Fresidenfs Address. 307 



nection with our previous remarks, undoubtedly assist us in 

 fixing the faunal value of the position of the Isle of May, 

 and indicate, in a very considerable measure, its importance. 

 It has been ascertained, with regard to the migrations of 

 land-birds across the North Sea and concerning the areas 

 which they cover in certain winds — whether these winds aid 

 or impede their flight — that certain fixed laws exist beyond 

 reasonable doubt of contradiction. It is not my intention to 

 speak of all these laws in detail, but only to show, so far as 

 I can, the distinct and direct bearing of some of these laws 

 upon the migratory fauna of the Isle of May. 



The first axiom I may state is : (a) The line of the autumn 

 migration of land-birds across the North Sea invariably takes 

 place from easterly directions to westerly ones, or from 

 directions south of east to north of west. This great autumn 

 movement is influenced from year to year by the prevailing 

 winds, which may, in some measure, retard or hasten on the 

 movement, according to its strength, exact extent of area, 

 direction, and duration. At Heligoland, however, influence 

 of the wind seems to be less exerted, as migrants cross from 

 E. to W., or thereby, over that island with marvellous 

 regularity of dates and direction. 



Another axiom is : (h) Birds prefer to travel with a heam 

 wind, that is, with a wind from two to four points, according 

 to strength of wind, against their line of flight ; because this 

 wdnd smoothes down their plumage and keeps it close to the 

 body, and enables them to use their tails as rudders. But 

 birds do not willingly migrate with a following wind, or start 

 upon a journey with a following wind, as such destroys their 

 equilibrium and ruffles up their plumage, and renders it 

 vastly more difficult for them to steer their course. But yet 

 it often happens that, caught unawares in the most unfavour- 

 able winds and weather, many thousands of land-birds are 

 carried helplessly away miles out of their intended course, 

 and drowned hundreds, even thousands, of miles out in the 

 Atlantic. 



A third axiom is : (c.) Should N.W. winds prevail in 

 autumn upon our east coasts, or westerly winds, or even 

 south-westerly winds, normal migration ensues. Such are 



