AJP - Regulatory, Integrative and Comparative Physiology, Vol 236, Issue 5 322-R327, Copyright © 1979 by American Physiological Society
Newborn northern fur seals (Callorhinus ursinus)--do they suffer from cold?
A. S. Blix, L. K. Miller, M. C. Keyes, H. J. Grav and R. Elsner
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.
