Tuesday, 5 September 2017

March of the Grey-throated Sand Martins

With all manner of errant behaviour reported for Sand Martins Riparia riparia in Japan (e.g. here), it doesn't seem at all unreasonable to expect that similar levels of depravity might occur in other closely related species. This afternoon, a corpse on the road at San Gu was proving to be of some interest to the local Grey-throated Sand Martins Riparia chinensis, and it appeared (just like the Sand Martins in Japan) that a number of males were doing their level best to mate with it.

All the signs that these birds were enjoying an afternoon's necrophilia were there, with 'victory poses', playful nibbling, some quite vigorous thrusting, and a frenzied scramble amongst those present to get in on the act whilst such an accommodating partner was available. There was no violent pecking at the eyes or head, nor pulling out of feathers or dragging the corpse around in any way, and the agenda appeared to be one of mating rather than one of aggression or attack.

It did come as a relief to find that at least some in the Grey-throated Sand Martin necrophiliac community were able to maintain an air of decorum, as there were those who were willing to queue in an orderly fashion and wait their turn. There were also others with a greater degree of self-awareness, and these finished up and left with an obvious look of guilt on their faces.

What was reportedly unique about the Sand Martin 'incident' in Japan was that the corpse with which the males were attempting copulation was itself male. Like Sand Martin, Grey-throated Sand Martins are not sexually dimorphic, hence it is not possible to tell males from females in the field. I have no idea whether or not a wing chord would allow such a determination to be made, but do know that, if present, a cloacal protuberance might do. Although difficult to see in the image below (due to me only having one hand to work with in a strong wind), there is a tubular 'protuberance' at right angles to the body which perhaps indicates that this bird too is most likely male.

However, it has been pointed out to me that the build up of fermentation gases in a dead bird will cause the cloaca in both sexes to expand (and many thanks to contributors on BirdForum for this insight). This reduces the levels of certainty with which the bird can be said to be male, and dissection of the corpse might be the only way to find out for sure. If it is male, then homosexual necrophilia might be more common in Riparia communities than is thought. If not, then this may be just another case of bog-standard necrophilia, which is by all accounts not at all that rare. It was certainly interesting behaviour to observe, anyway, and it was hard not to be impressed by both the rabid determination and sexual opportunism demonstrated by these depraved little monsters! Above photos taken at San Gu, Tainan County 5/9/17.

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