ing to
Andrew (1956:179), flicking of wing and tail in passerines are
intention movements of flight. These actions have been emancipated
from incomplete take-offs and incorporated in ritualized courtship and
agonistic behavior. In incipient courtship behavior the male is
governed by three conflicting tendencies; to flee, to attack, or to
behave sexually before his mate (Tinbergen and Hinde, 1958:256). When
pairing, Bell Vireos interrupt sexual chase with "greeting
ceremonies," the male's tendency to attack and the female's tendency
to flee are momentarily reduced, and the forming bond is strengthened.
Thus, the intention movements become an integral part of courtship.

In situations where attacking and fleeing are the two conflicting
tendencies, wing-flicking and tail-flicking are incorporated into
threat display, but do not lose all of their original function, for
they facilitate attack. Tail-fanning, as a display element, increases
the awesome aspect of the threatening bird and in courtship presumably
makes the sexes more attractive to one another.

Courtship feeding has not been recorded for the Bell Vireo. In
general, it is unknown in North American vireos, with the exception of
the red-eye (Lawrence, 1953:53). It would serve no "practical" purpose
in the Bell Vireo since the male regularly relieves the female during
incubation, thus allowing her ample opportunity to forage. In the
Red-eyed Vireo, only the female regularly incubates, and courtship
feeding is definitely functional. Nolan (1960:228) described a brief
pecking or pulling with their bills between pairing birds. This may be
incipient "symbolic" courtship feeding, or perhaps mutual preening.

SELECTION OF NEST-SITE AND NESTBUILDING

As far as can be determined, the nest-site is selected by the female.
Typically, the pair makes short, low-level flights from tree to tree
with the female invariably in the lead. The birds usually forage
within each tree; the female interrupts this activity to inspect small
forks of low, pendant branches and the male occasionally pauses to
sing. The singing is loud but not particularly regular, as it is later
when the male accompanies the female during actual nestbuilding.
Method of selection of site resembles that described by Lawrence
(1953:53) for the Red-eyed Vireo.

Nests are suspended from lateral or terminal forks about 27 inches
high in bushes and small trees that, in the study area, averaged 11
feet, four