The Tree Swallow with its snowy breast and iridescent green back feathers is one bird I welcome with joy each spring. This year I had for the first time in several years a pair of tree swallows nesting in my purple martin gourds in my yard. Several years back, there had been a killing snowstorm in April at the peak of the swallow migration and I believe “my” birds had perished in it. I saw one swallow in my yard that spring, and it looked bedraggled and wet.
Tree Swallows are cavity nesters, utilizing old woodpecker holes once upon a time. When we first moved to Center City 23 years ago, a pair was nesting in a cottonwood snag at the corner of County #37 and County #9—the only time I had ever seen swallows in a natural cavity. Today, we all see them frequently in man-made nest boxes that are put out for bluebirds, but tree swallows are always welcome in our boxes. Their pleasant twitters and attentiveness to parental duties fill the yard with activity and music.
Because of their embrace of artificial nest boxes, Tree Swallows are one of the most-studied songbirds in North America. Despite this, Cornell Laboratories claims that little is known about their migration or winter ecology. Occupying a broad range across the North American continent in summer, the birds migrate to a narrow rim bordering the Gulf of Mexico, and parts of Mexico in winter. This marks them as the most cold-tolerant swallow; unlike other swallow species, tree swallows eat berries and a small amount of seed. This might explain the more northern wintering grounds.
Tree Swallows are sociable and once the breeding season is over, will flock up with others. I spotted perhaps 50, a mixed flocks of tree and bark swallows on the telephone wire along County 9 in late August. That may seem like a great many, but here is what pioneer birdbander Marie Commons wrote in The Birds of Minnesota, published in 1932: As the time for leaving approaches they join [other swallow species] making enormous flocks, which frequently number in the thousands…
Bird watchers today have, really, a very limited time-frame with which to evaluate the status of bird populations, but consider: when was the last time you saw thousands of swallows in a flock?
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