Faced with competition from an invading species, a type of lizard in Florida took just 20 generations — about 15 years — to evolve feet better suited to climbing trees, a new study says.

Biologists have long believed that evolution could occur rapidly among some species facing sudden, intense competition. In 1995, as part of an unrelated study, researchers introduced a foreign species of brown anole lizards to three islands off the coast of Florida that were already home to green anole lizards. The green lizards are known to move to higher perches after an invasion of brown ones.

To test the rapid-evolution theory, researchers returned to the islands 15 years later and examined the feet of the green lizards (which had, as predicted, relocated to higher perches). They found that the lizards had developed larger and stickier toe pads, a characteristic not shared by green lizards on nearby islands that had not been populated with brown lizards.

"First, we saw the behavioral response," said Yoel Stuart, a biologist at the University of Texas and the lead author of the study. "And when we compared the anoles to islands with no invaders, we saw there was also this evolutionary response."

The ability to evolve rapidly could be a boon to species threatened with climate change, suggested the researchers, who published their study in the journal Science. Other species that have shown an ability to do so include Darwin's finches in the Galápagos Islands, which evolved smaller beaks just 22 years after the arrival of a competitive species, according to a Princeton study from 2006.

Australian birds sense, chase rain

The banded stilt, a graceful, nomadic water bird found in inland salt lakes in Australia, can somehow sense and move toward rainfall hundreds of miles away.

Australians often spot the birds within days of rainfall, said Reece Pedler, a biologist at Deakin University in Australia.

And then, abruptly, the birds will disappear.

The mystery, he said, is "How do these birds know when to leave one place for another, and how do they do it so fast?"

To better understand the movements of the nomadic birds, Pedler and his colleagues tagged 21 banded stilts with satellite transmitters. Their findings appear in the journal Biology Letters.

One tagged bird flew to a saline wetland more than 1,000 miles away in less than two and a half days. Another bird took six days but ended up in the same area. Other tagged birds made overnight flights of about 200 to 400 miles.

The banded stilts are interesting because their movements are so sudden and unpredictable. While many other birds migrate, Pedler said, most do it seasonally, "on a predictable time scale, and have time to plan, prepare and adjust flight-muscle mass."

NEW YORK TIMES