Blix A S, Miller L K, Keyes M C, Grav H J, Elsner R
Am J Physiol. 1979 May;236(5):R322-7. doi: 10.1152/ajpregu.1979.236.5.R322.
Several hundred thousand northern fur seals (C. ursinus) are born each summer during July at St. Paul Island in the Bering Sea. The weather in the area is usually cold, wet, and windy during the breeding season. At birth the pups are small (5--6 kg) and insulated only by a partly wettable pelt and a 2- to 4-mm layer of blubber. In air, the pups' lower critical temperature appears to be below the 6 degrees C 50-yr record low July temperature for the islands. During rainy weather much of the insulative value of the pelt is lost, and the pups, which already have a high resting metabolic rate of 3.5 W.kg-1, must increase heat production by shivering and/or nonshivering thermogenesis to maintain deep body temperature. The high level of metabolism (up to 18 W.kg-1) is supported by a very rich milk. The pups will, nevertheless, become hypothermic if their insulation is not improved through peripheral vasoconstriction and shedding of water from the pelt by periodic shudder. Even with these protections the newborn and very young pups are brought close to their limit of tolerance during rainy and windy days. Unfit pups are likely to succumb under such circumstances.
每年7月的夏季，几十万只北海狗（Callorhinus ursinus）在白令海的圣保罗岛出生。在繁殖季节，该地区的天气通常寒冷、潮湿且多风。幼崽出生时体型较小（5 - 6千克），仅靠一层部分可被水浸湿的皮毛和2至4毫米厚的鲸脂来保暖。在空气中，幼崽的下限临界温度似乎低于该岛有记录以来7月50年低温的6摄氏度。在雨天，皮毛的大部分保暖价值会丧失，而幼崽的静息代谢率已经很高，达到3.5瓦/千克，它们必须通过颤抖和/或非颤抖性产热来增加热量产生，以维持深部体温。高水平的代谢（高达18瓦/千克）由非常丰富的乳汁提供支持。然而，如果幼崽不能通过外周血管收缩和周期性颤抖使皮毛中的水分脱落来改善保温，它们就会体温过低。即使有这些保护措施，新生和非常年幼的幼崽在风雨天也会接近其耐受极限。体质不佳的幼崽在这种情况下很可能会死亡。
