THE MIGRATION OF BIRDS. 233 
are also the curious antics and contortions of body which 
many Birds affect at the time of courtship, as notably do the 
Capercalzie, the Grouse, the Blackeock, and the Cock of the 
Rock. 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. 
Tur MitcGRaTion OF 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 w hich | are not commonly thought to migrate at 
all, as the Robin 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 ‘ par tial 
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. 
Migration 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. 
