t of my data on song concern singing at heights of more than 20
feet. As indicated in foraging, the lack of competition from aboreal
species of vireos presumably contributes to the use of higher perches
by Bell Vireos.

No female song was recorded in 1959, but on May 26, 1960, a female was
heard to sing once. She appeared at nest 1-f (1960) shortly after the
male arrived. Unlike him, she did not participate in building, but
seemed to be inspecting the nest. After 30 seconds she sang once--a
low garbled phrase--and also scolded once. After this she left. In the
meantime the continuously singing male moved two feet away from the
nest, then back to it and resumed construction.

The song of the female signaled to the male her departure. Pitelka and
Koestner (1942:103) heard a female sing twice after she replaced the
male on the nest. Females of three other species of vireos, the
Black-capped Vireo, _V. atricapillus_ (Lloyd, 1887:295), the
Philadelphia Vireo, _V. philadelphicus_ (Lewis, 1921:33), and the
Latimer Vireo, _V. latimeri_ (Spaulding _in_ Pitelka and Koestner,
1942:103) have been heard singing. Lewis and Spaulding also suggest
that the song of the female functions as a signal prior to exchange at
the nest.

The primary song identifies the singer as a male Bell Vireo. It
aids in securing a mate and in warning potential adversaries; also,
the song is a signal in certain situations and serves to locate the male.

TABLE 1. REPRESENTATIVE SINGING RATES OF BREEDING BELL VIREOS.
ALL RATES WERE AT AIR TEMPERATURES LESS THAN 86 deg. F. EACH
INSTANCE REPRESENTS APPROXIMATELY 30 MINUTES OF OBSERVATION.

====================================================================
| | Average
Circumstance | Instances | rate per
| | minute
----------------------------------------------+-----------+---------
Attraction of mate | 2 | 6.3
Territorial dispute | 5 | 12.8
Nestbuilding | 6 | 7.0
Egglaying | 1 | 3.0
Incubation | 6 | 3.9
Exchange of partners in the incubation period | 1 | 4.0[A]
Foraging | 2 |