Tree swallows are among the earliest songbirds to migrate north in the spring. They are typically the first swallows to arrive. Like eastern phoebes, they able to migrate early because their diet is varied enough to survive short cold snaps. Unlike other swallows, they will eat seeds and berries if insects are scarce or unavailable. Thus if it should happen to snow the day after spring begins, they have a backup plan.
These easily-recognizable birds are characteristic of wetlands, which provide the steady stream of insect food that these swallows need to raise broods. Identifying tree swallows is a matter first of learning to follow swiftly-moving airborne birds with binoculars. (This can be quite fun, if a bit dizzying.) Once that skill is mastered, one can distinguish tree swallows from the rest by their glossy blue top parts and their all-white undersides. Juvenile tree swallows have all-white undersides but brown upperparts. The juveniles can be tricky to separate from northern rough-winged swallows and bank swallows.
Cross-posted at Blue Ridge Gazette