Scott Sainsbury suggested consulting Cornellís crow expert, Kevin McGowan. His website http://www.birds.cornell.edu/crows/ might provide some explanation for the crow fight I saw yesterday:
Crows are very social species and live in large extended family groups. That does not mean, however, that they are friendly with all other crows. Just as we humans are social and love our families and friends, we also have been known to fight and kill each other on occasion. Birds may fight for a number of reasons, such as defending territory boundaries, protecting their mate (or sexual access to them), or defending some other resource. Crow fights within a family are usually short and involve only a few pecks. (Crows, in my experience, actually seem to have very few intra-family squabbles compared to some bird species.) Fights between members of different families, however, can be protracted and deadly. I frequently see crows locked together tumbling out of trees in the spring. Although I have never witnessed an actual killing, I would not be at all surprised to see crows kill another crow from outside the family group that was trespassing.
Another possible explanation of extreme violence is that the attacked crow was already injured. Injured, sick, or oddly acting birds are often attacked by their own species. Crows are no exception. One explanation for this behavior is that having an injured individual around is dangerous to others in that it might attract predators. Not only that, but a vulnerable crow could teach a predator to hunt for crows, which might endanger other crows. With this line of reasoning, crows would be best served by getting rid of an odd ball. I do not know if crows would eat another crow they killed. They might, but I rather expect they would not.
This doesnít totally explain why the fight seemed vicious but didnít appear to end in injury (I wrote Kevin and will share his response), but itís an interesting look into the lives of these fascinating birds.
Maeve Kim, Jericho Center