1 9 1 8 . ] Birds of the Isle of May, 255 



In view of the above evidence, we hold that there are 

 strong grounds for believing that the route followed by birds 

 on migration depends largely on the direction o£ the wind. 

 It would appear that a bird's mo5^ fixed point is its breeding- 

 place, and that its migration routes, and even its winter 

 quarters, greatly depend on weather conditions during its 

 periods of movement. We wish to reiterate that we do not 

 consider that the direction of the wind, apart from its force, 

 stops birds migrating, but merely determines the route taken 

 on their long journeys. We believe that the deviation from 

 the direct route is largely, perhaps mainly, due to drift, 

 though voluntary " tacking " may be a factor. It seems i!n- 

 possible that it can be auy advantage to a European or Asiatic 

 bird breeding far north to make its journey southwards to 

 its winter quarters hundreds of miles longer by proceeding 

 via the British Isles, as many of them do under easterly 

 weather conditions. We must remember that the best 

 "migration- weather" for observers is probably the worst 

 for the birds, and when ideal conditions prevail for them we 

 see little or nothing of their migration-flights. 



On their migration journeys birds run the gauntlet of 

 many perils; foremost among these are adverse weather 

 conditions. We have found Fieldfares and Blackbirds 

 washed up by the sea, having evidently become exhausted 

 by the struggle against wind and weather, and having fallen 

 into the water and been drowned. We have also often seen 

 birds alight on the May in a thoroughly exhausted condi- 

 tion, too tired even to flutter a few yards farther, and after 

 such an arrival as this, we have picked up next morning 

 many corpses of migrants, evidently killed by exhaustion, 

 probably aided by starvation. This last is another peril 

 which besets the path of birds on migration. In the autumn 

 of 1913 this was brought home to us very forcibly. There 

 were a great many birds on the island, and of these many 

 Redwings, Thrushes, and Goldcrests literally starved before 

 our eyes. Day after day we saw them getting weaker and 

 weaker, till at last we picked up many dead. "We felt sure 

 that starvation was the cause of death but, wishing to have 



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