I think I heard them killing a couple of the neighbor's calves one night.
There were a few unusual vocals that night. I listened to them pass by here & move on toward a neighbor's pasture where he kept a large herd of cows & calves. It was rare to hear the cows get upset when the BFs were there, but this night, they started mooing & it sounded like they were running from something.
They got quiet for a few seconds, & I heard what sounded like a calf bawling frantically. Suddenly it was shut off in mid-bawl. Almost immediately, there was another bawl with the same ending.
All of the BF vocals stopped after that, & I imagined them carrying calves off somewhere to have for a midnight supper.