Swallows of the family Hirundinidae are small, adept aerialists with long, pointed wings and deeply forked tails. Although their bills are short, their mouths are wide for capturing flying insects. Overall, swallows resemble swifts but have stronger, more fluid flight. Highly gregarious, they form large flocks and may be seen perched in long rows along branches or wires. Three species of swallows occur in Yukon-Charley Rivers National Preserve; Tree, Bank and Violet-Green Swallows. Tree Swallows are named for their affinity for nesting in tree cavities and snags. Their Latin name, Tachycineta bicolor, means “fast-moving, two-colors,” referring to their rapid wingbeats and distinctive plumage.
Descriptions: Tree Swallows are common in wooded habitats near water, where dead snags are available. As their Latin name implies, these small, 15cm swallows are distinctly bicolored. Their glossy, blue-green upperparts starkly contrast with the bright-white of their underparts. The characteristic white cheek-patch (auricular) does not extend above the eyes (as it does in the Violet-green Swallow). Juveniles are uniformly gray-brown above, with white tips to their tertial feathers, white on the sides of the head and a pale-gray breast band.
Vocalizations: The sweet song of the Tree Swallow is composed of clearly whistled, liquid notes,” twit-weet, twit-weet, liliweet, twit-weet.” Their call is a high, liquid chirping or twittering. When alarmed, the call is a harsh chatter. Large autumn flocks give scratchy “tzeer” notes.
Nests: As their name implies, Tree Swallows nest in tree-cavities, snags or nest boxes, especially near water. These swallows nest in loose colonies and compete for nest cavities with other species. Nests are constructed by both parents of grasses and lined with feathers. A clutch consists of 4-6, 19mm, white and unmarked eggs. The female alone incubates the clutch for 16 days and young birds fledge in another 16-24 days. Both parents care for the offspring.
Diet: The diet of the Tree Swallow is composed of mostly insects, although berries may be eaten in winter. These birds are elegant fliers and dart to catch flying insects in aerial pursuit but occasionally may glean insects from the ground. Juveniles are known to attempt to steal food from nestlings and adults in adjacent nests!
Distribution: Tree Swallows aggregate in large, pre-migratory, communal roosts. Migrating in huge flocks, these birds are the first of the swallows to arrive in spring and linger farther north in fall. They winter in Honduras, Nicaragua and coastal Costa Rica. During the breeding season, they range throughout most of Alaska and Canada, southward from California and eastward across the Unites States to Georgia. Within Yukon-Charley Rivers National Preserve, a single Tree Swallow was detected in the boreal forest of the Ogilvie Lime/Dolostone Mountains (OM) ecological unit during the Avian Inventory in June 1999 and 2000. Tree Swallows are expected to be more numerous in the Preserve, but swallow species in general were not well inventoried using our survey technique.
