Data from: Optimal foraging or surplus killing: selective consumption and discarding of salmon by brown bears

Selective consumption of prey by predators, observed in many animals, is
often attributed to optimal foraging. Consistent with this idea, brown
bears (Ursus arctos) often exhibit partial consumption, feeding
exclusively on lipid-rich tissues of Pacific salmon (Oncorhynchus spp.),
and discarding remains. However, bears also kill and abandon salmon
without consuming any tissue. These discarded fish may be consistent with
optimal foraging choices if they are of poor quality and if bears have
easy access to better prey, or may reveal non-adaptive surplus killing
behavior if fish are killed and discarded at random or solely based on
prey abundance. Using 21 consecutive years of data from sockeye salmon (O.
nerka) carcass surveys in Alaska, we found that foraging to maximize
energy intake best explained prey discarding behavior. Specifically,
discarding was more common under high prey abundance, late in the salmon
run, and with low quality prey. Patterns of tissue consumption were
consistent with these findings; bears were less likely to consume belly,
body, and brain tissue when prey condition decreased. Other factors not
quantified here (e.g., bear demography, alternative food resources) almost
certainly influence prey discard and partial consumption, though the
salmon-related factors explored here strongly influenced bear foraging
decisions that were consistent with optimal foraging theory. We did not
find clear evidence of surplus killing behavior in brown bears foraging on
salmon, but prey selectivity manifested itself through both discarding and
partial consumption, which contributes to our ability to predict transport
of salmon nutrients by bears across ecosystem boundaries.