In an effort to better understand the diet of so-called “southern resident” killer whales, we collected prey remains from feeding whales and recorded information on behavioral cues of predation around the San Juan Islands in August and September 2004. During the seven days of effort, killer whales were encountered on eight occasions over four days, and attempts to collect prey remains were made during five encounters. Whales were followed for the purposes of prey sample collection for a total of 12.7 hours, and events suggesting predation were observed 27 times. Prey remains were collected from 10 of these events (37%). Only three of the 10 cases involved a series of fast non-directional surfacings or active prey chases, characteristics that have been used to indicate feeding in one previous study. Behavioral observations from four of the 10 sampling events indicated that the prey chase and capture occurred out of sight of surface-based observers, and in one further case the prey capture occurred beneath the surface, with only initial signs of the chase visible at the surface. Prey captures were observed simultaneous with social interactions that were not related to foraging, suggesting that foraging behavior and social behavior can occur simultaneously. Further, this suggests that studies observing behavior from distances that are too far to observe prey in the water column may not always accurately characterize the behavior of fish-eating killer whales.
Citation:
Baird, R.W., and M.B. Hanson. 2004. Diet studies of “southern resident” killer whales: prey sampling and behavioral cues of predation. Report prepared as partial fulfillment of Order No. AB133F-030SE-1070 from the National Oceanic and Atmospheric Administration, Seattle, WA.
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