INTRODUCTION. 
lix 
ful incentives. Thus various tribes, which, at certain seasons, cannot 
obtain in their customary haunts sufficient food, or securely rear their 
young, change, from necessity, the climate and their places of abode. Pos- 
sessing the means of conveying themselves, vyith celerity, from one part 
of the globe to another, and capable of accomplishing their aerial journies 
with a velocity almost as swift as the thought of the calculator, what, to 
animals less bountifully endowed, would be an exertion of trouble, pain, 
and fatigue, is to them an act of comparative ease. Of those that are 
compelled to seek their food in various climates, some live entirely on the 
insect tribes, which fill the atmosphere with their countless numbers, and 
which, at the approach of winter, commonly retire to a state of torpidit- 
and inaction. While others, confined to search for food in the tender sod, 
or near stagnant waters, or in miry places, which, when congealed, no 
longer afford them subsistence, are obliged to wander to more favourable 
skies in quest of sustenance. They are not operated upon by one cause 
alone; fear, as well as climate and temperature, is a powerful inducement to 
their ehanging of their abodes. 
Thus the Penguin, which once frequented the little islands near the 
shores of Newfoundland in immense multitudes, has now quitted its former 
retreats, and retired to some distant country, where man, her great enemy, 
seldom appears : and the Swallow', the Swift, the Goatsucker, the Cuckoo, 
the Whitethroat, the Redstart, the Blackcap, and other birds of passage, 
are tremulously alive to the state of the atmosphere. The migration of 
some birds appears to be more confined than that of others ; a simple line 
or track marks their journey, from which they rarely deviate. In winter, 
the Fieldfare, the Redwing, and the Woodcock, hasten from the north 
tow'ard the southern climes, and return at the approach of spring to its vast 
morasses and umbrageous forests, for the purpose of incubation ; and 
many species of the feathered race never desert us, and some of them 
merely range from one county to another. While birds of the Crane kind, 
universal wanderers, confined to no particular district, fly from climate to 
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