Summer kill rates and predation pattern in a wolf–moose system: can we rely on winter estimates?

Abstract

So far the vast majority of studies on large carnivore predation, including kill rates and consumption, have been based on winter studies. Because large carnivores relying on ungulates as prey often show a preference for juveniles, kill rates may be both higher and more variable during the summer season than during the rest of the year leading to serious underestimates of the total annual predation rate. This study is the first to present detailed empirical data on kill rates and prey selection in a wolf-moose system during summer (June-September) as obtained by applying modern Global Positioning System-collar techniques on individual wolves (Canis lupus) in Scandinavia. Moose (Alces alces) was the dominant prey species both by number (74.4%) and biomass (95.6%); 89.9% of all moose killed were juveniles, representing 76.0% of the biomass consumed by wolves. Kill rate in terms of the kilogram biomass/kilogram wolf per day averaged 0.20 (range: 0.07-0.32) among wolf territories and was above, or well above, the daily minimum food requirements in most territories. The average number of days between moose kills across wolf territories and study periods was 1.71 days, but increased with time and size of growing moose calves during summer. Over the entire summer (June-September, 122 days), a group (from two to nine) of wolves killed a total of 66 (confidence interval 95%; 56-81) moose. Incorporation of body growth functions of moose calves and yearlings and wolf pups over the summer period showed that wolves adjusted their kill rate on moose, so the amount of biomass/kilogram wolf was relatively constant or increased. The kill rate was much higher (94-116%) than estimated from the winter period. As a consequence, projecting winter kill rates to obtain annual estimates of predation in similar predator-prey systems may result in a significant underestimation of the total number of prey killed.

Prey selection and dietary response by wolves in a high-density multi-species ungulate community

“…The choice of method for diet analysis is crucial when small-size prey is abundant. Many authors, in fact, emphasize that kill analysis tends to underestimate the importance of smaller prey species in predators' diet, because such individuals are usually completely consumed and, as a consequence, remains of such a kill are more rarely found (Olsson et al 1997;Jędrzejewski et al 2002;Nowak et al 2005;Gula 2004;Sand et al 2008). Moreover, searching for fresh kills is only possible during winter and in countries with frequent snowfall.…”

“…However, these differences may be apparent, due to different diet analysis methodology and the tendency of kill analysis to underestimate the importance of smaller prey in predator diet. Moreover, most kill data are collected in winter and, as a consequence, results could be biased by differences among seasonal selection patterns (Sand et al 2008).…”

Hunting performance of captive-born South China tigers (Panthera tigris amoyensis) on free-ranging prey and implications for their reintroduction

“…All clusters were visited the day after the tiger was removed from the enclosure at the end of its study period with a maximum of 33 days between the occurrence of a cluster and its visit. This search schedule avoided displacing tigers from kills and was adequate to prevent losing information to carcass decomposition or scavenging since caracals (Caracal caracal), black backed jackals (Canis mesomelas), and small scavengers such as members of the Herpestidae family were also present in the camps (Miller et al, 2013;Sand et al, 2008;Webb et al, 2008). Prey remains were photographed and, if unconfirmed in the field, representative material was collected for identification at the Centre of Wildlife Management, University of Pretoria (South Africa).…”

Hair-Loss Epizootic in Moose (Alces Alces) Associated With Massive Deer Ked (Lipoptena Cervi) Infestation

“…Predation by wolves (Canis lupus) and a few brown bears (Ursus arctos) also may have some impact on the population (Sand et al, 2008).…”