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SNAKES that lie in wait to ambush prey, like the proverbial snake in the grass, are the most likely to suffer when people move into their neighbourhood. A study of venomous Australian snakes has found that half of the eight ambush species are endangered, while fewer than a tenth of the active hunters are at risk.

The discovery came from a search for ways of identifying vulnerable reptiles. Bob Reed of the Savannah River Ecology Laboratory in Aiken, South Carolina, and Rick Shine of Sydney University in Australia compared 10 endangered snakes with 65 more common species.

Ambushing prey turned out to be the top danger sign. 鈥淢any ambush predators already have fairly low reproductive frequencies,鈥� says Reed. This makes them vulnerable when prey declines, because reduced populations take longer to recover. And because ambush snakes tend to stay in one place, they also lose out to their more mobile active-hunter cousins when prey is scarce. Another problem is that people often disturb the hiding places favoured by ambush snakes, such as leaf clutter.

The study also found that combat between snakes was a factor. The males of some Australian ambush snakes fight each other, but the research showed that a species is at higher risk if its males don鈥檛 fight. That鈥檚 probably because the non-fighting species also tend to have larger females, which are more likely to be spotted and killed by people. Museum collections, for instance, have 13 per cent more females than males from endangered snakes.

Reed thinks these risk indicators could help people spot troubled species before they become endangered. He has discovered a further six that appear to be at risk. 鈥淲e should concentrate first on these six species, before population declines to the point where drastic measures are necessary.鈥