Salmon Fishing by Bears and the Dawn of Cooperative Predation
Publication Type: |
Journal Article |
Year of Publication: |
2012 |
Authors: |
Stephen F. Stringham |
Publication/Journal: |
Journal of Comparative Psychology |
Keywords: |
black bear, onchorynchous, optimal foraging, salmon, ursus americanus |
ISBN: |
1939-2087 0735-7036 |
Abstract:
Although bears are an epitome of solitary predation, black (Ursus americanus) and brown bears (U. arctos) occasionally act in pairs to capture salmon (Onchorynchousspp.). I sought to identify conditions that promote pairing and how this relates to optimal foraging. This study on Alaskan black bears assessed whether each mode of fishing (solo vs. paired) occurs mainly where it is most efficient at harvesting salmon—that is, whether modal group size (1 vs. 2) is also optimal size. Not in this case. Pairing increased captures per attempt (benefit/cost ratio profitability) by up to 47% and captures per minute by up to 5.2-fold. Yet, the ratio ofpaired versus solo fishing was significantly lower than either profitability or chance explains. Modal group size was 1, optimal size was 2. This discrepancy did not result from intervention by other current benefits and costs, but from unnecessary defensiveness toward any rapidly approaching conspecific, even though it was chasing salmon, not threatening. For bears to regularly hunt cooperatively, they would have to more readily habituate to agonistic-like predatory actions, communicate intentions from 10 m apart, and assess situational variations in benefit/cost ratios for solo versus paired hunting. It would be revealing to discover how social carnivores overcame these challenges.