The first wolverine field study in the lower 48!
The authors believe the wolverine population in their study area to be stable, but warn about overtrapping and disturbing habitat security with logging, roaded access, and winter recreation.

Notable Excerpts:
(some duplication with Hash 1987, but obviously this is the original source; the most notable excerpts are marked with "!")

Abstract (excerpted)
"A population of wolverines was studied in northwestern Montana for 5 years (1972-1977). Twenty-four wolverines were captured in live traps, individually marked, and released. Ten individuals were recaptured 74 times. Twenty wolverines were fitted with radio collars and 576 relocations were made over a 4-year period. A minimum population size of 20 was estimated for the 1300-km2 area, or one wolverine per 65 km2. The population was believed stable..." (1286)

"Results" section

Mortality
Fifteen of eighteen recorded mortalities during their study were removed by commercial trappers during the five winters of this study:
"Eighteen mortalities were recorded during the study... Three marked wolverines... died of "natural" causes. Fifteen wolverines, nine males, five females, and one of unknown sex, were known to be removed by commercial trappers during the five winters... In addition, six individuals, four males and two females, were caught by trappers in the South Fork drainage the winter before our study began." (1290)

Feeding Habits
Analysis of 56 scats collected in winter show that food items taken as carrion occur more frequently than those presumably taken as live prey (Table 3). Elk and deer occurred in 27% of the scats, domestic cow and horse appeared in 27 and 18% of the scats, respectively. We believe that most of these items were taken as carrion." (1290)

Movement, Range, and Habitat Utilization
"Males throughout the study area traveled noticeably greater distances than females. The maximum distance traveled in 3 days was 64 km for males and 38 km for females." (1290)
The average yearly range of male and female wolverines was 422 and 388 km2, respectively. Two lactating females exhibited very similar, greatly reduced spring and summer ranges of 100 km2 each." (1291)
! "Large areas of medium or scattered mature timber accounted for 70% of all relocations. The remaining location sites were in ecotonal areas, small timber pockets, rocky, broken areas of timbered benches. Areas of dense, young timber were used least." (1291)
"Wolverines selected Abies [Fir] types on a year-round basis... There was a definite strong selection for these alpine fir types in summer; these types occur at the higher cooler elevations sought by wolverines in hot weather." (1291-1292)
! "No wolverines were located in clear cuts of any size; however, tracks were observed crossing clear-cut areas 15 times. Wolverines were located within 1 to 3 km of clear cuts and active roads 12 times. Male wolverines were found farther from active roads, clear cuts, and burns than females." (1292)

"Discussion" section

Population estimates and characteristics
"Wolverines occur at low densities and even in optimal habitat are less abundant than other carnivores (van Zyll de Jong 1975; Krott 1959; Quick 1953). Quick (1953) estimated a density of one wolverine per 207 km2 in British Columbia, basing his estimate on returns from a registered trapline. Our density for a 1300-km2 area, based on our estimate of 20 wolverines, was one per 65 km2, or one per 25 mi2. This greater density may be a result of a more plentiful food supply." (1295-1296).

Mortality
! "Van Zyll de Jong (1975)*... states 'of the biotic factors in the wolverine's environment, predation by humans appears to be the most likely factor to have affected the number of wolverines.' Clearly this was the situation in our study. Of 18 known mortalities in the five winters from 1972-1973 to 1976-1977, 15 were human caused. In addition, six were known to be removed by trappers the year before our study began. Wolverines are highly susceptible to trapping because they travel widely and are readily attracted to baits. Any of the adult wolverines in our work were missing one or more toes and many had broken teeth. We believe many of these mutilations were the result of encounters with leg-hold traps." (1297)

Reproduction
"Our sample size is too small to draw any firm conclusions, but combined with other observations, it appears productivity in our area may be lower than Alaska." (1297)
! "We know... from our capture-recapture data, that not all females produce young every year or every 2 years... In fact, only two of the eight females mature at the time of first capture appeared pregnant. Therefore, we believe no more than half the females present on our area were reproductively active in each of the 5 years of our study." (1297)
"Our data indicate a stable population on the study area proper; dispersal may be acting to maintain that stability." (1297).

