Seasonal changes in the relative importance of different avenues of heat loss in resting and running reindeer.

Exhaled air temperature (Te), respiratory frequency (f), and rectal temperature (Tb) were measured in two reindeer before, during and after running for 45 min at a constant speed of 9.2 km X hr-1 on a level treadmill at different ambient temperatures (Ta), in summer with fur insulation at a minimum and in winter with fur insulation at its prime. Before and immediately after the 45-min running period, skin temperature (Tsk) and radiative surface temperature (Tr) were also measured. Te, Tsk and Tr decreased at rest with decreasing Ta both summer and winter Tb was elevated during running except at low Ta in summer. During running Tsk, Te and f were higher in winter than in summer, while Tr was higher in summer than in winter. The changes in Tr and Tsk in response to running were more pronounced on the legs than on the trunk. It is suggested that in the running reindeer the body surface is an effective avenue of heat loss during summer, while heat dissipation by way of the respiratory tract attains increased importance in winter, when fur insulation is at its best.