138 



NORTH AMERICAN FAUNA 74 



Tedford 1977). It is my contention that it was the change in feeding habits from 

 piscivory to moUuscivory which enabled the positive pressures of social 

 advantage to prevail and allowed the upper canines to evolve as tusks. 



Food and Feeding Behavior 



To the Eskimos and other coastal people of the Arctic, the fact that walruses 

 feed mainly on bivalve mollusks has been common knowledge, probably for 

 thousands of years. Documentation of that fact in the scientific literature was 

 meager until the present century, when Chapskii (1936), Tsalkin (1937), Vibe 

 (1950), Mansfield (1958a), and Loughrey (1959) reported their findings from the 

 North Atiantic region, and Nikulin (1941), Freiman (1941), Brooks (1954), 

 Krylov (1971), and Fay et al. (1977) presented comparable information from the 

 Bering and Chukchi seas. The information in most of those reports is only 

 qualitative, consisting of identifications of the kinds of organisms found in 

 stomach contents of walruses and estimates of relative importance of each class of 

 prey, based on the number of genera represented. Quantitative details of actual 

 numbers and weights of prey were presented principally by Vibe (1950) and Fay 

 et al. (1977), who compared their findings with faunal information from benthic 

 sampling, in efforts to evaluate the impact of the walrus' feeding on the food 

 resources available. 



Some additional information on kinds and quantities of prey consumed was 

 obtained in the present study. My primary objective, however, was to answer 

 other questions which would contribute to understanding of the feeding behavior 

 and energetics of walruses: 



• How long is the calf dependent on its mother for milk? 



• What quantities and qualities of milk are required? 



• When does the young walrus begin to feed on benthic invertebrates? 



• Where do those invertebrates reside and under what conditions? 



• How does the walrus locate, identify, and ingest them? 



• What quantities and qualities of prey does it require for sustenance? 



• Do those requirements differ seasonally, geographically, or in relation to 

 major biological events, such as mating and molting? 



The following account mainly addresses those questions. 



Diet of Calves and Other Young Animals 



Length of the Suckling Period 



The young walrus ordinarily stays with its mother for about 2 years (Chapskii 

 1936). After that time, young males may stay for 2 or 3 years longer with the 

 adult females before joining all-male herds; the young females tend to stay with 

 the adult females continuously. From examination of stomach contents, Chapskii 

 (1936), Freiman (1941), Nikulin (1941), Brooks (1954), Mansfield (1958a), and 

 Loughrey (1959) concluded that young walruses probably are dependent entirely 

 on the mother's milk for at least the first year after birth, and that they gradually 

 are weaned during the second year. 



