According to eBird.org, the Violet-green Swallow is a year round species in Orange County, CA and you've better odds of finding this species from late February through July. To the trained eye, it's fairly easy to tell this swallow apart from other swallows when in flight. Look for the white patch just above the tail on the back side of this swallow. Of course there are other identifying features such as facial pattern and color but this perhaps is the easiest if in flight. This species is not easy to locate and can be troublesome when amongst other swallows to the untrained eye. The swallows erratic flight pattern adds to the challenge. These photos were taken on the Bell View Trail SW in Rancho Santa Margarita in late May and found shortly after 5pm on both occassions. For exact location, please click the "Map" button within each photo. Here's more from Wikipedia: The violet-green swallow (Tachycineta thalassina) is a small North American swallow. Their breeding habitat is semi-open areas in western North America from Alaska to Mexico. They nest in cavities in a tree or rock crevice, sometimes forming small colonies. They migrate in flocks to Central and northern South America. These birds often forage in flocks, usually flying relatively high but sometimes flying low over water. They eat insects including mosquitoes, butterflies, mayflies and moths.