Energetics of embryonic development in the cockatiel ( Nymphicus hollandicus ) and the king quail ( Coturnix chinensis )

In this study the energetics of embryonic development and metabolism of the altricial cockatiel ( Nymphicus hollandicus ) were compared with that of the precocial king quail ( Coturnix chinensis ), which produces hatchlings of similar body mass (~4 g). On average, cockatiel invested 28% less energy in their eggs (principally as smaller yolks), which contained more water than king quail eggs. Cockatiel embryo mass and the accumulation of tissue solids increased at slower rates than in king quail. A similar fraction of egg energy was converted to yolk-free hatchling (50%) in both species; however, king quail consumed more energy during development and hatched about 3 days earlier. As a result, total production efficiencies of energy transformation into hatchling tissues was 64% for cockatiel, higher than for king quail (56%) and another parrot ( Agapornis 45%) despite the prolonged incubation period of cockatiel. Metabolic intensity increased more rapidly in the king quail during hatching, and thus functional maturity of hatchlings was higher; this was similar to the situation in much larger precocial species. However, there were significant increases in metabolic intensities during pipping and in the hatchling cockatiel to suggest that greater physiological maturation, as a prelude to the development of endothermy, occurs earlier than in Agapornis and altricial passerine species.