Coyotes invade woodland caribou range
Coyotes were historically restricted to the Great Plains of the Midwestern and western United States. Over the past two centuries, they have expanded their geographic range to encompass much of North America, including the entire eastern seaboard, south into Mexico and Central America, and north to Alaska. Such range expansion is believed to have been facilitated by two synergistic factors: additional habitat associated with expanding areas of intensive human activity, and reduced competitive pressures following the extermination of wolves from much of North America.
Coyotes invaded the boreal forest in northern Alberta, Canada, within the last 10–30 years. Many people believe this range extension is due, at least in part, to recent increases in silvicultural and energy extraction activities, but this has not been quantified. Because threatened woodland caribou occupy peatlands within the boreal forest, conservationists are increasingly concerned about the potential role of coyotes as predators of caribou calves. To answer this, Dave and Cecilia Latham attached GPS radio collars to nine coyotes to assess their habitat selection, diet and spatiotemporal relationships with caribou, wolves and industrial activity in caribou range in north-eastern Alberta.
Dave and Cecilia found strong evidence to support the hypothesis that industrial activity has facilitated the expansion of coyotes into caribou range. Coyotes showed strong annual affiliations with all-season roads and oil and gas pipelines, as well as winter preferences for areas close to garbage dumps and human settlements. These areas provide coyotes with novel foods such as human refuse and road-killed animals. Coyotes may also select areas of high human activity because they provide a refuge from wolves, which are persecuted by people.
Interestingly, coyote home ranges included areas used by wolves, particularly in winter, which suggests that spatial segregation between the two species is only partial and that coyotes may accrue some benefit from wolves. Although wolves kill coyotes, they also provide coyotes with significant scavenging opportunities. Dave and Cecilia observed coyotes scavenging wolf-killed moose and white-tailed deer carcasses, particularly in winter when deep snow makes hunting the more common small prey species more difficult. Based on scat analyses, deer hunted and scavenged were common (29%) in the diet of coyotes. Small prey species such as mice and voles (44%) and muskrats (40%) were also common food, whereas caribou (2%) was rare. Conversely, for wolves, beaver (48%), deer (41%), and moose (19%) were the most abundant prey.
Coyotes were found throughout the study area, indicating generalist habitat selection. Some individuals showed strong preference for well-drained forests, milled forestry blocks, and towns adjacent to caribou range; other individuals selected caribou-preferred habitats (coniferous swamps and bogs). Coyotes were also strongly affiliated with areas near rivers and streams throughout the year, and to areas near lakes in winter. However, most coyotes in caribou range showed some degree of transience, be it low home range fidelity or long-distance dispersal, with the longest dispersal recorded being 164 km straight-line distance.
Coyotes, together with other predators of woodland caribou, present wildlife managers with a conundrum. At the population level, caribou are not important prey for coyotes –merely an incidental or secondary prey species. However, for caribou, incidental predation by coyotes, wolves and black bears can have a significant impact. Some coyotes apparently specialise in foraging in caribou habitat and these animals may contribute to low caribou calf survival. Caribou decline in Alberta has been attributed to low adult female and calf survival and subsequent low recruitment. Thus management actions to conserve caribou should also consider coyotes, in addition to wolves (primary predator).
This work was funded by the Petroleum Technology Alliance Canada (Alberta Upstream Petroleum Research Fund) and the University of Alberta.