The way the actors interact with each other, whether loving or violent, may serve as a visual inspiration to the actors. The point of this scene in 2001 is to relate savage animal behavior to what we believe to be “human nature”. Corvid birds are next only to humans and primates in terms of brain-to-body mass ratio, and even an amateur birdwatcher could recognize human-like behavior patterns in corvids.
On the flip side, the actors might want to take note of their own acting, and make sure that they resemble birds, and not monkeys, who we are more closely related to. I don’t know why but when I rehearse with the actors I feel more like a monkey sometimes than a bird.