Believe me I have seen the devastation a pair of carrion crows can do to a loft, killing youngsters on the ground, picking birds out the sky, and going into the loft and eating eggs and squabs, They are crafty birds, they sit next to your team for days, giving your birds a false sense of security, then all of a sudden they attack. You tend to get trouble when one single pair are dominating an area, as i have a few pairs in my area, but they are always too busy fighting each other, however, I never underestimate the unpredictability of these killers. :-/