THE LIGHTHOUSE AT 



HELIGOLAND OS 

 A 3IIGRATI0S NIGHT. 



CHAPTER XX. 



Hybernation of birds- — Migration of birds — Reed-warblers — Origin of migration — 

 Transvaal warblers — The Mammoth age — Insect life — Lines of migration — 

 Heligoland — Its ornithologists — Variety of birds — ^Wind and weather — The 

 throstle-bushes — Migration by sight — Order of migration — Stray migrants — 

 The yellow-browed warbler — Migration on Heligoland — Skylarks — Migratory 

 instincts — Other facts of migration. 



It is very diEficult to reali-^e the fact tliat not longer ago 

 than towards the close of the last century the belief in the 

 hybernation of swallows was held by many ornithologists. 

 That certain species of mammals spend the winter in a 

 torpid state is proved beyond all possibility of doubt; but 



