Thermal Conductance in Aquatic Birds in Relation to the Degree of Water Contact, Body Mass, and Body Fat: Energetic Implications of Living in a Strong Cooling Environment

Thermal conductance of carcasses of 14 aquatic bird species was determined by the warming constant technique. The effect on thermal conductance of body mass, age, sex, fat deposits, and the degree of contact with water were studied. Only body mass and the degree of submergence in water had an effect. A negative exponential relationship between body mass and thermal conductance was found. Water contact increased the thermal conductance by a factor of 2.2 during swimming and a factor of 4.8 during diving. Leaving the water in order to reduce thermoregulatory costs is put forward as a behavioral option that might make several aquatic birds more flexible in adjusting their feeding time to meet increasing energetic requirements. Not being able to leave the water has obvious implications for both breeding and winter distributions for different-sized aquatic birds.