1906J The Migration of Birds. 37 



many birds migrate at night, some high up ; that the young birds 

 going the first time can have no knowledge and experience of the 

 route ; when they leave here in September the trees are yet full of 

 leaves and the fields not empty, whereas the landscape looks 

 entirely different in April or May, when no leaves are out and the 

 fields are bare, etc. Some seem to follow the coast line or the 

 rivers, especially day migrants, but this can not explain all. The 

 solution of the problem seems to be, that they have a sense of 

 direction^ and their instinct whatever that is seems to impel 

 them in the right, usually for them best direction. That they 

 must have such a sense, we can see from the Carrier or Homing 

 Pigeon. This may be put into a box, taken aboard a train and 

 carried on it hundreds of miles to a place where it never has been, 

 neither can it see the physical features! of the way, yet on being 

 liberated it will find its way back with most unerring directness. 



At what height do the birds travel during migration ? A 

 balloonist has seen an eagle soaring about at a height of 9,000 ft. 

 which does not say it was migrating. Some observers have 

 seen large bands of migrants at an altiiude of 5,000 ft. An ex- 

 perimenter with kites has seen large migrations of ducks at from 

 1,300 to 1,500 ft. high. Many birds are killed by flying against 

 lighthouses no more than 100 ft. high. So, no one answer can be 

 given to this question. Some species always, and others perhaps 

 only when the air is heavy and foggy, fly very low, not more than 

 perhaps 100 ft. over all trees and houses. We can hear their 

 voices plainly at night during migration. But the bulk of it seems 

 to be going on at a height of from 500 to 1,500 ft. They want to 

 stay below the lowest clouds. That they are sometimes bewildered 

 and driven out of their course by fog and strong winds is equally 

 certain. 



At what rate of speed do the birds proceed southward and 

 northward ? That this must be very variable we can see at once 

 when we look at the wings of the warbler, thrush or rail and at 

 those of the swallows, gulls and hawks. If we divide the distances 

 travelled by the number of days spent in migration, we obtain a 

 rate of from about 25 to 150 miles a day. This does, of course, 

 not mean, that the birds get up into the air, fly straight ahead for 

 a day and then are only so much farther on than the day before. 



