12 Feb 2018

Wooing Female Bowerbirds

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Archbold’s Bowerbird (Archboldia papuensis)

From Matt Ridley’s The Red Queen: Sex and the Evolution of Human Nature:

Consider, though, the case of Archbold’s bowerbird, which lives in New Guinea. As in other bowerbirds, the male builds an elaborate bower of twigs and ferns and therein tries to seduce females. The female inspects the bower and mates with the male if she likes the workmanship and the decorations, which are usually objects of one unusual color. What is peculiar about Archbold’s bowerbird is that the best decorations consist of feathers from one particular kind of bird of paradise, known as the King of Saxony. These feathers, which are several times longer than the original owner’s body and stem from just above his eye, are like a car’s antenna sporting dozens of square blue pennants. Because they are molted once a year, do not grow until the bird of paradise is four years old, and are much in demand among local tribesmen, the plumes must be very hard for the bowerbird to acquire. Once acquired they must be guarded against other jealous male bowerbirds anxious to steal them for their own bowers. So, in the words of Jared Diamond, a female bowerbird who finds a male that has decorated his bower with King of Saxony plumes knows “that she has located a dominant male who is terrific at finding or stealing rare objects and defeating would-be thieves.”

So much for the bowerbird. What about the bird of paradise itself, the rightful owner of the plumes? The fact that he survived long enough to grow plumes, grew longer ones than any other male nearby, and kept them in good condition would be an equally reliable indicator of his genetic quality. But it reminds us of the thing that most puzzled Darwin and got the whole debate started: If the point of the plumes is to indicate his quality, might not the plumes themselves affect his quality? After all, every tribesman in New Guinea is out to get him, and every hawk will find him easier to spot. He may have indicated that he is good at surviving, but his chances of survival are now lower for having the plumes. They are a handicap. How can a system of females choosing males that are good at surviving encumber those males with handicaps to survival?

King of Saxony Bird of Paradise (Pteridophora alberti)

HT: Karen L. Myers.


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