Feeding territoriality in migrant rufous hummingbirds: defense of yellow-bellied sapsucker (Sphyrapicus varius) feeding sites

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Abstract
Postbreeding migrant rufous hummingbirds (Selasphorus rufus) establish feeding territories in several habitats at Grizzly Lake, CA. Here we describe hummingbird territorial defense of tree sap made available by sapsucker feeding activity. Territorial hummingbirds fed almost exclusively on sap obtained on their territories, and they remained on the same territories for up to 6 days. The amount of energy produced on each territory was in excess of our estimates of hummingbird energy expenditures; sapsuckers, other birds, insects and small mammals remove almost all of the surplus. Comparisons of the time budgets of birds defending tree sap with those of territorial individuals in nearby habitats showed that these birds spent less time foraging and more time perching than birds in even high-quality subalpine meadows. Sap is thus a rich, easily defendable resource that may be of general value to temperate-zone hummingbirds. Utilization of sap may allow individuals to avoid critical, unpredictable energy shortages while migrating and may permit populations to exploit habitats that would otherwise be unavailable.