BONNERS FERRY — During the past several weeks I have been observing a remarkable darting bird. In fact he is so quick at times he is hard to follow in flight. The first time I saw him was about two weeks ago sitting on top of an old snag beside Myrtle Creek south of the Kootenai River. I knew it was a swallow but I consulted my “Birds of Idaho” field guide for identification. After further research I discovered the bird was a Tree Swallow.
The Tree Swallow is a handsome aerialist with deep-blue iridescent backs and clean white fronts. Tree Swallows are a familiar sight in spring and summer fields and wetlands across Boundary County and northern United States. They chase after flying insects with acrobatic twisting and turning, their steely blue-green feathers flashing in the sunlight. In flight it is a small and chunky bird with a shallowly forked tail and broad-based triangular wings.
The Tree Swallow is most often seen in open treeless areas, but actually gets its name from the habit of nesting in natural cavities of standing dead trees, old woodpecker cavities or nest boxes. On occasion they nest in hollow stumps, building eaves and sometimes in old Cliff Swallow burrows. They like to live in open country near water, marshes, meadows and lakes.
In my observation this spring, I noticed that Tree Swallows are highly social and pairs often nest close together, particularly where nesting opportunities are numerous. Tree Swallows are agile fliers and tend to glide more than other swallows. They bathe by flying low over the water and skimming their bodies against the surface, then rising quickly while shaking off droplets. Tree swallows line their nests with feathers, and they seem to display or even play with these feathers during the early nesting season. A bird flies above the nest with a feather held in its bill, sometimes leading to a chase in which the bird may drop the feather causing an aerial free-for-all to see which bird retrieves it.
The male arrives on nesting territory before the female. The courtship involves the male showing the female potential nest sites. Tree Swallows often choose new mates each year. The female does most of the nest building, taking between a few days and two weeks to finish the job. She collects material on the ground near the water’s edge, usually within 100 feet of the nest site. The nest is often made entirely of grass, but may include pine needles, mosses, aquatic plants and animal hair. Within the cavity the female presses her body against the nest material to shape it into a cup, about 2-3 inches across and 1-2 inches deep, and lines it with many feathers of other bird species. Generally the male gathers most of the feathers; however in some instances the male and females split the duty evenly. The clutch size is generally 4-7 eggs with 1-2 broods per year. The incubation period is 11-20 day. When the Tree Swallow hatches it is helpless, with eyes closed and pink skin sparsely covered with down. Both parents feed nestlings, and the female broods them while they are small. The young usually leave the nest about 18-22 days after hatching.
The popularity of the bluebird has been a boon to the Tree Swallow, which nests in holes of exactly the same size, and has taken advantage of bluebird houses over much of North America. In regions with no such ready supply of artificial nest sites, the swallows must compete with other cavity-nesting birds, arriving early in spring to stake out territories. Unlike other swallows, Tree Swallows eat many berries; allowing them to survive through wintry spells when other insect-eaters might starve.
Other swallows of Idaho include the Barn Swallow, the Cliff Swallow and the Violet-Green Swallow. The Barn Swallow has a rust belly and deeply forked tail. The Tree Swallow is similar in size to the Cliff Swallow and Violet-Green Swallow, but lacks any tan-to-rust color of the Cliff Swallow and any emerald green of the Violet-green Swallow. The Cliff Swallow is a colony nester and will carry balls of mud up to a mile to construct its nest.
The oldest Tree Swallow on record was 12 years, 1 month old when it was recaptured and released during banding operations in Ontario in 1998.