Wave-washing is an extraordinary hunting technique recorded in the pack-ice of the Antarctic, says Bob Pitman.
Orcas swim in synchrony to create waves that knock seals off small ice floes and into the water, where the predators can kill and eat them.
The waves can also be powerful enough to break up larger floes, throwing their occupants into the sea.
Orcas usually target Weddell seals, and though they have been observed wave-washing penguins, these birds are not a common target. This might be because they are comparatively small and thus simply not worth the effort: each wave-wash requires a synchronised charge from as far away as 50m. We have even seen young orcas wave-wash penguins off a floe only to swim away and leave the birds behind - they could have been practising or just playing.
We don't know how or when wave-washing evolved in orcas. family groups that stay together for decades, effective hunting strategies are passed down the generations, a process known as cultural transmission.
Youngsters have plenty of opportunities to learn - each individual will assist in catching tens of thousands of seals during its lifetime.
Orcas also work co-operatively underwater, not only to seize the dislodged seal, but to skin and dissect it.