100 CLASS AYES. 



their brood in them, and which do not make a second there. 

 This is evident from these last always bringing their young 

 ones with them ; and as the swallows which return to pass 

 the hot weather in these same countries, for the purpose of 

 reproduction, do not bring young birds with them, it is a 

 proof that they have not brought forth during their absence. 

 This is an additional argument that the birds do not repro- 

 duce in the two seasons of the year, although they change 

 countries. We may further remark, that the birds which 

 are purely birds of passage in a country, and do not repro- 

 duce there, never arrive during the brooding season of that 

 particular country ; and it is also not to be expected that 

 they should lay at a season when none of the indigenous 

 birds of the country do so. Such observations must of 

 necessity throw great light on the migrations of birds, if 

 travellers attend particularly to discover, in the countries 

 they visit, the species which reproduce there, and those 

 which do not. 



The observations of M. Levaillant on this subject are so 

 interesting, that we shall make a further extract of their 

 substance. 



He remarks, and the observation is of equal interest and 

 importance, that a certain species which makes its brood in 

 'one country, quits that country and goes elsewhere ; while, 

 frequently, other individuals of the same species which have 

 reproduced elsewhere, come and replace the former. This 

 would very naturally lead us to conclude that it is not always 

 the want of food that induces birds to expatriate, but an 

 absolute necessity of changing climate. In Europe, where 

 during winter no insects are found, it is very natural that the 

 species which have no other nutriment, should, all of them, or 

 for the most part, migrate. Some few, indeed, as we have 

 seen, remain, and pass this rigorous season among us, still 

 finding wherewithal to subsist. But in the very warm cli- 

 mates, from which all the swallows which have nestled there 



