Population Dynamics of a Recolonizing Wolf Population

Breeding populations of wolves (Canis lupus) were absent from the western United States for about 50 years following their extirpation by humans in the 1930s. Here we describe the recolonization by wolves of northwestern Montana and southeastern British Columbia, from the initial production of a litter by a pair of wolves in 1982 through the mid-1990s when 3-4 packs produced litters. Sex ratio of captured wolves favored females (38/54 = 70%; χ2= 8.96, 1 df, P < 0.005). Litter size in early summer (x̄ = 5.3, SE = 0.4, n = 26) and in December (x̄ = 4.5, SE = 0.5, n = 26) were relatively high compared to similar counts in established populations elsewhere. Pack size in May was unrelated to litter size in June (rs= -0.13, 23 df, P = 0.25) or the following December (rs= -0.12, 23 df, P = 0.28). Annual adult survival rate (0.80) was relatively high in this semi-protected population and was higher among residents (0.84) than among wolves that dispersed (0.66) from the study area (Z = 2.24, P = 0.025). Although dispersal was common among radiocollared wolves (19/43 = 44%), population growth within the study area averaged 20% per year from 1982 to 1995. Low human-caused mortality rates and maintenance of connectivity for wolves between this small population in the United States and larger populations in Canada will enhance the probability of persistence and expansion of this population.