The other day, David and I ran outside when we heard an aerial-predator-alarm call from our roosters. I don't know how to describe this exactly, but we've started to discern some subtle differences in this kind of alert. This time, our first reaction was that it must be a big bird coming in low overhead. Sure enough, we got outside just in time to see a pair of golden eagles cruising low overhead (the first one we saw wasn't much more than 50 feet up).
They were enormous, amazing, beautiful birds, and it was the first time we've seen golden eagles here, although we've had a lot of bald eagles around in the past year or so. Silly me, I had run outside without my video camera. David said to me later that for birders like us, the roosters' alarm calls can be helpful in letting us know not just that there's a potential predator in the vicinity, but that it might turn out to be a rare opportunity to see something like a golden eagle. (Golden eagles usually are higher up in the mountains than our place, which is at about 1000 feet.)
As I said, there seem to be some variations in the aerial-predator call. I'm going to try to get some recordings of these calls one of these days. In the meantime, I must remember to grab my camera next time I hear our helpful little roosters give the head's-up.