The tree swallow's personality seems to be more friendly and tolerant to the presence of people. They swoop and spin through the air following the mower as it throws moths and other insects into the air along with grass clippings. No matter where bluebird boxes are placed, but especially anywhere near water, tree swallows will be found. They're abundant nesters across Pennsylvania, usually in tree cavities and old woodpecker holes. But bluebird boxes are always appealing.
Tree swallows arrive in spring before any of the five other species of swallows.
As early as the first week or two of April the swift and agile fliers may be seen flitting above the Lehigh and Delaware rivers searching for early aquatic fly hatches. Only the barn swallow exceeds the tree swallow in abundance. A closer look in good light reveals a beautiful greenish to bluish iridescence. Its belly is pure white. The lackluster female is somewhat brown with duller underparts.