Stimulus-dependent response to disturbance affecting the activity of killer whales

Humans seeking to observe wildlife in their natural habitat can disrupt the activity of the individuals they target. One hypothesis is that behavioral reactions emerge from animals perceiving humans as a potential risk. If it was the case we expect the avoidance tactics to be mediated to account for the difference in risk factors different platforms might present. We examined whether behavioral responses of northern resident killer whales differed between powerboats and kayaks to test this prediction. Killer whales responded to kayaks by increasing their probability to switch to travelling activity more often than during control
(no-boat) conditions. As a result, killer whales spent significantly more time traveling when in the presence of kayaks than they did under control, no-boat conditions (11% increase in time spent travelling). Consistent with previous studies examining the effects of powerboats, killer whales significantly reduced overall time spent feeding in the presence of kayaks and powerboats (30% decrease in the time spent feeding). Overall, we show that killer whales have different avoidance tactics to deal with the two types of vessels (motorized or not) and that they will try to outpace kayaks because those cannot follow them. The presence of motorized vessels, particularly vessels targeting whales, decreased the odds that killer whales were feeding (odds ratio: 0.70, 95% CI: 0.62-0.79). The presence of kayaks increased the odds that killer whales were traveling (odds ratio: 1.13, 95% CI: 1.001-1.280). Silent vessels (kayaks) can therefore elicit avoidance tactics like boats that have an acoustic signature do. Such findings are consistent with observed risk avoidance strategies in long-lived mammals. These avoidance strategies have different energetic consequences. While both kayaks and powerboats affect both feeding and travelling behavior, kayaks tend to increase killer whales’ energetic demand while powerboats tend to decrease their opportunities to acquire energy