Foraging Behavior: Implications for Estimating Summer
Matthew C. Metz1,2*, John A. Vucetich1, Douglas W. Smith2, Daniel R. Stahler2, Rolf O. Peterson1
1 School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan, United States of America, 2 Yellowstone Wolf Project,Yellowstone Center for Resources, Yellowstone National Park, Wyoming, United States of America
Background: Understanding how kill rates vary among seasons is required to understand predation by vertebrate species
living in temperate climates. Unfortunately, kill rates are only rarely estimated during summer.
Methodology/Principal Findings: For several wolf packs in Yellowstone National Park,we used pairs of collared wolves
living in the same pack and the double-count method to estimate the probability of attendance (PA) for an individual wolf
at a carcass. PA quantifies an important aspect of social foraging behavior (i.e., the cohesiveness of foraging). We used PA to
estimate summer kill rates for packs containing GPS-collared wolves between 2004 and 2009. Estimated rates ofdaily prey
acquisition (edible biomass per wolf) decreased from 8.460.9 kg (mean 6 SE) in May to 4.160.4 kg in July. Failure to
account for PA would have resulted in underestimating kill rate by 32%. PA was 0.7260.05 for large ungulate prey and
0.4660.04 for small ungulate prey. To assess seasonal differences in social foraging behavior, we also evaluated PA during
winter for VHF-collared wolvesbetween 1997 and 2009. During winter, PA was 0.9560.01. PA was not influenced by prey
size but was influenced by wolf age and pack size.
Conclusions/Significance: Our results demonstrate that seasonal patterns in the foraging behavior of social carnivores have
important implications for understanding their social behavior and estimating kill rates. Synthesizing our findings with
previousinsights suggests that there is important seasonal variation in how and why social carnivores live in groups. Our
findings are also important for applications of GPS collars to estimate kill rates. Specifically, because the factors affecting the
PA of social carnivores likely differ between seasons, kill rates estimated through GPS collars should account for seasonal
differences in social foragingbehavior.
Citation: Metz MC, Vucetich JA, Smith DW, Stahler DR, Peterson RO (2011) Effect of Sociality and Season on Gray Wolf (Canis lupus) Foraging Behavior:
Implications for Estimating Summer Kill Rate. PLoS ONE 6(3): e17332. doi:10.1371/journal.pone.0017332
Editor: Wayne Getz, University of California, Berkeley, United States of America
Received November 8, 2010; Accepted January 27, 2011;Published March 1, 2011
This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public
domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
Funding: Funding was provided by the United States National ScienceFoundation (DEB-06137730), Yellowstone National Park, Yellowstone Park Foundation, an
anonymous donor, Annie and Bob Graham, Frank and Kay Yeager, Marc McCurry, Masterfoods, Patagonia, and the Natural Resources Defense Council. The funders
had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have read thejournal’s policy and have the following conflicts: Masterfoods provided funding for some field technicians and
volunteers. This in no way compromised the objectivity of the data collection. No patents or products were developed from this support. The interest of
Masterfoods was to support long-term wolf research in Yellowstone National Park. The data presented in this paper is public data...