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Behavior of brown bears foraging on sockeye salmon in Lake Aleknagik, Alaska (foraging tactics and success)

Wirsing, Aaron1

Published Aug 15, 2024 on Dryad. https://doi.org/10.5061/dryad.8sf7m0czc

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Aug 15, 2024 version files 108.45 KB

Abstract

Studies of foraging where focal animals are easily observed may miss common behaviours expressed under more cryptic conditions. For example, much of what is known about brown bears (Ursus arctos) foraging on Pacific salmon (Oncorhynchus spp.) comes from a few anomalous locations where bears congregate, leaving open the question of how bears exploit salmon in the small streams where most predation occurs. Here, we used motion-activated video recordings to study the use and success of foraging tactics of Alaskan brown bears preying on sockeye salmon (O. nerka) in six small streams over three summers. We identified eight tactics from 387 independent foraging bouts and used multinomial models to explore drivers of their use and generalized linear models to examine factors influencing their success in capturing salmon. Cubs were far more likely to use sporadic foraging, a haphazard approach characterized by low success and high energy expenditure, than were adults, suggesting that this tactic may reflect inexperience. Tactics also varied with diel period and year. Foraging success was affected by tactic; notably, bears engaged in mixed and sporadic foraging were far less likely to catch a salmon than those using active tactics, whereas bears foraging passively were far more likely to catch a salmon than those foraging actively. Foraging success also varied among years but was not related to salmon abundance. These findings 1) showcase the diverse approaches brown bears use to exploit salmon in small streams, 2) add to our understanding of the ontogeny and success rates of foraging behaviours in habitats where most predation on salmon occurs, and 3) highlight the utility of video for overcoming challenges to the direct observation of bear behaviour.