Hunting Behavior in type a and type b Orcas
Biology 342 Fall 2014
STRATEGIES THAT ALLOW CAPTURING PREY ON LAND
In the water, killer whales are deadly apex predators of marine mammals. They can swim at speeds estimated over forty kilometers per hour, easily capable of outstripping and catching prey, including most species of pinnipeds (seals)(Smith et. al, 1981). Given the whale’s natural advantage, the pinnipeds natural defense is to remove themselves from the water, seeking shelter on the shore or ice floes, outside the whale’s reach. This behavior is probably the evolutionary root of killer whale’s unique cooperative hunting behavior, such as self-stranding and wave-washing (Smith et. al, 1981). In response to pinnipeds amphibious escape behavior, killer whales have learned how to work together to rob their prey of their natural advantage. In arctic waters, where food can be scarce, the ability to capture all available prey, even when it leaves the whale’s natural environment, is an enormously advantageous adaptation.
Fig 1. An Orca attempting to grab a Weddel Seal off of a small ice floe. Pinnipeds haul out on land in order to avoid predation by whales; wave-washing and self-stranding strategies enable Orcas to capture pinnipeds even when they retreat to land.
Along with this cooperative hunting behavior comes cooperative feeding behavior. Researchers observing hunting groups of killer whales reported that, “All group members were usually involved in the feeding, and we never saw an overt signs of aggression or even tussling. This apparent cooperative feeding occurred not only within groups but sometimes between groups as well”(Pitman & Durban, 2012). Based on these observations, it seems killer whales have evolved greatly advantageous cooperative behavior . When killer whales cooperate, more prey is caught and more whales get to eat.
While these strategies have high adaptive value for Pack Ice (PI) killer whales living in polar waters, they are less advantageous for whales living in different environments. Thus, killer whale behavior tends to evolve differently depending on the whale’s global location. For instance, mammal-eating “transient” killer whales located around the North American coastlines commonly use hunting techniques like tail-slapping or body-slamming to capture pinnipeds, unlike the PI whales. However, PI whales have been observed using the transient technique of ramming from below to subdue smaller minke whales (Pitman & Durban, 2012). This suggests that the adaptive value of killer whale hunting behaviors is dependant on the whale’s environment and the prey on which it primarily feeds.
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