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Monday, March 20, 2006

Birds of the Mid-Atlantic #3: Tree Swallow

Within the past week our area has seen an influx of tree swallows. The numbers are not quite as high as they will be in another month. But the flocks we are seeing are more than a trickle; they represent the beginnings of a major northward push. I saw my first swallows here in DC on Saturday at the National Arboretum. I then saw a lot more of them on Sunday at Hughes Hollow in Montgomery County, Maryland. Other reports of tree swallows have been appearing on birding lists all over the region.

Photo by James C. Leupold / USFWS

Tree swallows are among the earliest songbirds to migrate north in the spring. They are typically the first swallows to arrive. Like eastern phoebes, they able to migrate early because their diet is varied enough to survive short cold snaps. Unlike other swallows, they will eat seeds and berries if insects are scarce or unavailable. Thus if it should happen to snow the day after spring begins, they have a backup plan.

These easily-recognizable birds are characteristic of wetlands, which provide the steady stream of insect food that these swallows need to raise broods. Identifying tree swallows is a matter first of learning to follow swiftly-moving airborne birds with binoculars. (This can be quite fun, if a bit dizzying.) Once that skill is mastered, one can distinguish tree swallows from the rest by their glossy blue top parts and their all-white undersides. Juvenile tree swallows have all-white undersides but brown upperparts. The juveniles can be tricky to separate from northern rough-winged swallows and bank swallows.

In the past half-century, tree swallows have greatly expanded their breeding range in Maryland, thanks to the placement of nest boxes in suitable habitat. Where once they were confined to the Eastern Shore, they can now be found throughout the state, including the western mountains.

Cross-posted at A DC Birding Blog



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