ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



43 



The Eskimos state that the fatness of female walruses varies more with their 

 reproductive status than with the seasons. They claim that the fattest individuals 

 are those that are pregnant with a full-term or near-term fetus in spring. If body 

 weight is proportional to fatness, then the data represented in Fig. 21 lend 

 support to that impression. The weights of mature females (> 10 years old) that 

 were pregnant with a near-term fetus in March-April (N = 10) were greater (x 

 = 995 kg, S.E. ±42.4 kg) than those of nonpregnant mature females taken at 

 the same time (N = 18, x = 752 kg, S.E. ±31.3 kg). 



Under circumstances as yet unknown, the baculum of the male occasionally 

 becomes fractured. Fifteen examples of fractures were reported by Murie (1936) 

 and four others by Brooks (1954). In my series, only one baculum was fractured, 

 from a specimen about 9 years old. In that animal, the break was about midway 

 of the length, and the broken ends had become slightly dislocated before healing, 

 similar to many of those illustrated by Murie. Murie's specimens were selected as 

 oddities from more than 1,000 walrus bacula collected from prehistoric Eskimo 

 middens on St. Lawrence Island (Geist and Rainey 1936). The others in that 

 series were not fractured (O. W. Geist, personal communication). Brooks' four 

 examples also were from a large series (N = 180), the rest of which were not 

 fractured. Thus, the incidence of fracture indicated by Geist's, Brooks', and my 

 samples, combined, was only about 1% (20/1,450). Although even this is a 

 remarkably high rate of occurrence for a condition likely to affect reproductive 

 performance, both Murie's examples and mine suggested that most of the 

 fractures took place at an early age, probably during the period when the bone 

 was increasing greatly in length but not much in density. That is, it seems that 

 most if not all of the fractures are fully healed before the animals attain 

 maturity. 



Whereas the baculum increases in size and weight with approach to maturity, 

 its homologue, the os clitoridis of the female, apparently diminishes in size. My 

 findings support the opinion expressed by Mohr (1963) that the frequency of 

 occurrence and the size of the os clitoridis in pinnipeds are inversely related to 

 age. I have found further supporting evidence of these relations in other northern 

 pinnipeds (unpublished data) . Most of the published accounts of occurrence and 

 size of the os clitoridis in other mammals also suggest a trend of retrogression 

 with increasing age or reproductive development (see Rinker 1944; Scheffer 

 1949; Layne 1952; Zeigler 1961; Arata 1965). 



Skin and Hair 



The skin of walruses is extraordinarily thick and tough and has been likened to 

 that of the African square-lipped white rhinoceros (Ceratotherium simum) in 

 both structure and topography (Luck and Wright 1964). Some details of its 

 dimensions and structure, in comparison with the skin of other pinnipeds, were 

 reported by Sokolov (1960) and Ling (1974). The characteristics of the adult 

 pelage were compared with those of other pinnipeds by Scheffer (1964). A few 

 additional points will be covered here, particularly regarding topographic and 

 age- and sex-related characters of the skin and their functional significance. 

 Some new information on the sequence of pelages and molts also will be 

 reported. 



