XIV 



especially refer to Mr. Seebohm's chapter on migration in his ' Siberia in Europe' (pp. 242-261), 

 the materials for which were to a large extent obtained from Mr. Gatke. I quite agree with 

 Mr. Seebohm that the desire to migrate is an hereditary impulse which has, during the lapse of 

 ages, acquired a force almost as irresistible as the instinct to breed in the spring ; but tempe- 

 rature, as well as the lack of superabundance of food, may have to do with migration, and cannot 

 be disregarded. Thus, during unusually mild winters some even of our insectivorous soft-billed 

 birds remain in their breeding-haunts instead of passing southward with the rest of their con- 

 geners, and the Chiffchaff has been known to winter in Great Britain. With us also several 

 species are resident which on the continent of Europe are true migrants — a fact to be explained 

 by the mildness of our winters compared with those in the northern portions of continental 

 Europe ; for with us they are able to find sufficient food during the winter, whereas in the north 

 of continental Europe they would probably be starved out ere long. The soft-billed insecti- 

 vorous birds appear to be the most persistent migrants, as they feed almost solely on insects. 

 The Tits, which feed on insects and vegetable diet also, are to a large extent only partial 

 migrants or, in some places, residents. Where they find a sufficiency of food they remain all the 

 year round ; but when food becomes scarce they lead a rambling, gipsy life, sometimes not 

 travelling far, and at others migrating to some distance. In countries where they are perma- 

 nently resident they develop into local races, or even fairly distinct species ; thus our English 

 Coal Titmouse has become in the course of time quite easily separable from Parus ater, its 

 continental ally, and has been separated under the name of Parus britannicus ; and the Blue 

 Titmouse of North Africa, Parus teneriffae, has diverged from Parus cceruleus into a perfectly 

 good species. The Dippers afford another instance of this ; for although they are exclusively 

 insectivorous, they are able to obtain a sufficiency of food without migrating to southern climes, 

 and are therefore residents, or only straggle from one stream to another, seldom traversing 

 any considerable distance. Consequently they have merged into several closely allied though 

 fairly separable forms, of which we have in Europe alone three, Cinclus melanogaster, Cinclus 

 aquaticus, and Cinclus albicollis. Our common Chaffinch, Fringilla c&lebs, which is a migrant 

 in most parts of the tract over which its range extends, is represented in the north of Africa 

 and in the Azores by two closely allied but perfectly distinct species, Fringilla spodiogena and 

 Fringilla tintillon, both of which are non-migratory, and consequently have in the course of 

 time become specifically separable. The common Turtle Dove is also replaced in North-east 

 Africa by a form (Turtur isabellinus) which evidently has sprung from the same parent stock, 

 but which, being resident in that portion of Africa, has become a perfectly valid and well- 

 separated species. 



It is especially noteworthy that the young birds of the year are the first to migrate south 

 in the autumn, and not, as one would at first suppose, the old birds ; and this may account for 

 the fact that so many of our rarer visitants appear in the autumn and are young birds, probably 

 such as have wandered out of the direct course. It appears also that birds when migrating 



