Biophysical properties of the pelt of a diurnal marsupial, the numbat (Myrmecobius fasciatus), and its role in thermoregulation.

Numbats are unusual marsupials in being exclusively diurnal and termitivorous. They have a sparse (1921 hairs cm(-2)) and shallow (1.19 mm) pelt compared with other marsupials. Coat reflectivity is low (19%) for numbats compared with nocturnal marsupials, but absorptivity is similar to that of diurnal North American ground squirrels (72%), indicating that the coat of the numbat may be adapted for acquisition of solar heat. Numbat coat thermal resistance decreases significantly with wind speed from 45.9 s m(-1) (at 0.5 m s(-1)) to 29.8 s m(-1) (at 3 m s(-1)). Erecting the fur significantly increases pelt depth (6.5 mm) and coat resistance (79.2-64.2 s m(-1)) at wind speeds between 0.5 m s(-1) and 3 m s(-1). Numbat coat resistance is much lower than that of other marsupials, and wind speed has a greater influence on coat resistance for numbats than for other mammals, reflecting the low pelt density and thickness. Solar heat gain by numbats through the pelt to the level of the skin (60-63%) is similar to the highest value measured for any mammal. However the numbat's high solar heat gain is not associated with the same degree of reduction in coat resistance as seen for other mammals, suggesting that its pelt has structural and spectral characteristics that enhance both solar heat acquisition and endogenous heat conservation. Maximum solar heat gain is estimated to be 0.5-3.6 times resting metabolic heat production for the numbat at ambient temperatures of 15-32.5 degrees C, so radiative heat gain is probably an important aspect of thermoregulation for wild numbats.