Bioclimatological Comparison of the Summer Day Microenvironments of Two Species of Arid‐Zone Kangaroo

Two large kangaroos, the red kangaroo (Megaleia rufa) and the euro (Macropus robustus) live in the arid regions of Australia. On hot summer days they are found in entirely different microenvironments: red kangaroos in the shade of small desert trees in relatively open country and euros around rocky outcrops in caves and under rock ledges. Measurement of the temperature and radiation characteristics of these microhabitats showed that the euro avoided much of the heat load of the desert, particularly the radiation heat load. While the solar radiation influx reaching the red kangaroo resting site was only about 20% of that incident on open ground it still resulted in the radiation temperature of this microenvironment exceeding the animal's body temperature by as much as 30°C when air temperature also exceeded the body temperature. Considerable evaporative water loss would be expected under these circumstances. Radiation heat loss from the red kangaroo microenvironment to the sky, possible in the late afternoon, may be used by the animal to reduce the amount of water required for temperature regulation.