86 THE BIRDS OF HELIGOLAND 



Nothing.' In the night from twelve to three A.M. the fog had dis- 

 persed, during which time enormous numbers of Thrushes, Chats, 

 Starlings, Golden Plovers, Lap wings, Oyster-catchers, and Sandpipers 

 were observed ; on the fog subsequently returning, not a bird was 

 afterwards either heard or seen at the glasses of the lighthouse. In 

 April, with light south-east winds and some rain, a powerful migra- 

 tion ought to have taken place, and the fog alone must have forced 

 it for the time being to clearer strata of the air above. Frequently 

 the height to which the fog extends is so inconsiderable that it is 

 possible to distinguish the thousand different call-notes of the 

 Larks travelling above the stratum of mist ; sometimes, indeed, one 

 may stand on the cliff two hundred feet high, in a perfectly clear 

 and cloudless atmosphere, and look down upon one continuous 

 heaving mass of mist extending to the distant horizon, and covering, 

 in one uniform shroud, the whole expanse of sea. 



Dew and hoar-frost, both probably traceable in their origin to 

 similar causes, also manifest a similar influence on migration. Both 

 are regularly accompanied by conditions of weather in all other 

 respects most favourable to migration ; yet, in spite of ' the most 

 splendid opportunity,' as Heligolanders express it, not a bird is seen 

 in the early hours of the morning, if there has been dew or hoar- 

 frost during the preceding night. Both of these conditions almost 

 invariably make their appearance concurrently with fair weather 

 i.e. with a calm clear air and light easterly and south-easterly winds, 

 so that they are here regarded as the precursors and sustainers of 

 fine weather. Accordingly, one finds oneself puzzled to know 

 what it is that makes them so disagreeable to birds. Even moths 

 are known not to swarm or migrate on evenings in summer on 

 which there happens to be a fall of dew, though all other conditions 

 may be favourable ; this is the more surprising, inasmuch as a light 

 warm rain does not by any means produce an immediate check on 

 their movements. 



As soon, however, as, during the hours of the forenoon in March 

 and early April, the dew has given way before the sun, Blackbirds 

 and Snipe almost regularly make their appearance, dropping down, 

 as it were, from the sky. Such, for instance, was the case on the 

 2nd of March 1883. The morning was clear and beautiful, and, 

 excepting for a scarcely-perceptible air-current from the north and 

 north-north-east, perfectly calm. Unfortunately, however, there 

 was a sharp hoar-frost ; but for the latter, Blackbirds and Snipe 

 would have unfailingly made their appearance during the early 

 hours, but not a bird was to be seen. In the course of the forenoon, 

 and later during the day, some Snipe and Blackbirds did make their 

 appearance, and Cranes, too, were observed to pass over the island. 



