Swallows are small birds common in the United States. These birds usually live in wooded areas and in the countryside. However, due to human expansion, swallows find places within the suburbs and cities to live. Although swallows are beautiful, their nests are sometimes built into crevices and cracks in walls, damaging buildings. Swallows are a protected species due to their shrinking wild population. Barn swallows and tree swallows are the most common swallows in North America.
Examine the coloration on a bird's body. Male barn swallows have blue-black upper bodies; females may have lighter coloration. Tree swallows are iridescent and shiny; males have greenish upper bodies and the females' bodies are slightly browner. Both species have white bellies.
Look at a bird's head and face. Male barn swallows have brownish-red foreheads, while females' may be a lighter shade. Tree swallows' heads are the same color as their bodies, and they have short black beaks.
Watch the bird in flight to get a good look at its tail. Barn swallows have forked tails, while tree swallows have fanned tails.
Examine the bird's nests. Barn swallows build muddy nests that dry against walls and the sides of buildings in cities. Tree swallows build nests with twigs in the eaves of buildings, in rafters, and in holes created by animals such as woodpeckers.