"Caribou and reindeer, a single grazing species with regional variations, inhabit the northern reaches of Eurasia and North America, from Scandinavia to Siberia and from Alaska to Greenland. Yearly, their vast herds make the single greatest migration of any ungulate in the Northern Hemisphere.
But in what they characterize as the first worldwide caribou census, scientists at the University of Alberta, Edmonton, find that populations have declined by nearly 60 percent in the past three decades.
Fluctuations in caribou numbers are normal, as they are for any animal that inhabits a harsh and highly variable environment. But these declines differ from usual population expansions and contractions in one crucial aspect, says Liv Vors, lead author on the study: They’re occurring simultaneously around the world."