92 



VERTEBRATE REPRODUCTIVE CYCLES 



course, none at all was naturally available in the snow- 

 bound countryside at that time. By means of this food 

 he was able to retrap the birds, and in this way most of 

 the untreated controls were repeatedly taken showing 

 clearly that they felt no overpowering urge to leave the 

 district. However, of the birds with stimulated gonads 

 some 80 per cent, were never seen again, and Rowan 

 concluded that they must have attempted an unseason- 

 able migration. 



Attempts to follow the movements of such birds were 

 then made by repeating the experiments with a larger 

 and more conspicuous species, the American 

 crow.163, 164, 166 Xhe gonads of the experimental birds 

 were stimulated by light treatment, and then all the 

 birds, experimental and control, were released in mid- 

 November. This release was timed to coincide with a 

 public holiday, and sportsmen who then went out with 

 guns were asked to keep a special watch for the birds, 

 which, to add to their distinctiveness, had their tails 

 sprayed with gold paint. Many birds were recovered 

 and many more were observed but not shot. All those 

 belonging to the untreated control group were found to 

 have moved south as though they had attempted a late 

 but otherwise normal autunrn movement. Of the ex- 

 perimental birds some had also moved south, but as 

 many again had travelled north. Of the latter, that which 

 had gone the farthest had flown some 100 miles in 7 

 days, and there were also reports of two flocks being seen 

 after 9 days on the shore of the Lesser Slave Lake some 

 200 miles to the north. All the north-bound birds that 

 were recovered came from the experimental group, and 

 thus there was leason to believe that a reversed migra- 

 tion had been induced in some, but not all, of the stimu- 

 lated birds. 



Confirmatory results were later obtained by 

 Wolfson^^^ who worked with the Oregon junco in its 

 winter area. He subjected the birds to extra light in 

 autumn, and then, when the gonads were maturing, he 



