Sunday, December 02, 2007

Vultures in the main building

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This image to me is iconic IISc. The Faculty building has been the face of IISc for donkeys years, its on every brochure, every handbook, every calender. No one notices the details.

Like the two Scavenger vultures that have been on its ledges for the many years (don't ask a lady her age, and a PhD student how long they've been) that I have been here. I'm told they've been there well over thirty years. They're reputed to mate for life and I think larger birds are relatively long lived (but 30 years? maybe they've turned over...) I wonder if Tsundue had a word with them when he was up there?

Anyway, a few years ago Nature news had a feature to which the title was "Faeces brings colour to birds' faces: endangered vulture eats shit to impress females". Now see thats just a brilliant feature to read with your breakfast chai. Its also the sort of thing that adds to the perception that theres not much 'substance' to biology just these silly 'observations', particularly the more classical branches like mine.

But lets put this whole observation in perspective. These birds eat feces in order to accumulate carotenoids which give their heads that characteristic yellow colour. This colour is a signal they can't fake as far as we know, they must eat shit to be yellow, hence its an 'honest signal'. The birds when they eat the shit are obviously taking a risk with endoparasites, enteric infection and so on. And a female could judge from the colour just how much of a risk a particular male took. She could also asses his present condition and tell whether he got away with the risk. Now then, the male bird is in essence signaling to her saying in a sense 'I can do well despite my handicap, hence I must have good genes!'.

Amotz Zahavi sometime ago came up with a brilliant theory called the handicap principle which he says explains many many examples of exuberant sexual display in organisms, which are hard to explain in terms of plain old natural selection. And this behavioral observation seems to fit quite well with his theory. And off course there is an opposing theory, which is Fisher's runaway selection hypothesis.

Here's the paper for the work I referred to. Here's the theoretical work that proved that the handicap principle can work as model. The history of the theory itself is full of some nice internecine evolutionary biology warfare, but I'll leave that to you to find out.

2 comments:

Divs said...

A silent reader and admirer of u're blog and pics.. keep up the good work.. my page has a link to u'rs too..

Natasha said...

thanks divs