Thirteen territorial male Anna’s Hummingbirds, Calypte anna, were observed during the 1981 and 1982 breeding seasons. Breeding territories were large, but size was not determined by energy availability. When a food source (sucrose solution in feeders) was present, the degree to which it was defended was a function of food quality. If a high-quality food source was absent, males did not exhibit the behaviors associated with defending a food source, but breeding territoriality remained intact. Territories were maintained for the entire breeding season even when food quality was varied. The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest that the primary function of the territory is reproductive and that an internal food sourcei s not necessaryfo r its maintenance.
Powers, Donald R., "Effects of Variation in Food Quality on the Breeding Territoriality of the Male Anna's Hummindbird" (1987). Faculty Publications - Department of Biology and Chemistry. Paper 18.