x INTRODUCTION. 
temperature congenial to the young, and an abundant supply of food suitable for their 
nourishment; we here allude more particularly to our summer visitants which have left the 
climate of Africa, too hot to be borne in summer, but well adapted for their winter retreat. A 
reverse of these circumstances takes place among our winter visitors; the high polar latitudes 
are their summer residence; but on the setting in of the cold in those regions the supply of 
food necessarily fails them, and this, with the extreme rigour of the climate, forces them to 
sojourn for a while in more temperate latitudes; hence while the Swallow, the Cuckoo, the 
Nightingale, many species of soft-billed Warblers, and numerous others visit us in spring from 
the south, for the purpose of nidification, and leave us on the approach of winter; the Fieldfare, 
the Redwing, the Woodcock, and various aquatic birds find a winter asylum with us, and depart 
again in spring to make room for a new succession of visitors. Independently, however, of the 
numerous migratory birds which are only temporary residents, a large number of species per- 
manently remain in our latitudes ; yet strange to say, of many of these the number is greatly 
augmented, especially during winter, by accessions from the north, among which latter are 
some of the smallest and most delicate of their race; we may mention the Golden-crested Wren 
as an example in point. Instances are not wanting of the arrival of multitudes of this species 
on our shores, but in such a state of exhaustion as to be almost powerless. In the case of the 
Lark and the Thrush, which also visit us in great numbers, the performance of a flight across 
the German Ocean does not much surprise us; but when we examine this little bird, which is 
by no means adapted for long-sustained aerial progression, we are at a loss to conceive how such 
a migration could have been performed. It is, however, only one amongst the many wonders 
of nature which are continually forced upon the attention of the naturalist. 
So much has already been written on the structural adaptation of birds to their respective 
habits, and on their periodical changes of plumage, that we may be readily excused if we 
omit any detail connected with these points, more especially as they rather belong to the 
physiology of the feathered race, than to the natural history of the species of one quarter of the 
globe. 
While the strictly tropical climates of the world abound with species infinitely diversified 
in form, and often adorned with the richest hues, the Birds of Europe are not only far 
DSI 
