These startled tigers were captured on film by a camera trap in Nagarhole National Park in India, as part of a nine-year monitoring study by biologist Ullas Karanth and his colleagues.

This month, the researchers report the astounding result: an average of one in four tigers living in the park dies or leaves each year — and yet, the tigers there are thriving. The study was conducted and analysed by Karanth's team from the Wildlife Conservation Society in India and by scientists from the US Geological Survey (K. U. Karanth et al. Ecology 87, 2925–2937; 2006).

How can the tigers survive despite such high annual losses? Karanth says the results bolster his hypothesis that tigers reproduce fast enough each year to make up for deaths due to poaching outside the park — as long as the big cats have enough prey to eat and are protected inside park boundaries.

Other conservationists want governments to place more emphasis on curbing the trade in tiger parts and skins, which are in high demand in Tibet and China. But to Karanth, trade controls aren't as crucial as efforts to secure healthy habitats for the tiger. So measures such as better park patrols and voluntary resettlement of people living in parks are the best way forward, he says.