- Outside of the breeding season the Tree Swallow congregates into enormous flocks and night roosts, sometimes numbering in the hundreds of thousands. They gather about an hour before sunset at a roost site, forming a dense cloud. They swirl around like a living tornado and as darkness approaches they then wheel low over the cattail marsh or grove of small trees. Large numbers drop down into the roost with each pass of the flock until the flock disappears.
- The Tree Swallow uses many feathers from other birds in its nest. The feathers help keep the nestlings warm so they can grow faster. They help keep levels of ectoparasites, like mites, low too.
- The Tree Swallow winters farther north than any other American swallow, and it returns to its nesting grounds long before other swallows come back. Its ability to use plant foods helps it survive periods of bad weather.