500 BIRDS. 



canaries, bullfinches, and parrots, it has been noted that the 

 food influences the colouring of the plumage. 



Migration. — The migrations of birds have been observed 

 and speculated upon from the earliest times, and in many 

 countries, but we are still far from possessing complete know- 

 ledge of the matter. The arrival in spring and departure in 

 autumn of the swallowis a fact familiar to every one ; but so far 

 from this habit being the exceptional one it was commonly 

 thought to be, it seems that there are few species of birds, 

 save those of the tropics, that do not change their habitat to 

 some extent in accordance with the varying seasons. One 

 of the most remarkable facts about the arrival and de- 

 parture of birds in any district is the regularity with which 

 it occurs ; thus the Red Indian names the months after the 

 birds whose arrival is peculiar to the time ; while in this 

 country many sea-fowls are credited with punctuality to the 

 day, regardless of weather. The wandering birds of any 

 country where migration has been observed, may be divided 

 into three classes — (i) those that arrive in spring, remain 

 during the summer to breed, and depart in autumn, as the 

 swallow and the nightingale do in this country; (2) others 

 that arrive in autumn, stay through the winter, and fly away 

 in the spring, for example, the fieldfare and the redwing ; 

 (3) some, like the sandpipers, which are only known for a 

 short time twice a year, in the spring and autumn, being 

 " birds of passage." These birds are not subject to different 

 influences; they illustrate different phases of migration. 

 Some have come from the north, driven southwards by 

 approaching winter, and find our climate warm enough for 

 them, these are the winter visitors ; others come from the 

 south as the weather becomes too warm for them, these are 

 the summer visitors ; while the birds of passage are those 

 that pass through the country in the course of a longer 

 migration. All birds nest in the colder countries of their 

 visitings. 



As migration is associated with the seasons, we are led to 

 suspect that its cause lies in the change of weather. Out of 

 the tropics all creatures have to adapt themselves to the 

 changing seasons. Alterations of climate may have a direct 

 or an indirect effect. Thus the direct effect of cold upon 

 some animals is such that they are killed ; most insects 



