Bruce Bagemihl - Biological Exuberance

Frequency: Same-sex pairs probably occur only sporadically in these three species: in Red-backed Shrikes, for example, female couples account for perhaps no more than 1 percent of all pairs.

Orientation: Female Red-backed Shrikes and Blue Tits are probably exclusively homosexual, at least for the time that they remain paired with their female partner, since they invariably lay eggs that are infertile (indicating no mating with males). Whether such birds ever subsequently form or have previously formed heterosexual pair-bonds is not known.

Approximately 17 percent of all sexual activity in opposite-sex pairs of Blue Tits occurs outside the female’s fertile period. Male Eastern Bluebirds also sometimes try to copulate when females are nonfertile, such as during incubation or after the breeding season is over. Other nonprocreative matings involve occasional interspecies encounters: juvenile Eastern Bluebirds have been observed being mounted by great crested flycatchers ( Myiarchus crinitus ). Courtship and mounting between pair-bonded Eastern Bluebirds sometimes involve considerable aggression, with males attacking their partner and violently pecking her head or knocking her over with their feet. Heterosexual copulations are also occasionally interrupted by neighboring birds that attack the mating pair. Within-pair copulation rates are quite high in Red-backed Shrikes, roughly three times a day during the female’s fertile period. In addition, nonmonogamous matings are common in these species: approximately 10 percent of Blue Tit copulations are promiscuous, involving birds that are not paired to each other. About a quarter of Bluebird nests and a third to nearly a half of all Blue Tit broods contain youngsters fathered by an outside bird. Promiscuous copulations also occasionally occur in Red-backed Shrikes, including forced matings or rapes in which males attack and mount females or violently push them off their perches. About 5 percent of Red-backed Shrike nestlings are fathered by a bird other than their mother’s mate, compared to 8–35 percent in Eastern Bluebirds, and 11–14 percent in Blue Tits.

Several other alternative parenting arrangements occur in these species. Red-backed Shrike youngsters sometimes move to adjacent territories where they are adopted by other families, and a few nonbreeding birds of both sexes help feed chicks belonging to other pairs (sometimes even assuming full responsibility for them later on). “Helper” males such as these may even replace the biological father as a model for song-learning by the youngsters. In addition, late-breeding Red-backed Shrikes sometimes become single parents when their mate deserts them; occasionally two such birds and their offspring join together to form a “blended family.” At least 15 percent of Eastern Bluebird mothers in some populations raise unrelated youngsters when outside females lay eggs in their nest. The divorce rate for Blue Tits varies considerably, from 8—85 percent (depending on the population); in addition, about a third of females and up to 20 percent of all males in some areas form polygamous trios (or occasionally quartets). Other more complex family arrangements also occur: one female Blue Tit was part of a polygamous trio with another female and a male; she also copulated promiscuously with a second male, eventually forming a new polygamous bond with both him and yet a third male, all of whom helped care for the young! Overall, however, more than 85 percent of Blue Tits never successfully breed, and about a third of all parents never have grandchildren. Red-backed Shrike parents occasionally cannibalize their own young or eggs.

Some male Pied Flycatchers ( Ficedula hypoleuca ), especially younger ones, are transvestite, having the same brownish plumage that females do; these birds are sometimes courted by other males.

*asterisked references discuss homosexuality/transgender

Alsop, F. J., III (1971) “Great Crested Flycatcher Observed Copulating with an Immature Eastern Bluebird.” Wilson Bulletin 83:312.

*Ashby, E. (1958) “Incidents of Bird Life [report on Red-backed Shrikes].” The Countryman: A Quarterly Review and Miscellany of Rural Life and Progress 55:272.

Birkhead, T. R., and A. P. Møller (1992) Sperm Competition in Birds: Evolutionary Causes and Consequences . London: Academic Press.

*Blakey, J. K. (1996) “Nest-Sharing by Female Blue Tits.” British Birds 89:279-80.

*Cramp, S., and C. M. Perrins, eds. (1993) “Red-backed Shrike ( Lanius collurio ).” In Handbook of the Birds of Europe, the Middle East, and North Africa, vol. 7, pp. 456—78. Oxford: Oxford University Press.

Dhondt, A. A. (1989) “Blue Tit.” In I. Newton, ed., Lifetime Reproduction in Birds , pp. 15—33. London: Academic Press.

———(1987) “Reproduction and Survival of Polygynous and Monogamous Blue Tit Parus caeruleus .” Ibis 129:327—34.

Dhondt, A. A., and F. Adriaensen (1994) “Causes and Effects of Divorce in the Blue Tit Parus caeruleus.” Journal of Animal Ecology 63:979—987.

Fornasari, L., L. Bottoni, N. Sacchi, and R. Massa (1994) “Home-Range Overlapping and Socio-Sexual Relationships in the Red-backed Shrike Lanius collurio .” Ethology, Ecology , and Evolution 6:169-177.

Gowaty, P. A., and W. C. Bridges (1991) “Behavioral, Demographic, and Environmental Correlates of Extrapair Fertilizations in Eastern Bluebirds, Sialia sialis .” Behavioral Ecology 2:339-50.

Gowaty, P. A., and A. A. Karlin (1984) “Multiple Maternity and Paternity in Single Broods of Apparently Monogamous Eastern Bluebirds ( Sialia sialis ).” Behavioral Ecology and Sociobiology 15:91—95.

Hartshorne, J. M. (1962) “Behavior of the Eastern Bluebird at the Nest.” Living Bird 1:131—49.

Herremans, M. (1997) “Habitat Segregation of Male and Female Red-backed Shrikes Lanius collurio and Lesser Gray Shrikes Lanius minor in the Kalahari Basin, Botswana.” Journal of Avian Biology 28:240—48.

Jakober, H., and W. Stauber (1994) “Kopulationen und Partnerbewachung beim Neuntöter Lanius collurio [Copulation and Mate-Guarding in the Red-backed Shrike].” Journal für Ornithologie 135:535—47.

———(1983) “Zur Phänologie einer Population des Neuntöters ( Lanius collurio ) [On the Phenology of a Population of the Red-backed Shrike].” Journal für Ornithologie 124:29—46.

Kempenaers, B. (1994) “Polygyny in the Blue Tit: Unbalanced Sex Ratio and Female Aggression Restrict Mate Choice.” Animal Behavior 47:943—57.

———(1993) “A Case of Polyandry in the Blue Tit: Female Extra-Pair Behavior Results in Extra Male Help.” Ornis Scandinavica 24:246—49.

Kempenaers, B., G. R. Verheyen, and A. A. Dhondt (1997) “Extrapair Paternity in the Blue Tit ( Parus caeruleus ): Female Choice, Male Characteristics, and Offspring Quality.” Behavioral Ecology 8:481-92.

———(1995) “Mate Guarding and Copulation Behavior in Monogamous and Polygynous Blue Tits: Do Males Follow a Best-of-a-Bad-Job Strategy?” Behavioral Ecology and Sociobiology 36:33—42.

Krieg, D. C. (1971) The Behavioral Patterns of the Eastern Bluebird (Sialia sialis). New York State Museum and Science Service Bulletin no. 415. Albany: University of the State of New York.

Massa, R., L. Bottoni, L. Fornasari, and N. Sacchi (1995) “Studies on the Socio-Sexual and Territorial System of the Red-backed Shrike.” Proceedings of the Western Foundation of Vertebrate Zoology 6:172-75.