42 



NORTH AMERICAN FAUNA 74 



Age (years) 



Fig. 28. Length and diameter of the uterine horns in Pacific walruses that were not 

 pregnant and had not recently given birth. Curves were fitted visually. 



to be leanest in spring and summer and fattest in autumn to early winter, at 

 which time their blubber may be up to 15 cm thick. If so, the weights shown here 

 may be very conservative. The heaviest male in my series (1,656 kg) was taken in 

 January, and its blubber was the thickest (7.6 cm) of any male that was meas- 

 ured. One of the heaviest males taken in summer (1,557 kg) had only 5.5 cm of 

 blubber, and most of the other, lighter specimens taken at that time had between 

 2 and 4 cm. By analogy with other pinnipeds in which the "fatted male phen- 

 omenon" is known to occur (Laws 1 953^7 ; Scheffer and Wilke 1953; McLaren 

 1958; Schusterman and Centry 1971), adult male walruses can be expected to 

 attain their fattest condition and heaviest weight just before the mating season, 

 which is in mid-winter. 



