The energetics of New Zealand's ducks.

Measurements on rates of metabolism and temperature regulation are presented from nine populations of seven species of ducks resident in New Zealand. An analysis of these data and those from 18 additional species obtained from the literature indicates that basal rate of metabolism in anatids correlates with body mass and restriction to the Australian-New Zealand region: these 'southern' species have basal rates that average 70% of those from the Northern Hemisphere. The low basal rates of southern anatids may reflect reduced pectoral muscle masses in association with the absence of migratory habits and/or life on land masses without eutherian predators. New Zealand flightless teal (Anas aucklandica nesiotis, Anas aucklandica aucklandica) do not have mass-independent basal rates that differ from those found in flighted ducks living in the same region, although flightless teal have lower total basal rates than most ducks as a result of small masses. Minimal thermal conductance in this sample is determined by body mass alone. Regulated body temperature is negatively correlated with body mass.