different from that of any other species of its group. A typical nest
(in the Thayer collection in Cambridge) is made mainly of a brown lichen
or moss mixed with other lichens and mosses, bud scales, flower scales,
and some plant down, reinforced with fine yellowish rootlets. All these
are compactly worked into and supported by the living needles of the
yellow pine in which the nest was built. The lining consists of plant
down and finer strands of the same yellowish rootlets. It measures 3-1/2
by 3 inches in outside diameter and 2-1/2 in height; the inner cavity is
about 2 inches in diameter and 1-1/4 inches in depth.
_Eggs._--Three or four distinctive eggs seem to constitute the full set
for the northern olive warbler. These are ovate to short ovate and have
a very slight lustre. They are grayish or bluish white, or even very
pale blue, liberally speckled, spotted and blotched with "dark
olive-gray," "dark grayish olive," "drab," "olive-brown," or "dark
brownish drab." These are interspersed with undertones of "mouse gray,"
"deep mouse gray," or "Quaker drab." On some eggs the spots are sharp
and distinct, while on others the olive, brown, and drab markings are
clouded into the undertones. The spottings are usually well scattered
over the entire surface, but tend to become heavier at the large end.
The measurements of 28 eggs average 17.1 by 12.8 millimeters; the eggs
showing the four extremes measure =19.0= by =16.0=, =16.0= by 12.2, and
18.1 by =12.0= millimeters (Harris).
_Young._--Information is lacking on incubation and care of the young.
_Plumages._--The plumages and molts of the olive warbler are as
distinctive as its nest and eggs. The sexes are not quite alike in
juvenal plumage. Ridgway (1902) describes the young male as "pileum,
hindneck, back, scapulars, rump, and upper tail-coverts plain dull olive
or brownish olive; supra-auricular region and sides of neck dull
yellowish buffy, the latter tinged with olive; chin, throat, and chest
dull yellowish buffy; otherwise like adult female." And of the young
female, "similar to the young male but paler and grayer above;
supra-auricular and post-auricular regions pale brownish buffy; chin,
throat, and chest still paler buffy, the chin and upper throat dull
buffy whitish." The white tips of the greater wing coverts are tinged
with yellowish.
I have not been able to trace the postjuvenal molt in the series I have
examined but it apparently occurs in July and produces very little
change, young birds of both sexes in their first winter plumage closely
resembling the adult female at that season, though the crown and nape
are grayer and the throat and breast are paler. I can find no evidence
of a prenuptial molt. Young males evidently breed in this plumage and do
not acquire the fully adult plumage until their second fall, or perhaps
later. In Brewster's series, collected in March, three males are in this
condition, of which he (1882) says that "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." This last may be a bird that is one
year older, for Ridgway (1902) describes the "second year" male as
"identical in coloration with the adult female." Judging from the series
that I have examined, including all of Brewster's birds, I am inclined
to think that the adult winter plumage is acquired at the first
postnuptial molt, or when the bird is a little over one year old.
There can be no doubt, however, that young males breed in this immature
plumage, for Price (1895) secured a pair that were feeding a brood of
young, and the "male was not in fully adult plumage and was very similar
in coloration to the female." Swarth (1904) writes: "The male bird
breeds in the immature plumage, for on June 21, 1902, I assisted O. W.
Howard in securing a nest, containing four eggs, the parents of which
were indistinguishable in color and markings. * * * I was surprised at
the large proportion of birds in this immature plumage that were seen.
At a very liberal estimate I should say that the males in adult plumage
comprised barely a third of the birds seen in the spring."
Adults have a complete postnuptial molt, mainly in July; all June birds
that I have seen are in worn plumage, and August and September birds are
in new, fresh feathers. The fall plumage of the male is similar to that
of the spring male, but the colors of the head, neck, and chest are
duller, more clay color, the back is more olive and the sides are
browner. In the female at this season the crown is tipped with grayish
and the throat and breast with buffy, while the sides are browner than
in the spring; the white tips of the greater wing coverts are tinged
with yellowish. The nuptial plumage is acquired mainly, if not entirely,
by wear, the edgings wearing away and the colors becoming brighter.
