スミレミドリツバメ Tachycineta thalassina

A relatively small swallow of western North America. Adult males have a white face and show turquoise-green upperparts and a purple rump in good light. Females and immatures are duller on the upperparts, sometimes just dusky-gray. In flight, note the prominent white "saddlebags" extending up from the underparts to the sides of the rump. Fairly common in a variety of open habitats, often foraging over meadows or ponds. Can be seen in large flocks, sometimes mixed with other species of swallow. Breeds as far north as Alaska; winters primarily in Mexico and northern Central America.