Predicting small endotherm body temperatures from scalp temperatures

We used 2-d to 3-d-old mallard ducklings (Anas platyrhynchos) to test whether remote thermographic measurement of scalp temperature could be used to estimate core (cloacal) temperature from a distance. The scalp was exposed by trimming down from an area of ⩽1 cm2, and surface temperature measured to ±0.12 °C with a radiometric thermal imager. For wind speeds of up to 2.5 m/s, we found cloacal temperature could be estimated to within 1 °C by using a regression model incorporating only scalp temperature and ambient temperature. The inexpensive method of dyeing the scalp black and painting it with temperature-sensitive cholesteric liquid crystal paint is more difficult and provides less accuracy, but appears to be a useful means for monitoring change in body temperature. These methods allow body temperatures of small or young endotherms to be monitored from distances of up to several meters without surgery or encumbering wires, minimizing stress that may alter behavior patterns and physiological parameters.