Since the early '80s, scientists have noted the "population crash," as SITES project director Jennifer Bine puts it, of amphibians worldwide. The populations of frogs, toads, salamanders and other amphibians have always fluctuated -- one year a group of frogs in one location seems to disappear, but a year later they're back and croaking. Lately, though, frog-census takers have observed that they haven't been reappearing. More and more, other frogs are turning up, with extra limbs and mutated faces. Several of those mutants have been discovered in Missouri, says University of Missouri-St. Louis amphibian biologist Dr. Godfrey Bourne.
Extinction and mutation ain't good, of course, but when it comes to frogs, we Homo sapiens have particular cause to worry, scientists agree. Amphibians are defined by their dual lives: as herbivores in the water and, later, as carnivores on land. As such, they are extremely sensitive to changes in the environment. Their moist, thin skin is similar to the inner lining of our lungs, and it literally breathes. "The routine description of what these animals are is that they're canaries in coal mines," says Bine. "They can tell us when an environment is suffering."
"They're a barometer," agrees Bourne. "If the environment is changing so drastically that we're actually losing species, then we'd better pay attention and find out exactly what it is that's wiping out those species in those localities and do something when we can, because the next group that might be impacted might be us."
The exhibit traces the many possible reasons for the decline of amphibians and the implications for the rest of our earthly zoo. Highlights include a model of the extinct Puerto Rican frog Eleutherodactylus karlschmidti, which last croaked in 1974, and a button visitors can press to hear its call. Visitors may push buttons to hear the calls of other frog species, too, as well as a chorus of different types of frogs croaking together. Listening for calls simulates the technique census-takers use to determine the concentration of frogs in a certain area.
So what's causing all these delicate frogs to hop into oblivion? Scientists agree that it's a variety of factors, depending on which part of the globe you're talking about. Habitats are ruined by pollution and agrichemicals; frogs starve as a result of the loss of prey species. The depletion of the ozone layer, accompanied by intensified solar radiation, is a killer. Bourne explains that the loss of wetlands also means the loss of frogs. Recently, scientists discovered a strangely powerful fungus that is lethal to any frog that touches it.
With so many culprits, it's easy to see how sensitive these animals are. The writing is on the wall.