They winter further north than other North American Swallows, often congregating in massive flocks on their wintering grounds. Tree Swallows have greatly benefited from the proliferation of bluebird boxes, as they will readily use boxes of that size and configuration.
Tree Swallows are known to “fight” over feathers in mid-air for reasons which are still under investigation. There is some speculation that this is a form of play.
Most of their diet is made up of insects. Unlike most swallows, tree swallows sometimes eat quite a bit of vegetative material, primarily berries and seeds.