Seasonal changes in standard metabolic rates in the white-browed scrubwren Sericornis frontalis (Acanthizidae) from arid, semi-arid and mesic environments

Abstract

1. 1. Standard metabolic rates (SMRs) of S. frontalis from resident populations at three sites in Western Australia, ranging from arid, through semi-arid to mesic environments, were measured in summer and winter. 2. 2. Significant seasonal differences in the mean SMR were observed only in scrubwrens from the arid environment where the mean (±SE) SMR was 31.3 ±1.7 ml O 2/10g·h in summer compared with 38.6 ±3.5 ml O 2/10g·h in winter. 3. 3. SMRs recorded in the arid zone were markedly lower than those measured in semi-arid and mesic areas in summer only. The lowered SMR appears to be an adaptation for (a) reducing energy expenditure as, although there is only a slight reduction in the available food supply in summer, foraging time is reduced by the need to shelter from the heat, (b) reducing production of body heat, and (c) conservation of body water. 4. 4. Possible causes of a high mean SMR recorded in scrubwrens in the semi-arid region in one summer sampling period are discussed.