How do they know?
The programme's researchers have read the scientific literature and condensed it to a narrative. Like any scientific claims, these are hypotheses on the basis of the available evidence, and inevitably the narration doesn't include all the caveats that appear in the science. (I think this is necessary simplification when making this kind of popular programme, but it's a shame that the BBC don't provide us with a way to trace back the narrative to the primary research.)
I questioned one statement by Attenborough which seemed just to hang in the air: it was about the orcas not being penguin eaters, but fish eaters, and they were only dancing on their tails to find out which way the open sea was.
Attenborough says (at 46:14 in
episode 2):
There is no real need for the penguins to be alarmed. These killer whales are a kind that only eats fish. Rising out is simply the best way for the whales to work out which cracks lead toward the coast and better fishing.
Pitman and Ensor (2003) is a paper supporting the first claim ("These killer whales are a kind that only eats fish"). The evidence for the restricted diet of population C comes largely from observation of stomach contents by Soviet whalers. See page 137: "Berzin and Vladimirov (1983) reported the stomach contents of 785 killer whales taken by the Soviet fleet in 1979/80". For this population the stomach contents was "98.5% fish, 0.4% marine mammals, 1.1% squid". On the other hand there's behavioural observation that goes the other way:
Various personnel at McMurdo Station, Ross Sea, have reported that they have seen killer whales attacking both penguins and seals just off the base there on several occasions. Although it is not known which type of killer whales were involved (or even if these were really attacks), Type C is by far the most common form in the McMurdo area and would be the most likely candidate."
Ballard and Ainley (2005) have some intriguing observations of killer whales chasing (but apparently not catching or eating) penguins in the Ross Sea, and speculate as to the whales' motivation:
... the presence of so many young whales, and the apparent focus of the adults on delivering single penguins to the young without any attempt to actually consume the penguins lead us to speculate that training was precisely the motivation. Such a scenario fits the definition of ‘training’ as reviewed by Baird (2000). While it seems killer whales rarely, if ever, eat Adélie penguins, penguins may offer a sort of “training simulator” for young learning to help provide food for the pod.
So the state of knowledge is more complex than can be summed up in a couple of sentences of narration, as you'd expect.
The second claim "Rising out is simply the best way for the whales to work out which cracks lead toward the coast and better fishing" is likely to be an informed guess based on watching the animals and tracking their movement using satellite-tracking tags attached to the whales' dorsal fins. Andrews et al. (2008) describes the research:
Since at least the early 1970s, killer whales have been recorded annually in McMurdo Sound shortly after the icebreaking has begun. The whales have apparently learned to take advantage of foraging habitat made available when the icebreaker(s) opens up the channel, which allows whales to forage deeper into the fast ice than they could otherwise (Pitman and Ensor 2003)."
(I couldn't find a paper that directly comments on the "rising out of the water to look for cracks" behaviour, but I only spent a few minutes searching. If you find something, post it here.)
References cited
Edit: I see from episode 3 that Bob Pitman was brought in by the BBC to be their killer whale consultant, so it's not a surprise to see his research featuring heavily.
