IT IS a picture that could save a thousand cats. This photo of a jaguar strolling through the Pantanal wetlands in south-west Brazil helped reveal how population sampling can overestimate numbers of big cats by up to 75 per cent – and could delay steps to save them until it’s too late.
Many big cats such as jaguars and tigers are loners and therefore hard to study in the wild. While automated cameras can snap the activities of individual animals, ecologists can only calculate their population density by estimating how far the animals range. To do this, they typically take the average maximum distance between snaps taken for each cat, and then extend the boundaries of the sampled area by half this distance in all directions.
While this extrapolation works well for small mammals, which do not travel far, it hadn’t been verified for big cats. So Marianne Soisalo, a PhD student at the University of Cambridge, teamed up with Sandra Cavalcanti of Utah State University in Logan, who has fitted Pantanal jaguars with global positioning devices. This revealed the cats roamed far more widely than a standard camera survey might suggest. For 2004, that slashed the pair’s estimate of population density from 11.7 jaguars per 100 square kilometres to 6.7 (Biological Conservation, DOI: 10.1016/j.biocon.2005.11.023).
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Alan Rabinowitz, director of science and exploration with the Wildlife Conservation Society in New York City, believes the study is long overdue. He says that camera traps work well if you put cameras all over the area occupied by a population. But many conservation biologists fall back on the cheaper extrapolation. “People misuse these tools,” he says.
