410 AISTNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



a basking shark swimming at even the slowest speed at which it can 

 filter its food out of the water — if a shark were to continue feeding 

 during the winter it would lose on the deal, for the energy produced 

 by the plankton it could obtain would be less than that expended in 

 the effort of collecting it ! The shark therefore throws its gill rakers 

 away, descends to the bottom in some quiet spot, becomes more or less 

 torpid, and probably uses the stores of oil accumulated in its enormous 

 liver as the source of energy to maintain a minimum level of vital 

 processes until next summer when its feeding grounds are restocked. 

 It is, however, by no means certain that during the winter the shark 

 draws upon the oil stored in the liver; there is justification for skepti- 

 cism about this physiological question after the discovery that hiber- 

 nating amphibians and reptiles do not utilize what appear at first sight 

 to be their obvious reserves. In these animals a deposit of fat ac- 

 cumulates when they are not hibernating; it is laid down in special 

 organs known as the "fat bodies," wliich are situated in the abdomen 

 near the sex glands in the amphibians and near the under wall of the 

 abdomen in the reptiles. But the energy needed to maintain the re- 

 duced metabolic rate during hibernation is derived not, as might be 

 expected, from the stores in the fat bodies which appear to be reserved 

 for the activities of breeding, but from the glycogen stored in the 

 liver and muscles. 



A BIRD THAT HIBERNATES 



Most of the warm-blooded animals are able to meet adverse condi- 

 tions without hibernating. They are well covered with fur or 

 feathers to keep out the cold, and are able to find sufficient food to 

 maintain their metabolism at its full level even in the depths of win- 

 ter. Until recently it was believed that no bird hibernated, in spite 

 of the ancient legends about swallows lying dormant conglobated in 

 the mud at the bottom of ponds ; the insectivorous species whose food 

 disappears in winter nearly all migrate to regions where it may still 

 be found. But since the war an American naturalist has discovered 

 one of the most startling facts to be reported in ornithology dur- 

 ing the last himdred years — ^he has found a bird that undoubtedly 

 hibernates. Far away in the Chucka walla Mountains of the Colorado 

 Desert of California at the end of December 1946, he came across 

 a specimen of a species of nightjar, Nuttall's poorwill, hibernating 

 in a state of torpidity in a rock crevice of a deep canyon among the 

 hills. The poorwill is an insectivorous summer migrant to parts of 

 the southern United States whence it departs at the onset of winter 

 to regions unknown. The new observations show that it does not go 

 to the happy feeding grounds of the Tropics where insect food abounds 

 at all seasons, but it gives up the struggle for existence and takes the 



