In what they’re calling the first worldwide census of caribou, scientists at the University of Alberta at Edmonton say the ungulates known for their long migrations have seen their numbers drop nearly 60 percent over the last three decades. Fluctuations in the caribou’s numbers are natural, Moises Velasquez-Manoff reports for the Christian Science Monitor. But traditionally, one herd’s numbers might go up while others dropped. In recent decades, though, all the numbers seem to be headed down, the lead author of the study says. Caribou and reindeer, which are related, are found across the Northern Hemisphere at upper latitudes.