Natural History of the Bell Vireo, Vireo bellii Audubon

by Jon C. Barlow

Displays and Postures

The principal courtship displays and postures that were seen throughout the nestbuilding phase are as follows:

1. Greeting ceremonies. Both birds are crouched from one to five inches apart. The feathers on one (the male?) are sleeked, and on the other are fluffed. Fluffing (Morris, 1956:80) denotes partial erection of the body feathers producing a rounded, unbroken body line and is not to be confused with ruffling, mentioned in the sections pertaining to territoriality and pre- and post-copulatory display. Fluffing is generally considered to be an appeasement display and it is seen in a variety of situations involving a dominant-subordinate relationship. Both birds flick wings and tails rapidly and reverse directions on their perches frequently. A low, rapid chee is uttered during this performance. This ceremony is repeated often in the first three days of nestbuilding, but less frequently thereafter. It usually occurs after building by one or both partners and prior to another trip in search of nesting material. It lasts from 10 to 50 seconds and is not immediately followed by any additional courtship activities. Nolan (1960:228-229) observed mutual displays between periods of violent sexual chase that suggest that the greeting ceremonies that I have described are an integral part of pair-formation as well as a component of continued maintenance of the bond.

2. "Pouncing." The female rapidly quarter-fans and partially depresses her tail. She utters a high pitched scold (chee). The male, from a perch within two feet of the female, fans the tail fully and depresses it vertically, and, with mouth open, lunges at the female; or, with similar tail mannerisms, the abdominal feathers ruffled, the wings held horizontally, and the primaries spread, he sways from side to side from four to six times, and then lunges at the female. The male is silent when he pounces; the chee or the courtship song is emitted when swaying precedes pouncing. The male strikes the female with his breast or with his open beak. The female rarely flees although she is usually 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.

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.

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°; vertically, they traverse an arc slightly less than 180°. 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.

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 slightly, 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.