Migrating and wintering Tree Swallows can form enormous flocks numbering in the hundreds of thousands. They gather about an hour before sunset and form a dense cloud above a roost site (such as a cattail marsh or grove of small trees), swirling around like a living tornado. With each pass, more birds drop down until they are all settled on the roost.
Tree Swallows winter farther north than any other American swallows and return to their nesting grounds long before other swallows come back.
They can eat plant foods as well as their normal insect prey, which helps them survive the cold snaps and wintry weather of early spring.
The Tree Swallow—which is most often seen in open, treeless areas—gets its name from its habit of nesting in tree cavities. They also take readily to nest boxes.
Tree Swallows have helped researchers make major advances in several branches of ecology, and they are among the best-studied bird species in North America. Still, we know little about their lives during migration and winter.
The oldest Tree Swallow on record was at least 12 years, 1 month old when it was recaptured and released during banding operations in Ontario in 1998.