60 



NORTH AMERICAN FAUNA 68 



dicate that rest periods are of longer duration because food needs 

 may be satisfied in a relatively short time. 



Mothers accompanied by young, especially large young at Am- 

 chitka, often continued to dive for food long after all other otters 

 in the general vicinity had retired for the night. On several occa- 

 sions I watched mothers feeding until they were obscured by dark- 

 ness. This is another indication that food species in the Amchitka 

 habitat have been overutilized by that local population. To obtain 

 sufficient food for herself and her young, a mother must search for 

 it after other otters have retired. 



The general daily cycle of behavior described above continues 

 throughout the year. When prolonged storms create violent wave 

 action, the daily cycle is disrupted and animals unable to obtain 

 sufficient food die (see Mortality Factors). 



Locomotion 



SWIMMING 



Methods of swimming 



Taylor (1914, p. 491) pointed out that the outer or fifth digit 

 of the sea otter's hind foot is the longest (fig. 8). In this respect 

 the sea otter differs from its nearest relative the river otter, from 

 seals, and from most if not all land carnivores. He considered that 

 "extra support" (presumably in walking) is furnished by this 

 unusual feature. Howell (1930, p. 284-287), however, after study- 

 ing the musculature of the pelvic limbs, surmised that the sea 

 otter swims by means of vertical undulations of the posterior part 

 of the body; that it uses the hind flippers held in the horizontal 

 plane, palms up, in combination with the tail to * 'present in a satis- 

 factory degree the lunate rear border theoretically desirable." 

 Thus, "the long fifth toes would form the outer borders of the 

 swimming organ." He was unable to confirm this theory by obser- 

 vation. He felt some doubt as to its validity because "It is true that 

 no other mammal is known ever to have employed this method of 

 swimming." 



On many occasions, from boats and cliffs, and in captivity, I 

 have watched sea otters swimming in clear water beneath the sur- 

 face. Howell's deductions were entirely correct. 



While the sea otter is swimming beneath the surface or diving, 

 vertical undulatory movements of the body, as described above, 

 furnish propulsion. While near the bottom, maneuvering and 



