510 LAND ANIMALS 



Arctic mammals and birds. — The conditions are radically dif- 

 ferent for warm-blooded animals. Their uniform body temperature 

 makes them independent of the temperature of the environment as 

 long as they can maintain it. The maintenance of their body tempera- 

 ture becomes especially difficult during the low temperature of the 

 polar winter. All the warm-blooded animals of the polar areas have 

 developed some means of conserving body heat. Insulation by means 

 of thick fur or feathers, effective on account of the enclosed air, is 

 general. Small forms, such as arctic fox, hare, and lemming, have a 

 silky fur with a woolly undercoat, and this affords them sufficient pro- 

 tection since they can avoid severe storms by retreating into crevices 

 or into the snow itself. Reindeer and musk oxen, however, require 

 further protection. The long hairs of the reindeer are thicker at the 

 end than at the root, and form an almost airtight coat. 13 The musk 

 ox has a fleece of 60-80 cm. length which hangs down over the woolly 

 undercoat. Many polar resident birds have the tarsi and the feet 

 feathered, as in the snowy owl (Nyctea nyctea) , and in the ptarmigan 

 (Lagopus) even the soles are feathered. Arctic hare, fox, and bear, 

 similarly have the soles furred. In spring there is molting of plumage 

 or shedding of hair so that a lighter covering is worn in summer; in 

 the barren-ground caribou, the summer coat is not fully developed 

 until September. 



An excellent protection against loss of heat is provided by a thick 

 layer of fat beneath the skin, which at the same time affords a store 

 of food for the winter fasts. This layer becomes 3 to 5 cm. thick in the 

 reindeer. 14 Even the arctic hare is very fat at the beginning of winter, 

 though its European relative {Lepus eurcfpaeus) rarely shows a trace 

 of fat. Such a storing of food depends primarily on favorable food 

 conditions in summer. A food store is the more required since the 

 consumption of food is increased by low temperature. According to 

 Richet's experiments the food consumption in winter compares with 

 that of summer as 3 to 2. 15 The external food supply is scanty. Where 

 the covering of snow is blown thin by the winds, herbivores dig for 

 lichens and moss, and some grasses and herbs. The ptarmigan eat 

 berries and leaves of species of Vaccinium. These supplies are supple- 

 mented by the fat layer which disappears completely before spring. 

 The occasional scarcity of food, combined with increased needs, 

 makes many northern animals, especially predators, into omnivores. 

 The snowy owl in time of need eats carrion and fish. Gulls feed on the 

 remnants of the meals of the arctic fox. The fulmar, Fulmarus glacialis, 

 follows ships for offal, and plankton and even plant materials have 

 been found in stomachs of this species. The purple sandpiper, Erolia 



