Maurine B. Neiman
Department of Biology, Carleton College, Northfield, MN, USA, 55057
Abstract. The high metabolic rate of hummingbirds demands that these birds respond quickly to changes in food (nectar) abundance. Nectar production in Hamelia patens, a common shrub in the laboratory clearing at La Selva Biological Station in Costa Rica, begins at 5:30 A.M. and ends by 9:00 A.M. The nectar of these shrubs is an important component of the diet of rufous-tailed hummingbirds (Amazilia tzacatl), a territorial species that is a common resident of the lab clearing. These birds often center their territories on H. patens. Some H. patens are infested by the hummingbird flower mite (Proctolaelaps kirmsei). These parasites have been found to consume a sizable fraction of the nectar of infested plants. I examined the impact of decreased nectar levels due to the daily cessation of nectar production and mite consumption on territorial and feeding behavior of A. tzacatl by observing the birds over their daily activity period from 5:30 AM-2: 00 PM. Statistical analysis of the data indicated that feeding and territorial behavior occur significantly more often in the time before nectar cessation. These findings suggest that there is a lower limit to economic defensibility of nectar resources for A. tzacatl.
Feeding and territorial behaviors were not affected by mite infestation levels. The lack of a correlation between mite infestation and these behaviors could be due to differences in condition between the plants examined rather than nectar levels per se.