NOCTURNAL MIGRATION 41 



others. The method followed by swifts and hum- 

 mingbirds is uncertain, but it is probable that the 

 former usually move by day. The ruby-throated 

 hummer has been seen flying by day from Point 

 Pelee, Ontario, across Lake Erie. 



It has been stated that small birds migrate by 

 night to escape the enemies that otherwise might 

 destroy them. Bluebirds, jays, and blackbirds fly 

 regularly by day without fear of attack, as do king- 

 birds, fork-tailed flycatchers, and waxwings. It is 

 highly probable, however, that small species, as 

 wrens, chats, ground- or thicket-haunting warblers, 

 and the small flycatchers that inhabit thickets or 

 dense woodland, habitually living in concealment, 

 feel safer under the protecting cover of darkness 

 during their prolonged flights above the earth. 



The procurement of food is perhaps a much more 

 weighty factor than timidity in regulating flight by 

 night. The stomach of a bird killed during the day 

 invariably contains remains of food, and often is full, 

 unless the bird is sick, or injured, or is in a situation 

 where food may not be obtained. Digestion is very 

 rapid, so that, to ensure a proper replacement of 

 the energy expended by the bird during its rapid 

 and sprightly movements, it is necessary that food 

 be secured at comparatively short intervals. In 

 studies of the food of starlings Kalmbach and 

 Gabrielson found that stomachs of a considerable 



