Tree swallow

Swallows and swifts really aren't hard to identify. They're just hard to get a look at. Flying almost incessantly and at high speed, they usually have to be identified on the wing. Once in a while, you get lucky and a swallow--like the bird above--perches. Tree Swallow is characterized by its almost metallic greenish-blue back and head with a white throat, breast, and belly. The color alone is enough to identify this bird, but color can be hard to see in flight or when the bird is backlit high in the sky. Some birds overwinter here, but more are migrants that spend the summer months in Sonoma County, often arriving as early as late February and staying through mid-October. Nests in many parts of the county, using abandoned woodpecker holes or cavities in old and decaying trees. Also uses nest boxes, notably at Shollenberger Park. Birds such as Starlings, House Sparrows, Western Bluebird, and House Wren compete for these cavities. Sometimes seen feeding fledged juveniles high in trees. Common over streams and ponds. Usually eats insects, but will eat berries when insects are not available. May form very large flocks.

Although the blue-green color of Tree Swallow is usually a give-away, identification is complicated by a number of factors besides the difficulty of seeing such fast-moving birds. Adults take on a somewhat duller, greener look in the autumn. Juveniles are a grayish-green color that may cause confusion with other swallows. In all plumages, however, there is a clear division between the darkish cheek and white throat, and face patterns may be the most reliable way to separate the five common species in the county--Tree Swallow, Violet-green Swallow (Tachycineta thalassina), Cliff Swallow (Petrochelidon pyrrhonata), Northern Rough-winged Swallow (Stelgidopteryx serripennis), and Barn Swallow (Hirundo rustica).

Barn Swallow is usually obvious because of its unmistakable, long, forked tail. Having eliminated Barn Swallow, only Tree Swallow and Violet-green Swallow have extensive clear white on the face (although whitish at the throat, Northern Rough-winged Swallow looks mostly brown with a dirty look to the face; Cliff Swallow has a little white at the forehead, but its throat and cheeks are dark--mostly chestnut with black at the base of the throat; also look for that bird's distinctive buff rump patch).

The problem then is to distinguish Tree Swallow and Violet-green Swallow. In good light, the color of the back and head is enough: Tree Swallow is metallic greenish blue, while Violet-green Swallow (not surprisingly) is violet and green on its back. Otherwise, look for the two white "pom-poms" at the rump of Violet-green Swallow that nearly meet over the base of the tail. White on either side of the rump and more extensive white on the face than in Tree Swallow serve to give Violet-green Swallow overall the "cleanest," whitest look of the five common local swallows (Violet-green Swallow's coloration always suggests a killer whale to me). Note, however, that Tree Swallow has some white at the rump as well, but it doesn't give the impression of two white balls, as the white patches on a Violet-green Swallow usually do. A Tree Swallow's face is fairly simply dark above, light below. Violet-green Swallow has white behind and above the eye, which makes it look like the white partially surrounds the eye. Flight patterns are different as well. Peterson notes that Tree Swallow tends to glide in circles and then end each circle with a few quick flaps of the wings and a climb--although I've never personally been able to distinguish swallows by their flight habits.