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.

A pair of hornbills comprising a Great (Buceros bicornis) and a Rhinoceros (B. rhinoceros), both females, have been visiting an old albizia tree (Paraserianthes falcataria) around the Eng Neo area from late February to April to check on a cavity as a possible nesting site.

Every morning and sometimes in the evening, the birds would fly to the tree and inspect the cavity. The Great Hornbill plays the role of a male, trying to lure the Rhinoceros to the cavity by placing food inside. It then flies to the nearby tree to join the Rhinoceros and sometimes feed the latter as part of their courtship ritual. Once in a while the Rhinoceros would respond to the Great’s urging and fly to the cavity to inspect it.
The Great has also been observed to peck hard on the periphery of the cavity in an effort to enlarge the opening.

After some time spent outside the cavity, both birds would fly around, to alight on the yellow flame (Peltophorum pterocarpum) and other trees around the area. There, the pair would stay close together for up to half an hour or so. The Great Hornbill, a probable escapee from Jurong Bird Park, has a metal tag on her right leg. The pair are obviously used to people as they appear tame.

This pair has been seen in Hindehede Quarry prospecting for a potential nesting cavity.

Ng Bee Choo has this to say: “A pair of Great Hornbills died in Sentosa island a number of years ago. This Great Hornbill must be very desperate. Morten Strange has seen it once in the Singapore Botanic Gardens, checking a nesting hole. Both hornbills belong to the genus Buceros. In Thailand, according to Dr Pilai Poonswad, these two hornbills mated and produced a hybrid. In the above case both birds are females. They have paired up for company… however, if they try to mate, this must be a case of lesbian birds. Must be recorded as a case study of birds in desperation.”

Top image (Great left, Rhinoceros right) and bottom of Great inspecting cavity by YC.

In an earlier posting it was mentioned that Asian Glossy Starlings (Aplonis panayensis) swallowed the fruits of Alexandra palm (Archontophoenix alexandrae) and a little while later regurgitated the large seeds. In subsequent observations I noticed that other starlings did not always swallow the fruits followed by regurgitating the seeds. They just pecked at the thin pulp surrounding the seeds, leaving the fruits on the inflorescence branch with patches of skin removed. It may be possible that when the fruits are ripe and the pulp soft, the birds will swallow the fruits whole. Short of conducting experiments with caged birds, we may not know when the birds swallow and when they just peck at the pulp.

The fruits of my ceram palms (Rhopaloblaste ceramica) are now ripening and I had the opportunity to observe a flock of starlings feasting on the fruits. These fruits are larger than the Alexandra palm, each about 35 x 20 mm as opposed to 12 x 10 mm fruits of the latter. The pulp of both seeds is thin, less than 2 mm thick. For a bird the size of the starling, it is understandable that it merely pecks off pieces of the pulp.

Yellow-vented Bulbul (Pycnonotus goiavier), about the size of a starling, similarly pecks on the pulp of ripe ceram fruits, without dislodging them from their inflorescence branch. Another bird that had been observed eating these fruits was the blue-crowned hanging parrot (Loriculus galgulus). As with the other birds mentioned earlier, it merely bit off pieces of the pulp.

Along my driveway below these ceram palms, I find seeds of the Alexandra and MacArthur palms (Ptychosperma macarthurii) totally devoid of the pulp. Obviously they have been regurgitated by birds that also feed on the ceram fruits. I know that the starling regurgitate the former seeds but I have no proof that any bird regurgitates seeds of the latter. Can it also be the starling? It would be interesting to find out!

Asian Koel (Eudynamys scolopacea) is reputed to be able to swallow seeds larger that 18 mm diameter but I have yet to observe this bird eating these fruits that is 2 mm larger in diameter, besides being 35 mm long. No doubt it would be an interesting observation.

It should be noted that these birds do not assist in the dispersal of the seeds of this palm as they merely fall on the ground below the palm. As the palm is native to the Moluccas where it grows in the rainforest, its dispersal agent is probably not present in Singapore.

Note: scale in mm. Text and images by YC.