320 HOMING WITH THE BIRDS 



us one minute and a mile distant tlie next. Who 

 can write of them with absolute certainty? Also, 

 in many cases, the sexes are so alike they can not 

 be told apart in freedom without glasses, and when 

 they differ, all males and all females of the same 

 species resemble each other so closely that it is a 

 dubious guess, with the exception of nesting time, 

 as to how long one can observe the same bird. 



One thing that they know is when to migrate 

 and when to return to us, for there is no question 

 but certain birds do return season after season not 

 only to the same state and county, but to the same 

 vine on the veranda and the same knot-hole under 

 the eaves. What determines the precise minute 

 of their starting to come to us or to leave us, or 

 how they follow their trackless path high in air 

 across seas and continents mostly under cover of 

 darkness, we do not know. The birds must know, 

 since barring disaster, they arrive, prompt to the 

 day and almost to the hour. 



I often read of "the birds that remain with us 

 in the winter." The birds that remain with me 

 are very few, confined almost entirely to owls, 

 which if undisturbed will spend a lifetime in one 

 hollow tree. I have other birds in winter, but I 

 have no way of proving that they are the same 

 birds which have been with me during the summer. 

 Instead, I think that it is very probable that they 

 are birds which have spent the summer farther 

 north and now make their migration to us, 



