Characteristics of Dispersal in a Colonizing Wolf Population in the Central Rocky Mountains

Abstract

Gray wolves (Canis lupus) were eradicated from Montana in the 1930s and the adjacent Canadian Rockies by the 1950s, but recolonized these areas in the 1980s. We studied wolf recovery in and near Glacier National Park (GNP), Montana, from 1979 to 1997. During this period, 31 of 58 tagged wolves dispersed. Most wolves (57%) did not make exploratory forays 3 months before permanent separation from their natal pack. Wolves usually left their natal home range quickly (median = 4 days; mode = 1 day) after separating from the pack. Mean dispersal distance was not different (P > 0.05) between males (113 km) and females (78 km), excluding an unusually long dispersal of 840 km by a yearling female. Wolves tended to disperse in a northerly direction to areas of higher wolf density. January-February and May-June were peak months for dispersal. Mean dispersal age (M = 28.7 months; F = 38.4 months) was not correlated with maximum pack size. Twenty percent of dispersers were ≥57 months old at dispersal. Sex ratios of dispersers and captured wolves (both 71% F) differed from parity (P = 0.002). Annual survival rate (x ± SE) for dispersers and biders (philopatric wolves) did not differ (dispersers = 0.76 ± 0.10; biders = 0.77 ± 0.14). Wolves killed by humans died closer to roads (x = 0.13 km) than wolves that died from other causes (x = 0.85 km). Eighty percent (n = 30) of wolf mortalities were caused by humans, with proportionately more dispersers (90%) than biders (60%) dying from human causes. Dispersers produced more litters than biders. Effects of mountainous terrain and management on wolf recovery are discussed.