Snake Populations Mysteriously Plummet

The world's snakes may be in trouble. New research shows that snake numbers have plummeted in a number of populations worldwide.

"Of 17 populations of snakes covering 11 species, 11 populations had declined. That covered eight species," said study lead author Christopher Reading of the Center for Ecology and Hydrology in Wallingford, U.K. "They hadn't just declined, they had declined drastically and in exactly the same time and in the same way."

Reading and nine other researchers pooled their data tracking snake numbers as far back as the late 1980s in the U.K., France, Italy, Nigeria and Australia. Over the period from the late 1990s until about 2005, eleven of the populations dropped steeply.

The team published their findings in Biology Letters.

"We don't know what the reason for those declines is," Reading said. "The idea of this paper is to flag it up to other herpetologists and snake ecologists around the world and say, 'We've got this. Have you got something similar? If so, let's talk about it.'"

"For them all to be synchronous does suggest that there is something at a higher level that has affected everything," Reading added. "It's just too much of a coincidence that this would have happened at the same time for different reasons."

Although the researchers can't say why the snakes are declining, there may be some clues. "We looked at the snakes that had declined and we realized that many of them had common traits," Reading said.

"They tended to be snakes that didn't move around very much. They tended to be sit-and-wait sort of predators. That suggests that we are dealing with something about the carrying capacity of the habitat. We don't know whether it's something affecting the prey or something affecting the habitat."

More mobile snakes would be better able to seek out new habitat, if their usual spot developed problems.

Among the declining species are several types of vipers.

"The vipers are slow growing, long living. Those are exactly the things that are in trouble when people come along and either kill snakes or degrade habitats in way that degrades the prey that is available," said Rick Shine of the University of Sydney in Australia, who was not part of the study.

"I don't think anybody would have guessed that we would have seen this hugely synchronous decline in the species that are being studied," he added. "I think it's frightening."

Climate change is the kind of global force that could cause change across continents, as the researchers observe, perhaps changing habitat or availability of prey. But Thomas Madsen of the University of Wollongong, in Australia, does not think that's the problem in this case.

"Most reptile populations are driven by either increased predation or more or less food," he said. "Climate change is probably not at the moment a major concern. There are so many good and definite stories out there that show the effect of climate change on animal populations. This one isn't one of them."

"I'm very dubious about this report," he added.

He suspects the reported declines are just coincidence. "It's most likely true that these snakes are declining" he added. However, he noted that one of the populations he studied crashed but after watching for a few more years it came back.

If the decline is widespread, the snakes may be following their amphibian cousins. Amphibian populations have declined globally, with at least 42 percent of species declining as of 2008, and many threatened with extinction. Habitat loss and a widespread fungal disease are two major causes, but in many cases, the cause remains mysterious.

"I think we do need to be worried," said Shine. "Exactly how worried -- I think the jury is still out."