Do killer whales hunt in groups?

There is a scene, now famous, filmed in Antarctica by the BBC team for the documentary Frozen Planet. Three killer whales swim in tight formation towards a floating ice floe on which a Weddell seal is lying. At the last moment they all dive together beneath the floe, then rise vertically, their combined wake creating a single wave that sweeps across the ice and slides the seal into the water. It is over. What biologists call wave washing is one of the most complex hunting techniques ever documented in the animal kingdom. It requires timing coordinated to the quarter second, a mental representation of fluid dynamics, and cultural transmission of the technique across several generations. Welcome to the world of killer whales.

One species, several cultures

Officially, there is a single killer whale species in the world. But this taxonomic unity conceals an extraordinary behavioural and cultural diversity. Biologists have identified at least ten distinct ecotypes, populations that resemble one another little in diet, calls, morphology and social organisation, and that even avoid one another in the wild when they meet. The best known distinction sets the resident killer whales of the north-eastern Pacific (which eat almost nothing but salmon) against the transient killer whales (also called Bigg’s, after Michael Bigg, who first described them), which hunt marine mammals.

A 2024 paper in Royal Society Open Science (Morin et al.) formally proposes splitting these two ecotypes into two distinct species, Orcinus ater for the residents and O. rectipinnus for the Bigg’s, which would be the first major taxonomic split in decades. In the Antarctic, five ecotypes are recognised, labelled A, large B, small B (“pack ice“), C and D, each specialised on a particular prey, and at least two of them could also warrant separate species status.

The hunting techniques in detail

Strand feeding, observed at Península Valdés in Argentina and in the Crozet Islands, is probably the most spectacular technique. Killer whales charge in from deeper water towards a beach where juvenile elephant seals are hauled out. They strand themselves partly on the sand, seize a young seal in their jaws, then wait for the next wave to slip back into the water. The technique is risky, one bad wave and the animal can be left stuck, and it is the object of explicit teaching. Mothers teach their calves by first taking them to strand without prey, on an empty beach, then with dead prey, then with live prey. Lopez and Lopez documented this mentoring as early as 1985.

The wave washing described at the start is practised by the “pack ice” type B killer whales in Antarctica. A study (Pitman & Durban, 2012, Marine Mammal Science) documented that this technique is used almost exclusively against Weddell seals, never against crabeater seals, which are nonetheless more accessible. That selectivity suggests precise knowledge of how effective the technique is depending on the prey. Crabeater seals do keep their balance better on the ice and resist waves better, so the energy spent would not be worth it. The killer whales have worked that out.

The residents of the north-eastern Pacific hunt salmon by fanning out. Several members of the pod spread out and sweep an area of Chinook salmon (very nearly their only food), signal to one another continuously with stereotyped calls, and coordinate their individual pursuits. These killer whales are extremely vocal: their prey, salmon, hear poorly in the band used, so staying silent would bring no benefit.

The Bigg’s transients, by contrast, are almost silent while hunting. Their prey, seals, porpoises and whale calves, hear in much the same range as they do. A call would give their presence away for kilometres. They approach in complete silence, in small groups of two to six animals, sometimes hiding behind the hull of a passing vessel to mask their acoustic signature. It is one of the most telling illustrations of the cultural divergence between ecotypes.

Killing a great white

In 2017, two killer whales named “Port” and “Starboard” appeared in Mossel Bay, South Africa. For several months, great white shark carcasses were found along the coast, all eviscerated to an identical pattern: a precise incision between the pectoral fins, and the liver, rich in squalene, fatty and energy dense, meticulously removed. Underwater cameras eventually identified those responsible. Port and Starboard belong to a poorly documented ecotype that appears to have specialised in hunting large sharks.

The ecological impact was immediate. The great whites, which had frequented certain South African beaches for decades, deserted those areas almost overnight. The fur seal colonies that were their usual prey saw their survival rate rise again. A study published in 2022 in African Journal of Marine Science (Towers et al.) documented this cascading restructuring of the coastal food web, brought about by two killer whales.

The role of the matriarchs

Among resident killer whales, the pod is led by an old matriarch, past the menopause. This trait is shared by the killer whale and only two other mammals besides humans, the short-finned pilot whale and the beluga. Old matriarchs hold the memory of the migration routes and of the productive hunting grounds. Studies (Brent et al., 2015) have shown that when salmon becomes scarce, it is the groups guided by the oldest matriarchs that fare best. Their accumulated knowledge of ecological cycles is an indispensable cultural asset.

More striking still: Croft et al. (2017) showed that the survival of adult males depends on the presence of their mother. When she dies, the son’s risk of death in the following year is fourteen times higher. It is one of the longest and most critical mother-son bonds ever documented in a wild mammal.

Sources

• Ford, J.K.B. & Ellis, G.M. (1999). Transients: Mammal-Hunting Killer Whales of British Columbia, Washington, and Southeastern Alaska. UBC Press.
• Pitman, R.L. & Durban, J.W. (2012). “Cooperative hunting behavior, prey selectivity and prey handling by pack ice killer whales (Orcinus orca), type B, in Antarctic Peninsula waters”. Marine Mammal Science, 28(1).
• Towers, J.R. et al. (2022). “Killer whales hunt and kill White Sharks”. African Journal of Marine Science, 44.
• Lopez, J.C. & Lopez, D. (1985). “Killer whales of Patagonia and their behavior of intentional stranding while hunting”. Journal of Mammalogy, 66.
• Croft, D.P. et al. (2017). “Reproductive conflict and the evolution of menopause in killer whales”. Current Biology, 27.
• Morin, P.A. et al. (2024). “Revised taxonomy of eastern North Pacific killer whales”. Royal Society Open Science.

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Further reading