_Food._--Nothing definite seems to have been recorded on the food of the
olive warbler, but its habit of creeping over the branches and twigs of
the pines, much after the manner of the pine warbler, would seem to
indicate that it was foraging for the many small insects that infest
these trees. It is evidently one of the protectors of the pine forests.
Brewster (1882b) says: "In their actions these Warblers reminded Mr.
Stephens of _Dendroeca 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."
_Behavior._--One of the members of Henshaw's (1875) party brought in a
specimen of this warbler, on September 20, "which he stated he had shot
from among a flock of Audubon's Warblers and Snowbirds, which he had
started from the ground while walking the pine woods. With the rest, it
had apparently been feeding upon the ground, and had flown up to a low
branch of a pine, where it sat and began to give forth a very beautiful
song, which he described as consisting of detached, melodious, whistling
notes."
W. E. D. Scott (1885), writing of his field work in the Santa Catalina
Mountains in late November, says:
Associated with flocks of the Mexican Bluebird (_Sialia, mexicana_),
which was, by the way, the only kind of Bluebird observed, was always to
be found one and sometimes two representatives of the Olive Warbler
(_Peucedramus olivaceus_). The Bluebirds were generally feeding on some
insects in the tall pines, in flocks of from six to ten individuals. The
Olive Warblers were on the best of terms with their blue friends, and as
the Bluebirds were shy and restless they made it difficult to obtain or
observe very closely their smaller allies. I did not in these pine woods
see the two species apart, and became at length so well aware of the
intimacy that existed between them, that I would fire at any small bird
passing high overhead in company with Bluebirds. They were chance shots,
certainly, but the only two small birds obtained flying in this way with
the Bluebirds were Olive Warblers. * * * Generally they preferred the
largest branches of the pines when they alighted, though I took one not
more than three feet from the ground in a small bush. Their movements
while feeding or searching for food are very deliberate, though I
noticed now and again certain motions when at the extremity of a bough
that reminded me of a Kinglet or a Titmouse.
Swarth (1940) says: "Though frequenting the tree tops to a great extent,
they seem singularly tame and unsuspicious, and several times I have had
one feeding in some of the lower branches, within arm's reach of me,
without its showing the least sign of fear."
_Voice._--The olive warbler has a rather loud, attractive, and
distinctive note, but few observers have referred to it as a song. The
"beautiful song" mentioned above consisted of "detached, melodious,
whistling notes."
One of its whistling notes sounds very much like the _peto_ note of the
tufted titmouse and might easily deceive the listener. Scott (1885)
observed that these warblers "had a call-note so like that of their
associates [the bluebirds] as to be almost identical. It seemed to me
only a clearer whistle of more silvery tone." Price (1895) saw a male
alight on a twig near his mate, during nest-building, uttering "a liquid
_quirt, quirt, quirt_, in a descending scale." Mr. Henshaw (1875) heard
"a few strange Vireo-like notes coming" from an olive warbler. A bird
that Dr. W. P. Taylor (MS.) watched in apparent courtship gave "a
whistled call with descending inflection."
_Field marks._--In general appearance and behavior the olive warbler
suggests the pine warbler, especially as it creeps over the pines. The
orange-brown head, neck, and breast of the adult male, with the
conspicuous black band through the eye, is distinctive; these colors are
much paler and more yellowish in the female, and the band through the
eye is grayish. Both adults have two white wing bars, a white area at
the base of the primaries and much white in the tail, the white areas
being more restricted in the female. Young birds are much like the
female (see descriptions of plumages).
