I have red headed and black headed vultures around here. The black headed ones showed up about 5 years ago in my area of SW Ohio. The Ohio Dept of Ag sent out fliers describing them and warning about them killing calves, lambs, fawns, etc. I had several of them sitting on top of one of my barns watching a cow calve. Soon as she calved she got the calf up and actually shoved it up hill to the main barn, as far away from the vultures as she could get. That particular cow I bought as a calf from Barkhurst Ranch in Wyoming; those Wyoming cows know how to protect against varmints!
I had the cow/calf pairs in the back part of my pasture. It borders a creek and a woods, although they can't get into the creek and woods. They could get into 2 lots and barns near the house during the day and then they would go to pasture in the evening. Then they suddenly stopped going into the pasture. They stayed in the lots and picked the grass down to the dirt. I thought if they got hungry enough they would go to the pasture but they didn't; I finally had to feed hay. I weaned those calves Aug 21 and the cows hung around for a couple of days and THEN WENT TO THE PASTURE. I think they must have had a close encounter with a pack of coyotes or a bear and were afraid to take the calves back out there.
Who knows what goes bump in the night or flies over head!