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Big Snoods

November 25, 2010

How do you choose your turkey? It might be by weight. Perhaps it is from a favorite farm. Or it could be a brand that you like. But if you were a female turkey, you’d be looking at his snood.

The snood is a fleshy appendage that attaches just above the beak. When tom turkey is just chilling his snood can be fairly short, but when he struts for the ladies his snood engorges with blood and hangs awkwardly down the beak.

It would seem that the snood is just a piece of flesh that is only good for the bling-bling. And we’d be half right, but given that this week is the publishing anniversary of Charles Darwin’s book, On the Origins of Species, I think we might ponder a bit about sexual selection. Darwin was first to suggest that mate choice and competition for mates might be a selective pressure that shapes the evolution of populations.

But why would female turkeys choose a big snood in the first place? Is this simply a sexy ornament or is it perhaps a signal that the male has good genes or is healthy? Richard Buchholz, a biologist from the University of Mississippi, pondered these very questions and Wild Turkeys were a perfect study animal for questions of sexual selection. Males mate with multiple females (called polygyny), and the sexes look very different (sexually dimorphic). Buchholz designed some fancy mating tests, checked out the health of the males, and eureka, the answers to snood fashion.

First, Buchholz found a non-sexual function for the bare parts on the head. They are crucial for cooling down strutting tom when he is exerting himself on a hot day. Snood or no snood, he needs his radiator. So there is a clear reason for the bare skin. But that still doesn’t explain the long snood.

He did show that a long snood is indeed selected by females, but males also select it. Females were attracted to a long snood and males deferred to other males with longer snoods. But what is it about a long snood?

It turns out that the longer the snood a male has the less intestinal parasites he has. Long snooded males appear to be more resistant to parasitic infections. Buchholz suggests that if that is true, this might be a case of females choosing males with good genes. And males that are free of parasites are probably more dominant over other males. Short snooded males that defer to long snoods might be able to assess the competition before fighting with them and avoid wasting energy in fruitless fights that they are sure to lose to the healthier snood.

I think we picked a good snood this year for our traditional supper. I hope you’ve been successful in selecting your snood. Have a Happy Thanksgiving.

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