Distinct populations of snake species have crashed over the last decade, raising fears that the reptiles may be in global decline, according to a study.

The pattern across the eight species monitored was alarmingly similar despite their geographical isolation, which points to a common cause, say researchers.

Factors thought to play a role include climate change, habitat loss, pollution, disease, lack of prey and over-exploitation, either for food or trade.

The study showed that of the 17 snake populations in Britain, France, Italy, Nigeria and Australia, 11 had dropped off sharply over a four-year period starting in the late 1990s.

"Our data revealed an alarming trend," the authors report in the journal Biology Letters.

"Two-thirds of the monitored populations collapsed, and none have shown any sign of recovery over nearly a decade since the crash. Unfortunately, there is no reason to expect a reversal of this trend."

They add that while the sample size of 17 species is small, "the declines are sufficiently striking to warrant attention".

Foragers most vulnerable

Snakes are among the top reptile predators, and a sharp decline in their numbers would likely have serious consequences for many ecosystems.

Earlier studies have turned up dwindling numbers for certain species and in some regions, especially the Mediterranean basin.

But the new study presents the first evidence that snakes in the tropics are also in trouble.

Depending on the continent, population declines varied depending on sex, with females disappearing significantly more rapidly than males in most cases.

So-called 'sit-and-wait' foragers - snakes that lie motionless, waiting for prey to come within striking distance - are also more severely depleted in numbers than counterparts which are active hunters.

The only Australian snake in the study - the tiger snake (Notechis scutatus) - defied the trend maintaining a stable popuation throughout.

The fact that the declines observed happened in different corners of the globe over the same short time points to a single problem.

"We suggest that there is likely to be a common cause at the root of the declines, and that this indicates a more widespread phenomenon," the researchers write.

-ABC/AFP