Looking at the wide array of beak shapes on Galapagos Island finches, it's clear that they are adapted to different feeding tasks¿an observation Charles Darwin first made more than a century ago. For example, whereas the lowland birds have evolved large beaks that enable them to crack open hard seeds, smaller forest birds sport daintier beaks for eating insects. But beak form affects more than just diet. According to a report published today in the journal Nature, the beaks of Darwin's finches shaped their songs, which may have in turn spurred speciation.

Evolutionary biologist Jeffrey Podos of the University of Massachusetts analyzed beak structure and frequency structure of songs in eight finch species. "Birds with large beaks are in essence playing cumbersome musical instruments, while birds with smaller beaks, by comparison, should be more proficient as musicians," Podos predicted. His observations bore this out: birds with smaller beaks trill more quickly and produce a wider range of notes. Thus, as the birds' beaks adapt to different food sources, their songs, too, might shift. Since females use songs to select mates, Podos says, the diversification of these mating signals may promote speciation, which could explain the radiation that has defined the Galapagos finches.

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