J 6 INTRODUCTORY CHAPTER. 



on the contrary, like those quadrupeds which feed on herbage, 

 are gentle, inoffensive, and social ; and may for the most part be 

 easily domesticated. Man has in consequence availed himself 

 ef this tractable disposition, and judiciously selected from the 

 numbers which on every side surround him, such as were likely 

 to be the most useful ; among which the hen, the goose, the 

 turkey, the duck, and the pigeon, are the principal, and furnish 

 »i.? with a store of nutritious and palatable food. 



To enter into a minute history of the feathered part of the 

 creation, is incompatible with our present purpose: one par- 

 ticular circumstance, however, has been so long the subject of 

 remark and investigation, that it cannot be suffered to pass un- 

 noticed. 



The annual migrations of those, which from that circumstance 

 are denominated birds of passage, have exercised the specula- 

 Uon of all ornithologists, and given rise to a variety of conjee- 

 1 ires among writers on that subject. Most birds are in some 

 measure birds of passage ; for although they do not migrate to 

 distant regions, the greatest part of them make frequent re- 

 movals from one neighbouring district to another, or from the 

 interior of the country to the sea-coast. The causes of these 

 migrations, although enveloped in obscurity, appear, according 

 to the most probable conjectures, to arise from the failure of 

 their accustomed food, or the change of the seasons. 



The manner of performing the long flights, which many of 

 those birds take across immense tracts of water before they ar- 

 rive at any place of rest, throws formidable difficulties in the 

 way of investigation : but we ought to consider, that being ac- 

 customed to measure distance, with relation to time, by the 

 q>eed of those animals with which we are well acquainted, we 

 are apt to overlook the superior velocity of birds, and the ease 

 with which they continue their exertions. 



Our swiftest horses are supposed to go at the rate of half a 

 mile in somewhat less than one minute ; but such a degree of 

 exertion soon produces debility, and cannot be long continued. 

 With birds, the case is very different ; their motions are not im- 

 peded by similar causes. They glide through the air with a 

 velocity superior to that of the fleetest quadruped, and can for 

 a great length of time continue their motion. If we suppose a 

 bird to proceed at the rate of no more than a mile in two min- 

 utes for the space of twenty-four hours, it will in that time have 

 passed over an extent of more than seven hundred miles ; and, 

 if aided by a favourable current of air, there is reason to sup- 

 pose that the same may be performed in a much shorter space 

 of time. 



If it be asked how they know the time when to commence 



