Dynamics of reintroduction in an indigenous large ungulate: the wood bison of northern Canada

We document the recolonization of an indigenous large herbivore into its historic range. Eighteen wood bison (Bison bison athabascae) were reintroduced into the Mackenzie Bison Sanctuary of the Northwest Territories, Canada, in 1963. The population subsequently increased in number and range, peaking at about 2400 in 1989; numbers were estimated at about 1900 in 1998. Recolonization occurred through a series of increases in local areas followed by pulses of dispersal and range expansion. This pattern was originally described for exotic species' introductions. Differences in diet and overwinter survival of calves over the bison's range suggest that intraspecific competition for food provided the stimulus for range expansion. For a conservation strategy, the reintroduction of animals into several independent sites in their historic range would facilitate recolonization and achieve a faster spread than a reintroduction into one site followed by waiting for the population to spread as a result of its own density dependent responses.