THE USE OF IR THERMOGRAPHY TO MEASURE THE RADIATIVE TEMPERATURE AND HEAT-LOSS OF A BARN OWL (TYTO ALBA)

Infrared (IR) thermography was used to identify the major sites of hea t loss from a female barn owl at an air temperature of 17.6 degrees C. When perched, the mean radiative temperature of the owl was 21.1 degr ees C (SD = 3.5). The facial disc averaged 23.9 degrees 6 (SD = 9.1) a nd the temperature of the eyes was greater than 33 degrees C. Images s howed an area on the lower abdomen that was warmer than 27 degrees C. During flight, the temperature of plumage overlying wing muscles was m ore than 30 degrees C. The metabolic heat production of the barn owl w as estimated to be 42 W m-(2) (1.68 W) at 17.6 degrees C which agreed with previous measurements of metabolism. Heat loss from the head was almost double that from the body as a whole, indicating the importance of reducing exposure of the head during roosting. The metabolic rate during flight was calculated to be 13 x BMR (Pennycuick, 1989). This s uggested that barn owls lose considerable amounts of heat during prolo nged periods of flight. It is hypothesised that by being active in coo l nocturnal conditions, barn owls may exploit waste metabolic heat for thermoregulation. (C) 1998 Elsevier Science Ltd. All rights reserved.