Mortality and seasonal distribution of elk in an area recently recolonized by wolves
Bureau MJ. 1992. Mortality and seasonal distribution of elk in an area recently recolonized by wolves. University of Montana
Gray wolves fCanis lupus) have recolonized northwest Montana's Glacier National Park area after 50 years of absence. Wolves from this new population have dispersed to other areas of Montana. Elk (Cervus elaphus) are one of Montana's most important big game animals, and there is much public concern over the impacts that wolf recovery may have on elk populations. From January 1990 to June 1992, I examined mortality and seasonal distribution of elk in the North Fork of the Flathead River drainage in northwest Montana and southeast British Columbia using radio telemetry. Prey age selection was based upon elk kills found while backtracking mountain lions and wolves during winter (Wolf Ecology Project) , and from hunter check stations. These age distributions were compared to the age distribution of trapped cow elk. I implemented an index of elk abundance to monitor population changes. I also estimated sex and age composition of the population, and estimated elk reproductive success and calf survival from aerial surveys. Of 38 radio-collared cow elk, mountain lions (Felis cpncplpr) killed 9, wolves killed 2, a grizzly bear (Ursus arctps) killed 1, and hunters killed 2. Mortality due to mountain lions was significantly greater than mortality due to wolves, hunters, or bears. Annual survival for cow elk was 75% over the entire study period. Survival was greatest during summer (100%) and poorest during late winter-early spring (86%). Survival during winter (96%) and autumn (91%) was intermediate. There was no difference between the age distribution of cows killed by mountain lions and the trapped population. Wolves killed significantly more old and young and fewer prime cows relative to the trapped population. Hunters killed fewer old elk. Most radio-collared elk summered in subalpine areas of British Columbia and wintered along the river corridor in Montana's Glacier National Park. Use of the 1988 Red Bench Burn by elk during winter was heavy. I used mark-recapture aerial surveys and pellet counts to form an index of abundance that will detect a 20% change with 90% certainty and suggest improvements on the techniques. Cow:bull ratios averaged 100:31, though confidence intervals were high. Cow:calf ratios appeared to reflect the severity of the preceding winter. Following the heavy-snow winter of 1990-91, June cow:calf ratios of 100:50 fell to 100:30 by August and 100:16 by the following January. Following the light-snow winter of 1991-92, June cow:calf ratios were 100:70 and fell to 100:50 by August. Management recommendations regarding cow mortality and calf survival are presented.