THE PHILOSOPHY OF MIGRATION. 8i 



ground all the summer, suddenly become aerial, and 

 mount upwards to pursue their way to distant lands. 

 The majority of species appear to fly low as they 

 near land ; but others, as for instance the Wood- 

 cock, keep at a considerable altitude until the land 

 is below them, when they drop suddenly down into 

 the nearest cover. 



There is another matter which bears very im- 

 portantly on the altitude of Migration Flight, and 

 that is the singular influence of bright lights on 

 birds during passage. As every observer of migra- 

 tion knows, the various lighthouses and light-vessels 

 that stud the seas and coasts across or along the 

 routes of migration are frequently the centre of 

 attraction of various pilgrim birds, most especially 

 during a spell of fog or haze, or a few hours' pre- 

 valence of cloud. The question arises. Why do 

 birds thus make for these liery points of attraction, 

 a proceeding which only too often ends with fatal 

 results ? It is out of no mere curiosity or desire to 

 examine an unfamiliar object, for the visits are con- 

 ditional and exceptional, whilst to many of these 

 birds lights must have been common enough 

 throughout the preceding summer. The most pro- 

 bable explanation is, that the sudden appearance of 

 fog or the drifting of cloud-banks between them 

 and the earth has caused them to lose their bear- 

 ings, to flutter aimlessly down into a lower stratum 

 of air, and then to make for the nearest object at 

 all likely to guide them to a place of safety. The 

 brilUant lamps of the lighthouse are too often the 



