The birds' bait ball becomes a bite-sized snack for a hungry humpback
Humpback whales have come up with a novel way for getting an easy snack - stealing birds' dinners.
A BBC crew filmed seabirds carefully corralling unwieldy shoals of herring into tightly packed "bait balls" from which the fish are easy to pluck.
But they discovered that passing whales would wait for the birds to complete their hard graft before devouring the ball of fish in a single gulp.
The team said this was the first time they had seen this behaviour.
The footage, filmed off the coast of North America, forms part of the BBC wildlife series Nature's Great Events: The Great Feast.
The team witnessed the whales' crafty behaviour as they set up to film vast shoals of herring as they gathered to feed on plankton blooms.
The whale came in and scooped up the whole thing in pretty much one gulp - mouth open, whoosh, and the whole thing was gone
Joe Stevens, producer
While the fish feast, diving birds also congregate, eyeing an opportunity for their own fishy banquet.
Joe Stevens, a producer on the programme, said: "Murres (a type of guillemot) dive under the shoal and whittle it down into a ball of fish, using the surface of the water to contain it. They dart around it, picking off the fish.
"Other seabirds like gulls then come in to get bits of the bait balls."
But while the team expected to capture this spectacle on camera, they were unprepared for what came next.
Mr Stevens explained: "We had a cameraman in the water - and we started to notice lots of whales.
"And we thought: 'What would happen if the whales got interested in these balls of fish?' And then the whales did get interested.
Humpbacks migrate from Hawaii to reach the fish feast
"One came in and scooped up the whole thing in pretty much one gulp - mouth open, whoosh, and the whole thing was gone."
It was a bit of a shock for the underwater cameraman, he added.
Mr Stevens said the crew witnessed the humpbacks scoffing the bite-sized bait balls several times.
He said: "It was like the whales had noticed what the birds were doing, and let the birds do all the hard work of creating the balls of fish so they could then come in to scoop them up."
He added: "You have to take your hat off to them - it is when you see them doing things like that, you realise that they are really very very clever and that they are aware of their environment and what is going on."
The four whales launch a co-ordinated attack on the huge sea lion
While filming the series, the Natural History Unit crew also captured another rare event on film - a clash between four killer whales (orcas) and a one-tonne Steller's sea lion.
The footage shows the whales launching a co-ordinated attack on the lone male, eventually beating it to death.
Smaller sea lions often fall prey to whale attacks
While attacks on smaller sea lions are common, it is rare for whales to take on such an enormous and therefore potentially dangerous creature.
Mr Stevens said: "The males can be absolutely massive - about one-tonne in weight - and they have got really big teeth. For an orca, a bite from one of those big sea lions could be fatal.
"But in this case, this male sea lion was out in open water, and for whatever reason they came across him and decided to attack."
The team filmed the killer whale family as they set about their assault.
Mr Stevens said: "The whales would come through as a pair, one would be slightly in front and would distract the sea lion's attention so he would look one way, and then the second one would hit him.
"Basically they were trying to beat him up to tire him out and wear him down. They would leave him for a few minutes and then come back and continue with the onslaught, before eventually taking him underwater to feast."
Mr Stevens said it was difficult to film the sea lion's ordeal.
He said: "Both of those creatures were doing what they do - in one way you feel amazingly privileged to see it and film it, but to actually witness it in the flesh is actually quite harrowing."
Nature's Great Events: The Great Feast on Wednesday 18 March on BBC One at 2100 GMT and is repeated on Sunday at 1800 GMT
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