ally displaced several inches along the branch upon which she is
sitting. However, the female may fly several inches to a new perch.
The failure of the female to adopt a solicitation posture presumably
indicates sexual unreadiness. Instances of the male deliberately
colliding with the female as she flies in the course of gathering
nesting material are probably analogous to pouncing. In none of the
above situations are females observed to fight back in any way. Nice
(1943:174) believed pouncing to be analogous to sexual chasing found
in such species as the Red-winged Blackbird. In the Song Sparrow,
pouncing is observed most often in the first and second days of
nestbuilding.

3. "Leap-flutter." The male, in the course of displaying with the tail
fanned before the female, suddenly leaps eight inches to ten inches
vertically and flutters in mid-air several seconds, before dropping to
the original perch. This display occurs in full view of the female. It
is often associated with pouncing and is also seen prior to
copulation. In the latter instance it is probably pragmatically
functional, for it permits the male to orient above the female before
dropping to her back to copulate. No vocalization is uttered during
the leap-flutter.

4. Pre-copulatory display (Fig. 3). The male faces the female. The
tail is fanned fully and depressed at a sharp vertical angle to the
body. Body feathers, both dorsal and ventral, are ruffled, almost
tripling the apparent volume of the thorax. The head is withdrawn and
slightly thrown back. Feathers of the head are not erected. The mouth
is opened wide. The legs are slightly flexed and the body is swayed
laterally. Horizontally, the head and body traverse an arc of about
100 deg.; vertically, they traverse an arc slightly less than 180 deg.. At the
low point of any one swing, the delivery of the courtship song begins.
At the termination of the swing the two normal, ascending notes are
emitted. This performance may last as long as three minutes.

[Illustration: FIG. 3. A single male Bell Vireo in the
pre-copulatory display. Note the ruffled dorsal and ventral
body feathers. The male on the left has reached the zenith of
a single swing. The male on the right has nearly reached the
low point of a swing.]

The pre-copulatory display of the male elicits receptive behavior in
the female. She crouches in a solicitous manner, with the body
feathers fluffed and the tail raised slig