ice (1929:17) mentions a
similar decrease in singing when the temperature exceeded 85 deg. F.

Passerine birds typically sing at a high rate throughout courtship and
nestbuilding, but at a markedly lower rate thereafter. Most vireos are
atypical in this respect. In the study area in 1960 Bell Vireos sang
more often than Robins, Mockingbirds, Field Sparrows, Brown Thrashers,
Catbirds, and Doves breeding in the same habitat, about as often as
the Meadow Larks in the adjacent fields, and less often than Painted
Buntings.

The Bell Vireo seems to sing less often in the undisturbed state than
when aware of the presence of an observer. Observations from my car,
at a site approximately equidistant from territories 1 (1960), 2
(1960), 4 (1960), and 6 (1960) indicate that the rate of song during
incubation is decidedly less when no disturbing influence is present.
Normally, in this period, song aids in maintaining contact between the
members of a pair, serving to locate the male as he forages. Mumford
(1952:230) noted that the males often came out to meet him as he
entered their territories, singing as they approached. The male
typically continues to sing for some time after the intruder has
departed. Here the song acquires the additional functions of alerting
the female to danger and threatening the trespasser. Even after
allowance is made for this reaction to disturbance, Bell Vireos sing
more often than most of their nesting associates, and, on a seasonal
basis, they are vocal for a much longer time.

_Singing Postures_

In the normal singing posture the body of the Bell Vireo is maintained
at an angle of 35 deg. to the horizontal. Occasionally, during nest
building, I have observed the body held at angles as severe as 80 deg.
from the horizontal.

The head of the White-eyed Vireo is distinctly bobbed up and down, two
or three times, during the utterance of a song phrase. A bob involves
a deliberate withdrawal of the head towards the body and subsequent
sharp, almost vertical, extension of the neck. The head of the Bell
Vireo does not bob, although it vibrates as the song is delivered.

_Flight Song_

The Bell Vireo does not have a distinctive flight song; in fact, it
rarely sings or calls while in flight. Nolan (1960:240) has recorded a
male singing the normal song while in flight. Sharp scold-notes are
uttered in mid-air when a bird is agitated or actually attacking an
enemy. These notes and songs recorded by N