136 



NORTH AMERICAN FAUNA 74 



is minimized and often amounts to no more than a show of strength (Carthy and 

 EbUng 1964:3; Geist 1966; Miller 1975a). The evolutionary impetus leading to 

 enlargement of such structures is now recognized as self-reinforcing; the success 

 of the bearer in establishing his dominance during mating is reflected in his 

 greater contribution to the gene pool (Bartholomew 1970). The individual that 

 lacks those social appendages may survive and even prosper, but he probably 

 will not be able to mate. 



The walrus' use of its tusks in threat displays (Frontispiece) was formally 

 reported first by Loughrey (1959:48), who observed that an animal with very 

 large tusks can intimidate others "to move out of its way simply by threatening 

 them," whereas one with smaller tusks is met with active opposition from his 

 peers. Both large tusks and large body size exert positive influence on 

 achievement of a socially dominant position in male walruses (Miller 1975a), and 

 I feel certain that the same is true in females, on the basis of my own general 

 observations. 



The real test of social importance of the walrus' tusks probabh' will be derived 

 from analysis of the behavior of adult males in the mating season, for it is in the 

 competition for mates that such organs, whether epigamic or rank-symbols (or 

 both), play their primary role and have the greatest immediate and long-term 

 impact on the gene pool (Bartholomew 1970; Geist 1971; Miller 1975g). 



For the females, the information now^ available does not show any clear 

 indications of specific seasons or activities in which social or other functions of 

 the tusks are paramount. By analogy with other mammals in which appendages 

 of this kind are present in both sexes, I presume that the maximum social value of 

 the female's tusks is in competition for some resource that is important for 

 survival of the young or for maintaining the ability to reproduce (cf. Henshaw 

 1969). That they do function as rank symbols in the minor day-to-day contests 

 within the herd is apparent, but it is not yet clear how important the outcome of 

 those conflicts (mainly for space on the haulout) may be to the individual female 

 or her calf. 



Other Functions 



Ancillary functions of the tusks include their use as weapons, both offensively 

 and defensively. This has been reported many times, mainly in anecdotal 

 accounts of the animals' attacks on hunters and their boats (e.g., Lamont 

 1861:85,138; Hayes 1867:404-411). These attacks appeared to be mainly by 

 females in defense of their young, although the interpretations are open to ques- 

 tion. Many similar incidents have been reported to me and to others (e.g.. Vibe 

 1950:49) by the Eskimos. In most of those reports, however, the aggressors were 

 juveniles and subadults, rather than adults (see Brooks 1954:71). 



Use of the tusks as auxiliary appendages for locomotion, especially when 

 hauling out on ice or land, also has been recognized for a long time (Allen 

 1880:137) and was the basis for the generic name Odohenus (Greek: odus, 

 odonto = tooth; baeno = walk). Their use in this way is common and is, I 

 believe, one of the principal causes of fracture of tusks, especially when the 

 animals haul out on rocl<y islets. 



I have observ^ed that the tusks also are used occasionally in other ways, some 

 examples of which are as follows: 



