Energetics and Growth Patterns of Three Tropical Bird Species

Abstract

Abstract Energy budgets and growth data are presented for nestlings of three species of tropical insectivores: White-bellied Swiftlets (Collocalia esculenta), Blue-throated Bee-eaters (Merops viridis), and Pacific Swallows (Hirundo tahitica). A comparison with temperate nestlings, matched for body size, shows that the peak energy demand in our tropical sample averaged around 60% of temperate counterparts. We attribute savings to slow growth rates, reduced thermoregulatory requirements, a low resting metabolism (in swallows only), asynchronous hatching (in bee-eaters), and low nestling activity levels. Patterns of energy storage as lipid in nestlings of the three species were similar to the pattern in temperate swallows (Hirundinidae) and swifts (Apodidae), with those species feeding at the greatest heights, and hence on the most unpredictable supplies, storing the most fat while in the nest.