Tree Swallows -Fall 2017

by: Virginia Andrews

One of the amazing spectacles of fall on Nantucket is the annual “swallow tornado” as migrating Tree Swallows mass in the air and pour down into their temporary roost for the night. We start to see them during the day around the island: a few in Tom Nevers, or over the Milestone Cranberry Bog, in Bartlett’s Farm fields, or Head of the Plains.

They are seldom single birds: a group of a dozen, perhaps, or a hundred, or several hundred, or even a thousand or more. They perch on bushes or snags, sometimes giving dead trees the appearance of a brief flowering of blue leaves. They swoop and dart over fresh-water ponds, they cruise in the wind over salt marshes, back and forth and up and down, making aerial sweeps for insects.

Although fall is the peak time to see them en masse on Nantucket, some have been around all summer. We see them starting in late March or early April arriving from the south, a sign of spring. Many will keep moving as their migration carries them further north. A few will find nest boxes here attractive and stay to breed, spending the summer raising a family.

They are cavity-nesters, meaning that in the wild they depend on finding hollows in trees or old woodpecker excavations. In fact this is what probably gave them the name “tree” swallows, despite the fact that they are most often seen out in the open over ponds, marshes or fields. But they are not really very fussy, and will readily use bird houses. They will also use boxes put up for other birds such as mallards or wood ducks.

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