (Auk, 1901,
pp. 49-63) the fact that Gulls and Terns pass through a perfectly
definite series of plumages separated by definite moults. This
record, modified only a little in details, is as applicable today, as
it was then, to the Gulls of the world, and it is only because I have
gathered together new characters for determinibg the age of the
so-called "immature" specimens that I have again brought up
the subject.
While each species has pecularities of plumage at different ages
that are specific, it must be remembered that not all species at the
same age have equally developed plumages, nor do all birds of the
same species at the same age have equally developed plumages.
The large species require a longer time to attain adult plumage
than do the smaller ones; and there is always a percentage, prob-
bably a small one, in every species of laggards or backward birds
that require a longer time in reaching maturity than do the aver-
age individuals. These laggards are a source of confusion and
have been largely responsible for wrong estimates of age and of
the duration of "immature" plumages. They are apparently
about one plumage behind their fellows, but in a series of skins
taken at random, it is hardly possible to do more than guess the
percentage that deviates from the average plumage. At each
successive moult, however, birds advance in their plumage towards
maturity, but not equally. We do find, however, some very defi-
nite characters that are correlated with age, and by combining
them, we find that the smaller Gulls attain fully adult plumage
at their first postnuptial or annual moult, which is at the begin-
ning of their second year, medium sized Gulls, at the beginning of
their third, and large Gulls at the beginning of their fourth year.
The percentage of laggards is apparently greatest at the first period
of moult and progressively diminishes afterwards.
1920 J Dwight, Plumages of Gulls. Zbo
Another source of confusion in the study of Gulls is due to the
fact that different areas of plumage in the same bird advance to-
ward maturity at different paces, although no changes in plumage
save fading occur except at periods of moult. The flight-
feathers of the wings and the quill-feathers of the tail are moulted
but once in the year while the plumzge of the body is moulted
twice, so that evidences of immaturity are lost sooner in the body
plumage. Nor do discrepancies of development stop here for we
may find well developed wings and tail combined with a backward
body plumage or vice-versa. But in spite of complications it is
possible to group together certain characters so that we have defi-
nite plumages representing the average advance made at each
period of moult. It may be well to first take up separately each
of the several characters by which we may judge the age of a given
specimen.
1. Shape of primaries and rectrices. Perhaps the most import-
ant of the characters is the structural difference in the shape of the
primaries and tail-feathers of birds in their first year as compared
with those of a second or later year. My attention was directed
to this by Mr. H. Ira Hartshorn who in making drawings to scale
for me found discrepancies to exist. An examination of specimens
of Gulls of the world shows that throughout the first year, and un-
til the first postnuptial or annual moult, the primaries as a rule
are more pointed and the rectrices more rounded than in later
years. The new second year primaries acquired at this moult,
which removes the juvenal wings and tail, have more rounded,
broader tips than in the first year, being practically the shape of
fully adult feathers. There is some variation, but as a rule in
first year birds, the extreme tip appears to be pinched to a point,
the outer or distal feather usually showing this pecularity more
markedly than the others (see Plate X, fig. l,and Plate XI, fig. 1).
A similar difference in shape prevails in the tail-feathers of Gulls,
first-year or juvenal rectrices being rounded (see Plate X, fig 2,
and Plate XI, fig. 2) and replaced at the first postnuptial moult
by feathers of the second year which are more or less squared at
the tip (see Plate XII, fig. 2). The outer rectrix is perhaps the
most diagnostic and as the wings and tail are moulted only once a
year the value of these characters is great, for many birds after
264 Dwight, Plumages of Gulls. [^pril
the partial prenuptial or spring moult resemble very closely the
second-year birds that have not as yet begun this moult.
2. Pattern of primaries and rectrices.—Next to shape, the pat-
terns that mark the quill-feathers of the wings and tail are of im-
portance. Every species has a definite adult wing pattern, which,
except in the smaller species, is not even foreshadowed in first, and
only occasionally indicated in second-year plumages. The same
thing is true of the tails. The juvenal or first year primaries in
the larger and medium-sized Gulls are as a rule uniformly dingy
or black and the second-year primaries that come at the first
postnuptial moult scarcely differ although the medium-sized
species may have faint indications of "wedges" of a lighter shade
on the inner primaries, obscure apical spots or perhaps a dingy
"mirror" on the distal quill. The small Gulls during the first
year are marked by primaries with more or less dusky areas, but
the adult pattern is usually indicated. After the first postnuptial
moult then, the new primaries of small Gulls are of adult pattern,
those of the larger sized Gulls have a slight suggestion of adult
pattern, while those of the largest Gulls at this period hardly differ
from the first year primaries. The " wedges " develop sooner than
the apical and other spots and the distal primary is the slowest
of them all in acquiring adult characters.
Tails develop a little faster than do primaries, but in the largest
Gulls three moults are required and often four before all traces of
immaturity disappear leaving the tail either pure white or banded
as it is in the adults of some foreign species.
