Possible Snake Shortage Looms

Declines in Europe and Africa raise worries of widespread slide.

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By Susan Milius, Science News

The world might be facing a new kind of sssilent ssspring if researchers are correct that snake numbers are declining.

Out of 17 snake populations monitored over many years in Europe and Africa, 11 populations plummeted about 10 years ago and have not bounced back, says herpetologist Chris Reading of the Centre for Ecology & Hydrology near Oxford, England. Just what caused the declines between 1998 and 2002 is not yet clear, but Reading and nine other biologists sound an alarm in a Biology Letters paper released the week of June 7.

Losing a lot of snakes can upset the way ecosystems work, Reading says. Snakes often rank as top predators, and even ophidiophobes may appreciate the job that snakes do in controlling rats and mice.

The new finding strikes herpetologist Harry Greene of Cornell University as “deeply troubling.” Checking for trends in other populations will be difficult, he says, because snakes are notoriously hard to count. “Being secretive is a very snakey thing.”

No data were included on U.S. snakes, but Greene notes worrisome signs from eastern king snakes in Florida and southern hog-nosed snakes throughout their range. “Of course some snakes seem to be doing fine, but overall the trend is alarming,” Greene says.

Declines of wild creatures have become a recurring theme since Rachel Carson’s 1962 book Silent Spring warned of pesticides threatening birds. Today, the IUCN estimates that many bird, mammal and amphibian species are threatened with extinction.

Reading’s concern about snakes grew out of a dinner conversation last December with herpetologist Luca Luiselli of the Centre of Environmental Studies Demetra in Rome. Reading had just given a lecture about declines in the smooth snake population he studies in a protected forest in southern England, and Luiselli noted that one of his long-term study populations had also shrunk at about the same time.

Asking around for other studies with comparable data, the two scientists turned up data on various populations of eight species in England, France, Italy, Nigeria and Australia. Eight of the 17 total populations had been monitored since 1980s and the rest since the 1990s.

Even among widespread declines, five populations have hung in as stable and one increased slightly. Tiger snakes on an island off Western Australia, for example, seem to be doing OK, says study coauthor David Pearson of the Western Australia Department of Environment and Conservation near Perth. These snakes feed on chicks in the island’s seagull colony, a reliable bonanza as gulls thrive by commuting to the mainland to feed at garbage dumps.

Pearson speculates that either changes in habitat or food supplies, such as frogs that are also declining, might be a problem for other snakes. Those that live long, reproduce slowly and hunt by lurking in ambush until something edible scampers by, such as the asp viper, seem particularly at risk.

More data may or may not bear out the pattern, says ecologist Rick Shine of the University of Sydney, who was not part of the study. “The jury is still out on whether or not there is a general crisis here, but the reports are alarming.”

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