January 26, 2009--Birds from the family Zosteropidae—also called "white eyes"—could be poster children for rapid evolution.
They form new species faster than any other known birds, according to new research.
DNA analysis reveals that all 80 species of white eyes emerged in the last 2 million years.
A handful of other birds and mammals have been known to adapt to new environments in such short order, but white eyes are unique because their speciation isn't a simple reaction to shifts in local habitats, said study author Christopher Filardi, a biologist affiliated with the American Museum of Natural History in New York City.
"White-eyes evolved into dozens of new species extremely fast while simultaneously spreading across much of [the southern] hemisphere," he said. "At this geographic scale, there is no one thing from the outside that could have made this happen; there is something special about those birds."
White eyes may evolve faster, in part, because females can start breeding as young as four months old. It takes most tropical songbirds closer to a year to reach sexual maturity, Filardi explained.
And unlike most birds, white eyes are hardwired to be social. They forage, travel, and even preen together, making it easier for them to colonize, according to the study.
Once they arrive at a new location, they quickly settle in for the long haul, genetically isolating themselves. Different species in the Solomon Islands exist just 1.2 miles (2 kilometers) from one another.
The splendid white eye, pictured above, is endemic to the Solomon Island of Ranongga and has a range that can be traversed in a single day's walk.
The study appears this week in the journal Proceedings of the National Academy of Sciences and was funded in part by the National Geographic Society's Committee for Research and Exploration. (The National Geographic Society owns National Geographic News.)
Read more about evolution in National Geographic magazine's Darwin's First Clues.