Of a Feather: Swallows: Convivial to solitary

By BILL CHAISSON
By Bill Chaisson

We have a pond on the property where we live. The owner has put up a number of blu ebird boxes and he has a barn. So, I have been waiting for the swallows to show up, and this past week, they did. I wasn’t all that surprised that they were tree swallows, which are the hardiest of this family. Their call note is at a lower pitch than that of the barn swallow, and although both species have blue backs, the flight of the tree swallow is less swoopy and fluid and when they make a turn and their undersides flash in the sun, they are as white as snow from their throats to their tails.

I wonder if we will get barn swallows, because our landlord does not leave his barn doors wide open as per tradition, which allows the birds to fly in and out and nest freely in the rafters. The nearby pond is important not just as a place for swallows to hawk for flying insects, their primary food, but the shores of a pond are a source of mud. Barn swallows (Hirundo rustica) alight along the edge of the water and roll mud into little balls with their bills and then carry it back to the nest site to build up a masonry cup with bits of straw, hay, and other vegetation wound through it as infrastructure.

Cliff swallows (Petrochelidon pyrrhonota), which are less common in the Northeast than barn swallows, roll mud too, but their nests are gourd-shaped, an adaptation to building them exposed to the weather. While barn swallows are more apt to nest inside of a structure, cliff swallows paste their nests on the walls outside. P. pyrrhonota nests are glued into the space between a horizontal overhang and a vertical wall. H. rustica nests generally sit on something horizontal, although it can be the smallest of protrusions, like the head of a large nail. These species are colonial nesters. The cliff swallow in particular may nest together by the hundreds (rarely thousands).

The least often encountered colonial swallow, perhaps because of the specificity of its nesting behavior, is the bank swallow (Riparia riparia). I first saw them nesting in an abandoned pile of sawdust outside a former saw mill in Bristol, New Hampshire, which is a bit outré for this species. Unlike the other colonial types, bank swallows are cavity nesters. The males excavate a tunnel into a vertical bluff of unconsolidated material, and the females choose a mate based on shared real estate values.

But not all swallows are as convivial. Tree swallows (Tachycineta bicolor) may choose sites more or less near one another, but do not pack their nests together like cliff swallows or within feet of each other like barn and bank swallows. Tree swallows, like bank swallows are cavity nesters, but they are more drawn to tree cavities—natural or woodpecker-excavated—and nest boxes. Their nests are therefore slightly more scattered, but they are otherwise quite social, feeding together over the same pond and swarming invading predators to dive-bomb them in tandem.

The northern rough-winged swallow (Stelgidoptyerx stennopennis) is least social of the family. Like bank swallows, they are cavity nesters, and indeed will sometimes use an abandoned burrow at the edge of a bank swallow colony. Unlike R. riparia, the rough-wing does not excavate its own nesting site, but will use that of a kingfisher or fellow swallow. They are not wed to bluffs and will raise young in gutters, drainpipes, under bridges, or anywhere they can find a suitable hole.

The rarest member of this family (Hirundidae) is not called “swallow.” The very colonial purple martin (Progne subis) has declined drastically in abundance in the Northeast, although its numbers remain good elsewhere in its range. The spring we are having right now is deadly to martins, which are prone to expiring in droves during cold snaps. They are regarded as a threatened species in New Hampshire, and are seen mostly in scattered locations through Merrimack, Belknap, and Carroll counties. Their nesting habits have become focused almost entirely on man-made nesting boxes, so if you want to attract them, you must follow the plans available from NestWatch or some other non-profit more interested in ecology than fashion. And make sure your next box is erected at the prescribed height and proximity to water.

In North America, only H. rustica is truly “swallow-tailed” while the others—excepting the cliff swallow—have tails that are, to varying degrees, forked. As can be seen by their binomials, while these six species are all in the same family, they are in six different genera, which is to say they are not very closely related.

What they have in common is bodies built for flight. Their legs are short, but unlike the swifts’, long enough to allow them to perch easily, although they cannot really walk. Their bills are short and broad at the base, built for catching insects on the wing. Insects are their exclusive diet (although tree swallows will eat berries), which is why spring cold snaps are dangerous for them.

Their wings tend to be relatively long and pointed, although those of tree swallows are broader and those of cliff swallows more rounded. While all of them are eminently maneuverable in the air, their wing shapes determine their varying styles of flight. Because of their broader wings, tree swallows glide more than other species, more accipiter than falcon. At the other end of the spectrum, the tiny bank swallow, the smallest of the tribe, flies with quick, flicking wingbeats. Allaboutbirds.org describes them as “less twisty in flight than barn swallows, and more direct than rough-winged or tree swallows.”

All of them, except the tree swallow, migrate out of North America for the winter. No wonder T. bicolor is the first one back.

Bill Chaisson has been a birdwatcher from the age of 10. He is a former managing editor of the Eagle Times and now lives and works in the town of Wilmot. Contact him at [email protected].