88 THE BIRDS OF HELIGOLAND 



night of the 12th of August 1877, during a light east wind and 

 very light warm rain, ' myriads ' of Plusia gamma migrated in com- 

 pany with the shore-birds already mentioned, and many young birds 

 of the Wheatear, the Willow Warbler, and other small species. 



Of quite special interest is the occurrence here, on the 23rd of 

 June 1880, during perfectly calm, warm weather, of the Desert 

 Chat, a southern species extremely rare in Central and Northern 

 Europe, side by side with Papilio podalirius, a butterfly which is 

 rather rare in Germany, and in Heligoland had only been seen on 

 one previous occasion. The weather previously from the 15th of 

 the month had been clear and warm, with light-easterly and 

 south-easterly winds. 



On no previous occasion, however, have the migrations of 

 Plusia gamma reached to such an extent as they did during the 

 middle of August 1882. On the 15th of that month the wind was 

 south-east, and the weather fine and warm. Of birds, the following 

 had made their appearance : the Redstart, the Whitethroat, the 

 Willow Warbler, the White Wagtail, the Red Flycatcher, the Whin 

 Chat, the Ortolan Bunting, the House Martin, the Sand Martin, and 

 the Swift. During the night the wind was south, with a calm and 

 warm rain; the small birds above enumerated continued to migrate 

 in abundance, as well as large numbers of ' Waders,' i.e. Plovers, 

 Sandpipers, etc., and intermingled with these, from 11 P.M. to 

 3 A.M., myriads of P. gamma, like a dense snowstorm, all tra- 

 velling in a direction from east to west. Early on the morning 

 of the 16th, the wind was west, with rain ; the afternoon was fine, 

 sunny, and calm. In the evening, and during the night, the wind 

 was south and the weather fine and calm ; there was again a strong 

 migration of small birds and ' Waders,' together with countless 

 numbers of P. gamma. These migration-phenomena were repeated 

 during the nights of the 17th and 18th, with very light southerly 

 and westerly winds. On the 19th, with a south-east wind and fine 

 weather, many Warblers, Flycatchers, and like species were seen 

 during the day. During the night the sky was overcast, but large 

 numbers of ' Waders,' again accompanied by P. gramma in millions, 

 were still seen, all travelling from east to west. During the night 

 of the 20th there was a thunderstorm at some distance, which 

 put an end to migration of every kind. 



This leads us up to the question as to the influence which 

 powerful electrical changes in the atmosphere exert on migration. 

 Thus, the regular migration of P. gamma, above referred to, had 

 actually commenced as early as on the night of the llth of August, 

 during which a migration of birds also took place ; both, however, 

 were soon after interrupted by thunderstorms. My diary has the 



