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Flight Lines: Tree swallows are a nice second choice

Tree swallows are common nesting birds over much of North America, and will readily use artificial nest boxes. Keith Corliss/The Pioneer

Matt is a friend who lives on a nearby rural farmstead. He's not a farmer, mind you, but he and his wife prefer the quieter atmosphere of country living. It also allows her to keep her horses at home instead of boarding them somewhere else.

During the few years they've lived out there, Matt has worked tirelessly to create a landscape favorable to themselves and to their animals. In doing so, they've cleared brush, planted numerous trees and maintained a large garden. He's also tried to lure in bluebirds by placing nest boxes along a fence row.

Anyone who has attempted to entice a certain species to nest in a box understands it's a bit of a crap shoot. The if-you-build-it-they-will-come approach works. The sticking point is you never really know for sure who they will be. In this particular case, instead of bluebirds, it's tree swallows (Tachycineta bicolor).

Of the six species of swallows which breed in the Red River Valley, only two regularly nest in boxes, purple martins and tree swallows. And purple martins rarely nest alone, preferring instead to group up in communal sites designed for them. Tree swallows, on the other hand, will regularly occupy single nest boxes, usually the ones folks put out for bluebirds.

It's not difficult to identify this bird, being pure white underneath (except for juveniles) with a dark, blue, iridescent cape covering its head and running down the back and wings. Like all swallows, it's got a short, stout beak and long wings extending beyond the tail when at rest.

The only other swallow to be reasonably confused with tree swallows is the violet-green swallow. Since violet-greens are confined to the badlands in this state, however, the only white-breasted iridescent greenish blue swallow around here will very likely be a tree swallow.

I'm not sure why, but tree swallows seem to have a fascination with feathers. A single bird can often be seen flying around with a small feather in its mouth, dropping it in midair only to catch it again. The nests are usually lined with the feathers of other birds also. This is thought to increase warmth for the nestlings and help limit parasites.

Though placed among the songbirds, swallows are not typically considered great singers. But among its swallow brethren, tree swallows are perhaps the most vocally pleasing. The birds will often sing high-pitched clear whistles along with a variety of twitters and chirps.

Like all swallows, this one feeds primarily on flying insects, making them rather beneficial to humans. However, tree swallows incorporate some berries into their diet especially in winter when invertebrates can be scarce. This allows the species to winter farther north than any other swallow. As a result, it's the first swallow to appear in spring across most of North America.

Tree swallows have been migrating south for nearly a month already, the birds having finished raising young. Fall migration will continue until nearly freeze-up. Migrant flocks of tree swallows can be impressive, with some locations reporting numbers in the hundreds of thousands often mixing with other swallow species. While not so numerous this far north, flocks of many thousands can still be expected. Pay particular attention to open areas such as marshes and wooded swamps where the birds usually gather.

My friend told of some interesting behavior at his swallow nests a few weeks ago. When he would approach a box containing young, adult tree swallows would mob him in an attempt to protect the nestlings. Not just the doting parents but other adults as well.

This type of cooperation is common among gregarious flocking birds and serves to benefit the species in a three musketeer sort of way. Unus pro omnibus, omnes pro uno (all for one, and one for all).

While bluebirds have yet to nest in the structures put up for them, Matt is not chagrined. The tree swallows have helped to keep the nearby bug population down and provided hours of enjoyment through their aerial antics and fascinating behaviors. As stated previously, one never knows which species will nest in an artificial box, but a person can't be too disappointed if it's tree swallows.

Corliss is a West Fargo resident, avid birder, and ND Game and Fish volunteer instructor. He serves as a corporate pilot for Forum Communications.