Biological Exuberance: Animal Homosexuality and Natural Diversity

EUROPEAN SHAG

IDENTIFICATION: Similar to Great Cormorant, but smaller and uniformly black, with a prominent forehead crest. DISTRIBUTION: Northwestern Europe, Mediterranean basin. HABITAT: Coastal waters; nests on cliffs. STUDY AREA: Lundy Island in the Bristol Channel, England; subspecies P.a. aristotelis.

Social Organization

Great Cormorants and Shags form mated pairs and generally nest in colonies, which may contain as many as 20,000 pairs in some populations of Great Cormorants. Outside of the mating season, these species are moderately gregarious, wandering solitarily but sometimes forming flocks.

Description

Behavioral Expression: Homosexual pairs consisting of two males sometimes form in Great Cormorants and last for up to five years (heterosexual pairs in this species are usually seasonal but may also last for several years). Male pairs often build oversize nests because both birds contribute to the construction of the nest. They often sit on the nest as if incubating eggs; similar behavior is also seen in heterosexual pairs prior to egg laying. In some homosexual pairs, one partner may use vocalizations that are typical of females (such as panting or purring sounds), or else calls that are intermediate between male and female vocal patterns. Male pairs are sometimes incestuous, composed of two brothers.

In European Shags, males occasionally court other males. As one male approaches—hopping along the rocks, pausing every now and then in an erect pose known as the UPRIGHT-AWARE POSTURE—the other male performs two displays. In the DART-GAPE, he pulls his head back and then darts it forward, at the same time opening his bill to expose the yellow interior and fanning his tail. In the THROW-BACK, he arches his neck along his back and points his beak upward while quivering his throat pouch. Sometimes the courting male will become aggressive and attack another male that approaches too closely, which also happens frequently when females approach courting males.

Frequency: Homosexual pairs and courtship occur only occasionally in these two species: no more than perhaps 1 in 500 pairs of Great Cormorants, for example, is composed of two males.

Orientation: Great Cormorants in homosexual pairs are sometimes sequentially bisexual, divorcing their male partners and going on to breed in heterosexual pairs. However, others re-pair with another male partner, and some homosexual pairs appear to last much longer, perhaps even for the birds’ lifetimes—in which case such individuals are exclusively (or extensively) homosexual for a significant part of their lives. Male European Shags that court other males are simultaneously bisexual, alternating heterosexual courtship with homosexual interactions (and probably a greater proportion of the former).

Nonreproductive and Alternative Heterosexualities

Several forms of nonprocreative sexual behavior are exhibited by these Cormorants. REVERSE mountings constitute 8 percent of European Shag heterosexual copulations (and also occur in Great Cormorants), while at least a quarter of all sexual activity takes place prior to the female’s fertilizable period. Great Cormorants sometimes copulate during the incubation period, while heterosexual copulations may continue even after Shag chicks have hatched. In a few cases, adult male Shags have been observed mating with their own chicks, and incestuous pairings sometimes also develop between brothers and sisters when they are still young. Nearly half of all heterosexual copulations in Shags involve mounting without genital contact, often because the female will not permit it. In addition, males are frequently hostile to females during the early phases of courtship (as noted above).

Courtship between two male European Shags: the “uprightaware” posture (left) and the “throw-back” display

Nonmonogamous matings and courting of birds other than one’s partner occur in both of these species. In European Shags, for example, 14 percent of all copulations are promiscuous. Almost 18 percent of all chicks are fathered by a male other than their mother’s mate, but nearly 80 percent of all nonmonogamous matings are nonreproductive, taking place before females can be fertilized. At least 4 percent of all chicks are related to neither of the parents caring for them; this results from adoption and from females’ laying eggs in nests other than their own. About 3—5 percent of male Shags bond polygamously with two females; in addition, 30— 40 percent of heterosexual Shag pairs divorce and re-pair with new mates the next season. Individuals may also change mates during the season. Some Shag parents are severely neglectful, refusing to feed their offspring, who may, as a result, die of starvation. In addition, about a third of all eggs lost through breakage result from interference by the females in polygamous associations. Finally, nonbreeding is a regular feature of some Shag populations: on average, 12—25 percent of all adults skip breeding at least once during their lifetime, and in some years as many as 60 percent of all birds forgo reproduction.

Sources

*asterisked references discuss homosexuality/transgender

Aebischer, N. J., G. R. Potts, and J. C. Coulson (1995) “Site and Mate Fidelity of Shags Phalacrocorax aristotelis at Two British Colonies.” Ibis 137:19 —28.

Aebischer, N. J., and S. Wanless (1992) “Relationships Between Colony Size, Adult Non-Breeding, and Environmental Conditions for Shags Phalacrocorax aristotelis on the Isle of May, Scotland.” Bird Study 39:43—52.

*Fukuda, M. (1992) “Male-Male Pairing of the Great Cormorant (Phalacrocorax carbo hanedae).” Colonial Waterbird Society Bulletin 16:62—63.

Graves, J., R. T. Hay, M. Scallan, and S. Rowe (1992) “Extra-Pair Paternity in the Shag, Phalacrocorax aristotelis as Determined by DNA Fingerprinting.” Journal of Zoology, London 226:399—408.

Harris, M. P. (1982) “Promiscuity in the Shag as Shown by Time-Lapse Photography.” Bird Study 29:149—54.

Johnsgard, P. A. (1993) Cormorants, Darters, and Pelicans of the World. Washington and London: Smithsonian Institution Press.

*Kortlandt, A. (1995) “Patterns of Pair-Formation and Nest-Building in the European Cormorant, Phalacrocorax carbo sinensis.” Ardea 83:11—25.

*———(1949) “Textuur en structuur van het broedvoorbereidingsgedrag bij de aalscholver [Texture and Structure of Brooding-Preparatory Behavior in the Cormorant].” Ph.D. thesis, University of Amsterdam.

*Snow, B. K. (1963) “The Behavior of the Shag.” British Birds 56:77—103, 164— 86.

SILVERY GREBE

IDENTIFICATION: A ducklike bird with grayish white plumage, bright red eyes, and yellow facial tufts. DISTRIBUTION: Western and southern South America. HABITAT: Lakes, marshy ponds. STUDY AREA: Laguna Nevada, southern Patagonia, Argentina.

HOARY-HEADED GREBE

IDENTIFICATION: Similar to Silvery Grebe, but with a buff or chestnut wash on the breast, white