THE SEI WHALE 253 



and April. Parturition and lactation appear to take place in temperate latitudes and 

 lactation generally appears to be completed by the time the whales arrive on the 

 southern feeding grounds after the spring migration. There is thus a definite, if rather 

 prolonged, breeding season. Risting (1928) discusses the results obtained from an 

 examination of ninety-five Sei whale foetuses from the Norw'egian seas and finds that 

 the majority of pairings took place from November to March, that is during the 

 northern winter, an exact parallel to the conclusion here arrived at about the southern 

 Sei whale. 



Only three whales from South Georgia are recorded as lactating, all in the month of 

 March, and they are all noted as only lactating slightly. These are presumably whales 

 that paired late in the previous season and had given birth so late that lactation was not 

 quite complete by the time that they arrived on the southern grounds. Similarly, the 



Jan Feb Mar Apr Mai) Jun Jul Aug Sep Oct Nov Dec 



Fig. 78. Sei whale. Pairing and birth frequency. 



one carrying a 3-35 m. foetus, taken at South Africa in October, was probably a late 

 breeder. These late breeders may be whales that have lost their calves and come into 

 oestrus at abnormal times. With these whales may be compared three recorded as 

 ovulating, two in February and one in March, which, if paired on the southern grounds, 

 would produce such examples of late pregnancy in the following season. It is also of 

 interest in this connexion to note that whale No. 2370, taken on 19 February 1929, was 

 reported by the gunner to have paired immediately before capture. 



Further information on the breeding season is given by Fig. 78. If on Fig. 76 the 

 curve in Fig. 77 is superimposed, and lines are drawn parallel to it but taking their 

 origin at monthly intervals on each side of it, the points are divided up into groups 

 representing pregnancies starting in each month. When these pregnancies are counted 

 and the numbers plotted by months the curve in Fig. 78 is produced. This shows that 



