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Estimating number of prey killed by carnivores such as wolves (Canis lupus) per unit time, or kill rate, is important for the conservation and management of carnivores and their prey. We reviewed published methods to estimate wolf kill rates and found them inconsistent and lacking a basis in statistical sampling theory. We developed a general statistical estimator for kill rate and variance using ratio-variable sampling theory. We illustrate our ratio estimator by estimating wolf kill rates in a multiple-prey system in Banff National Park, Alberta, for winters from 1986 to 2000. We used snow tracking and radiotelemetry to locate 429 kills during 195 sampling intervals covering 1,294 days. Mean kill rate by wolf packs (expressed as the number of kills/day/pack, k/d/p) was 0.33 k/d/p, most of which, 0.23 k/d/p, were elk (Cervus elaphus), the most abundant ungulate. Kill-rate estimates were variable despite intensive sampling effort. The mean kill rate of 0.33 k/d/p had a pooled 95% confidence interval of 0.29 to 0.37. An intensive sampling effort of ≥6-8 individual sampling intervals covering approximately 25% of the winter was required to minimize sampling variation. We compared our method to 3 other published methods for estimating kill rates and examined the bias and precision of kill-rate methods using simulations. Our ratio estimator approach was the least biased and most precise when compared to other approaches. Ratio estimators provide a standardized method to estimate kill rates in other predator-prey systems and will facilitate comparison across studies and examination of patterns of kill-rate variation. [ABSTRACT FROM AUTHOR]

Wolf-prey research has focused on single-prey systems in North America dominated by moose, Alces alces, or white-tailed deer, Odocoileus virginianus. Predator prey theory has historically focused on the direct lethal effects of predators on prey, giving rise to Lotka Volterra-type population models that ignored the effects of behavior. How different behavioral processes affect the encounter and attack stages of predation is critical to understanding the consequences of behavior for populations. Elk, Cervus elaphus, are social ungulates and the main prey item of wolves, Canis lupus, at the Banff National Park (BNP) in Alberta. Grouping behavior may affect the functional response of predators by changing how predators encounter and kill prey. We studied wolf predation on elk in BNP during the winters of 1997-1998 and 1998-1999 and tested how elk group size affected the availability of and encounter rates with elk groups and attack success of wolves. The product of these relative risks is proportional to the wolf-predation risk for individual elk in different group sizes in BNP during winter. Elk group size increased with elk density in BNP. Increased rates of encounter with and success of attacking large elk groups, and the positive group size—density relationship may be a mechanism for density-dependent predation. We developed a predation-risk model to test the prediction that grouping will benefit individual elk, given this predation regime. Elk appeared to adopt two different strategies to minimize predation risk: living in small herds that were rarely encountered by wolves or living in large herds that reduced their predation risk through dilution.

Gray wolves, Canis lupus, recolonized the Bow Valley of Banff National Park in the mid-1980s after a 30-year absence in Alberta. We studied the effects of wolf predation, snow depth, elk density, and human-caused mortality on the elk population growth rate in the three different wolf recolonization treatments from 1985 to 2000. Density-dependence and environmental stochasticity are determinants of ungulate population dynamics in areas without major predators. In the low wolf predation zone, elk population growth was density-dependent and limited by human-caused mortality. In the zone that wolves recolonized in 1991, elk population growth was limited by the combined effects of snow depth and wolf predation after wolf recolonization, in addition to preexisting mortality caused by humans and other predators. Our correlative approach failed to yield insights into population dynamics in the zone where wolves were present throughout the study. However, by comparing zones we demonstrate important differences in ungulate population dynamics in the presence and absence of wolf predation. Wolf predation increases with snow depth.