Sep. 26, 2013 — As one species of European songbird island-hopped to colonize mid-Atlantic archipelagoes over the course of a half million years, their songs lost their sense of syntax.
Chaffinches (Fringilla coelebs) on the furthest island of their dispersal, Gran Canaria in the Canary Islands, still sing the same notes, but with a much less structured pattern from one bird to the next, sort of like an island of Charlie Parkers.
"A chaffinch from mainland Europe always sounds like a chaffinch from mainland Europe," said biologist Robert F. Lachlan who completed the 15-year study of chaffinch song structure during a post-doctoral fellowship at Duke University. But on Gran Canaria, it's much harder for a human to pick them out by hearing alone, he said.
Lachlan recorded the songs of 723 males in 12 different populations across the European mainland, the Azores and the Canary Islands and compared them computationally. Subunits of the songs, which he calls syllables, differed slightly between populations, but the sequencing of the syllables -- the syntax -- was progressively less predictable the further the birds got out on the chain of colonization.
The work appears Oct. 7 in the journal Current Biology. It was funded by the Dutch Science Foundation and Duke University.
Syntactical structure was lost in a step-wise fashion that matches the known dispersal of the species across these islands. At the end of the island chain, "the syntax isn't just changing, it's disappearing," Lachlan said. "It's not about changing the rules, it's about losing them."