THE MIGEATIOSr OF BIEDS. 233 



are also the curious antics and contortions of body which 

 many Birds afiect at the time of courtship, as notably do the 

 Capercalzie, the G-rouse, the Blackcock, and the Cock of the 

 Eock. It is then the Peacock is seen in all its pride, and it is 

 probably for courtship that the Bower-bird makes its singular 

 structure of twigs set on end in two rows, with shells, bright 

 feathers, or other conspicuous objects, disposed at the mouth 

 of its curious avenue. 



The Migration oe Birds. 



Everyone knows that various Birds which are with us in the 

 summer (such as the Swallow and the Cuckoo) leave us before 

 the near approach of the winter season, returning to us with 

 the warmth of spring, to breed and hatch their young. This 

 annual movement is " migration," and is a far more general 

 practice than is ordinarily supposed, if, indeed, it may not be 

 said to be to some degree universal. 



Many Birds which are not commonly thought to migrate at 

 all, as the Eobin and the Song-Thrush, yet do so to a greater 

 or less degree in some localities, though in others this may 

 not be readily perceptible. Such species are called '\partiat 

 migrants." Birds have exceptional powers of changing their 

 dwelling-place with ease, and mutations of temperature with 

 diminished supplies of food seem to determine a movement to 

 warmer climes. Many birds are for us winter visitants, that is, 

 breed in the North and visit us in the winter ; while others 

 breed with us, as does the ^Nightingale, and are winter visitants 

 (that is, pass our winter months) in more southern climes. 

 Some Birds not only breed to the north of us, but are not con- 

 tent with the conditions found in England during the winter, 

 but pass beyond us to southern latitudes. Such Birds as never 

 make any prolonged stay, though passing us each way on very 

 prolonged annual journeys, are distinguished as " Birds of 

 passage." Sometimes Birds collect in large flocks before leaving, 

 as do the Swallows ; but most species slip away almost unob- 

 served. The same species does not, however, behave, in this 

 respect, invariably in the same way. 



Sligration takes place in part at night, and various anecdotes 

 have been told of the multitude of passing Birds, giving abun- 

 dant evidence of their passage to the ear, though darkness may 

 make them imperceptible to the eye. ^ 



