htly, and utters a muted
_chee_.

5. Copulation. The male abruptly terminates his swaying display with a
leap-flutter that positions him above the female's back. He then
descends and copulation occurs. The male continues to flutter his
wings to maintain balance throughout the two seconds of cloacal
contact. Following an unsuccessful copulation on June 23, 1960,
displacement preening and bill wiping were performed by both sexes.

6. Post-copulatory display. On June 25, 1960, after a second attempt
at copulation with a stuffed bird in which semen was actually
deposited on the dummy's back, male 10 (1960) performed a swaying
display. In this instance, however, instead of addressing the dummy
from the front, the male alighted one inch to the right of the stuffed
bird. When swaying to the left (toward the dummy) the head of the
displaying male actually passed above the neck of the stuffed bird.
This ritualized behavior could conceivably be derived from
hetero-preening.

_Discussion_

Within the scope of my research it was difficult to detect the
over-all sequence of epigamic displays that result in synchronization
of the physiological states of the sexes throughout the period of
courtship. Possibly all displays, except the post-copulatory one,
occur in no particular order in the courtship period. However, each
ritualized display seemingly strengthens the pair-bond.

Swaying has been recorded in a variety of situations of a sexual and
semi-sexual nature for the Solitary Vireo (_V. solitarius_; Townsend,
1920:158) and the Red-eyed Vireo (Tyler, 1912:230; Bent, 1950:342). In
every instance the body feathers of the swaying birds were sleeked.
Courtship behavior in any species of North American vireo seems
closely to resemble that of any other; pairing and nestbuilding of a
female _V. solitarius_ and a male _V. flavifrons_ as reported by
Hauser (1959:383) support the idea of close resemblance.

A marked similarity will be detected between certain basic elements of
aggressive and epigamic displays. These basic elements are wing- and
tail-flicking, tail-fanning, and high-intensity delivery of the
_chee_. Pouncing and supplanting attacks are essentially similar. Such
similarities suggest either a common origin for certain aggressive and
epigamic displays or the derivation of one from the other.

High-intensity _cheeing_ is obviously a function of excitement,
whether in conjunction with hostility or sexual behavior. Accord