True, crows are primarily scavengers, but, they are also very busy minded birds and find ways to amuse themselves. Chances are they won't eat the chicks, but will kill them or drag them off. Used to live on a farm as a kid and watched them do this very thing on several occaisions. Told the farmer about it, he had no idea. He took a bunch of pot shots at the crows, and that seemed to deter them. They would also dive-bomb the roo everytime they saw him in the yard! They are great for keeping hawks away, but they are very clever and mischeivious as well. I've never lived near ravens, but they are as smart, if not smarter than crows from what I've heard. In any case, I'd take pre-emptive measures, why take the chance??