DIFFERENTIATION, MIGRATION, AND MIMICRY. 371 



A. modularis, by delicate difference of hue. But, though in gait 

 and manner it closely resembles it, I was surprised to find the 

 Japanese bird strikingly distinct in habits and life, being found 

 only in forest and brushwood several thousand feet above the sea. 

 I met with it first at Chiusenze — 6000 feet — before the snow had 

 left the ground, and in summer it goes higher still, but never 

 descends to the cultivated land. If both species are derived, as 

 seems probable, from A. immaculatus of the Himalayas, then the 

 contrast in habits is easily explained." The lofty mountain ranges 

 of Japan have enabled the settlers there to retain their original 

 habits, for which our humbler elevations have afforded no scope. 

 On the solution of the problem of the Migration of birds, the 

 most remarkable of all the phenomena of animal life, much less 

 aid has been contributed by the observations of field naturalists 

 than might reasonably have been expected. The facts of migra- 

 tion have, of course, been recognised from the earliest times, and 

 have afforded a theme for Hebrew and Greek poets 3000 years 

 ago. Theories which would explain it are rife enough, but it is 

 only of late years that any systematic effort has been made to 

 classify and summarise the thousands of data and notes which 

 are needed in order to draw any satisfactory conclusion. The 

 observable facts may be classified as to their bearing on the 

 whither, when, and how of migration, and after this we may pos- 

 sibly arrive at a true answer to the Why ? Observation has 

 sufficiently answered the first question, Whither ? 



There are scarcely any feathered denizens of earth or sea to 

 the summer and winter ranges of which we cannot now point. Of 

 almost all the birds of the holoarctic fauna, we have ascertained 

 the breeding-places and the winter resorts. Now that the Knot 

 and the Sanderling have been successfully pursued even to 

 Grinnell Land, there remains but the Curlew Sandpiper (Tringa 

 sabarquata) , of all the known European birds, whose breeding- 

 ground is a virgin soil, to be trodden, let us hope, in a successful 

 exploration by Nansen, on one side or other of the North Pole. 

 Equally clearly ascertained are the winter quarters of all the 

 migrants. The most casual observer cannot fail to notice in any 

 part of Africa, north or south, west coast or interior, the myriads 

 of familiar species which winter there. As to the time of migra- 

 tion, the earliest notes of field-naturalists have been the records 

 of the dates of arrival of the feathered visitors. We possess 



