fees) DW BON BULLETIN 
Published Quarterly by the 
fe miele Ne Osos sel DUB ON, °S.0:.C, LE TY 
ROOSEVELT ROAD and LAKE SHORE DRIVE, CHICAGO 5, ILL. 
Number 74 June, 1950 
Yellow Warbler Nesting Notes 
By LEE G. JOHNSON 
THE MALE YELLOW warblers arrive from the south at their nesting sites in 
the Rockford area the last week in April, or more often, the first week in 
May, with the females following a few days later. In the last six years my 
sister and I have found many nests of these birds in this area, but it is only 
during the last two years that I have made any systematic study of them 
and taken notes. The observations in this paper are, therefore, confined prin- 
cipally to the years of 1948 and 1949. During that period I took notes on 15 
pairs in their various activities, including nest building, incubation, and 
feeding of the young. Observations were made of at least 10 additional pairs 
that were obviously nesting, but their nests were not located. 
Nesting of 10 pairs of the 15 studied were successful, or partially suc- 
cessful. Man was directly responsible for at least three of the five nest 
failures: one was upset by berry pickers; one disturbed by thoughtless 
people and deserted, and another was torn down by children. One was 
blown down by a storm and one disappeared completely, leaving no trace 
of how it was removed. 
Upon arrival, the male yellow warbler goes immediately to his favorite 
area and selects his territory. He prefers a habitat with willows, alders, 
other young trees, weeds, and low underbrush near water, and usually a 
place away from the habitations of man. 
Somewhere in the territory he selects is a tree taller than the surround- 
ing vegetation. This tree becomes his singing perch, and his song increases 
in frequency and volume until the female arrives. The song continues until 
the nest is built and the eggs are hatched. After the hatching of the young, 
the male parent has less time to sing and instead of mounting on his perch 
to sing, he gives short snatches of song from the lower vegetation while he 
is searching for food. He sings again for a short time after the young have 
left the nest; then he quits entirely. 
The selection of the nesting site takes place after the female arrives. 
The yellow warbler spends most of its time near the ground; therefore, it 
selects a site near the ground. I found the highest nest to be 20 feet, with 
the average about 12 feet. The nest is usually placed in a vertical fork of a 
tree branch, although occasionally it is placed in a horizontal fork or be- 
tween two stems. 
The nest is not started until there is enough foliage to conceal it. Most 
of its construction is done by the female, and she shows the greatest in- 
; (ts) 
