Time and Energy Budgets of Territorial Hummingbirds

Abstract

From laboratory data of flying and resting metabolism and field data on time budgets of territorial male Eulampis jugularis hummingbirds we were able to estimate caloric energy budgets associated with territorial behavior. The relative time and energy expenditures for territorial defense, foraging, and sitting varied in territories with different species of flowers. For example, territories centered around banana flowers had lower foraging costs than those centered around Myrtaceae or Inga—Hibiscus. The costs for flycatching, hovering,and perch changes accounted for relatively little of the time and energy budgets at any of the territorial defense and foraging were expended in sitting on perches within the territory. Territorial defense was of relatively low cost in time and energy because of the inactive defense utilized by Eulampis. Selection will optimize time and/or energy budgets, but the type of budget optimized will depend in large part on the exploitation technique of the species. For birds that do not fly to forage, but exploit food items that require a long search time per calorie, time that can be released for other activities may be more important than major shifts in energy budgeting. For hummingbirds, however, optimizing energy may be more important to insure a positive energy budget.