Evolving Bird Songs

This week the New York Times published an interesting story about how some songbirds change their songs over time.

For Some Birds, It’s Not Always the Same Old Song
By Henry Fountain
Published: April 19, 2010

Songbirds are not born with songs in their heads, but learn them from others. And as in a game of telephone, it would seem natural that, over generations, the songs might change.

That is what happens with many species, some more dramatically than others. The songs of indigo buntings change so much, for example, that songs that are five years apart are almost completely different.

But with other species, the songs are more stable. Now, thanks to some old audio recordings, researchers have determined just how stable some songbirds’ songs can be.

The songbird in question is not just any old bird, but a member of a famous group of finches that Charles Darwin studied in the Galápagos Islands. Using recordings of Geospiza fortis, the medium ground finch, made 38 years apart, Jeffrey Podos of the University of Massachusetts and Eben Goodale, who is now at the University of California, San Diego, found that some songs have persisted over four decades.

The researchers conducted a statistical analysis of songs, using elements like number of notes, note duration and trill rate. As they report in Biology Letters, in each year’s recordings there is a lot of variability in the songs. But from one period to another, there are some songs that match quite closely.

“Seemingly random songs are maintained over time,” Dr. Goodale noted. “There must be some force maintaining these songs.” As to what that might be, there is no clear answer as yet. But he said one potential clue is that, unlike many songbirds, Darwin’s finches learn their songs not from a neighbor but from their fathers.