Surface Temperatures and Radiant Heat Loss from White-Tailed Deer

Abstract

Measurements of surface temperatures and radiant heat loss from the trunks of two penned white-tailed deer (Odocoileus virginianus) fawns were made remotely with a portable radiometer during the winter. Surface temperatures were 6-8 degrees C higher than air temperatures. No difference was observed between the two deer in the surface temperature: air temperature relationships. The difference between air temperature and the surface temperature of the deer increased as air temperature decreased. Measurements of thermal radiation under clear skies at night showed a greater quantity of heat energy emanating from cedar cover than from upland hardwood cover or the clear sky in an open field. The radiant heat from the animal can be integrated with that from the different cover types if the radiation profile of the animal is known. The profile for white-tailed deer has not been determined, but may be estimated. Physiological evidence is cited which indicates the importance of radiant heat when the energy balance of an organism is being considered. The behavior of white-tailed deer with respect to observed weather conditions has been considered by several investigators. Observed responses of the animals have been assumed by some to be causally related to existing weather conditions, or perhaps to the microclimate surrounding the animal. An elucidation of these relationships is, indeed, a worthy goal for the animal ecologist. I suggest, however, that without a quantitative application of appropriate heat transfer parameters, it may be difficult to separate behavioral responses caused by weather conditions from those which may be related to social or psychological phenomena. The basic concept of energy, the means by which energy is transferred, and the energy environment of plants are discussed by Idso et al. (1966). Analyses of the energy exchange of sheep (Priestley 1957 and Blaxter et al. 1959), cattle (Kelly and Ittner 1948, Thompson et al. 1952, and Blaxter and Wainman 1964), swine (Bond et al. 1952) and chickens (Clayton and Boyd 1964) have been presented. The radiant 1 Study supported by the Graduate School, University of Minnesota. 2 Present address: Department of Conservation, Cornell University, Ithaca, New York. 338 energy exchange of the human with its environment has been studied by Hardy and DuBois (1938) and Suggs (1965). The energy relationships of wild species, including ruffed grouse (Brander 1965), whitetailed deer (Moen 1966), and Canada geese (LeFebvre and Raveling 1967) have been considered. Kelly et al. (1954) discuss the importance of thermal radiation in a consideration of animal-environment relationships. An important characteristic of the papers cited above is the explicit consideration of rates of heat transfer between the animal and its environment by different processes, as opposed to the simple comparison of animal behavior and weather data. This paper describes the radiant energy loss in relation to air temperature from the trunks of two well-fed white-tail fawns measured remotely in an outdoor pen during winter months. Measurements of radiation flux under clear skies at night in a nearby open field, upland hardwood stand, and cedar (Thuja occidentalis) habitats are also presented. The radiation data can be applied to the whole animal and integrated with other sources of heat loss (conduction, convection, and evaporation) if the radiaTEMPERATURES AND RADIANT HEAT LOSS FROM DEER * Moen 339 tion profile of the animal is known or assumed. Research was completed at the Cedar Creek Natural History Area (T34N, R23W), operated by the University of Minnesota, and about 35 miles north of the campus. The cooperation of Dr. W. H. Marshall, Director, Field Biology Program, is acknowledged. He also offered suggestions during preparation of the manuscript. The Minnesota Department of Conservation provided the test animals. Alvar Peterson, Resident Manager, and Bruce Kohn, Student Assistant, assisted in handling the deer.