Robert R. Ream

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 northwestem 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%; X 2 = 8.96, 1 df, P < 0.005). Litter size in early summer (x = 5.3, SE = 0.4, n = 26) and in December (x = 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 (r s = -0.13, 23 df, P = 0.25) or the following December (r s = -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.

DIETARY OVERLAP BETWEEN WOLVES AND COYOTES IN NORTHWESTERN MONTANA

Abstract We studied effects of recolonizing wolves (Canis lupus) in the North Fork of the Flathead area of northwestern Montana on the diets of coyotes (C. latrans) from 1994 to 1997. Wolf and coyote diets differed in frequency of occurrence of prey species during 3 of the 4 summers and winters (P < 0.001) during the study. Coyote diets contained more murid prey items, and wolf diets contained more deer (Odocoileus virginianus and O. hemionus) in the summer and elk (Cervus elaphus) in the winter. Coyotes and wolves ate prey of different size during both the summer (P < 0.001) and winter (P < 0.001) months in 1994–1996: wolves took a greater proportion (P < 0.001) of large (>45 kg) prey species and coyotes, small (<2 kg) prey (P < 0.001). Wolves selected a larger proportion of adults (P < 0.001), whereas coyotes selected a larger proportion of juveniles (P < 0.001) during summer. We believe that differential use of food resources facilitates coexistence of wolves and coyotes in the North Fork of the Flathead area.

Prey Taken by Colonizing Wolves and Hunters in the Glacier National Park Area

The recent colonization of the northwestern United States by an endangered wolf (Canis lupus) population has raised concerns among hunters regarding competition for prey. Data on wolf prey selection may dispel misperceptions and thereby decrease human-caused wolf mortalities that would affect wolf recovery. We assessed the extent to which the early stage of colonization affected wolf prey selection by comparing our results with those from established wolf populations. We examined 243 prey killed by colonizing wolves in the Glacier National Park area of Montana and adjacent British Columbia during winters 1985-91 and compared characteristics of these with those of ungulates killed by hunters

FACTORS CORRELATED WITH FORAGING BEHAVIOR OF WOLVES IN AND NEAR GLACIER NATIONAL PARK, MONTANA

Abstract We examined prey selection, search distance (measured as km traveled/kill), and spatial use of recolonizing wolves (Canis lupus) in a multi-prey system in northwestern Montana, USA, and southeastern British Columbia, Canada, from 1986 to 1996. Our objective was to explore factors affecting these parameters to better understand wolf–prey relationships of recolonizing wolves. Within white-tailed deer (Odocoileus virginianus) winter ranges, wolves selectively killed elk (Cervus elaphus) over deer. Number of wolves (r = 0.67, P = 0.03), year (r = 0.68, P = 0.02), and possibly human hunter-days/elk harvested (r = 0.55, P = 0.08) were positively correlated with variation in proportion of deer killed by wolves annually. Outside of severe winters, white-tailed deer, elk, and moose (Alces alces) appeared to be equally vulnerable to wolf predation. Search distance of wolves varied by up to 12 times annually. Snow depth (r = 0.73, P = 0.03) and proportion of total kills by wolves that were deer (r = 0.66, P = 0.06) were negatively correlated with the annual variation in the total search distance of wolves. Search distance per wolf was correlated negatively with year (r = 0.66, P = 0.06) and exponentially with hunter-days/elk harvested (r = 0.70, P = 0.04). Space use by wolves may have been in response to local changes in deer abundance. Wolves appeared to select the most profitable prey species. Severe winters and wolf selection for deer, coinciding with a decrease in elk numbers, increased wolf hunting efficiency by reducing search distance. Further research is needed to determine whether reduced search distance equates to increased kill rates by wolves in this system. Based on the time, expense, and difficulty of gathering data on wolf search distance in this sytem, however, we recommend against assessing impacts of wolves on prey via measuring kill rate. Rather, we suggest monitoring impacts of recolonizing wolves by directly assessing cause-specific mortality and recruitment rates of prey species.