3. Color and pattern of body plumage.—Under this heading may
be included all of the plumage except the remiges and rectrices,
and while there is the greatest divergence between the various
consecutive plumages, the advance towards maturity in most of
the species may be traced through the gradual elimination of the
dusky feathers of youth. As the body plumage undergoes two
moults each year, the advance is rapid, but at the early moults
some brown or dusky feathers are acquired that differ little if any
from those that precede them and these immature feathers are
often a ready clue to age. The moults of young birds are pro-
tracted and the postjuvenal overlaps the prenuptial. Small Gulls
at the postjuvenal moult in the autumn acquire a considerable
!920 ] Dwight, Plumages of Gulls. Zo5
part of their adult body plumage, and they assume at the first
prenuptial moult a plumage that is adult save for wings and tail
and finally through the first postnuptial moult they become fully
adult. Larger Gulls are quite or very nearly adult in body
plumage after the second postnuptial moult but the largest are
usually not in full adult dress until after their third postnuptial
moult.
4. Colors of bill and feet.—The bill is not only rather slow in de-
veloping color, but the color often varies between winter and sum-
mer. Doubtless there is much more to be learned from fresh
birds but museum specimens show indications of immaturity in
dark bands and dusky cloudings up to the third and possibly
fourth year in the larger species while in the smaller, the time
varies from perhaps less than a year to one or two years as the
size increases.
The color of the feet and tarsi and eye-ring (the iris too) may be
studied successfully only in fresh birds for these parts change
color as skins dry so that no clue to their original color remains.
In young birds the colors are, as a rule, pale deepening with age
to the more brilliant tints or deeper shades of maturity.
It has been my endeavor to show the characters as we find them
in average birds and it is difficult not to blur the picture with too
many details of exceptions. It is no easy matter to pick out typi-
cal average birds even with large series to choose from but the
accurate sketches by Mr. Hartshorn of wing tips and tails speak
for themselves. In explanation of them I will first give a brief
diagnosis of the plumages of a small species, Bonaparte's Gull
(Lams Philadelphia) which acquires adult plumage at its first
postnuptial moult and then of a large species, the Herring Gull
(Larus argentahis) which does not acquire adult plumage until its
third postnuptial moult, some few specimens retaining slight evi-
dences of immaturity even until the fourth.
Larus Philadelphia. Bonaparte's Gull.
1. Natal Down. Wholly a body plumage and like most Gulls at this
stage, the downy chick is whitish or buffy brown clouded with large and
small dusky spots.
266 Dwight, Plumages of Gulls. [April
2. Juvenal Plumage. Primaries, pointed, largely white, the tips and
outer webs in part, black (Plate X, fig. 1). Tail with rectrices rounded
at tips, white, banded subterminally with black (Plate X, fig. 2). Body
plumage has much to suggest the adult being chiefly white below but the
upper surface is washed and clouded with browns. Bill, pale with dark
tip.
3. First Winter Plumage. A partial postjuvenal moult in the late fall
replaces many of the brown feathers by adult gray ones, but a number of
mixed ones may also come in. The juvenal wings and tail remain.
4. First Nuptial Plumage. A partial first prenuptial moult in the late
winter brings the body plumage a little nearer to that of the adult, the
browns being farther diminished.
5. Second Winter Plumage. The first postnuptial moult produces the
adult plumage except in a very small number of backward buds. The
primaries are rounded with the white areas larger (Plate X, fig. 3). The
tail has square tipped rectrices and is pure white (Plate X, fig. 4). After
this moult, only an occasional bird shows traces of immaturity in slight
smudging of the tail or in duskiness of the primaries.
Larus argentatus. Herring Gull.
1. Natal Down. At this stage only body plumage is found which is
grayish or buffy, coarsely mottled or clouded with dull clove-brown.
2. Juvenal Plumage. Primaries, pointed and dull brownish black.
(Plate XI, fig. 1). Rectrices, rounded at tips, dull brownish black, vari-
ously but coarsely mottled with white, especially on the outer feathers
and basally. (Plate XI, fig. 2.) Body plumage, mostly grayish or sooty
brown irregularly mottled and barred with buff, the markings coarsest on
the upper surface, the lower parts being of a more uniform grayish brown.
Bill, black.
3. First Winter Plumage. More or less of the body plumage is renewed
by a partial postjuvenal moult which may be delayed until well into the
winter. The new growth resembles the old, but it usually shows less mot-
tling, the color areas being larger and less broken up. The juvenal wings
and tail remain.
4. First Nuptial Plumage. A partial prenuptial moult renews some of
the now worn and faded body plumage, brown feathers, much like those
of the juvenal or first winter stages, growing for the third time. The bill
during the winter slowly grows paler at the base, the extent of the black
diminishing. The postjuvenal and the prenuptial moults seem to overlap,
the former often being delayed and perhaps in some cases suppressed, but
as brown feathers mark all renewals during the first year, many specimens
of this period appear superficially at least to be in juvenal plumage.
