Killers in the dark—Acoustic evidence for night-time predation by mammal-eating killer whales (Orcinus orca) in Alaska

Abstract

North Pacific killer whales that specialize on hunting marine mammals do not typically echolocate while searching for prey. This suggests that they detect prey by either relying on visual cues or listening for sounds generated by prey animals. If prey detection requires vision, hunting should be limited to the daylight hours. Documenting predation at night would therefore provide evidence supporting a passive listening hypothesis of prey detection. We used digital recording tags (DTAGs) to study the behavior of mammal-eating killer whales in Southeast Alaska. These tags recorded the underwater movements of the tagged individual and any sound emitted or received. Predation events were identified using distinctive sounds generated during prey capture and handling. We deployed 13 tags, of which 7 remained attached for at least part of the night. The majority of tags recorded night-time predation, even though nights were short (average of 4:18 h) during the study period. These findings show that mammal-eating killer whales can detect prey at night and thus suggest that passive listening is an important part of their hunting strategy. Acoustic data from digital recording tags can therefore provide valuable insights into the night-time activities and foraging behavior of killer whales and other marine mammals.