Effects of Circadian Rhythm and Breeding Stage on Resting Metabolic Rates in Fasting Leach's Storm-petrels

Abstract

The oxygen consumption of fasting Leach's Storm-petrels Oceanodroma leucorhoa was measured in captivity with a metabolic chamber at nest burrow temperature (16°C). The average mass-specific oxygen consumption of incubating birds (2.84ml/g/h at night and 2.10ml/g/h in day) was lower than that of chick rearing birds (3.31ml/g/h at night and 2.98ml/g/h in day). Three days of fasting did not affect mass-specific oxygen consumption. At each breeding stage mass-specific oxygen consumption was higher at night than during the day (1.1-1.3 times). In the wild, body mass of incubating birds (45.7±2.9 SDg) was greater than those rearing chicks (43.1±2.7 SDg). It appeared that incubating birds may tolerate fasting for the 3 day incubation spell by reducing resting metabolic rate and spending metabolic energy on body fat reserves.