( '3 ) 



Y. Bird Migration. 



It will be seen from the narrative of my journey, and from the special part on 

 the birds collected and observed, that innumerable mii;-rants pass through the 

 Western Sahara. For every ornithologist, Ijird-migration is a most interesting and 

 fascinating subject ; and next to egg-collecting, my earliest occupation with orni- 

 thology took the form of observing migration on the Baltic shores. Since then 

 tliis subject has become one of the foremost in ornithology, chiefly through 

 Giitke's Vogchoarti' ndijolaiid, the activity of the Royal Hungarian (Central Bureau 

 of Ornithology uuiler its gifted chief. Otto Herman, and, more recently, the 

 Vogelwarte Rossitten, and the "ringing" in Germany, England (Witherby's 

 activity), and other countries, and last, but not least. Eagle t!larke's Studies in 

 Bird Miy ration. 



In spite of all the great work dune so far, many t|uestiuus are still imperfectly 

 answered or i^uite unsolved. 



My explorations in Algeria, with and without the Hon. Walter Eothschild, 

 have given me some opportunities of observing migration, and, together with former 

 experiences, I came to the following conclusions : 



The popular belief and the description of the late Professor Newton,* that 

 northern migrants by the end of the summer, when food becomes scarce in the 

 most northern limits of the range of a species, " begin to press npon the 

 haunts of other individuals ; these, in like manner, upon that of yet others, 

 and thus 



' The waves behind impel the waves before,' 



until the movement which began in the far north is communicated to the indi- 

 viduals occupying the extreme range of the species at that season," is entirely 

 without foundation. I have never been able to see the logic ; to my mind it is 

 quite clear that birds are not able to "press upon the haunts of other individuals "; 

 especially in late summer and early autumn there is such a quantity of food, and 

 nowhere are birds so numerous that the immigration of a host of birds could " press 

 npon their haunts," and this movement be " communicated to the individuals 

 occupying the extreme range of the species at that season." Just the contrary 

 takes place: the northernmost individuals are, of course, first compelled to quit 

 their haunts, and they migrate — generally much more slowly and leisurely than on 

 their return journey in spring— farthest south. Thus we see the northern Waders 

 arrive on our shores in the summer, when none of our birds, or hardly any, begin to 

 move. We see birds from the arctic regions migrating south to the equator and 

 beyond, Siberian birds pass the winter in Australia, while Manchurian forms only 

 go as far as middle and southern China ; we find the northern Yellow Wagtails 

 going south, at least as far as the Mediterranean form, instead of pressing the latter 

 on before their host ; and where the same species inhabits more southern latitudes, 

 the southern form becomes resident, instead of being compelled to move before the 

 invading nortiierners. Our Wheatear and the Greenland Wheatear {Oenanthe 

 oeiiardhe oi'ittmtlie and Oenanthe oenanthe leucorrhou) wander as far south as 

 tropical Africa, while the Mediterranean Wheatears only just reach their winter 

 quarters, and are not jiushed on farther south. Oenanthe hispanica lias not been 

 observed farther south than Sencgambia, where it appears to be very rare, but the 

 majority winter perhaps in the Saharan oases ; and of the black-throated Oenanthe 

 oenanthe seebohmi the winter quarters are not yet known. 



' Ct. liict, B. p. 555, and Noe. Zool. 1905. p. IG. 



