Short-term thermoregulatory adjustments in a South American anseriform, the black-necked swan (Cygnus melanocoryphus)

Avian bioenergetic studies suggest that, compared with other vertebrates, birds are efficient thermoregulators. However, most avian physiological studies have been performed in species of small body masses (less than 1 kg). In contrast to what might be anticipated, thermoregulatory abilities of large, flying birds are scarcely studied, especially in temperate zones and aquatic systems. In order to determine short-term metabolic adjustment after thermal challenge, we studied the bioenergetics of a South American anseriform, the black-necked swan (Cygnus melanocoryphus). Our results suggest that this swan species exhibits lower resting metabolic rate compared with other anseriforms, and some hetherothermia. In addition, the black-necked swans in our study changed "wet" thermal conductance at different ambient temperatures. At our working Ta range (5, 10, 15, 20 and 25 degrees C) calculated values were considerably higher than expected (23%, 26%, 39% and 51% higher than expected, respectively). Our results differ considerably from the only two previous reports in swan species, suggesting that C. melanocoryphus, perhaps due to its temperate distribution, is more sensitive to changes in environmental temperature.