56 THE RIDDLE OF MIGRATION 



hand since they become exhausted in a few minutes 

 and can be picked up. The same bird, released in a 

 heated room immediately after, shows no signs of 

 undue fatigue when being re-caught and it certainly 

 cannot be taken by hand. Many of my canaries 

 (which winter out) continue to sing to about 30° 

 below zero but at lower temperatures they are 

 silent. Food consumption goes up enormously at 

 these times. 



In regions of really heavy snowfall the supply 

 may become entirely inaccessible. 



The food problem thus comes to be not merely a 

 question of supply, but of availability, temperatures 

 and day-length. 



Low temperatures in themselves are probably of 

 little moment. No native birds that I have kept 

 in the aviaries have shown any particular disability 

 apart from the lethargy already commented on. 

 The lowest temperature my captive birds have 

 actually experienced was — 52°F., i.e. 84 degrees of 

 frost. The canaries are quite frequently exposed to 

 temperatures ranging from —30° to — 45°F. yet I 

 have never had a winter death among these sub- 

 tropical birds. The feet and legs of Australian 

 budgerigars freeze at — 12°F. 



There is yet another factor in the northern 

 winter environment to be considered but it seems 



