What are those birds swirling around over Bear Creek by the hundreds doing aerobatics? They are small birds with white on their undersides. They look like they are enjoying themselves. If they weren't so joyful-looking they could be something out of Alfred Hitchcock's "The Birds."

What are those birds swirling around over Bear Creek by the hundreds doing aerobatics? They are small birds with white on their undersides. They look like they are enjoying themselves. If they weren't so joyful-looking they could be something out of Alfred Hitchcock's "The Birds."

— Sue. W., Medford

What those birds are doing, Sue, is making a living.

They are snatching flying bugs from the air and eating them. We cannot say how much they are enjoying themselves, but if you're a tree swallow, a bug is a good thing. Tree swallows last month began returning from Central America, where they spend the winters.

You also could see violet-green swallows, which are somewhat similar-looking if you're not using a binocular, and which sometimes flock with tree swallows. And any day now you could start seeing barn swallows and cliff swallows, each of which nests where its name suggests.

Tree swallows nest in loose colonies and perform amazing courtship flights. They eat from dawn to dusk. They are cavity nesters, which means their enemies are starlings, house sparrows and the removal of dead trees from forestry plots. And yes, they are amazing acrobats.

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