Evolution in the Fast Lane
Members of the Zosteropidae family are not birds of a feather. White-eyes, sparrow-like songbirds, are the fastest-evolving bird on record. According to a recent genetic analysis of several dozen subspecies by Chris Filardi, a biologist at the American Museum of Natural History in New York, 80 species have emerged in the past two million years. Among vertebrates, only the cichlid fish evolves faster, probably due to abrupt changes in its geographically confined habitat, a common catalyst for speciation. But white-eyes populate three continents, so Filardi suspects that sexual selection and social behavior drives the birds' speedy diversification, which includes changing plumage and songs.