CHAPTER VII 



WHY BIRDS COME AND GO 



Whoever notices what is going on in the natural 

 world about him must be impressed with the fact 

 that no two months in the year are alike so far as 

 the bird population is concerned. In winter, bird 

 life is at its minimum ; in June, at its height ; and be- 

 tween the two extremes there is constant fluctuation. 

 Great flocks of migrants stream southward across 

 the sky in autumn. Then, if we search the heavens 

 with a telescope on moonlight nights, we find the 

 vast procession stealing a march on its watchful ene- 

 mies of the day, some detachments moving slowly, 

 laboriously; others, like the wild ducks, at the rate 

 of over a mile a mmute. Hour after hour, both by 

 day and by night, day after day, week after week, 

 the procession passes ; yet in the spring, doubtless, 

 every one of these birds that has survived will reverse 

 the tedious journey. With the coming of warm 

 weather we waken every morning to find in our 

 gardens birds that may have been a hundred miles 

 away — yes, or even a thousand — only the day before. 

 Chimney - swifts fly at almost incredible speed. 

 Audubon picked up in Kentucky a dead wild pigeon 

 in whose crop were berries that did not grow nearer 

 than five hundred miles from his home, yet they 

 were only partly digested ! Why do so many birds 

 aiUempt these wearisome journeys twice a year? 



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