Bird fads weaken sexual selection

Every year, there’s a new fashion pick for the hot male. With lark buntings, that is.

A study of style among birds adds new dimensions to the understanding of how female taste drives the evolution of male charms. This process of sexual selection can lead to outrageous male ornaments, but only if females swoon over the same traits over many generations.

Something different goes on with sex appeal among lark buntings (Calamospiza melanocorys) in Colorado’s Pawnee National Grassland, says Bruce Lyon of the University of California, Santa Cruz. He and Alexis Chaine of the CNRS Experimental Ecology Station at Moulis, France, tracked the characteristics of Colorado male birds who found mates. Trends certainly did appear in size and looks but varied by year, the researchers report in the Jan. 25 Science. In 2000, for example, big white wing patches were in. In 2002, it was small patches.

Fickle as the shifts sound, they might be important, says Lyon. More of a particular year’s hot-male traits than expected by chance turned up in the dads that successfully raised chicks that year. Lyon suggests that either the traits themselves, or something linked to them, tells females who’s the right fellow for a particular year’s conditions.

As for sexual selection, Lyon says the various strong trends in particular years had pretty much canceled out each other’s effects by the end of five years. Flip-flops in taste, he says, might help explain what keeps variety within a species.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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