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, while the sample size of 17 species is small, "the declines are sufficiently striking to warrant attention".
Foragers most vulnerable
A sharp decline in snake 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.
Hard to study
Co-author and wildlife scientist, David Pearson of the Western Australian Department of Environment and Conservation, says there has been limited information on snake numbers.
"They're not easy things to study," he says.
According to Pearson a previous study found a dramatic drop in death adder numbers near Darwin, but that had been attributed to the invasion of cane toads into the Top End.
This current study shows no decline in Australian species, but Pearson says it does serves as a warning.
"It's a warning that climate change, and other factors, can potentially change prey resources," he says. "We're already seeing frog numbers declining ... one of the main predators of frogs are snakes."
And while the prospect of less snakes may appeal to some, Pearson says it could have a damaging flow-on effect.
"They are an important part of biodiversity. [Less snakes] could unbalance the system and cause all sorts of problems."