36 BIEDS. 



MIGRATION. 



Distribution should not be confounded with migration. Birds migrate year 

 after year, according to a more or less fixed rule, from one locality to another, 

 with the seasons. 



Migration is perhaps the greatest mystery which the whole animal kingdom 

 presents. " The Hawk that stretches her wings toward the south is as familiar 

 to the latest Nile boat traveller or dweller on the Bosphorus as of old to the 

 author of the Book of Job. The autumnal thronging of myriads of water-fowl 

 by the rivers of Asia is witnessed by the modern sportsman as it was of old by 

 Homer. Anacreon welcomed the returning Swallow. The Indian of the fur 

 countries, in forming his rude calendar, names the recurring moons after the 

 birds of passage whose arrival is coincident with their changes " — the theme of 

 comment in all ages and in all lands — and yet our " ignorance is immense." 



Chief facts of migration. In almost all countries there are — 



(a) Some species which arrive in spring, remain to breed, and depart in autumn. 



(6) Others which arrive in autumn, stop for the winter, and depart in spring. 



(c) Others (birds of passage) which show themselves but twice a year, in passing 

 through the country, their short transient visits occurring about spring and autumn. 



All these three classes are affected by the same impulse, and the nature of their 

 movements is almost uniform, inasmuch as — 



(a) Have their winter abode nearer the equator. 



(6) Have their breeding quarters much nearer the poles, and in returning to 

 tJiem on the approach of spring are but doing exactly as do those species which, 

 having their winter abode nearer the equator, arrive in the spring. 



(c) Like winter visitants, have their breeding places nearer the poles, but, like 

 summer visitants, they seek their winter abode nearer the equator, and thus per- 

 form a somewhat longer migration. 



Partial migrants. While there are some species in the British Isles, such as 

 the Swallow or the Fieldfare, of which every individual disappears at one period 

 of the year or another, there are other species, such as the Eed Wagtail or the 

 Woodcock, of which only the majority of individuals vanish, a few being always 

 present, and these species form the so-called "partial migrants." 



Migration almost universal. There is scarcely a bird of either the Palsearctic 

 or Nearctic region, whose habits are at all well known, which is not subject to 

 the migratory impulse, and hence we are led to the conclusion 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 inference, 

 viz. 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 especially tropical, countries does not allow us to declare that such 

 is the case, it seems very probably to be so. With the additional fact that birds- 

 exhibit a real partiality year after year to occupy the same quarters in the breeding 

 season, we may begin to try and account for the cause or causes of migration. 



Causes of migration. Want of food would seem to be enough, and it is the 

 most obvious cause. Even among many of those species which we commonly 



