Tree Swallows, especially the adult males, are distinctive. The males have blue-green feathers above and white below, trimmed with blackish flight feathers and a thin black eye mask. Adult females are duller with more brown in their upper parts.
Their name — Tree Swallow — comes from their preference of nesting sites in tree cavities and not from the bird’s usual habitat, which consists of open, treeless areas. Tree Swallows also use nesting boxes, if available. And that leads to conflicts with Eastern Bluebirds, another cavity dweller found in fields in Central Ohio in the spring.
Male Tree Swallow in a field, Sharon Woods Metro Park, Westerville, Ohio.
I’ve watched ownership of a nesting box change hands multiple times within minutes. A bluebird will be standing on top, adopting a threatening pose whenever a Tree Swallow flies near. But eventually a swallow will be successful in its efforts to claim the box, chasing off the bluebird and replacing it on top of the box until a bluebird is successful in chasing away the swallow. The process is repeated many times each spring day.