Parrot Eggs, Embryos, and Nestlings: Patterns and Energetics of Growth and Development

Abstract

The Psittaciformes constitute a distinct and homogeneous order, members of which lay multiple egg clutches of relatively small eggs that have prolonged incubation periods. The chicks are altricial but nevertheless grow comparatively slowly. The contents of parrot eggs contain more solids (19.4%) than is typical for altricial or semialtricial species. The rate of embryonic oxygen consumption increases throughout incubation. The relative rate of increase in V̇o2 (percent per day) and the relative growth rate of the embryo decrease throughout incubation. The relative growth rate continues to decrease after hatching. In the six parrot species I studied, total embryonic energy metabolism is greater than predicted for altricial species owing to the prolonged incubation periods. Pre-pipping and hatching levels of oxygen consumption are lower than in the same size eggs of precocial species. In Agapornis roseicollis, mass-specific metabolism decreases through the first 15 days of incubation, then is relatively constant until immediately prior to hatching, increases sharply for about 4 days after hatching, becomes relatively constant for about 6 days, and then begins decreasing. This pattern reflects (1) changing maintenance costs due to increasing size and changes in maturational state and (2) changing growth costs which reflect the decreasing relative growth rate throughout the incubation and nestling periods.