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Prey selectivity of wolves in Banff National Park Huggard, David John


The functional response of wolves to changes in the abundance of their prey must be understood to manage wolf-ungulate systems, but is difficult to measure directly. In this study, behavioral and environmental components of wolf predation were assessed and used to predict features of the dynamics of the wolf-large ungulate system in Banff National Park, Alberta. Elk were the most abundant ungulate, while white-tailed deer, mule deer, bighorn sheep, mountain goats, moose and several non-ungulate species provided a diverse prey base. Two packs of wolves were followed using radio-telemetry and snow-tracking, and 652 scats and 130 animals killed by wolves were analyzed to determine wolf diet. Aerial total counts, ground classified counts, incidental sightings during field work and pellet group counts were used to estimate the numbers, composition and herd sizes of the ungulate prey species. Numerous animals killed on the road and railway provided information on the age structure and physical condition of the elk population. Non-ungulate prey were used by one wolf pack, when ungulate prey were scarce. All available ungulate species were included in the diet of wolves. Bighorn sheep and mountain goats were underrepresented in the diet, due to their use of habitats segregated from the wolves. For social ungulates, the herd is the unit of available prey, and herd size and composition substantially influenced the selectivity of wolves. Abundance, habitat overlap and herd size determined encounter rates and were more important in determining diet than inherent preferences of the wolves, since all ungulate species were expected to be equally profitable upon encounter. How wolves encounter their prey determined the predicted functional response of wolves to different prey species. Within elk, wolves preferred calves over adults and took adult males and females equally, but herd size and composition resulted in a slight overall selectivity for calves and adult males, and apparent avoidance of females. Adult elk killed by wolves were older than elk killed on the road or railway, but this may be due to a bias in obtaining the population age distribution from a mortality source, rather than due to selectivity by the wolves. Adult elk, but not calves, killed by wolves had lower reserves of marrow fat than road and rail kills. Wolf kill rates increased with depth of snowpack and wolves killed primarily calf elk in moderately deep snow (51-58cm) and adults in deeper snow. Scavenging occurred more often in shallow snow and at low kill rates, because wolves travelled more and encountered more scavengeable carcasses under these conditions. In an auxiliary study, the error associated with telemetry relocations in a mountainous environment and the effect of this error on assessment of habitat use were measured. Mean error distance in complex topography was greater than in simple topography (234m versus 156m). The error distance was correlated weakly with observer distance and size of the map error polygon, but neither was a good predictor of the error of a single relocation. Simulations showed that the habitat of a radio-collared animal would be assessed correctly 80% of the time for large habitat units, and would decline rapidly for units comprising less than 2% of the study area. Matrices were developed to correct for biases in habitat use information which is based on telemetry relocations.

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