_Winter._--The olive warbler, as a species, is probably permanently
resident throughout most of its Mexican and Central American range. But
the northern olive warbler is evidently partially migratory, though some
individuals, perhaps many, remain in Arizona during part, or all, of the
winter. All of the 15 specimens taken by Stephens for William Brewster
(1882b) were collected in March, probably too early to be migrants, and
he says that Stephens had previously taken one in February 1880,
evidently a wintering bird. Mr. Swarth (1904) writes: "I have not found
this species very abundant in the Huachucas at any time, but it is
probably resident to some extent, for I secured an adult male on
February 21 when the snow was deep on the ground. During March I saw
several more, all adult males and single birds, usually with a troop of
Pygmy Nuthatches; but it was not until the first of April, when the
other warblers were arriving, that they became at all abundant." Scott
(1885) found them on the Catalinas under winter conditions, with snow on
the ground, and says: "I think there can be little if any doubt that
they are residents all the year." And Dr. W. P. Taylor (MS.) took one in
the Santa Ritas on February 4, 1923. Just how far south go the birds
that migrate away from Arizona does not seem to be known, but apparently
they have not been detected beyond Chihuahua and Tamaulipas. Perhaps
they do not migrate at all.
DISTRIBUTION
_Range._--Southwestern United States to northern Nicaragua.
_Breeding range._--The northern olive warbler breeds =north= to central
Arizona (Baker's Butte and White Mountains) and central western New
Mexico (Reserve). =East= to western New Mexico (Reserve and McKnight's
Canyon); Chihuahua (Colonia García); southeastern Coahuila (Diamante
Pass); and southwestern Tamaulipas (Miquihuana). =South= to southwestern
Tamaulipas (Miquihuana) and southern Durango (Durango). =West= to
Durango (Durango); Sonora (Sierra Saguaribo); and southeastern and
central Arizona (Huachuca Mountains, Santa Catalina Mountains, and
Baker's Butte).
Other races occur in southern Mexico and Central America.
_Winter range._--The northern olive warbler is probably migratory to
some extent, individuals withdrawing to the southern part of the range,
but it is found in winter occasionally or in small numbers as far north
as southern Arizona.
_Egg dates._--Arizona: 14 records, May 23 to July 1; 7 records, June 2
to 18, indicating the height of the season.
DENDROICA PETECHIA AESTIVA (Gmelin)
EASTERN YELLOW WARBLER
PLATES 24, 25
HABITS
The familiar yellow warbler, also commonly called the summer yellow bird
or wild canary, is the best known and the most widely known of all of
our wood warblers. It is one of the few birds that almost everybody
knows by one of the above names. It is universally beloved as it comes
to us in the flush of budding spring, gleaming in the shrubbery, like a
rich yellow flame among the freshly opening leaves, or bringing to the
apple orchards a flash of brilliant sunshine to mingle with the
fragrant blossoms. As Dr. Chapman (1907) says: "In his plumes dwells the
gold of the sun, in his voice its brightness and good cheer. We have not
to seek him in the depths of the forest, the haunt of nearly all his
congeners, he comes to us and makes his home near ours."
The yellow warbler, as a species, is also the most widely distributed
member of its family. Its breeding range extends from the Atlantic to
the Pacific in both Canada and the United States (110 degrees of
longitude), and from the Barren Grounds in northern Canada to Mexico and
the Gulf States (40 degrees of latitude). Its winter range covers 54
degrees of longitude and 31 degrees of latitude in Central and South
America. Professor Cooke (1904) says: "The extreme points of the yellow
warbler's range--northern Alaska and western Perú--are farther separated
than the extremes of the range of the black-polled warbler, which is
considered the greatest migrant of the family." But it must be
remembered that the yellow warbler breeds much farther south than the
black-poll.
_Spring._--The spring migration of the yellow warbler is long and
partially circuitous; eastern yellow warblers that winter as far east as
British Guiana probably make a roundabout flight to Central America, as
there seem to be no springtime records for this bird in the West Indies
and few for it in Florida. These birds may fly across the Gulf from
Yucatán to Cuba and Florida, but the main flight is probably directly
north from Yucatán to Louisiana and other points on the Gulf coast; they
have been repeatedly seen flying northward in the middle of the Gulf.
There is also a considerable migration along the coast of Texas, which I
have personally observed.
