Snakes in unexplained global decline

Snake populations have shown an alarming decline across the world over the last 22 years, report scientists today. Of 17 snake populations, including 11 species from five countries, 11 dropped sharply. The scientists say they don't yet know the exact reasons for the drops, but have...

9 June 2010, by Tamera Jones

Snake populations have shown an alarming decline across the world over the last 22 years, report scientists today.

Zamenis longissimus

Zamenis longissimus.

Out of 17 snake populations, including 11 species from five countries, 11 have dropped sharply. The scientists say they don't yet know the exact reasons for the drop, but have suggested a possible 'common cause' such as climate change.

'There could be different causes in different populations, but it's too coincidental for snakes from so many countries to be going through the same steep decline. There has to be a common cause,' says Dr Chris Reading from the Centre for Ecology & Hydrology, who led the research.

The researchers collected data on 11 species of snakes, including Britain's rarest – the smooth snake – vipers from Europe and north Africa, pythons and whipsnakes. These snakes came from populations in the UK, France, Italy, Nigeria and Australia.

'We want to raise a red flag to other snake researchers. Have you found anything similar?'

Dr Chris Reading, Centre for Ecology & Hydrology

Britain's smooth snake Coronella austriaca was among the species showing the sharpest drop, as well as two snakes from France, Italy's orsini's viper Vipera ursinii and three species from Nigeria.

The team, which included scientists from all five countries, describe in Biology Letters how they found that many populations were stable up until around 1998. But after this numbers started to plummet over an average four-year period, before hitting a short patch of what appears to be relative stability.

'Most of the populations look like they hit a tipping point in the late '90s,' says Reading.

Surprisingly, some of the populations showing drops were in protected areas, such as nature reserves. This suggests that a change in habitat quality rather than loss – like a reduction in the amount of prey around – could be to blame.

Unexpected

None of the populations have so far recovered to pre-crash levels.

'We just didn't expect a widespread decline like this. But it's sufficiently striking to warrant attention,' says Reading.

They also found that five populations were stable, while one – the western whipsnake Hierophis viridiflavus from France – is showing signs of a weak increase.

Many long-term studies show drops in numbers of amphibians, reptiles, birds and mammals worldwide. But this is the first documented evidence showing a widespread decline in snakes.

'We want to raise a red flag to other snake researchers. Have you found anything similar?' says Reading.

Reading points out that this was purely a chance finding.

'An Italian colleague and I were discussing snakes over a beer and he happened to mention a drop in numbers of snakes in Italy, which is what I'd seen in Britain's smooth snake,' explains Reading. 'So we decided to look through existing datasets.'

Reading and his colleagues are now hoping to look at data on other snake species from the States and South America to see if they can see the same patterns.

'The problem is that there are very few long-term studies, so it's difficult to compare,' he explains.

Snakes are top predators and play a vital role in places like rice paddy fields and sugar cane plantations where 'they're an important agent controlling mice and rats,' says Reading.

'Most people don't like snakes, but the planet would be a much poorer place without them,' he adds.

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