The raven is sometimes known as “the wolf-bird.” Ravens, like many other animals, scavenge at wolf kills, but there’s more to it than that.
Both wolves and ravens have the ability to form social attachments and they seem to have evolved over many years to form these attachments with each other, to both species’ benefit.
There are a couple of theories as to why wolves and ravens end up at the same carcasses. One is that because ravens can fly, they are better at finding carcasses than wolves are. But they can’t get to the food once they get there, because they can’t open up the carcass. So they’ll make a lot of noise, and then wolves will come and use their sharp teeth and strong jaws to make the food accessible not just to themselves, but also to the ravens.
Ravens have also been observed circling a sick elk or moose and calling out, possibly alerting wolves to an easy kill. The other theory is that ravens respond to the howls of wolves preparing to hunt (and, for that matter, to human hunters shooting guns). They find out where the wolves are going and following. Both theories may be correct.
Wolves and ravens also play. A raven will sneak up behind a wolf and yank its tail and the wolf will play back. Ravens sometimes respond to wolf howls with calls of their own, resulting in a concert of howls and calls.
Sources: Mind of the Raven, Bernd Heinrich, The American Crow and the Common Raven, Lawrence Kilham