Thursday, January 26, 2006

Bank Swallows Gone Wild!

Thursday, January 26, 2006
My friend Myrna Pearman from Alberta sent along this incredible story and photo from a birding experience she had last summer on the way home from work. First of all, here's the photograph:
I'll let Myrna set the stage:
I saw what appeared to be bizarre bird behaviour last night while driving home from Ellis Bird Farm. There is a section of road along Twnship Road 40-0 with wetlands on both sides of the road. Last evening, dozens and dozens of bank swallows were feeding over these wetlands as well as over a nearby cultivated field. One had been recently killed, likely hit by a passing car. What caught my eye as I drove by was the frenzy of birds copulating with this dead bird. There were up to 7 at a time trying to mate with the corpse, and the sight of one mating seemed to stir the others so much that they actually tried to copulate with the copulator(s)!!! The corpse got flipped around on both its back and stomach, but both positions seemed irresistible. I took quite a few photos, some of which turned out to be fairly clear (it was about 8:30 pm and very overcast, so the lighting was lousy). Perhaps this is well-known behaviour and I ve just never heard of it before.

Myrna sent her observation along to several ornithologists and biologists in Canada, and one, sent her this reply:
Dear Ms. Pearman:
The behaviour you described, known in the literature as Davian behavior, has been recorded previously in birds, but infrequently. To my knowledge, however, the contexts in which this behaviour occurs has not been determined, that is, what the relationships, if any, were between the participating individuals, what were the ages of the birds involved, and so on. That there were so many individual bank swallows copulating or appearing to copulate with the corpse suggests no relationship among the individuals and whether true copulation occurred, with a transfer of sperm, cannot be confirmed. As the breeding season of bank swallows may be over for this year, the behaviour is even more puzzling. Is it possible that at least some the individuals involved were juveniles?

I have witnessed this behaviour once, involving silvery-throated jays in a Costa Rican cloud forest. The freshly dead bird on the ground (cause of death not determined although the bird, an egg-laying female, was skinned out and no visible wounds were detected) was being mounted by two unsexed individuals.

You may want to consider preparing a written account of your observation for the Blue Jay or Alberta Naturalist, accompanied by your photograph. Keep the bird in the freezer as its status, i.e., sex and age, would be important to know.

I appreciate receiving the highlights of your observation. All the best with your work.

Birders and ornithologists always talk about how anyone can make a contribution to our knowledge of birds, through citizen science projects, through organized research projects and field work. But we can also make contributions simply by sharing our observations of bird behavior, like this rather unusual one that Myrna witnessed.

Myrna is one of North America's leading experts on bluebirds and a longtime member of The North American Bluebird Society. She works at The Ellis Bird Farm near Red Deer, Alberta, where the mission is to help conserve birds (especially mountain bluebirds and violet-green swallows), to do field research, and to help to educate the public about birds and nature.

Thanks, Myrna, for sharing this with me (and with the readers of Bill of the Birds). I believe I speak for all of us when I say that we'll never look at bank swallows quite the same again....


On February 2, 2006 at 9:14 AM Clare said...

Wow. Incredible behaviour. You wonder what would lead to it. If birds were more olfactory one might think that perhaps some scent lead to it, but it seems unlikely.

On February 2, 2006 at 1:09 PM cpbvk said...

Amazing! I've seen necrophilia among ducks, but no other birds. Since many swallow species nest on freeway overpasses, and are commonly killed by cars, you'd think such behavior would be well documented if it were very common. From now on, I'm keeping my eyes wide open around the onramps! Thanks for the post!

On May 18, 2007 at 1:32 AM Anonymous said...

It was interesting to see the formation of the birds in your photograph. Notice how the wings on the middle bird seemed to be blanketing the corpse of the vulnerable bird. It may even appear so much to seem that he is attempting to covet it as its own. The displeasure in the top most bird is apparent and such pursues the other male from the rear. Now what I find peculiar, is the fact that the bottom bird does nothing to thwart off attack.

It was nice that you were able to obtain such a great angle of the interaction. It will be amazing to see what you come out with next.