A three-year-old cottonmouth sits on a mat of fallen palms on Seahorse Key, Florida.

Biologist Harvey Lillywhite has found that cottonmouths that live near seabird nests are bigger than snakes elsewhere on the island. The snakes closest to the nests receive an abundance of dead fish dropped by the birds, the scientist explained.

In return for this fishy bounty, the cottonmouths refrain from eating the birdsincluding baby chicks that fall from the nestsand deter other predators from raiding the nests, he added.

The result is a win-win for both snakes and birds that Lillywhite said he has not seen on any other island.

"There are a lot of island systems where there are birds and snakes. Of all the cases I know, the snakes are predators on the birds," he said.

"At Seahorse Key it's totally different. Here the snakes do not eat the birds, and the birds are providing food for [the snakes]. So it's a pretty cool system."

 See More Photos in the News
 See Today's Top News Stories
 Get Our Free email Newsletter: Focus on Photography