CALIFORNIA YELLOW WARBLER. Dendroica aestiva brewsteri
size of Junco. Yellow color predominating; no black or white markings
whatsoever. Male: Clear yellow beneath (narrowly streaked with chestnut,
but this not discernible at a distance); upper surface greenish yellow.
(See pl. 9c). Female and young: Pale yellow beneath, unstreaked;
upper surface dull greenish yellow. Movements quick and nervous; hops
along small branches in zigzag course. Voice: Song of male very
high pitched, piercingly shrill, 4 or 5 sharply enunciated notes
followed by quick series of shorter ones; call note a sharp
visitant at both bases and on adjacent lower slopes of Sierra Nevada,
extending up through the Transition Zone. Recorded from Snelling and
near Lagrange eastward to Yosemite Valley; and again about Mono Lake.
Chiefly in cottonwoods and willows along streams, foraging up to 40 feet
from the ground; nests in same general surroundings, but usually less
than 15 feet from ground. Solitary.
Long ago the appellation "summer yellow bird" was
given to the Yellow Warbler in recognition of its clear yellow
coloration and of the fact that it comes to our latitudes only during
the warmer months of the year. The species is well represented in the
Yosemite section from late spring until early fall, and is found from
Snelling and Lagrange eastward to Yosemite Valley, and again, east of
the mountains, near Mono Lake. Everywhere it exhibits a strong
preference for deciduous trees near streams.
The California Yellow Warblers which are to nest on
the west slope of the Sierra Nevada arrive there some time before those
individuals destined to nest east of the mountains reach their
particular haunts. Thus yellow warblers were already present in Yosemite
Valley on April 28, 1916, while in the same year the species was not
noted near Mono Lake until May 19. The fall departure takes place toward
the end of August. The birds do not wander to the higher zones, as do
the Lutescent Warblers, for example, but leave their nesting haunts
rather early for the lowlands to the west, en route to their winter
quarters to the south of the United States. Our own latest definite
record for Yosemite Valley was made on August 19 (1915), but Mr. Joseph
Mailliard (1918, p. 19) states that in 1917 the species was present
until somewhat later, disappearing in early September. In 1920 the last
seen by Mr. C. W. Michael (MS) in the Valley was noted on September
Numerically the Yellow Warbler is an abundant bird
within its restricted environment. Fully 20 were seen or heard during a
4-hour census taken in Yosemite Valley on May 31, 1915. These were
practically all in the cottonwoods, alders, willows, and in other
deciduous growths near the Merced River or its tributary streams.
Similarly, along the lower reaches of the big rivers where these emerge
from the foothills, these birds are plentiful in the month of May.
The song notes of the California Yellow Warbler are
shriller than those of any of our other warblers, and, indeed, are
exceeded in height of pitch by the notes of only a very few birds. This
feature alone is often sufficient to identify the song. Syllabification
can do little more than indicate the theme of the song, for the notes
are well above those of the human voice. Wee, wee, wee, sit, sit,
sitsitsit, sieu, is one of our renderings; and chee, chee, chee,
chee-e-e-e-e-e-er another. The call note is a loud chip or
tsip. Song is not heard often after the first part of July, but
there may be a partial revival of singing in the latter part of August
just before the birds depart for the season.
Yellow warblers like many other birds have definite
forage beats which they traverse repeatedly through the day. This was
well illustrated by observations on a bird of this species seen at
Chinquapin in mid-May, 1919. A small black-oak sapling had grown up
through the sea of chaparral near our camp and from time to time this
tree would be occupied, momentarily, by a California Yellow Warbler. The
bird always arrived from a certain direction (coming from another
similar station) and upon departing went to still another definite tree
situated about 50 yards distant.
Nesting with the California Yellow Warbler begins
soon after the birds arrive in the region, our earliest record being for
May 29 (1911); on this date, in Yosemite Valley, a female was flushed
from a nest containing four eggs. Two nests seen on June 5, 1915, at
Smith Creek, east of Coulterville, each contained young a few days old.
Nest construction in each of these instances must have commenced in the
middle or early part of May. June marks the height of the nesting season
for the Yellow Warblers here; in this month the greatest number of nests
comes to attention. An adult was seen feeding young recently emerged
from the nest, on July 24 (1915) in Yosemite Valley. This instance
marked about the close of the nesting season. The one nest found east of
the mountains (near Williams Butte) was only under construction on June
Yellow warblers nest abundantly on the floor of
Yosemite Valley. Some of the nests are in growths close to water,
whereas others are located in brush tangles or other rank growths back
some distance from the streams. A nest found June 7, 1915, may be taken
as fairly typical. It was 52 inches above the ground in the crotch of a
forking stem of a chokecherry which grew in a clump of the same plant,
and was shaded by a black oak. As usual it was higher than wide outside,
being 3-1/2 inches in height by 3 to 3-1/4 inches in diameter. The
cup-like cavity was 1-3/4 inches across at the top and the same in depth
at the center. Shreds of bark and flat plant fibers were the principal
materials used in construction, the lining being of horsehair and a few
When found, this nest contained three eggs; the
following day a fourth was laid. During our first approach to the nest
on the 7th, both male and female were about and voiced their alarm.
Returning to the nest later that day we noticed only the female. She
departed at once, dropping close to the ground and then speeding off
through the underbrush. A nest of this species probably used in the
previous year was seen 8 feet away in another cherry bush and 36 inches
above the earth. Still another occupied nest was seen 7 feet above the
ground in a small incense cedar, close to a well traveled road.
One of the nests found at Smith Creek on June 5,
1915, was 4 feet above ground in a chokecherry bush and near the stream.
It was 2-1/2 inches in diameter and 4 inches in outside height, and was
made of plant fibers and feathers. There were 3 young, about 2 or 3 days
old, and one unhatched (evidently infertile) egg. The other nest was 4
feet above the ground in a mountain lilac (Ceanothus
integerrimus). it also contained young, 4 in this instance, and not
over 3 days from the shell. The parents of this brood were
tsip-ing excitedly about 30 to 50 feet from the nest.
None of the nests just mentioned was watched until
the young emerged; but observations on still another nest, in Yosemite
Valley, help to complete the story. This nest was found by Miss Margaret
W. Wythe (MS), who watched it at intervals from June 13 to 27, 1915. It
was placed about 15 feet above the ground in a small pine tree growing
at the margin of a pond. It rested on the next to the topmost whorl of
branches and one side was against the slender trunk of the tree. On June
23, the male was seen with his bill full of 'green worms.' The young
left the nest on or before June 27; on that day they were perched in
adjacent shrubbery while being fed at frequent intervals by the parents.
No more than three young birds were seen at any one time.
But little is to be seen of the yellow warblers after
the young are grown. They then take to foraging, individually and
unobtrusively. Soon the molt with its quieting influence comes on, after
which the birds slip off southward for the winter.