Scientists studying the ecology of the Chernobyl exclusion zone in Ukraine have made the most of freezing conditions there - using footprints in the snow to study the population of mammals.

Prof Tim Mousseau, seen here on the right, and his colleagues have been studying the exclusion zone surrounding Chernobyl's infamous nuclear power plant for more than a decade. Their ongoing aim is to measure the effect of background radiation on wildlife.

In a recently published paper in the journal Ecological Indicators, the team described their method - counting tracks in the snow along 161 straight lines, called transects, in and around Chernobyl in February of 2009. The team took background radiation readings as they moved through the zone.

"We recorded 445 mammals belonging to 12 different species," the team reported in the paper. The most abundant mammals in the zone were foxes, followed by wolves, a footprint from which is pictured above.

The team says their study shows that the number of mammals was lower in areas where radiation levels were higher, although other researchers say the background radiation in the zone has little to no effect on the wildlife there.