The migration is also prolonged or very irregular, for according to the
dates of departure given to me by Alexander F. Skutch (see under
_Winter_), the last of these warblers do not leave Central America until
the very last of April, or the first of May, after the first arrivals
have reached New England; some of these records, however, may apply to
one of the western races. After the birds reach the United States, the
migration fans out northward and northeastward and seems to be more
rapid. Of this Frederick C. Lincoln (1939) says: "Coming north from the
Tropics these birds reach New Orleans about April 5, when the average
temperature is 65° F. Travelling on northward much faster than does the
season, they reach their breeding grounds in Manitoba the latter part
of May, when the average temperature is only 47°. Encountering
progressively colder weather over their entire route, they cross a strip
of country in the 15 days from May 11 to 25 that spring takes 35 days to
cross. This 'catching up' with spring is characteristic of species that
winter south of the United States and of most of the northern species
that winter in the Gulf States."
_Territory._--Soon after their arrival on their breeding grounds the
males begin to select their territories and then to defend them. Dr. S.
Charles Kendeigh (1941) made a study of the territories of birds in a
prairie community in northwestern Iowa, and writes:
A special study of the Yellow Warbler indicated that territorial
requirements included suitable nest-sites, concealing cover, tall
singing posts, feeding areas in trees, and space, and that when certain
of these factors were lacking, territorial relations became confused and
the behavior of the birds was modified. * * * These warblers possessed
territories that averaged about 150 feet in diameter, or approximately
two-fifths of an acre. Even in locations where trees were included, the
territories appeared to be of about the same size. The limits of the
territory often did not coincide with the boundaries of the thicket in
which the nest was located but extended over the neighboring grassland
and often included parts of neighboring thickets. These territories were
defended by the males partly by singing, although in shrubby areas
lacking trees they were handicapped by lack of singing posts from which
to proclaim their ownership and to advertise themselves. A few made use
of fences from which to sing and also of tall posts and wire from an
abandoned electric line that extended through the area. The rôle of the
female in defense of territory was not determined.
Probably due to this lack of singing posts and to the unusual abundance
of birds, chasing was also extensively used as a defense measure, and
during the height of the nesting season squabbling birds were a common
sight all over the area. * * * Neighboring males seemed to lack any
conception of the limits of each other's territories and moved about
indiscriminately until chased out. No actual fighting was observed.
* * * In other parts of the area where trees were available, the males
commonly sang at a height of 18 feet, often up to a height of 45 feet,
and chasing was not often observed.
For yellow warblers observed by Wendell P. Smith (1943) at Wells River,
Vt., "territorial exclusiveness scarcely existed. In one season a
Chestnut-sided Warbler's nest was located within five feet of that of
the Yellow Warbler. The following species were represented by one
nesting pair within a radius of thirty feet: House Wren, Catbird, Black
and White Warbler, Chestnut-sided Warbler, Northern Yellow-throat and
Indigo Bunting. Unless another individual came very close to the nest,
no hostility was shown by either male or female. Too close an approach
would bring a swift attack by one or the other, however, but for only a
short distance when the pursuer would give up the chase."
A. D. Du Bois mentions in his notes a nest that was about 6 feet from
the door of a screened porch in daily use and tells the following story
about the territory involved: "Twelve yards south of this nest was a
spruce tree. On several occasions the male met another male at this tree
or beyond it. Both alighted at times in the treetop. Their boundary
arguments had the appearance of pushing-contests in the air; and
sometimes the contestants revolved in the air, about an imaginary axis
between them. Once, while one of the warblers was in the tree, the other
was seen to poise near the tree on fluttering wings, remaining for two
or three seconds as nearly stationary in the air as a hummingbird.
Twelve yards beyond the spruce I found a nearly completed nest in tall
lilacs; but this nest was not finally occupied." Apparently, a second
pair of warblers had tried to build a nest too near the territory of the
first pair and had been driven out of the territory.
_Courtship._--Mr. Smith (1943) says on this subject:
Courtship begins soon after arrival of the species. Within a period of
from four to six days greatly increased singing is noted which marks its
inception. Persistent and lively pursuit of the female by the male was
observed, taking place within a restricted area (once within a radius of
thirty feet). From one to four days elapsed before courtship was
completed. Sexual union may not take place until nest building begins as
the following observations in 1938 tend to show. Pursuit of the female
began on May 23, continued on the 24th but frequent attempts at
intercourse on the part of the male were unsuccessful. On the 26th
copulation was seen to take place and on that date the nest was
completed. * * * A period of several days intervened between nest
completion and egg laying. During two seasons of rather intensive
observation, this was two days.
