Spring visitants on the Farallon Islands are considered post-breeding wanderers. Feeding territory usually set up by adult or first-year male before breeding, and centered around a rich food source. Breeding territory more actively defended and larger than feeding territory. Nestling period 18-23 days. Prolonged cold periods exert heavy metabolic demands on these small birds, reducing food supplies by killing nectar sources and insects.
Hummingbirds are important for hummingbird-pollinated flowers.
Widespread planting of exotic flowering plants in recent decades has led to expansion of range to north, and increase in overwintering, in coastal California. Life histories of North American cuckoos, goatsuckers, hummingbirds, and their allies. DeSante, D. F., and D. G. Ainley. The avifauna of the South Farallon Islands, California. Studies in Avian Biol.