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Fall flocks of these beautiful birds can be very large. One flock was estimated to contain 20,000 birds in Sherburne County, MN (north and west of the Mississippi National River and Recreation Area).
Like all swallows, these birds feed on insects that they pluck from air during flight, although they have also been known to eat berries in wintering areas. Their flight is strong, acrobatic, and entertaining to watch.
While these birds once nested in natural cavities, usually near water, they now readily take up residence in bluebird houses. Perhaps this is due to the loss of natural cavities near water. While many birds are not tolerated by bluebird enthusiasts, tree swallows are an exception. Many bluebird nest boxes are "paired" so that bluebirds may nest in one box and tree swallows can nest in the other box.
Tree swallows dive on threats, such as predators, in an effort to drive them away from the vicinity of their nests. This sometimes includes people, however they don't actually strike a person or predator. Still, it can be a very intimidating display even by a very small bird such as a tree swallow.
Fascinating Facts
The female tree swallow, unlike other swallows, retains its brownish juvenile plumage until its third year. It's thought that the juvenile plumage may permit the young female to remain in the territory of a breeding pair ready to take the place of the older female if something should happen to her.
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