LIGHT COLLECTION AND SOLAR SENSING THROUGH THE POLAR BEAR PELT

The pelt of polar bears acts as a translucent insulation through the hairs of which diffuse light is transferred by a combination of scattered light and luminescence light collection. The optical and morphological differences with respect to the white hair of other mammals have been investigated by scanning light microscope and UV-laser-induced luminescence studies and model experiments performed which support the suggested mechanism. An evaluation of physiological information on the energy turnover and dissipation in the polar bear suggests that comparatively little additional energy can be gained by harvesting solar radiation. However, due to the peculiar energy transparent pelt of the polar bear and the significant cooling of peripheral tissues suffered during cold ambient conditions, solar irradiation may change subcutaneous temperature by as much as 10-degrees-C. It is suggested that the polar bear's skin, using the temperature pattern produced on its surface by scattered light, calibrated for wind chill against the body-temperature-controlled latissimus sheets, may be used as a kind of sensory system. This may help the polar bear to determine the approximate position of the sun and thus to navigate under diffuse arctic visibility but also to locate ice-free sea surfaces with significantly reduced light scattering properties as compared with ice-covered surfaces.