On the behavior of the Black Swift

The behavior of Black Swifts was studied in southern California from 1990 to 1992. Four types of aerial interactions were distinguished: (a) group chase, (b) pair chase, (c) pair contact, and (d) touch and grasp. The latter two interactions can be intraspecific or interspecific. Aerial copulation was not observed. Nestlings, from age 18 days onward, and adults gave hostile or deterrence displays by wing-raising. Begging by nestlings was silent but aggressive toward the adult. Silent begging may be an antipredator strategy for a species that produces a single chick per season. Nestlings have a far more conspicuous white facial marking than adults; this may function as a target signal to guide food delivery in the dimly lit nesting conditions and as an aid for the adult to find the nest when arriving late at night. Adults roosted on the nest for the first half of the nestling period and then most roosted on the cave walls. During incubation and early brooding, an adult always remained at the nest, and food transfer between adults was observed during this period.