We generally think of evolution in terms of many, many years. Snail kites in Florida have made a life-saving change in slightly more than a decade.

The kites eat snails, small snails known as apple snails. The birds have lived on those snails for ever. Their beaks were the correct size for that prey.

Both species live in the Everglades. Water quality there has declined. Drainage had made some parts of the Everglades too shallow for the snails, other parts too deep for the birds to hunt successfully.

The kite population had declined from about 3,500 birds in 2000 to about 700 in 2007. Things seemed to get worse when an invasive snail species arrived. It is two to four times larger than the native apple snails. The kites had trouble extracting the snail from the larger shell.

Then, very quickly, the kites adapted. Historically, there was a natural range of kite beak sizes, some larger than others. The birds with larger bills had less problem with the larger snails.

The kites found more nourishment in larger snails. They survived to produce chicks with larger bills. The generational change continues. Larger bills produce larger bills.

Thirteen years after the invasive snail appeared the kite population of 700 has tripled.

Scientists studying the kites call the change "incredibly rapid."

A study of this behavior recently was published in the journal Nature Ecology and Evolution.