percent of males are SATELLITES, who associate with territorial males but do not display; they often eventually inherit the territory themselves. Finally, 48 percent of males are FLOATERS, who travel widely and do not hold any territories themselves. The mating system of Ocher-bellies is polygamous or promiscuous. No male-female pair- bonds are formed; instead, males mate with as many females as they can, but the female raises the young on her own.
Description
Behavioral Expression: Female Ocher-bellied Flycatchers are usually attracted to males displaying and singing on their territories, but sometimes another male approaches and is courted by the territorial male. The approaching male behaves much like a female, moving toward the center of the display court flicking his wings while the other male sings more intensely (making whistlelike notes), crouching and wing-flicking. The territorial male then trails the other male, following him closely and sometimes making soft ipp calls. The courtship sequence continues as in a heterosexual encounter with a series of three types of flight displays by the territorial male. The HOP DISPLAY involves the male bouncing excitedly back and forth between two perches uttering an eek call. In the FLUTTER FLIGHT, the displaying male traverses an arc between two perches with a special, slow wing-fluttering pattern, while in the HOVER FLIGHT, the male slowly rises in a hover above his perch or between two perches, often fairly close to the other male. The courtship sequence typically ends abruptly with the territorial male chasing the other male off while making chur calls.
Frequency: Approximately 17 percent of courtship sequences involve a male displaying to another male, and about 5 percent of male visits to territories result in courtship. Although no mountings or attempted copulations between males have been seen, heterosexual matings have rarely been witnessed either. At one study site, for example, only two male-female mountings were observed during more than 560 hours of observation over ten months.
Orientation: It is difficult to determine the relative proportion and “preference” of heterosexual versus homosexual behavior in Ocher-bellied Flycatchers. Some researchers believe that territorial males who court other males do not realize they are displaying to a bird of the same sex, in which case they would be exhibiting superficially heterosexual behavior toward (behaviorally) “transvestite” birds. For the males who approach territorial males, however, the situation is even less clear: many of these are probably floaters who presumably are aware that they are being courted by another male, i.e., they are ostensibly participating in homosexual activity. However, in at least one case the approaching male was a neighboring territorial male who also displayed to females on his own territory, i.e., his courtship interactions were actually bisexual.
Nonreproductive and Alternative Heterosexualities
As noted above, more than half of the male population consists of nonbreeders, since floaters and satellites rarely, if ever, mate heterosexually. Moreover, the absence of breeding activity in these males cannot be attributed to a shortage of available display sites, since more than three-quarters of suitable territories go unused (and nearly a quarter of these are especially prime pieces of “real estate”).
Sources
*asterisked references discuss homosexuality/transgender
Sherry, T. W. (1983) “Mionectes oleaginea.” In D. H. Janzen, ed., Costa Rican Natural History, pp. 586-87. Chicago: University of Chicago Press.
Skutch, A. E (1960) “Oleaginous pipromorpha.” In Life Histories of Central American Birds II, Pacific Coast Avifauna no. 34, pp. 561-70. Berkeley: Cooper Ornithological Society.
Snow, B. K., and D. W. Snow (1979) “The Ocher-bellied Flycatcher and the Evolution of Lek Behavior.” Condor 81:286-92.
Westcott, D. A. (1997) “Neighbors, Strangers, and Male-Male Aggression as a Determinant of Lek Size.” Behavioral Ecology and Sociobiology 40:235-42.
———(1993) “Habitat Characteristics of Lek Sites and Their Availability for the Ocher-bellied Flycatcher, Mionectes oleagineus.” Biotropica 25:444-51.
———(1992) “Inter- and Intra-Sexual Selection: The Role of Song in a Lek Mating System.” Animal Behavior 44:695-703.
*Westcott, D. A., and J. N. M. Smith (1994) “Behavior and Social Organization During the Breeding Season in Mionectes oleagineus, a Lekking Flycatcher.” Condor 96:672- 83.
SWALLOWS, WARBLERS, FINCHES, AND OTHERS
IDENTIFICATION: A small to medium-sized swallow with iridescent blue-green upperparts, white underparts, and a tail that is only slightly forked. DISTRIBUTION: Canada and northern United States; winters in southern United States to northwestern South America. HABITAT: Forests, fields, meadows, marshes; usually near water. STUDY AREA: Allendale, Michigan.
Social Organization
Tree Swallows are extremely social birds: outside of the mating season, they gather in large flocks that may contain several hundred thousand individuals, while during the breeding season they form pairs and often nest in aggregations or colonies.
Description
Behavioral Expression: Groups of male Tree Swallows sometimes pursue other males during the mating season in order to copulate with them. When the object of their attentions alights, the males hover in a “cloud” above him, constantly fluttering and making the distinctive tick-tick-tick call that is characteristic of males when they are mating with females. If one of them succeeds in mounting the male, a complete homosexual copulation ensues: the male on top holds on to the other male’s neck and back feathers with his bill, while the male being mounted lifts his tail so that genital contact can occur. As in heterosexual mating, multiple, repeated genital contacts may occur during a single copulation between two males, which can last for up to a minute (male-female mounts generally last about 30 seconds). The cluster of males may also engage in several consecutive episodes of homosexual mating: when the male who was mounted flies off, the group will continue pursuing him until he lands again, and the whole process is repeated.
Frequency: Homosexual copulations have been observed only occasionally in Tree Swallows. However, heterosexual nonmonogamous matings are also rarely seen in this species, yet they are known to be very common because of the high rate of offspring that result from them (see below). Most such copulations therefore probably occur in locations where (or at times when) they are not readily observed. Homosexual matings (which follow the pattern of nonmonogamous copulations) probably also occur more often than they are observed.
Orientation: Some males that participate in homosexual pursuits and copulations are probably bisexual: for example, one male who was mounted by other males was the father of six-day-old nestlings when he participated in homosexual activity. The males mounting him were not paired with female mates in the same nesting colony, however, and may have been nonbreeders (although they could also have been heterosexually paired birds visiting from another colony).
Nonreproductive and Alternative Heterosexualities
Heterosexual pairs of Tree Swallows sometimes copulate well before the female is fertile, and
