Thanks everybody.
Phil, the same thing happens here when I mow pastures or cut hay. The other interesting birds that invariably show up are red-tailed hawks, usually at least two but sometimes three or four. They perch in tree tops near the field if there are any close by, or just circle and hover, much higher up than the circling swallows.
The swallows are after insects stirred up by mowing, the hawks are watching for field mice and rabbits, and invariably they get a few. They swoop down at high speed and deliver a knock-out blow, then land nearby, pick up the victim and fly off with it. Usually they return a few minutes later and start the process again. But a couple of times I’ve witnessed a hawk catch or knock down a swallow, in mid-air.
Ken


