Buzzards killing mature cows

[KyNewbie]

I came home from work to find my second dead cow of the week. Both had healthy October calves by their sides and I had laid eyes on both sets of cow calf pairs walking in the pasture and nursing. No signs of the cows being sick in any type of way. I've received phone calls while at work last week with people telling me that they have observed the buzzards pestering the herd. I've had my grandfather go out and run them off multiple times and I myself have gone out and shot at them to scare them off. They are the black buzzards, and seem to be way more aggressive than the turkey vultures. I find it odd that they have targeted two mature cows as opposed to going after calves. I've never personally seen buzzards be this aggressive and I personally have not lost any cattle to buzzards that were not either newborn or seemed to be terribly old or injured. Any thoughts? Am I wrong to think it's buzzards and maybe should be looking for another cause of death? Thanks in advance