Migration of Birds 331 



during our cold season, but a vast portion of the last-named 

 continent remains still a terra incognita to the naturalist, 

 and though we have specimens of our Nightingale, Willow 

 Warbler, and Cuckoo from the Gold Coast, no one is able to 

 say that the birds have gone in a direct line from England 

 or France to the coast of West Africa. To prove this we 

 shall require an ornithological station at Timbuctoo, which 

 must tell whether, or not, our migrants cross the Sahara. 



That the Nile Valley receives a vast stream of migrants 

 is certain, and that there is a convergence towards this 

 migration-centre seems to be a determined fact, but there 

 are other lines by which the streams of migration trend 

 towards the African continent, by way of Gibraltar, by 

 Genoa, Corsica, Sardinia, Italy, Malta, Greece and the 

 coast of Asia Minor. Too much stress, however, has, as it 

 seems to me, been laid on the certainty of these routes of 

 migration, and the truth will be reached, not by drawing 

 lines like telegraph-wires across the world's surface, as if 

 every one of the routes indicated was known and proved 

 by statistics, but rather by the patient accumulation of the 

 latter. Further, it would seem to be the case that birds 

 impelled by the instinct of migration, which is undoubtedly 

 an hereditary faculty, wing their way to their southern 

 homes according to the circumstances which impel them, 

 some travelling by day and some by night, as the conditions 

 of the weather are favourable for their journey, or the reverse. 

 It is possible for a Londoner to stand on Primrose Hill 

 on an autumn night and hear the small Plovers and other 

 \Vading-birds calling as they pass overhead in the dark- 

 ness, and I have also heard Godvvits pass low over Bourne- 

 mouth in pitch-darkness. I have, however, also listened 

 to a flock of Knots, in the early days of August, flying over 

 Chiswick in full sunlight in the middle of the day, though 

 they were at such a height as to be quite invisible, and were 

 only detected by their notes, as they called to one another. 



