MIGRATION OF ANIMALS. 275 



of swallows, there are three opinions adopted by different 

 naturalists. The first and most probable is, that they remove 

 from climate to climate at those particular seasons when 

 winged insects, their natural food, fail in one country or dis- 

 trict and abound in another, where they likewise find a tem- 

 perature of air better suited to their constitutions. In support 

 of this opinion, we have the testimony, as formerly mentioned, 

 of Sir Charles Wager, of M. Adanson, and of many navigators. 

 It is equally true, however, that some species of swallows 

 hcive been occasionally found in a torpid state during the winter. 

 Mr. Collinson gives the evidence of three gentlemen who 

 were eye-witnesses to a number of sand-martins being drawn 

 out of a cliff on the Rhine in the month of March, 1762. Mr. 

 Barrington, in the year 1768, communicated to Mr. Pennant, 

 on the authority of the late Lord Bellhaven, the following 

 fact : " That numbers of swallows have been found in old dry 

 walls, and in sand-hills, near his lordship's seat in East 

 Lothian ; not once only, but from year to year ; and that, 

 when they were exposed to the warmth of a fire, they revived." 

 These, and other facts of the same kind, seem to be incon- 

 trovertible ; and Mr. Pennant infers from them, that " we must 

 divide our belief relating to these two so different opinions, 

 and conclude, that one part cf the swallow tribe migrates, and 

 that others have their winter quarters near home." But we 

 should rather incline to think with those naturalists who sup- 

 pose that the torpid swallows which are occasionally, though 

 very rarely, discovered in the winter season, have been obliged 

 to remain behind, because they were too young, weak, dis- 

 eased, or superannuated, to undertake a long and fatiguing 

 flight. Still, however, that the torpidity of the feathered 

 tribes should be solely confined to the swallow, is a very 

 singular fact in the history of nature. Among quadrupeds, 

 there are many species who lie in a dormant or torpid state 

 during winter. But, if the swallow be excepted, not a single 

 species of birds, notwithstanding the great numbers, which, 

 at stated times, appear and disappear in every corner of the 

 globe, has ever been discovered in that state. This circum- 

 stance alone, though we cannot yet ascertain the precise 

 places to which different species of birds of passage resort, 

 is a most convincing proof of migration in general. 



It has been asserted, and even believed, by some natural- 

 ists, that swallows pass the winter immersed under the ice, al 

 Jie bottom of lakes, or beneath the waters of the sea. Olaus 

 Magnus, Archbishop of Upsal, seems to have been the first 



