MIGRATION AND FLIGHT. 19 



may be observed that when the feathers (as on the head of the 

 chaffinch, reed bunting, and stone chat) are of two distinct hues, 

 the webs of the exterior one are joined to the main body of the 

 feather by a line of separation of finer texture, thus forming an 

 additional margin to the inner part. 



I have thought it right to notice the alteration of colour at 

 different times of the year, because, like the alteration of many 

 birds in their progress to maturity (which sometimes takes several 

 years, and each year different), an erroneous multiplication of 

 species is the inevitable result, unless great care is taken to 

 reduce such variations into their proper species. The study of 

 this has been lately one of the chief advances in the science of 

 ornithology, and one well worthy the careful study of every 

 student of it. 



Migration and Flight. 



The Laiv of Migration to the general reader may require some 

 explanation. 



The terms Summer and Winter visitant, Polar and Equatorial 

 migrant, may occur in these pages. Therefore, to illustrate my 

 meaning, the Summer visitant or Polar migrant means a bird 

 resident during the summer in Britain — as being the most 

 northern parallel of latitude to which its migration extends, from 

 the Equator towards the Pole — such as the willow and yellow 

 woodwrens, the cuckoo, nightjar, swallows, &c. 



To the Winter visitant or Equatorial migrant, Britain is the 

 southernmost parallel to which their winter migration reach es, 

 from the Pole to the Equator, their summer being passed in 

 colder regions. Included in these visitants are some of the 

 ducks, the woodcock, the fieldfare and redwing, the snow 

 bunting, &c. 



The Occasional visitant is a bird found here only at un- 

 certain intervals — the waxwing and crossbill are instances. It 

 also applies to stragglers that have been driven out of their 

 regular course of migration by tempests or other casualties. 



Migration is an instinctive law of Nature, particularly shown 

 by the feathered race from their superior ability of locomotion, 

 which has long engaged the study of naturalists. A great 

 latitudinal movement, from the Equator towards the Poles, takes 

 place on the approach of spring, when Nature calls for the per- 

 petuation of the species. Another movement — the reverse of 



