We analyzed the diet of nestling White-throated (Aeronautes saxatalis) and Black Swifts (Cypseloides niger) in southern California. White-throated Swifts fed their nestlings boluses of insects that were more taxonomically diverse, on average (over 50 arthropod families represented), than those fed by Black Swifts (seven arthropod families, primarily ants). In some cases, White-throated Swift boluses contained primarily one species, while other boluses showed more variation. In contrast, all Black Swift samples contained high numbers of winged ants with few individuals of other taxa. Our results provide new information on the White-throated Swift’s diet and support previous studies of the Black Swift.