MIGRATION OF BIEDS. 327 



by looking on the earth beneath them. When birds on 

 migration are overtaken by a very dark night or a fog 

 they descend from their high line of flight towards the 

 surface of the sea or land, and it is on these occasions that 

 they are seen flying round about the lighthouses in a state 

 of apparent bewilderment. On this account it has been 

 thought that dark nights and hazy weather are favourable 

 for migration, but there is nothing to support this view, 

 except that on these occasions the birds are seen at the 

 lighthouses on the coast. In clear weather they doubtless 

 fly both during the day and night at such an immense height 

 that they are not visible to the unaided eye. With the help 

 of a telescope, however, they have been observed migrating 

 at a height of about four miles above the surface of the earth 

 and travelling at a rate of about forty miles an hour. At 

 this speed and with a favourable wind they could cross 

 the widest part of the North Sea in about eight or nine 

 hours, and from the coast of Holland to England in about 

 one-third of that time. Birds on migration seldom fly 

 either directly against or with the wind, but generally 

 within three or four points of it. 



It is supposed that during hazy weather, with dark 

 nights, when birds on migration fly low, they enter Berwick- 

 shire by two routes one being across the Tweed from the 

 adjoining county of Northumberland, where the sea-board 

 is low, and the other from the neighbouring county of East 

 Lothian, where the shore has little elevation. The sea-coast 

 of Berwickshire is very lofty and precipitous, and on a dark 

 night the high black cliffs probably appear like a barrier to 

 the birds while they are approaching the land from the 

 German Ocean and flying at no great height above the 

 waves. They consequently continue their flight along the 

 open sea towards the Firth of Forth, on reaching which 

 numbers of them doubtless spread over the low grounds 



