At birth in late December the polar bear is small (700 g), uninsulated, and helpless. It probably has a modest capacity for metabolic heat production and depends on the female and a snow den in which it is born for thermal protection. The microclimate of an artificial polar bear den was investigated at Point Barrow, AK, and the temperature therein found to stay around 0 degrees C provided a heat source (200 W) equivalent to an adult polar bear was introduced. When the bears desert the den in early April the cub has grown to about 10 kg and has a well-developed fur insulation, but almost no subcutaneous fat. The cub has a high resting metabolic rate (4.6 W.kg-1), which is supported by the fat polar bear milk. Its lower critical temperature is about -30 degrees C, and an ambient temperature of -45 degrees C results in only a 33% increase in metabolism. The cub can tolerate a wind chill of 2.3 kW.m2 without apparent stress of drop in rectal temperature. If the cub is immersed in ice water rectal temperature drops 11 degrees C in 30 min. It is concluded that the cub can tolerate extremely low temperatures in air due to fur insulation and high metabolic heat production, but is unable to cope with the chill of ice water for any prolonged period of time.

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ABSTRACT. Alaskan polar bear mark and recovery studies from 1967-1976 and concurrent studies elsewhere indicate some interchange of polar bears between Alaska and the mainland coast of northwest Canada, but not between Alaska and the rest of Canada, Gmdand, and Svalbard. The extent of movement between Alaska and the U.S.S.R. remains unknown. The number of Alaskan bears recovered in the same general area as marked suggests that the same animals tend to occur in the same general area in late winter and early spring each year. Distance traveled between marking and recovery sites and the proportion of animals that move to a different area are about the same for bath sexes and for subadults and adults. Bears tend to disperse from commonly used areas in years when ringed seals are less available. The rate of movement in late winter and early spring is about the same for both sexes and for subadults and adults. After mid-April the predominant movement of bearsmorth of Alaska is to the east. Key words: polar bear, Alaska, Arctic, mark-recovery, movement &SUM&

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