If you look up in the sky and see swallows flying, look at the tail, if it is forked it is a barn swallow. They have a very deep v or notch in the tail that helps them maneuver in flight as they catch insects. The barn swallow has a dark uniform blue back, the throat is a deep red color that fades into a light brown belly. A white stripe runs through the tail underneath.
To tell the sexes apart is easy. When barn swallows are at rest sitting on a branch or wire just look at the tail length. The females tail is shorter than the males and is only slightly longer than her wings in a sitting position.
The barn swallow is quite willing to live its life right next to us and its choice of building sites show this. They love to nest under bridges and the eaves of houses or in barns and sheds and are not shy around humans and go about their ways without regard to us.
While several barn swallows may nest near each other, new pairs form each spring, they do not form dense colonies. They are usually monogamous during the breeding season, but extra-pair copulation is common. These other birds not only help build and guard the nest but also incubate the eggs and brood the young, although they generally do not feed the young.
Barn swallows like to build their nests on eaves, bridges, docks, or other man-made structures with a ledge that can support the nest, a vertical wall to which it can be attached, and a roof. Both members of the pair build the nest which is a mass of mud, straw, feathers, and sticks. Barn Swallow nests are quite messy. Both males and females incubate the eggs for up to 17 days, and both feed the young. The young leave the nest within 21 days of hatching.