Homosexuality in birds

An earlier posting on a pair of hornbills of different species, both females, prospecting for a nesting site, has raised the question of homosexuality among birds. But how aware are local birders of such behaviour among our feathered friends? Not much, I am afraid. But homosexuality among birds is a common phenomenon.

Thanks to Lin Yangchen who made an online search and alerted us of the presence of such literature, I have managed to read a few of such reports.

Many species of birds lack sexual dimorphism. Thus we cannot differentiate the male from the female. During courtship and any subsequent mating, there is no way to tell whether the two birds are of the same or different sex. However, among birds showing sexual dimorphism, same sex courtship and mating can be obvious.

People have always been aware of homosexuality in captive birds, especially parrots. Such behaviour here can be due to the circumstances of confinement and may not be normal. However, there have been accounts of homosexuality among wild birds.

A pair of male Orange-fronted Parakeets (Aratinga canicularis) was observed to indulge in courtship behaviour in the wild. Ultimately one bird attempted to mount the other. Both birds were collected for scientific examination and found to be adult males.

Homosexual copulation has also been recorded in feral populations of Rock Pigeon (Columba livia) (left), Cattle Egret (Bubulcus ibis) and Common Murre (Uria aalge). Although no cloacal contacts were mentioned in these cases, it was specifically observed in the case of Tree Swallow (Tachycineta bicolor).

The above are instances of homosexuality between birds of the same species. Homosexuality between birds of different species has also been reported. Among Canada Geese (Brania canadensis), unisexual pairings of both males and females are common. What is uncommon was the instance of pairing between a male Giant Canadian Goose (B. canadensis maxima) and a male Snow Goose (Chen hyperborean). As both these birds were tagged and their sex had been determined earlier during handling, there was no question that they were a homosexual pair. The former assumed the female role, followed the Snow Goose everywhere and roosted close to him at night. However, there was no attempt at mating or nest building.

Another case of interspecific homosexuality was between a Brown-headed Cowbird (Molothrus ater) and a House Sparrow (Passer domesticus) (right). The male sparrow mounted a male cowbird, grabbed its head feathers and attempted copulation. This was repeated twice before the former flew to a nearby fence. The cowbird flew to join the sparrow and nudged the latter until it mounted it a few more times. This behaviour continued for 5-8 minutes.

So, our Great Hornbill pairing with a Rhinoceros Hornbill and checking nesting cavities around Eng Neo is not all that strange after all.

Comment by R. Subaraj: Homosexuality - But then again, maybe it is still strange as most of the other cases mentioned involved males, not females.

References:
Brackbill, H (1941). Possible homosexual mating of the Rock Dove. Auk 58:581.
Buchanan OM (1965). Homosexual behavior in wild Orange-fronted Parakeets. Condor 68:399-400.
Griffin, DN (1959) Apparent homosexual behavior between Brown-headed Cowbird and House Sparrow. Auk 76:238-239.
Lombardo, MP, Bosman, RM, Faro, CA, Houtteman, SG & Kluisza, TS (1994). Homosexual copulation by male Tree Swallows. Wilson Bull. 106:555-557.
Starkey, EE (1972). A case of interspecific homosexuality in geese. Auk 89:456-457.