Narrator: This is Science Today. For years, scientists studying changes in the environment have looked to declining amphibian populations as an early warning sign for ecological damage. Biologist Tyrone Hayes of the University of California-Berkeley says frogs serve this purpose because they offer a sensitive model for scientific study.
Hayes: One, their eggs are unprotected. So whereas a bird or a reptile is inside of an eggshell, and a mammal is inside of the mother, from the time of fertilization an amphibian is exposed, throughout all those critical developmental stages where limbs are developing and sex is developing, they're exposed to whatever is in the environment.
Narrator: Research has so far focused on declining frog populations in North America, Europe and Japan, but Hayes says new work is showing the scope of the problem.
Hayes: There's good evidence that the problems are global, and that they are increasing. You know the number of people who report areas, in some cases pristine areas, where historically we know there were lots of amphibians and now there are none.
Narrator: For Science Today, I'm Larissa Branin.