26 



VERTEBRATE REPRODUCTIVE CYCLES 



song and on egg laying in birds, the credit for the first 

 logical approach to the subject belongs to Rowan. His 

 original paper^^^ ^^s published in 1925, and years later 

 in 1938 he wrote a review of his pioneer work.^^^ His 

 original aim was to obtain information on the mechanism 

 of bird migration, and the first step was to discover 

 whether the gonads of birds could be artificially stimu- 

 lated to growth in the autumn 'in the belief that if this 

 were possible, and the birds were liberated in such 

 condition, they might migrate north on release'. It will 

 be appreciated from this that he started with the 

 assumption that northward migration in the northern 

 spring is a form of sexual behaviour, which depends for 

 its seasonal recurrence on the development of the 

 gonads. This point is considered on p. 91. 



Rowan showed considerable prescience in discarding 

 from the start any consideration of the effect of tempera- 

 ture. His first experiments^^^ were made with the 

 common Canadian bunting, Junco hyemalis, which he 

 trapped as it was passing through Edmonton, Alberta, 

 in Western Canada, on its southern migration in 

 September 1924. Due to an accident caused by interfer- 

 ing children many of the birds were lost so that the 

 experiment was almost wrecked, but the remaining 

 specimens, all except one of which were males, were 

 maintained in two open-air aviaries. In both of these 

 the birds were fully exposed to the weather, but in one 

 of them two 50 watt electric light bulbs were fitted. 

 From I October the experimental birds were sub- 

 jected to an increasing day-length of 5 minutes per 

 day, which was achieved by switching on these lights at 

 sunset. By the middle of November the testes of these 

 birds were increasing in size, and by the end of Decem- 

 ber, when the last bird was killed, they were larger than 

 those of the first juncos to arrive in Edmonton in the 

 spring. All this time the control birds were kept in normal 

 autumn conditions and their testes remained at a min- 

 imum size. 



