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Transient killer whales

Diet 

Transient killer whales prey on marine mammals. In British Columbia over half of the transient kills reported by Dr. John Ford and colleagues in a 1998 paper were harbour seals.  Other marine mammals, such as sea lions, dolphins, porpoises, and other whales, are also taken when the opportunity arises. Sea birds are sometimes harassed and killed by transient killer whales but are not thought to be a significant prey item.

 

Acoustics

Transients do not vocalize or echolocate nearly as often as resident killer whales. Marine mammals have far better underwater hearing than most fish and are better at escaping when they detect a predator, so transients have to be quiet and stealthy to be successful hunters. Transients are completely silent when searching for prey.  Calls can usually be heard in the final stages of an attack or while feeding. See Communication to hear transient calls. 

One important way that transients find their prey is by listening very attentively for their sounds. Their acute hearing allows them to detect calls, surfacing and breathing noises and other sounds made by marine mammals. On the rare occasions when transients use echolocation while foraging, they make very quiet, irregular sounds referred to as “cryptic clicks”.


Photo:  Jim Borrowman
Transient killer whales will often ram their prey.

Range

Transients range all along the western coast of North America, from Alaska to the southern California coast. They often hug the coastline, where seals and harbor porpoises are most common, and sometimes head offshore to search for Dall porpoises and other open-water marine mammals.  Transients make a business of being unpredictable and rarely stay in one place for more than a few hours. Their strategy of moving between widely-separated prey hotspots is sometimes referred to as "trap-lining".  They generally frequent the same areas in both summer and winter. 

 

Status

At least three distinct transient populations inhabit the coastal waters of the NE Pacific.  The population seen in BC ranges from California to SE Alaska, and is referred to as the west coast transient population.  It contains over 250 members and is listed as threatened under the Species at Risk Act in Canada.



Photo:  Kathy Johnson

Habour seals are the primary prey for transients in British Columbia.

 

Social Structure

Transient killer whales usually travel in smaller groups than resident whales. Many transients spend most or all of their lives in matrilines, but—unlike residents—some leave  their mothers once they reach maturity, especially females with young  calves of their own. Sometimes these dispersing individuals rejoin their birth matrilines after years of separation. 

 


Photo: Meghan Mckillop

Transients are silent while seeking prey to avoid detection.

 

Behaviour

Probably for the same reason that transients are quiet acoustically-- to avoid detection by their prey--transients engage in conspicuous activities like breaching and playing at the surface less frequently than residents.

However, transients often engage in dramatic activity while attacking their prey. Depending on the size of the animal being pursued, transients may ram their prey (sometimes knocking it into the air), use strike it with their tails, or swim on top of it to force it underwater until it drowns. These techniques reduce the risk of the transients being bitten or otherwise injured while subduing their prey.