Hunting and Feeding: Orca (Orcinus orca)

Orcas, more commonly known as killer whales, are the largest dolphin species in the world, growing up to 8m (26ft) long (Uhlenbroek, 2008). They inhabit coastal and offshore waters in oceans worldwide from Polar Regions to the tropics, and are characterized by black bodies with white undersides and flanks and prominent white patches behind the eyes (Uhlenbroek, 2008). The dorsal fin of males is very large and triangular, whereas female dorsal fins are shorter and more curved (Uhlenbroek, 2008).

Orcas are extremely intelligent and very social animals, often travelling in large, maternally based pods and communicating with each other using a range of whistling and clicking calls (Brault & Caswell, 1993). There are many physical, behavioural and genetic difference between orca populations and it is unknown exactly how many sub-species, or even species, there are (Uhlenbroek, 2008). Throughout the five distinct orca types that HAVE been identified, a large range of prey are targeting including a variety of fish shoals, sharks, cephalopods, turtles, seals, sea lions and even whales (Baird, 1997).

The feeding behaviour depends on the type of orca and its selected prey; orcas that following migrating shoals of herring either choose to feed singly or work in a group to corral the fish into a tight ball, often sing their powerful tail flukes as bats to stun or kill them (Simila, 1997). Orcas that hunt marine mammals kill their prey by ramming them, hitting them with their tails or tossing them into the air and in shallow waters orcas often beach themselves to feed on prey along the shoreline (Baird, 1997). Orcas that hunt for whales will generally select a calf or weaker adult and chase it to tire it out and separate it from the group, the orcas will then drown it by not letting it resurface for air (Uhlenbroek, 2008).

Orcas also have a very unique cooperative hunting technique for catching seals who are resting on small icefloes known as wave hunting (Smith et al, 1981). Wave hunting begins with a lone orca – or a few – propping its head out of the water in order to spot a lone seal resting on the ice, a behaviour known as spy-hopping (Smith et al, 1981). Once a seal has been spotted, other orcas may join in an attempt to knock it into the sea; several orcas will swim together towards and under the ice floe to create a large wave to wash over the ice and carry the seal into the jaws of a waiting orca or just force it into the sea (Smith et al, 1981). To ensure the seal becomes dislodged, another orca will deliberately bump the ice from one of the sides (Smith et al, 1981).

This technique is an indication of the killer whales intelligence as it relies on complex planning, coordination and communication in order to be effective (Uhlenbroek, 2008).

References:

Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.

Baird, R. W. (1987). Foraging Behaviour and Ecology of Transient Killer Whales (Orcinus orca).  Department of Biological Sciences, 1(1), 1-34.

Simila, T. (1997). Sonar observations of killer whales (Orcinus orca) feeding on herring schools. Aquatic Mammal, 23(3), 119-126.

Brault, S. & Caswell, H. (1993). Pod-Specific Demography of Killer Whales (Orcinus orca). Ecology, 74(5), 1444-1454.

Smith, T. G., Siniff, D. B., Reichle, R. & Stone, S. (1981). Coordinated behaviour of killer whales, Orcinus orca, hunting a crab eater seal, Lobodon carcinophagus. Canadian Journal of Zoology, 59(6), 1185-1189.