THE PENTLAND SKERRIES. 51 



numbers now vastly increased by the addition of their young, are 

 collected into a smaller area. 



Third, Fogs are more prevalent at that time of year, and these 

 seem to bewilder the birds, which are thus brought down from 

 their great migratory fly-lines, which are often very high in the 

 air, to a much lower level. 



In spring, on the other hand, birds do not appear to come in 

 such rushes ; they then almost invariably migrate by night, and, as 

 the weather is generally finer, do not fly so low. 



Were the Skerries rather larger, with a more broken surface, 

 and especially if they possessed a small plantation, however stunted, 

 no doubt the returns of warblers would be much greater ; as it is, 

 there is no inducement for these latter birds to remain, once the 

 daylight returns. 



It can easily be understood why the Migration Keturns from 

 these places vary so much year by year, the wind and weather 

 having much to do with it. Birds like a wind a point or two 

 forward of the beam to cross with, i.e. on the shoulder, and 

 they dislike a following wind, as that disarranges their feathers and 

 their tails (or steering gear), and blows them helplessly about. 

 But, at the same time, this stern- wind is the one most favourable 

 to ornithological observation on our coasts. When birds travel 

 with a gentle wind on the shoulder (i.e. near the wind, like a ship), 

 they are often least seen ; but should the wind shift after they 

 have started, dead ahead, or, equally bad, dead astern, the first 

 landing-place and shelter is crammed with them, and then it is 

 that so many rarities turn up. 



When the night is clear, and the wind and weather favourable, 

 birds travel at a great height, and are thus less attracted by lights, 

 and pass on ; but a hazy night, with a strong wind from the east 

 and south-east, causes them to lose their way ; they thus lower 

 their flight, and are attracted by the strong rays of the light- 

 houses, and such nights give us the best-filled schedules. 



However, we need not pursue this subject further. All those 

 who wish to study migration should read the reports published by 

 the committee before mentioned. Of these there are nine, begin- 



