Range expansion of raccoons in the Canadian prairies: review of hypotheses

The raccoon (Procyon lotor) has greatly expanded its range in the Canadian prairies during the 1900s. Four non-exclusive explanations may explain this range expansion: introductions, mesopredator release, availability and suitability of winter denning sites, and food availability. No introductions of raccoons were documented for the prairies, suggesting that range expansion was not directly caused by humans. The suggestion that raccoons moved north because of “mesopredator release” appears implausible because, even where larger predators such as bobcats (Lynx rufus) and coyotes (Canis latrans) exist, raccoons experience low predation rates and also because raccoons have expanded their range into treeless areas where coyotes are abundant. The third hypothesis, suggesting that availability of winter denning sites limits raccoon distribution, also receives little support, mostly because of the raccoon's flexibility in using a variety of natural and anthropogenic structures for denning. The last hypothesis, the idea that raccoon range expansion has followed an increase in availability of food, appears most plausible. The effects of global warming, which affects not only the availability and diversity of foods but also the duration of the growing season (and thus temporal availability of food), probably helped raccoons colonize new areas.