The Shivering Response in Common Eider Ducks
In homeotherms total body thermosensitivity (TBTS) can be determined at any given ambient temperature (Ta) by relating an induced fall in body core temperature (Tc) to the resulting increase in metabolic heat production (M). Experimental determinations of TBTS usually involve using heat exchangers (water perfused thermodes) to lower body core temperature (e. g. Intravascular heat exchangers; Jessen et al., 1977, intestinal thermodes; Ionomoto & Simon, 1981). Some of the inherent problems related to the use of heat exchangers have been previously discussed (see Fig.2, Mercer & Simon, 1984). For example, in order to determine a correct TBTS it is important that temperature sensors are not directly influenced by the cooling thermode. i. e. there should be no hysteresis between the curves describing the relationship between Tc and M during body core cooling and in the recovery period following the end of body core cooling. In the avian class of homeotherms Tc can also be lowered by making use of the paradoxical effect resulting from local cooling (clamping) of the brain stem (Simon et al., 1986). In this case TBTS can be calculated by relating Tc to M during the recovery period following release of the thermal clamp.
KeywordsHeat Exchanger Body Core Body Core Temperature Cooling Period Point Determination
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