In the Northeast Pacific, “Bigg’s Killer Whales” (formerly known as “Transients”) are believed to have diverged from the “resident” (inshore fish-eating) and “offshore” (offshore fish-eating) ecotypes some 700,000 years ago (Morin et al, 2010), to refine a culture of stealth and unpredictability in order to hunt their marine mammal prey.
I would suggest that we humans are the last species that should be judging others for how much they eat. However, often Bigg’s Killer Whales are profiled and misunderstood for interpretations of their feeding behaviour. This includes that they don’t always eat what they kill.
From Kuker and Barrett-Lennard (2010) “Like many other predators, transient killer whales sometimes demonstrate ‘surplus killing’, killing greater numbers of prey than they consume (DelGiudice 1998, Wobeser 2000, Short et al. 2002). In surplus killing incidents, the whale plays with animals, such as sea birds (Stacey et al. 1990) and harbour seal pups (Gaydos et al. 2005). The whales may breach on the victim or toss and ram it until it dies, but it is not consumed. This behaviour could be part of the process of learning to hunt, in which adults are training young to capture and handle prey, or it could be simply play behaviour (Ford et al. 1998, Gaydos et al. 2005).”
Below is my account of one such surplus killing events witnessed on August 31st, 2011. It was not a good day for some Rhinoceros Auklets (Cerorhinca monocerata) in Johnstone Strait, British Columbia, Canada.
That day, I witnessed a very socially active group of Bigg’s Killer Whales repeatedly harassing these birds – mouthing them and slapping them. At least 3 juvenile Rhinoceros Auklets were involved. Since these are diving birds, they cannot “alight” and escape the teeth and fins below them. Yet, I believe they survived.
I personally had never seen such a prolonged display of this play behaviour before. In fact, I had never seen Bigg’s Killer Whales socialize quite so rambunctiously! [Update 2020, now that seals and sea lions are more readily available, members of this population appear to be far less stealthy).
Clearly, when their bellies are full and social needs dominate, this type of Orca is anything but stealthy. On August 31st, this incredibly socially active group of 20+ Bigg’s took about 1.5 hours to travel only +/- 4.5 km (2.5 nautical miles) – slapping birds, rolling over one another, tail slapping, vocalizing and breaching along the way. The whales would go on to bound past the community of Alert Bay, Cormorant Island. I have have previously written about this in the blog item “Might As Well Jump.”
Jared Towers of the Department of Fisheries and Ocean has confirmed the IDs of the Bigg’s Killer Whales in the August 31, 2011 encounter to be: T010s, T034s, T035s, T037s, T046Bs, and T146s.
Further insight into this behaviour is provided by Dr. John Ford’s and Graeme Ellis. The following interpretation of the behaviour is from the chapter “Seabirds: Playthings and Practice, or Between-Seal Snacks?” in Transients: Mammal-Hunting Killer Whales of British Columbia, Washington, and Southeastern Alaska.
“It is not unusual to see transients chasing and harassing seabirds. During most of these incidents, the whales do not seem intent on eating the birds. Rather, they let the bird escape or they abandon it after it has been injured or killed. Seabird harassment appears to be a favourite activity of juvenile transients. They young whales will sometimes swim upside down and on their sides, looking for birds paddling at the surface above. Once a victim is sighted, they will try to slap it with their tail flukes, jump on it, or seize it in their mouth. This interaction may continue for several minutes, before the bird is eaten, incapacitated, or left dead in the whale’s wake. We and others have recorded at least 10 seabird species that have become casualties of transients. Frequent victims are common murres, which are flightless for several weeks during the late summer and are like “sitting ducks” for transients. Other species include black brant, common loon, white-winged scoter, surf scoter, cormorant (species uncertain), western grebe, marbled murrelet, rhinoceros auklet, and red-breasted merganser. Seabirds seem to be more important as objects of play or harassment than as a dietary item. Juveniles playing with seabirds no doubt learn useful skills in prey capture and handling that may enhance their success in hunting harbour seals and other wily prey.”
Barrett-Lennard, L.G., Heise, K. 2007. The Natural History and Ecology of Killer Whales: Foraging Specialization in a Generalist Predator. In Estes, J.A., Brownell, R.L., DeMaster, D.P., Doak, D.F., Williams, T.M. Whales, whaling and ocean ecosystems. University of California Press, Berkely, C.A.
Ford, J.K.B., and Ellis, G.M. 1999. Transients: Mammal-Hunting Killer Whales of British Columbia, Washington, and Southeastern Alaska. UBC Press, Vancouver, and U. of Washington Press, Seattle. 96 pp
Kuker, Katie & Barrett-Lennard, Lance. (2010). A re‐evaluation of the role of killer whales Orcinus orca in a population decline of sea otters Enhydra lutris in the Aleutian Islands and a review of alternative hypotheses. Mammal Review. 40. 103 – 124. 10.1111/j.1365-2907.2009.00156.x.