Nonlinear effects of group size on the success of wolves hunting elk

Behavioral Ecology
By: , and 



Despite the popular view that social predators live in groups because group hunting facilitates prey capture, the apparent tendency for hunting success to peak at small group sizes suggests that the formation of large groups is unrelated to prey capture. Few empirical studies, however, have tested for nonlinear relationships between hunting success and group size, and none have demonstrated why success trails off after peaking. Here, we use a unique dataset of observations of individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park to show that the relationship between success and group size is indeed nonlinear and that individuals withholding effort (free riding) is why success does not increase across large group sizes. Beyond 4 wolves, hunting success leveled off, and individual performance (a measure of effort) decreased for reasons unrelated to interference from inept hunters, individual age, or size. But performance did drop faster among wolves with an incentive to hold back, i.e., nonbreeders with no dependent offspring, those performing dangerous predatory tasks, i.e., grabbing and restraining prey, and those in groups of proficient hunters. These results suggest that decreasing performance was free riding and that was why success leveled off in groups with >4 wolves that had superficially appeared to be cooperating. This is the first direct evidence that nonlinear trends in group hunting success reflect a switch from cooperation to free riding. It also highlights how hunting success per se is unlikely to promote formation and maintenance of large groups.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Nonlinear effects of group size on the success of wolves hunting elk
Series title Behavioral Ecology
DOI 10.1093/beheco/arr159
Volume 23
Issue 1
Year Published 2012
Language English
Contributing office(s) Northern Prairie Wildlife Research Center
Description 8 p.
First page 75
Last page 82
Country United States
State Idaho, Montana, Wyoming
Other Geospatial Yellowstone National Park
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