FIRST WOLF DEN IN WESTERN U.S. IN RECENT HISTORY

Gray wolves (Canis lupus), once common throughout the conterminous United States, were exterminated everywhere except northeastern Minnesota by the 1930s (Mech 1970). The last wolf taken in Montana by a government trapper was in 1936 (Ream and Mattson 1982). In the northern Rocky Mountains, wolves have been observed and killed occasionally during the past 50 years, but no reproduction or dens have been documented (Brittan 1953; Day 1981; Ream and Mattson 1982; Singer 1979; Weaver 1978). This note describes a wolf den in Glacier National Park (GNP), Montana in 1986 and reports 5 additional dens in GNP and adjacent British Columbia (BC) in 1982, 1985, and 1987. The study area was in the North Fork Flathead River drainage and adjacent Wigwam River drainage immediately to the west and covered approximately 5000 km2. The North Fork originates in BC and flows 50 km southeast where it crosses into the U.S. and forms the west boundary of GNP for 70 km. Wolf surveys in Montana from 1972 to 1979 yielded no evidence of wolf reproduction, and an adult female wolf radio-collared 7 km northwest of GNP in 1979 did not den in 1979 or 1980 (Ream and Mattson 1982). The closest known breeding population to Montana prior to 1982 was approximately 100 km north of GNP in Alberta (Ream and Harris 1986). In 1982, a litter of 7 pups was discovered at a rendezvous site 10 km northeast of GNP (B. McLellan, pers. comm.). On 18 May 1985, McLellan captured a lactating female wolf (W8550) in a grizzly bear (Ursus arctos) leg hold snare, radio-collared and released her, and she returned to her den 12 km north-northwest of GNP within 24 hours. Seven black pups were observed near this den on 8 July 1985. W8550, another gray adult, 3 black adults and the 7 black pups (Magic Pack), moved south into GNP in November 1985, where it remained for most of the time thereafter. The size of the pack was reduced to 8 when 4 members of the pack disappeared in March, 1986. W8550 initiated denning activity 20 km south-southeast of the Canadian border in GNP on 15 April 1986, and remained at the den until 20 May when she began to move short distances. On 31 July she was observed from a fixed-wing aircraft at this den, with 5 pups and 7 other adults. The pack remained at the den and rendezvous site until 29 July when they moved 15 km north to another rendezvous site in GNP. On 6 August the authors hiked in to examine the den. The 1986 den consisted of 5 den openings dug into a flat-topped, heavily forested knoll that rose 3 m above an adjacent 2 ha meadow. Scats and trampled vegetation, and earlier aerial observations, indicated that the meadow was used as a rendezvous site after the pups left the den. The den openings were located within an area of 400 m2 extending 40 m along the edge of the knoll. Den openings were well hidden in Engelmann spruce (Picea engelmanni), Douglas-fir (Pseudotsuga menziesii), and lodgepole pine (Pinus contort) forest, with Engelmann spruce dominating at the immediate den openings. When visited in August, most of the meadow was dry, although wet meadow vegetation dominated the lower portions and the intermittent creek that meandered through the meadow. Three openings were dug down into the flat top surface of the knoll and 2 were dug into the steep, north-facing side. By wriggling in as far as possible and reaching with a 3 m wood stick, we could not reach the end of 1 north-facing den hole, probably the natal den. The other 4 holes were 1, 2, 2, and 3 m in depth. The entrance holes averaged 30 cm in width and 50 cm in height. Another den hole had been dug to a depth of 1 m, 400 m northwest of the den area described above. It probably was dug in the early spring and and not used much as there were only 2 old (>2 months) scats found near the entrance. It was in lodgepole pine, 5 m northwest of a 40 ha meadow and was more conspicuous than the other den holes. W8550 was apparently displaced as the alpha female of the Magic Pack in late January 1987 and was seen alone for several months thereafter north of the border. Later, 4 other members from the Magic Pack joined her and she denned in BC during late May. Remaining members of the Magic Pack denned in GNP in late April but we never found what we were sure was the natal den. Radiocollared male W8401, alone for 2 years, found a mate and denned in late April,40 km west-northwest of GNP in BC, 7 km north of Montana.