552 MIGRATION 



Drosselzug is regarded in many places nearly as the Twelfth of 

 August or the First of September is with us. In most localities 

 in Britain the new comers depart after a short sojourn, and are 

 accompanied by so many of the home-bred birds that in some 

 parts of the island it may be safely declared that not a single 

 Song-Thrush can be found from the end of November to the end 

 of January, while in other districts examples can always be seen. 

 Much the same may be said of the Redbreast. Undeniably resident 

 as a species, attentive scrutiny will reveal the fact that its numbers 

 are subject to very considerable variation according to the season 

 of the year. At no time do our Redbreasts collect in bands, but 

 towards the end of summer they may be seen in the south of Eng- 

 land successively passing onward, the travellers being mostly if not 

 wholly young birds of the year ; and so the majority disappear, 

 departing it may be safely presumed for more southern countries, 

 since a few weeks later the markets of most toAvns first in France 

 and then in Italy are well supplied with this species. But the 

 migratory influence affects, though in a less degree, many if not 

 most of the Redbreasts that remain with us. Content during the 

 autumn to occupy their usual haunts, the first sharp frost has a 

 decided eftect upon their distribution, and a heavy fall of snow 

 drives them towards the homesteads for the larger supply of food 

 they find there, while should severe and long-continued hard 

 weather follow even these birds vanish, leaving only the few which 

 have become almost domesticated. 



These two species have been here chosen as illustrative cases 

 because they are at once plentiful and familiar, and want of space 

 only forbids us from citing others, but we shall find on inquiry 

 that there is scarcely a Bird of the Holarctic Region, whose habits 

 are at all well known, of which much the same may not be said, 

 or in other words, that every Bird of the northern hemisphere is to 

 a greater or less degree migratory in some part or other of its 

 range. Such a conclusion brings us to a still more general in- 

 ference — namely, that Migration instead of being the exceptional 

 characteristic it used formerly to be thought, may really be almost 

 universal, and though the lack of observations in other, and especi- 

 ally tropical, countries does not allow us to declare that such is the 

 case, it seems probable to be so. Before proceeding, however, to 

 any further conclusions it is necessary to examine another class of 

 facts which may possibly throw some light on the matter. 



It must be within the experience of every one who has ever 

 been a birds'-nesting boy that the most sedentary of Birds year 

 after year occupy the same quarters in the breeding-season.^ In 

 some instances this may be ascribed, it is true, to the old haunt 



^ Two remarkable instances of this persistency may be noticed. The nest of 

 a Falcon {Falco peregrinus) on Avasaxa — a hill in Finland somewhat celebrated 



