Energy Substrates and Metabolic Acclimatization in small Birds
Many small birds wintering at middle or high latitudes encounter temperatures that require elevated thermogenic rates for months at a time. Although selection of favorable microclimates (Marsh and Dawson, 1988) and shallow nocturnal hypothermia (Reinertsen, 1983) may reduce metabolic demand, these energy saving mechanisms only partially offset the need for regulatory thermogenesis. In this context, survival depends critically on the ability to sustain high rates of thermogenesis, i. e., thermogenic endurance. Thermogenic endurance of small birds varies seasonally (Dawson and Marsh, 1988), and we regard this variation as one of the definitive characteristics of metabolic acclimatization to cold. Improved cold tolerance by winter birds is demonstrable both in acute studies (e. g., Dawson and Carey, 1976) and in longer-term exposures (e. g., Blem, 1973). This short review examines a series of studies that attempt to elucidate the role of metabolism of energy substrates in the process of metabolic acclimatization.
KeywordsKetone Body Cold Exposure Muscle Glycogen Pectoralis Muscle Small Bird
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