Movement and range
! We believe that food availability is the primary factor determining movements and range in our area. Breeding activity influenced seasonal movements of males but not females. Food is apparently more available, either as carrion or prey, in the mature or intermediate timber stands preferred as wolverine habitat, especially edge or ecotonal areas around cliffs, slides, blowdowns, basins, swamps, and meadows. These habitats also were preferred by fishers (Martes pennanti) radio tracked concurrently with this study, and by a marten (Martes martes) [Martes americana?] population in the Selway-Bitterroot Wilderness Area in Idaho (Koehler and Hornocker 1977). Cover provided by mature or intermediate timber is also important in habitat selection. Wolverines appear reluctant to cross openings of any size such as recent clear cuts or burns. Tracking revealed that wolverines meandered through timber types, hunting and investigating, but made straight-line movements across large openings. Tracks further indicated they often ran or loped across such openings" (1298-1299)

Management implications
The authors report that many wolverines were killed by humans up until 1975, when they received state protections (specifically including an annual "bag limit" of one wolverine per trapper, and a limited season): "The annual take has declined markedly despite the fact that some wolverines are trapped incidentally to the taking of other furbearers." (1299) Note that not only does this quote indicate high levels of intentional killing of wolverines in Montana prior to 1975, it also implies that there is an ongoing problem of incidental human-caused wolverine mortalities.
! "Clear cuts have altered the nonwilderness portion substantially (see Ramirez and Hornocker 1981). These areas functioned in a similar manner to burns in the wilderness, relative to small mammal habitat. Such habitat changes can enhance herbivore and small mammal populations and thus increase the food supply for predatory species. In such habitat manipulations, however, with wolverine ecology in mind, consideration should be given to size, shape, and aspect of individual clear cuts. Wolverines in this study preferred basins, southerly and easterly slopes, and edge and ecotonal areas. These areas ideally should be left intact. Further use of roads built in logging operations should be strictly regulated, particularly in winter. If higher inaccessible country is adjacent to clear-cut areas, wolverines will separate themselves naturally from human activity in summer. In winter and early spring, however, human access on snowmobiles or all-terrain vehicles could bring about disturbance and conflict, not to mention ease of access for fur trappers." (1300)
! The authors argue the need for a regional approach to wolverine conservation and management:
"Regional, rather than local, populations must be considered in any management program. Our study area was large, relative to that for other species, yet it became clear we were dealing with a local unit of a regional population. Individuals routinely traveled far beyond the boundaries we set arbitrarily, but because of logistics, necessarily set. By traveling widely in a short period of time, individual wolverines give a false impression of abundance. Tracks encountered in widely separated major drainages, often divided by high mountains ranges, may in fact be made by the same individual. This should be taken into account when unit or area harvest regulations are set." (1300)
! "Because of their scavenging nature, wolverines come readily to bait and are vulnerable to skilled trappers. In areas where enhancement of wolverine populations is the goal, bait trapping for all species should be curtailed. Further, seasons should be adjusted for closure in late winter and early spring when young are born. Females with newborn young are limited in their ranging and foraging and are especially vulnerable to easily obtained trap baits." (1300)
"Wolverine populations in northwestern Montana survived the years of unlimited hunting and trapping solely because of the vast expanses of official wilderness and remote, essentially wilderness habitat. These areas functioned as both refuge and reservoir for wolverine populations. With more stringent harvest regulations now in effect, with cessation of nonselective control measures aimed at other species, and with adequate wilderness habitat, wolverine populations should be secure in Montana." (1300)

 

* Van Zyll de Jong, C.G. 1975. The distribution and abundance of the wolverine (Gulo gulo) in Canada. Can. Field Nat. 89:431-437.

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