BREEDING AND LIFE CYCLE 275 



about fifteen months. This rough estimate is helpful as a working figure in examining the growth of 

 the calf to weaning. The proportion of resting whales indicated in Table 24 is discussed at the top of 

 page 276. 



In 1954 Senhor Reis examined two whales, one male (F 306) and one female (F 307) and each 6-58 m. 

 long, whose stomachs contained milk. Details of these are included in Table 25 which records the 

 stomach contents of small whales (less than 8-o m. in length) examined at Horta. The twelve whales 

 larger than 6-7 m. had been feeding on their own account. Thus the stomachs of ten contained 

 squids: whale F 128, measuring 6-8 m., must also have been feeding independently because its stomach 

 contained nematode worms; and Dr S. K. Kon, of the National Institute for Research in Dairying, 

 informs me that the 'chestnut-coloured water' in the stomach of whale F118 is far more likely to 

 have been discoloured by squid chyme or blood than by digested milk. The data in Table 25, 

 so far as they go, bracket the length at weaning between 6-6 and 6-8 m., and it may for the present 

 be said that the sperm whale calf in the North Atlantic is weaned when about 6-7 m. or 22 ft. in length. 



Table 25. Stomach contents of whales less than 8-o metres long, examined 



at Horta from 1949 to 1954 

 Length 

 Serial no. Date in m. Sex Stomach contents 



Blood and water 



Milk and water in the first stomach, and cloudy water in the second 



Milk and water in the first stomach, and cloudy water in the second 



Water and worms 



Water, worms and a little digested squid 



First and second stomachs crammed with squid 



Much food in the first stomach, less in the second 



Sparse amount of squid 



Moderate amount of squid and many squid beaks 



Chestnut-coloured water in the first stomach 



A little water 



Moderate amount of squid and a few squid beaks 



Sparse amount of squid and masses of squid beaks 



Water, worms and a little squid 



Much food in the first stomach, less in the second 



The whaling statistics collected at Horta between 1944 and 1954 record four other whales smaller 

 than 6-7 m. There is no information on the stomach contents of these, but they are grouped with the 

 three recorded in Table 25 to make a total of seven whales presumed to be calves. Five were caught in 

 July and two in September. Fig. 10 reproduces the foetal growth curve with the lengths of the calves 

 plotted at their appropriate dates a year beyond the point of birth. One might have plotted them two 

 years beyond birth, but the proportion of lactating whales in the catch has given indications of a nurs- 

 ing period lasting about fifteen months, which is not much more than a year. In Fig. 10 the mean 

 curve of foetal growth is extended with a slight reduction in slope to pass through the mean length of 

 calves in July at the mean time in the month. The extrapolation of this curve fairly passes through 

 the point for the two proven calves in September: and the curve attains to 6-7 m., the point of wean- 

 ing, at thirteen months after the mean point of birth. So far as the seven records go, Fig. 10 suggests 

 there is no difference in the growth of the sexes during the nursing period, males and females both 

 being weaned at the same length. From Fig. 10 the normal period of lactation in the sperm whale 

 is taken to last about thirteen months. 



Resting or anoestrum completes the sexual cycle. In normal conditions the resting whale must 

 inevitably come into oestrus in the first sexual season following the end of lactation. This season is three 



