OASES OF ADAPTATION 161 



sake of iDointing out a very important error as to the cause 

 of a very singular fact recorded there, by Herr Gatke, who 

 for fifty years, observed and registered the migrations both 

 in spring and autumn, with great accuracy, and formed a 

 collection of birds there, perhaps more extensive than could 

 be made at any other station in Europe. The fact observed 

 was, that, during the autumn migration, as regards many 

 of the most abundant species, the young birds of the year, 

 that is, those that had been hatched in the far north in the 

 preceding June or July, and who w^ere, therefore, only about 

 three or four months old, arrived in Heligoland earliest and 

 alone, the parent birds appearing a week or two later. This 

 is the fact. It has been observed on Heligoland for half a 

 century; every resident on the island knows it, and ]\Ir. 

 Seebohm declares that there can be no doubt whatever about 

 it. The inference from this fact (dravni by Herr Gatke and 

 all the Heligolanders, and apparently accepted by almost all 

 European ornithologists) is, that these young birds start on 

 their migration alone, and before their parents, and this not 

 rarely or accidentally but every year — and they believe also 

 that this is a fact, one of the most mysterious of the facts 

 of migration. Neither Mr. Seebohm nor Professor Lloyd 

 Morgan (in his Habit and Instinct) express any doubts about 

 the inference any more than about the fact. Yet the two 

 things are totally distinct ; and while I also admit the fact 

 observed, I totally reject the inference (assumed to be also 

 a fact) as being absolutely without any direct evidence sup- 

 porting it. I do not think any English observer has stated 

 that the young of our summer migrants all gather together 

 in autumn and leave the country before the old birds ; the 

 American observers state that their migrating birds do not 

 do so; while many facts observed at Heligoland show that 

 no such inference is required to explain the admitted fact. 

 Let us see what these additional facts are. 



The enormous rushes of mic^ratorv birds which rest at 

 Heligoland always occur at night, and are very intermittent. 



