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

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.