Their swept-back, crescent-shaped wings give them phenomenal agility in the air. When they fly low over fields, hawking for insects, that is often a sign of imminent rain. They drink by skimming over stretches of water and snatching sips from the surface.
Swallows are easily distinguished from house martins by the chestnut colour on the throat and forehead, and by the long, pointed outer feathers of their forked tails. Unlike swifts, which are much larger and hardly ever touch down, they often settle on telegraph wires or rooftops. Their nests are cups of mud, grass and straw, generally perched on rafters in barns, sheds or garages. A pile of whitish droppings on the ground is always a giveaway sign of activity under the roof.
The birds are monogamous. The hen incubates her eggs, and the male helps feed the chicks. But if the birds nest in colonies the male becomes distracted, trying to mate with other females. Sometimes he goes so far as to kill the chicks in a strange nest, so that the hen will lay again - this time eggs that he himself has fertilised.