IT MIGHT be gruesome, but counting road kill could be a quick and effective way to spot local changes in wildlife populations.

In 1984, 1994 and 2005, Bob Brockie and Richard Sadleir, two retired ecologists, drove the length of New Zealand’s North Island, counting dead animals along the way. Then, along with Wayne Linklater of Victoria University of Wellington, they compared their data with road kill counts going back to 1949.

In some cases, the counts agreed with known changes in a population. For instance, the number of dead possums on the roadside fell by 60 per cent between 1994 …