Meeting Abstract

75.4  Tuesday, Jan. 6  Avian seasonal metabolic adjustments in a southern subtropical desert: winter down-regulation of basal metabolic rate SMIT, B.; MCKECHNIE, A.E.*; Univ. of Pretoria; Univ. of Pretoria aemckechnie@zoology.up.ac.za

One of the major patterns of phenotypic flexibility in avian basal metabolic rate (BMR) consists of seasonal adjustments. At present, the vast majority of data is from species inhabiting temperate and boreal latitudes in the northern Hemisphere, with BMR typically up-regulated during winter. We measured summer and winter BMR in the field for five species resident year-round in the Kalahari Desert of southern Africa, and found that BMR was generally lower in winter compared to summer. Mass-specific BMR was significantly lower in winter in three diurnal species, the Crimson-breasted Shrike (Laniarius atrococcineus; 29%), Fork-tailed Drongo (Dicrurus adsimilis; 35%) and White-browed Sparrow-weaver (Plocepasser mahali; 17%), and in a crepuscular species, the Pearl-spotted Owlet (Glaucidium gnoma, 30%). In contrast, the nocturnal African Scops-owl (Otus senegalensis) did not show any significant seasonal variation in mass-specific BMR, but significantly reduced body mass, and thus total BMR, in winter. The limited data currently available on avian seasonal metabolic adjustments suggest that whereas northern Hemisphere species generally up-regulate BMR in winter, the opposite is true in the southern Hemisphere. However, north-south comparisons are complicated by differences in body mass and absolute latitude, and more data are required before global patterns can reliably be identified. Nevertheless, our data reveal a dichotomy in the direction of seasonal adjustments in avian BMR, and raise the possibility that in some cases such adjustments are related to reductions in winter energy requirements, rather than enhanced cold tolerance.