Mountain sheep

Abstract: Longitudinal studies of survival are valuable because age-specific survival affects population dynamics and the evolution of several life history traits. We used capture–mark–recapture models to assess the relationship between survival and sex, age, population, year of study, disease, winter weather, and population density in two populations of bighorn sheep (Ovis canadensis) in Alberta, Canada. The Ram Mountain population, monitored for 20 yr, more than doubled in density; the Sheep River population, monitored for 13 yr, experienced a pneumonia epizootic. Yearling survival varied among years and was lower than that of older sheep of the same sex, except for yearling males at Ram Mountain. Yearling females at Ram Mountain were the only sex-age class exhibiting density dependence in survival. Senescence was evident for both sexes in both populations. Female survival from age 2 to age 7 was very high in both populations, but males aged 2 and 3 yr enjoyed better survival than males aged 4–6 yr. Our data support the suggestion that where hunters remove many males older than 5 yr of age, the natural mortality of males increases at 3–5 yr, possibly because young males suffer a mortality cost of participating in rutting activity. The decline in survival for sheep older than 7 yr was greater for males than for females. Survival was lower for males than for females, both among prime-aged sheep (0.896 vs. 0.939 at Sheep River; 0.837 vs. 0.945 at Ram Mountain) and among older sheep (0.777 vs. 0.859 at Sheep River; 0.624 vs. 0.850 at Ram Mountain), but not among yearlings. Survival of sheep aged 2–7 yr was not significantly different between the two populations. Winter weather did not affect survival. Survival of sheep 2 yr of age and older did not vary significantly between years, except at Sheep River where survival of prime-aged sheep of both sexes was lower in the year of the pneumonia epizootic. Studies of survival of mountain sheep based upon skull collections may have overestimated survival of young rams. Our results underline the need for accurate information on age-specific survival.

Abstract: Prescribed burning elevated the concentration of protein and in vitro digestible organic matter (IVDOM) in winter diets of mountain sheep (Ovis canadensis) and mule deer (Odocoileus hemionus) feeding in grassland and mountain shrub communities. We observed no effect of burning on ungulate nutrition during spring. In both communities, the magnitude of treatment effects tended to depend on the month we observed diets. Effects of burning on diet crude protein persisted for 2 years in both communities. Treatment effects on diet IVDOM lasted for 2 years in mountain shrub, but were absent during the 2nd year in grassland. Effects of fire on diet quality resulted from changes in ungulate diet selection rather than improvements in the quality of individual forages. Differences in the amount of green grass in ungulate diets accounted for much of the enhancement in diet quality we observed. We conclude that prescribed fire can improve winter habitats for mule deer and mountain sheep. J. WILDL. MANAGE. 48(2):551-560 Prescribed burning is frequently used to improve and enlarge habitats for wild ungulates. It is widely believed that fire benefits ungulates by enhancing their nu- trition. Although intuitively appealing, this belief has rarely been tested (Taber 1953, Springer 1977, Rowland 1981). Instead, many previous studies have focused on fire effects on the quality of forage. Inferences on the nutritional quality of animal diets drawn from observations on the quality of forages are unreliable whenever animals feed selectively. We tested the hypothesis that prescribed burning improves the nu- tritional quality of diets of mule deer and mountain sheep grazing in montane plant communities during winter and spring. This project was supported by Fed. Aid

Abstract: Etude du choix de l'habitat et du comportement alimentaire chez Ovis canadensis du Waterton Canyon, Colorado. Conclusions quant a la protection de cette espece