ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 201 



bloody ice floe in the St. Lawrence concentration area. Instances of unusually 

 late births were indicated by Tsalkin's (1937) finding of a full-term fetus in a cow 

 taken at Franz Josef Land in July, a small calf possibly no more than a month old 

 at Nunivak Island in November (T. E. Smith, personal communication), and the 

 St. Lawrence Islanders' report to me of an animal taken in Februar\^ that was 

 comparable in size to those normally taken in November. The Thule Eskimos 

 told Vibe (1950) that calves can be born in any season, probably meaning that 

 births occasionally occur outside the normal spring season. 



Newborn Calf and Its Environment 



The calf at birth weighs about 63 kg. The placenta, which is about 35 cm 

 wide and weighs about 6.8 kg, is expelled soon after the calf is born and is 

 consumed by scavengers (mainly gulls), rather than by the mother. The calf is 

 pale gray to gray-brown overall, with a dense, but very short and soft pelage. 

 The naked areas on its appendages are of about the same pale color as the rest of 

 the animal. A short remnant of the umbilical cord, up to 15 cm long, remains 

 attached to the calf. 



In the first days or weeks after birth, the calf not only grows larger and more 

 robust but acquires a different coloration. The pelage takes on a reddish-brown 

 to tawny hue, and the naked surfaces of the flippers become contrastingly dark, 

 almost black. The remnant of the umbilical cord debrides, usually by late June 

 or July (Nikulin 1941). 



Single births are the rule. Twin fetuses have been recorded only three times 

 (Nikulin 1954; Krylov 1962) in more than a thousand births recorded by Soviet 

 and American investigators. There are no confirmed records of females 

 successfully rearing twin calves. 



Physical Conditions 



In the season of birth, the Pacific walrus population is mainly concentrated in 

 the northern end of the Bering Sea, in the vicinity of St. Lawrence Island and 

 Bering Strait, and is in the course of its annual spring migration to the Arctic. 

 Surface water temperatures there at that time are about -1.5°C, and the 

 deteriorating winter pack ice covers from 30 to 80% of the area. Air 

 temperatures range from about -20 to -i- 10 °C but are mostly in the range of 0 ± 

 5°C. High winds are infrequent, and severe storms with heavy precipitation 

 occur less often than in any other season. In general, the weather in May and 

 June is regarded by local inhabitants as some of the most pleasant and favorable 

 of the year, although it is still relatively cool. Judging from the findings of Ray 

 and Fay (1968), the thermal environment in air is mainly within the 

 thermoneutral range for adult walruses but probably is somewhat cooler than 

 the optimum (about 10 ± 5°C) for the calves. The suboptimal air temperature 

 may be counterbalanced, however, by the frequent occurrence of fair weather at 

 this time; solar radiation is near its maximum intensity and duration for the year. 



Maternal-Neonatal Behavior 



A brief account of the birth of a Pacific walrus calf was provided me by R. A. 

 Ryder (personal communication), based on his observations from the icebreaker 



