The early ontogeny of ventilation and hemeothermy in an altricial bird, Agapornis reseicollis (psittaciformes)

Abstract

The body temperature (Tb) of brooded Agapornis nestlings increased with age from 36.2 on the day of hatching to 38.9 °C on day 11.5, whereas the thermally neutral ambient temperature (Ta,n) decreased with age. The Tb of nestling after a 20 min exposure to Ta ≈ 5 °C < Ta,n increased from 31.9 on day 0.5 to 37 °C on day 11.5 At Ta,n, both resting V̇ O 2 and mass-independent resting V̇ O 2 increased with age. Ventilation frequency (f) at Ta,n increased with age from 14.9 br/min on day 0.5 to 65.6 on day 11.5. This trend is the opposite of the allometric prediction based upon data from adult birds. At hatching, tidal volume (V T) was larger than predicted allometrically, whereas minute volume (V̇ I) was smaller. After 20 min exposure to Ta 5 °C < Ta,n, f, V T and V ̇ I in nestlings 1 to 3 days old remained unchanged, but V̇ O 2 and oxygen extraction efficiency decreased. This mild cold-challenge caused a transient increase in V̇ O 2 of nestlings 5 to 8 days of age and 20 to 35% of adult mass. By the time the nestlings were 11.5 days old and had a mass 44% that of adults, their metabolic response, to a mild cold-challenge was equal to that of an adult of the same mass. However, they were not capable of effective homeothermy over a wide range of Ta's.