Wolf dispersal in the Rocky Mountains, Western United States: 1993–2008

Abstract

Gray wolves (Canis lupus) were extirpated from the northern Rocky Mountains (NRM) of the United States by the 1930s. Dispersing wolves from Canada naturally recolonized Montana and first denned there in 1986. In 1995 and 1996, the United States Fish and Wildlife Service reintroduced 66 wolves into central Idaho and Yellowstone National Park. By 2008, there were ≥1,655 wolves in ≥217 packs, including 95 breeding pairs in the NRM. From 1993–2008, we captured and radio‐collared 1,681 wolves and documented 297 radio‐collared wolves dispersing as lone individuals. We monitored dispersing wolves to determine their pack characteristics (i.e., pack size and surrounding pack density) before and after dispersal, their reproductive success, and eventual fate. We calculated summary statistics for characteristics of wolf dispersal (i.e., straight‐line distance, age, time of year, sex ratio, reproduction, and survival), and we tested these characteristics for differences between sexes and age groups. Approximately, 10% of the known wolf population dispersed annually. The sex ratio of dispersals favored males (169 M, 128 F), but fewer dispersed males reproduced (28%, n = 47) than females (42%, n = 54). Fifty‐nine percent of all dispersers of known age were adults (n = 156), 37% were yearlings (n = 99), and 4% were pups (n = 10). Mean age at dispersal for males (32.8 months) was not significantly different (P = 0.88) than for females (32.1 months). Yellowstone National Park had a significant positive effect on dispersal rate. Pack density in a wolf's natal population had a negative effect on dispersal rate when the entire NRM population was considered. The mean NRM pack size (6.9) from 1993 to 2008 was smaller than the mean size of packs (10.0) from which wolves dispersed during that time period (P < 0.001); however, pack size was not in our most supported model. Dispersals occurred throughout the year but generally increased in the fall and peaked in January. The mean duration of all dispersals was 5.5 months. Radio‐collared wolves dispersed between Montana, Idaho, and Wyoming to other adjacent states, and between the United States and Canada throughout the study. Mean straight‐line distance between starting and ending points for dispersing males (98.1 km) was not significantly different than females (87.7 km; P = 0.11). Ten wolves (3.4%) dispersed distances >300 km. On average, dispersal distance decreased later in the study (P = 0.006). Sex, survival rate in the natal population, start date, dispersal distance, and direction were not significant predictors of dispersal rate or successful dispersal. Wolves that formed new packs were >11 times more likely to reproduce than those that joined packs and surrounding pack density had a negative effect on successful dispersal. Dispersal behavior seems to be innate in sexually mature wolves and thereby assures that genetic diversity will remain high and help conserve the NRM wolf population. © 2017 The Wildlife Society.

Stable pack abundance and distribution in a harvested wolf population

“…Most breeding adults were replaced by local dispersers or by an individual within the pack (Ausband , Bassing ). In addition, most harvest coincided with the breeding season and the pulse in dispersal typical for wolves in the Rocky Mountains (i.e., late winter–early spring; Mech and Boitani , Webb et al , Jimenez et al ). Replacement of breeding adults can occur rapidly under these conditions (Rothman and Mech , Fritts and Mech , Stahler et al , Mech and Boitani ); thus, breeder turnover may have occurred quickly, preventing some destabilizing effects of breeder loss on the pack (Ballard et al ).…”

Where can wolves live and how can we live with them?

“…However, the USFWS would likely never have to relist the wolf.Wolves have been off the federal Endangered Species List during some years in Minnesota, Wisconsin, and Michigan (2007-2008, part of 2009-2014, Montana, Idaho and eastern Oregon and eastern Washington (2009, and2011 to the present) and managed by those states.The populations, nevertheless, have maintained themselves or increased.Dispersers from these populations continue to show up in other states (Treves et al, 2009;Jimenez et al, 2017).…”

Effects of wolf pack size and winter conditions on elk mortality

“…Over the past several decades there has been a broad‐scale decline in elk recruitment across the western United States (Lukacs et al ). Concomitantly, wolves have become well established in many areas of the western United States since their reintroduction in 1995 (Jimenez et al ) and there is pressure for state wildlife management agencies to manage wolves to benefit ungulate populations. Although studies relating elk dynamics to wolf populations are beginning to emerge (Hebblewhite et al a , Hebblewhite , White and Garrott ), quantitative models for predicting how elk survival might change in response to numerical changes in wolf populations are mostly absent.…”