Violet-green swallows (Tachycineta thalassina) closely resemble tree swallows (Tachycineta bicolor). Both have white underparts and dark, shiny backs. As they fly about, or even perched, identification can be difficult.
Violet-green swallows possess longer, narrower wings and shorter tails than tree swallows. But, I assume as with most casual birders, my skills at discerning such fine differences are lacking. The white underparts of a violet-green swallow extend onto its cheek, behind the eye and above the eye while the white on a tree swallow’s face stops below the eye. In flight a violet-green swallow appears to be wearing a “diaper” or “pantaloons” because the white on its flanks extends up the sides of the rump. The tree swallow lacks white patches on the sides of the rump. Finally the tree swallow’s upperparts are a shiny blue-green while those of the violet-green swallow are more, of course, violet green.
The female violet-green swallow is duller than the male. Where the male’s underparts are pure white, the female has an ashy brown wash on her throat.
The violet-green swallow eats insects which it catches in flight, often foraging in flocks.
Violet-green swallows breed in Western North America from Alaska to Mexico and winter in Central America. Cavity nesters, violet-green swallows build their nests in tree holes or cliff cavities and will also utilize nest boxes. These violet-green swallows were photographed in the chalky cliffs along the Hat Creek Canal (Shasta County CA).