Responses to Seasonal Change in Polar Mammals

Living history: G. Edgar Folk, Jr.

“…Folk found that polar bears exist on an all-fat diet and will consume only the blubber and small amounts of skin from seals they kill (25). When their lipid levels were compared with levels of fasted brown bears, Folk and collegues (28) were surprised that lipid concentrations (lethal to rabbits and dogs) were lower than those reported for fasted animals. This result indicated a "unique" feature of fat metabolism in Arctic bears (28).…”

“…In an early study (38) with two species of bats, he suggested that the acclimatization process involved neural and hormonal mechanisms. He was the first to demonstrate that exposure to short photoperiods of light would enhance the process of cold acclimatization in rats and mice, to achieve a state of "cold acclimatization without cold" (28). His study in hedgehogs and woodchucks was important because it demonstrated that cold acclimatization was not a "necessary requirement for the dormancy of mammalian hibernation" (20).…”

“…On the other hand, the red squirrel (a cold-resistant polar mammal with higher resting plasma FFA concentrations) did exhibit marked elevations with cold exposure while facilitating cold acclimatization. When measurements of plasma FFA concentrations were obtained from Arctic mammals (n ϭ 14) during summer and winter months and compared with those secured from non-Arctic mammals, the polar animals had not only consistently higher summer values but also had winter plasma concentrations that were at least twofold higher than their nonpolar counterparts (28).…”

Mammalian activity – rest rhythms in Arctic continuous daylight

“…These are the Arctic porcupine (Erethizon dorsatum myops) and the Arctic ground squirrel (Spermophilus undulatus kennicottii). We also compare findings from studies in the laboratory with those from the field (Folk et al 1995;Folk 1996).…”