Every winter in the northern expanses of Canada, hunters shoot and trap wolves for their pelts. The animals are known as tundra-taiga wolves (pictured) because they inhabit a landscape extending from the forests in the southern part of the Northwest Territories to the treeless arctic tundra farther north. They are also extremely stressed by the annual hunts, a team of scientists reports online this week in Functional Ecology. The researchers studied reproductive hormones and cortisol, a stress hormone, in tufts of wolf hair collected over a 13-year period. They compared the hormones from 103 of these wolves with those from hair taken from 30 boreal forest wolves that are not as intensively hunted. The tundra-taiga wolves had much higher levels of cortisol, the scientists say. In other species, including humans and dogs, chronically elevated levels of stress hormones adversely affect the immune system, leaving animals more susceptible to disease. The tundra-taiga wolves also had elevated levels of progesterone, a hormone produced during pregnancy, which suggests these packs have an unusually high proportion of breeding females. Normally, wolf packs have only one breeding female and male who produce the pups, while the other wolves assume subordinate roles. The heavy hunting is thus disrupting the wolves’ usual, clearly demarcated social structure, the scientists say, which may cause more human-wolf conflicts. Such continued population disturbances, they note, can also lead to a loss of genetic diversity and ultimately an increased risk of population extinction. Humans consider the tundra-taiga wolves as competitors because they hunt caribou. But trying to control the wolves by severely reducing their numbers is the wrong approach, the scientists say. They urge wildlife managers to consider other factors, such as the wolves’ social structure, when setting management objectives.