5. Second Winter Plumage. The result of a complete first postnuptial
moult. Primaries, rounded and dull black, indistinct " wedges "showing
!920 J Dwight, Plumages of Gulls. 267
on several of the proximal (Plate XII, fig. 1)). Rectrices, square-tipped
and dull black, more finely peppered or sprinkled with white than in the
first winter. (Plate XII, fig. 2). Body plumage, much like the first win-
ter, but usually whiter below and about the head and with a few gray
feathers on the back. Bill, black from tip to nostrils, the base pale and
yellowish in dried skins.
6. Second Nuptial Plumage. A partial second prenuptial moult renews
some of the body plumage, birds becoming much whiter below and grayer
on the back. Many of the new feathers, however, are still brown or parti-
ally so.
7. Third Winter Plumage. A complete second postnuptial moult wid-
ens the field for variation because pattern is now pronounced in the pri-
maries (Plate XIII, fig. 1). They are black with more or less white
tipping, a "mirror," often with blurred margin, of variable extent is
found on the "first" or distal, and gray "wedges" of greater or lss extent
appear. The tail also shows new pattern (Plate XIII, fig. 2), smudges of
black on the white rectrices varying greatly in extent. In some birds the
red spot on the bill appears indistinctly but as a rule a dusky band or
clouding is found. The body plumage is either adult or there may be a
few obscurely dusky areas on the outer surface of the wings.
8. Third Nuptial Plumage. A partial third prenuptial moult is hardly
noticeable among the body feathers that are already mostly adult.
9. Fourth Winter Plumage. After the third postnuptial moult, which
is of course complete, it is unusual for evidences of immaturity to remain.
The primaries (Plate XIV, fig. 1) are all white tipped and the "mirror"
on the first is large and clearly defined, sometimes merging with the white
tip, although it is possible that such specimens are still older. A white
spot may or may not be found on the next primary, and the "wedges"
are more extended but vary with each primary. The tail is now wholly
white (Plate XIV, fig. 2). The body plumage is fully adult. The bill is
bright yellow with a red spot at angle of mandible.
So it is possible to trace the development of plumages in the
Gulls with considerable accuracy and it is a pity to see writers of
recent date still clinging to the inadequate term "immature,"
and to the old-fashioned idea that many years are required to
attain adult plumage. With moulting specimens to bridge the
gaps between plumages and knowing the characters that develop
in sequence much can be learned about age and it is with such ma-
terial at hand that I have endeavored to show as briefly as the
conditions permit, the correlation that exists in the Gulls between
plumage and age.
Taking the Gulls of the North American Check List, they may
be grouped as follows:
Zibo Swarth, Races of Branta canadensis. [April
1. Two-year plumage-cycle (like Larus Philadelphia):—Xema
sabini, Rhodostethia rosea, Larus minutus, Larus franklini, Larus
atrieilla, Rissa brevirostris and Rissa tridactyla.
2. Three-year plumage-cycle:
—
Larus hecrmanni, Larus canus,
Larus brachyrhynchus, Lams dclawarensis and Pagophila alba.
3. Four-year plumage-cycle (like Larus argentatus):—Larus cali-
fornicus, Larus vegae, Larus affinis, Larus occidentalis, Larus schis-
tisagus, Larus marinus, Larus nelsoni, Larus kumlieni, Larus glau-
cescens, Larus leucopterus and Larus hypcrboreus.
JiS W. 70th Street, New York, N. Y.
THE SUBSPECIES OF BRANTA CANADENSIS (LINNAEUS) 1
BY H. S. SWARTH
In the January, 1920, issue of 'The Auk' (pp. 94-102) Mr. J. D.
Figgins has a paper on "The Status of the Subspecific Races of
Branta canadensis." This paper is devoted in large part to severe
criticism of a publication of my own upon the same subject. 2 I
could not possibly take exception to Mr. Figgins for differing from
me in matters of opinion, nor for publishing his conclusions. I am,
however, perfectly justified in feeling resentful at the ungracious
wording of his argument. I object to such statements, for ex-
ample, as that measurements I have taken are unreliable and that
I have suppressed such measurements as did not answer my pur-
pose. I object to having statements ascribed to me that I did
not make. I object to having statements of mine "interpreted"
—I do not think they need it.
Before discussing in detail some of the statements he has made,
it is best, perhaps, to give Mr. Figgins' conclusions, then some of
my objections to them. He says finally: "It is, therefore, pro-
posed that 'hutchinsi' and (occident(dis , be eliminated as subspecific
forms, that minima be raised to specific rank and that the occas-
^ontribution from the Museum of Vertebrate Zoology of the University of
California.
2 A study of a collection of geese of the Branta canadensis group from the San
Joaquin Valley, California. Univ. Calif. Publ. Zool., vol. 12, 1913, pp. 1-24, pis.
1-2, 8 text figs.