Swallows are the trick pilots of the bird world. They fly with deep, liquid wingbeats, suddenly dodge hard to grab a juicy caddisfly out of the air, and then bank hard and up into the air to reverse direction.
Swallows are often best identified by how they fly. Other birds catch insects out of the air - flycatchers wait on their perch and then zip out and back; swifts glide and bank a little more stiffly and higher up in the air - but no others fly with this kind of daredevil quickness and agility.
Three species of swallows are common in Philadelphia (a few others show up too in smaller numbers):
Tree swallows have iridescent, malachite blue backs and clean white bellies.
Barn swallows have cobalt blue backs and tan or reddish-brown bellies. They also have classic swallow tails with long feathers trailing at the corners.
Rough winged swallows are plain by comparison, brown with paler undersides.
All three species can be found over water and other open areas in Philadelphia, though they each choose a different setting for nesting.
Tree swallows nest in cavities in trees or in nest boxes we humans set up for them around water.
Barn swallows build mud nests on the ceilings of human structures such as… barns, as well as boardwalks and bridges.
Rough winged swallows nest in holes in riverbanks or in artificial holes such as drainage pipes and crevices in bridges.