A sure sign of spring flew back into Iowa this week. The barn swallows. Step outside in the late afternoon and you’ll see them swooping and soaring as they catch mosquitoes and other flying insects. This week I've seen them at the Russell Wildlife Area, flying over Maskunky Marsh and nesting in the barn at Caldwell Park. Adults have a long, deeply forked tail that distinguishes them from other swallows. The upperparts are glossy blue. The rest of the wings and tail are black with a blue or blue-green gloss. On the underside of the tail are small white patches. The forehead, chin and throat are deep chestnut color. Males and females look the same.

As their name suggests, barn swallows often nest in barns. A barn usually supports a colony and the nests of six to eight pairs. Nests are built with straw and mud and lined with feathers. These birds may take 1,000 trips to gather mud, which is worked into a pellet and carried to the nest site in the birds’ bills. Barn swallows usually build their nests close to the ceiling on a beam or tucked under the eaves.

Originally, barn swallows built their nests on cliff faces and in caves and rock crevices, but now such nest sites are rare. These days you’ll find most barn swallow nests on human built structures such as buildings, bridges, mine shafts and culverts. I always love to watch the ones that nest on my porch. Their graceful swooping and soaring mean less bugs in the yard on summer evenings.

When feeding young, the swallows fly all day long. It seems that they hardly ever rest. When a cat or other predator approaches their nesting site, the entire colony immediately mobs the intruder in a display of aerial acrobatics. Most of their hunting is done near ground level, over open fields and especially near water. However, on late summer afternoons, they can be seen hunting high in the air. They simply follow the insects, which, in turn, may be reacting to differences in air temperature.

Keep your eyes out for barn swallows this week and if you lucky enough they just might choose your building for a nest site.