56 MANNER OP MIGRATION. 



highways of migration. Through telescopic observations 

 it has been learned that migrating birds travel at a great 

 height. The exact height remains to Ije determined, bnt 

 it is known that many migrants are at least a mile above 

 the earth. From this elevation they command an ex- 

 tendeil ^dew, and in clear weather prominent features of 

 the landscape are doubtless distinguishable to their pow- 

 erful vision at a great distance. 



It is when foffs and storms ol^scure the view that birds 



o 



lose their way. Then they fly much lower, perhaps seek- 

 ing some landmark, and, should a lighthouse lie in their 

 patli, they are often attracted to it in countless numbers. 

 Thousands of birds perish annually by striking these 

 lights during stormy fall weather. In the spring the 

 weather is more settled and fewer bii'ds are killed. 



Although birds are guided mainly by sight, hearing is 

 also of assistance to them on their migrations. Indeed, at 

 night, young birds, who have never made the journey be- 

 fore, must rely largely upon this sense to direct them. It 

 is difficult for us to realize that on favorable nights during 

 the migratory season myriads of birds are passing through 

 the dark and apparently deserted air above us. Often 

 they are so numerous as to form a continuous stream, and 

 if we listen we may hear their voices as they call to one 

 another while flying rapidly onward. 



Some idea may be formed of the multitude of birds 

 which throng the upper air on favorable nights during 

 their migration by using a telescope. One having a two- 

 incli object glass will answer the purpose. It should be 

 focused on the moon, when the birds in passing are sil- 

 houetted against the glowing background. At the proper 

 focal distance they appear with startling distinctness. In 

 some cases each wing-beat can be detected, and with a 

 large glass it is even possible to occasionally recognize 

 the kind of bird. 



