Notes on the Breeding Biology of the White-Throated Swift in Southern California

Abstract

Reproductive activities of White-throated Swifts (Aeronautes saxatalis) were examined from 1997 to 2006 at two nest sites in a human-made structure in southern California. The start of egg-laying was from 27 April to 30 May and hatching of the first chick ranged from 21 May to 23 June; all chicks had fledged by late July, 42–43 days after hatching. The annual molt of adults began in early June and broadly overlapped with the chick-rearing period. Year to year adult survival was minimally 73.9% and nesting pairs showed strong mate and nest site fidelity; pairs reused nests up to five consecutive years. The composition of the arthropod food (insects and spiders) brought to nestlings was different in the periods 1997–2000 and 2001–2004 but prey size was similar in both periods. The onset of breeding was more varied from year to year than the start of the primary feather molt suggesting differing environmental stimuli for these important components of the annual cycle.