Friday, November 7, 2008

Animal of the day: Snowy Sheathbill

This morning a largish white bird landed outside my window and looked at me quizzically. To my mind she was saying "can I come in ?".

The bird was one of our local snowy sheathbills, a species that is by turns amazing and pedestrian, stunningly attractive and even a bit repulsive.

Around here we affectionately refer to them as "chickens" or "pigeons" because of the way they hang around the humans like pigeons in a park, but they are actually more closely related to wading birds like plovers. The adults weight 1 or 2 lbs and are about 12" long. Their beaks are covered in horny sheaths which give them their name.

Sheathbills are well adapted for life in the Antarctic environment with their short, stout legs, an insulating coat of dense gray down, and a thick layer of subcutaneous fat. They are fearless around humans, gathering around the buildings on station. They seem to especially like our boats and the hot tub. An oddity is that they almost always prefer to use just one foot, standing or hopping along with just the one. This is confusing to me at first; when I first arrived to station, I thought we had a population of one-legged birds.






Master scavengers, sheathbills serve as the clean-up crew of the continent. Because they lack webbed feet, they must find their food on land; in the winter prowling for invertebrates and detridus in the intertidal zones. In the long summer months however, Sheathbills move right into colonies of penguins and seals where they time their own nesting to coincide with the birth of young in the colony.

Nest sites are located in small caves and cracks in rocky areas where the parents can protect their young from wind, precipitation and danger from predatory skuas (Stercorariidae). The nests may be abandoned sites from other species and are constructed from feathers, pebbles, bones, shells, lichens, grasses, and seaweed.

Once the clutch of one to three eggs is laid in late November or December, the parents gorge themselves on everything organic in the penguin colonys: eggs, placentas, carcasses, sometimes chicks and always lots of excrement. The sheathbills have even perfected a nifty trick called kleptoparasitism in which they steal food right from the mouths of feeding chicks. This is typically accomplished by harassing or jostling the chich before the parent finishes reguritation. Food is dropped on the ground and the result is a happy sheathbill, a hungry chick and a penguin parent who has to go out fishing again. Researchers have shown it is important nutritional strategy for the sheathbill but has little effect on the penguin colony.

















5 comments:

TemporaryLibrarian said...

I love being introduced to the inhabitants of your site - had never heard of the snowy sheathbill before. Hope you are keeping a Life Birding List - you'll collect some rare ones there.

Louise Hamlin said...

Hi Ginny, good point - I'll get on that list.

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