Abstract:
The adjustment of resting metabolic rates represents an important component of avian
seasonal acclimatization, with recent studies revealing substantial differences between
summer and winter in birds from a wide range of latitudes. We compared seasonal
variation in basal metabolic rate (BMR) and summit metabolism (Msum) between
temperate and tropical/subtropical latitudes, and examined correlations with latitude
and temperature. The direction and magnitude of seasonal adjustments in BMR are
broadly related to temperature and latitude, but are significantly more variable among
tropical and subtropical species compared to those inhabiting temperate zones. Winter
adjustments in BMR among subtropical species, when expressed relative to summer values, range from decreases of approximately 35 % to increases of more than 60 %,
whereas the majority of temperate-zone species show increases in BMR during
winter. Relatively few seasonal Msum data exist for tropical/subtropical species, but
those that are available involve responses ranging from winter decreases to increases
of similar magnitude to those characteristic of many temperate-zone species. Recent
studies also highlight the substantial variation in seasonal adjustments that may occur
within species, and reiterate the need for further investigations of the relative roles of
environmental variables such as temperature and food availability as determinants of
seasonal metabolic variation.
