Something is killing the world's frog population and it just might be stress, according to experts who gathered recently at Indiana University.

Around the world, scientists are recording mysterious declines and even extinction of various frog and toad populations:- In California, the Yosemite toad has declined by 80 percent in recent years.

- In Puerto Rico, the golden toad is disappearing.

- In Australia, the gastric-brooding frog - females gestate their young in their stomachs - has not been seen in several years.

- And the common North American garden toad or the Western toad is also on the decline.

Everyone agrees that the world's population of frogs is diminishing. But there's great debate about what's causing it.

"It's a very controversial topic," said Joseph T. Collins, co-author of the Peterson series guidebook "A Field Guide to Reptiles and Amphibians."

Collins, who works at the University of Kansas' Museum of Natural History, was among the scores of researchers attending the Society for the Study of Amphibians and Reptiles' annual meeting.

The scientists discussed whether the recent declines are the result of natural fluctuations or manmade problems such as acid rain, the thinning of the ozone layer and habitat destruction.

The one seemingly bright spot for the frog population has been the Midwest flooding.

"Much as you hate to say it, it's been a wonderful year in the Midwest for frogs," Collins said.