Studies on seasonal variation in metabolic rate related to changes in body composition with particular reference to shorebirds (Charadrii)
The basal metabolic rate of three species of shorebird was measured throughout the non-breeding season. These measurements were related to change in body mass and body composition. No seasonal pattern in BMR was apparent after variation related to changes in body mass and body composition had been accounted for. Seasonal variation in body mass of captive Grey Plover and Redshank was found to resemble that of the same species in the wild. This was not so for Sanderling. Body composition changes were either inferred from destructive analysis, or measured using a technique known as total body electrical conductance (TOBEC). The intraspecific relationship between TLM (Total lean mass) and TOBEC index was found to be best described by a linear equation. Separate intraspecific allometric equations were derived relating BMR to body mass for two shorebird and one wildfowl species. The mass exponents in these equations were found to be 1.03, 0.62 and 0.61 for Redshank, Grey Plover and Wigeon respectively. The results were related to the current interpretations of the BMR/body mass exponent. The within-individual BMR/body mass relationship was investigated for Redshank and Grey Plover. The mean mass exponent was found to be 1.23 and 0.92 respectively. No significant relationship was found for any individual Sanderling. Variation in BMR within an individual was related to variation in body composition. In most cases variation in body fat was found to be the most important predictor of within-individual variation in metabolic rate. In Vitro determinations of the oxygen uptake of avian fat, liver and muscle tissues indicated that the energy consumption of fat was less than one tenth that of liver and muscle. This indicates that within-individual increases in BMR with increased levels of fat are probably associated with increased metabolic output of the lean tissues.