INTRODUCTION. 17 



weather in the autumn makes them sooner quit our shores. 

 A very mild year will, on the other hand, induce some 

 stragglers to remain the whole winter. The differences 

 between the appearance and habits of these and those of 

 their brethren that have performed the two migratory- 

 voyages in the interim, are well worthy of attention. 



The long nights which the migratory birds take, are of 

 course much affected by the winds; and it is worthy of 

 notice, that at the season when our birds are migrating 

 northward, south winds are most prevalent, and north winds 

 are most prevalent about the time that they are coming south- 

 ward. But though these are the predominating winds, they 

 are not the only ones; for the times of the migration of 

 birds, both the spring and the autumn, are times when the 

 weather is unsettled, and severe gales often blow from the 

 cross points. These winds cause the numbers and also the 

 species of migratory birds to vary in different seasons. An 

 easterly wind, at either season, will cause the birds to be 

 more numerous, and also bring stragglers of those which, 

 though common on the continent, do not regularly visit 

 Britain. A west wind will, on the other hand, lessen the 

 number, and keep away the stragglers. We have not so 

 many summer stragglers on the west side of the island as 

 we have on the east, when the wind is from the west during 

 the time of migration, because the Atlantic is wider than 

 the mere lee-way which any land bird, guided by meridional 

 impulses, is likely to make. In the autumn the numbers 

 that straggle from that side are greater, because the absolute 

 distance in latitude is less towards the north ; but the 

 stragglers then are principally rare birds, and they seldom 

 come farther than the western coast. Upon examining the 

 position of Britain on the map, it will be apparent that the 

 summer migrants must be more abundant in the south-east 

 of England than in any other part of the country, while 



VOL. i. c 



