Territorial Defense against Hummingbirds and Insects by Tropical Hummingbirds

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Abstract
Data presented on a single rufous-tailed hummingbird (Amazilia tzacatl) defending a feeding territory from hummingbirds and insects correlated quite well with predictions of optimal behavior based on time and energy considerations. The majority of time spent in defense was in chasing hummingbird intruders. Less time was spent chasing large bees and butterflies; small bees and butterflies were not chased from the territory. The amount of time spent chasing different types of intruders appeared to correspond to their size and hence to the potential threat that they posed to the territory in terms of depletion of nectar resources and displacement. The territory occupied by the hummingbird was probably worth defending because the average amount of energy available there at the beginning of each day was approximately 3 times the amount used by the bird during 10.3 h of active defense. Comparisons of the amount of energy expended by the defender in chasing hummingbirds and large bees, and the amount of energy in nectar that these visitors could potentially steal from the territory indicated both types of intruders to be worth pursuing. The defender''s behavior when chasing hummingbirds differed from that when chasing bees. Hummingbird chases were more frequent, longer, and consequently, required significantly greater energy expenditures than bee chases. Observations on Amazilia and Chalybura hummingbirds supported the conclusion that insect chases by hummingbirds may occur with greater regularity and frequency than previously suspected and may represent an important component of defense against competitors at some types of feeding territories.

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