42 THE MIGRATIONS OF BIRDS 



number taken between eight and ten in the evening, 

 when the birds had been at roost for three to five 

 hours, were almost entirely empty. Stomachs of 

 birds killed by striking obstructions during night 

 flight are nearly always empty, from which fact at 

 times has come the belief that the wanderers had 

 died of starvation. It appears, therefore, that diges- 

 tion empties the stomach completely when food is 

 not taken at short intervals. If tiny migrant way- 

 farers flew by day across the great stretches of land 

 and sea that they must necessarily compass in their 

 migrations, they would arrive at nightfall, tired, per- 

 haps almost exhausted, at some destination where 

 they would be unable to procure food until the fol- 

 lowing morning, as they are diurnal in habit. Such 

 circumstance might lead to unnecessary exhaustion 

 of their powers and so delay their further flights. 

 Or might, if coincident with unusual cold, or expo- 

 sure to heavy rains or snows, prove fatal, as in a 

 condition of reduced vigor sufficient bodily heat 

 and vital energy might not be available to enable 

 them to weather the unseasonable condition. On the 

 other hand, where migrational flights are pursued by 

 night, when the travellers pause at daybreak, they 

 may rest for a brief space and then may begin a 

 search for food. The entire day may be occupied 

 alternately in feeding and resting, and the travellers 

 may so recuperate that, if it is desired, further flight 

 may be begun at nightfall. 