_Nesting._--Although we have come to regard the yellow warbler as a
sociable and friendly little bird that seeks our company and builds its
nest in the shrubbery about our homes, often close to our houses or in
the bushes under our windows, such were not the original nesting sites
and even now are far from being the commonest situations chosen,
although they may seem the most evident.
The favorite nesting sites in southern New England are along small
streams and brooks, around the borders of swamps and ponds and lakes, or
in the more open brushy swamps (where the land is moist but not too wet)
among willows, alders, elderberry and blueberry bushes, and other
moisture-loving shrubs and small trees. They also nest in drier
situations, in shrubbery about open spaces, along brush-grown fences and
hedgerows and roadside thickets, or in cut-over lands grown up to
sprouts and to thickets of wild raspberry, blueberry, and other bushes.
In such situations the nest is built in an upright fork or crotch of a
bush or sapling, seldom over 6 or 8 feet from the ground or less than 3.
Nests are sometimes built at higher levels in apple trees in orchards or
in small trees about houses but rarely as high as 30 or 40 feet. Near
human habitations, clumps of lilac bushes, often close to windows or
doors, are decided favorites, while various kinds of ornamental shrubs
about our gardens or grounds also provide suitable nesting sites.
Mr. Du Bois has sent me the data for 30 nests of the eastern yellow
warbler found in Minnesota, Illinois, and New York. Among these, 4 were
in willows, 3 each in lilacs and alders, 2 each in elms and boxelder
saplings, and 1 each in a grapevine, an ash sapling, a spirea bush, and
a currant bush. One of these latter, in an unspecified bush, was 14 feet
from the ground, and another, in a wild grapevine climbing on a tree
beside a coalbin, was 8 feet from the ground; those in the elms were 12
and 14 feet, respectively, from the ground. The remainder were mostly 5
feet or less above ground, the lowest being at a height of 2 feet, in a
currant bush near a vegetable garden. He tells of a nest that was built
in a wild rose bush at the edge of a small run near his vegetable
garden; "this nest was so compactly fabricated as to hold water for some
time; I saw about one-fourth inch of water standing in the bottom of it
after a heavy rain."
On two occasions, he has found the new nest to have been built on top of
the old nest of the previous year.
F. G. Schrantz (1943) has published the results of a careful study of 41
nests of the eastern yellow warbler in Iowa, during 1938 and 1939, on
the restricted grounds of the Iowa Lakeside Laboratory. Among those at
heights from 1-1/2 to 5 feet from the ground were 27 in wolfberry bushes
(_Symphoricarpos occidentalis_), 8 in young saplings of boxelder (_Acer
negundo_), 2 in wild gooseberry (_Ribes gracile_), 1 in wild currant
(_Ribes floridum_), and 1 in an introduced species of honeysuckle. One
nest was in a cottonwood at a height of about 10 feet, and another in a
boxelder about 15 feet above ground.
Dr. Roberts (1936) says that in the prairie regions of Minnesota, where
underbrush is scarce, the yellow warblers build their nests in the
cottonwoods in the tree-claims, "against the trunks of the large trees,
supporting them on small lateral branches and twigs. * * * These
arboreal nests are often fifteen to twenty-five feet from the ground and
occasionally still higher." And in the huge cottonwood trees along the
river, he has seen nests placed at elevations of 40 to 60 feet. Others
have also recorded nests at heights of 40 and 60 feet.
In Dr. Kendeigh's (1941) prairie community, "twenty out of twenty-nine
nests were placed in buckbrush, with the rest in boxelder, lilac,
willow, or currant. The buckbrush is a low bush usually three or four
feet high, growing in rather dense thickets in the open, especially in
grassy areas of _Poa_ and _Agropyron_. Nests placed here varied between
two and three feet above the ground. The nest found closest to the
ground (18 inches) was, however, in a small boxelder. In taller shrubs
and trees, the nests were found up to about seven feet above the
ground."