Frogs follow their noses - North American wood frogs use smell recognition in searching for ponds - Cover Story

Ranger Rick, March, 1994

A scientist named Bruce Waldman has made a big discovery about a tiny North American frog.

Waldman studies wood frogs (above). These frogs spend most of the year under leaves in the woods. Then each spring they come out and begin looking for a pond where they can mate and lay their eggs.

But Waldman noticed something really strange: The frogs hop from pond to pond before finding one that suits them. What's going on? Waldman wondered. Why would the frogs choose one pond over the others?

Waldman began to do some experiments. He soon discovered that each pond has a different smell. The smell comes from different kinds of tiny plants called algae (AL-jee) living in it. And each frog searches for the pond that smells exactly like the one it hatched in and grew up in.

Why do frogs go back to the ponds where they hatched? Waldman explains: "Those ponds must have been OK places for frogs to grow up in, otherwise the frogs wouldn't be alive.

"Other little pools of water might dry up or get flooded more easily than their home ponds. Or there might be fish in a pond that would eat the frogs' young. So the frogs head for home, where their eggs and tadpoles have a good chance of turning into healthy frogs."