384 



Let us proceed then to consider those points in bird-Hfe to which 

 the local naturalist should particularly give his attention. After 

 having ascertained what birds are to be found, or are known to 

 have occurred, in the district he has marked out for himself, he 

 will first separate these into the usual classes of fixed residents, 

 regular or occasional migrants, stragglers, &c. But this part of 

 their history has been so generally noted down in faunas, it is 

 unnecessary to say much about it. 



At the same time there is one question connected with our 

 regular summer migrants which the local naturalist might weU 

 attend to, not often considered, viz., what are the relative numbers 

 of each species that return to a given locality in the spring, where 

 an estimate can be made, compai-ed with the numbers that left the 

 autumn previous? AVhite, speaking of the house martin, has 

 remarked that " the birds that return yearly bear no manner of 

 proportion to the birds that retire." This is, however, probably 

 to be explained by the old birds driving the young away and 

 " obliging the latter to seek for new abodes " — an explanation given 

 by AVhite himself in another part of his work in reference to the 

 swift, of which he " was confirmed in the opinion " that they had 

 at Selborne " every year the same number of pairs invariably."* 

 Obsei-vations bearing on this matter made in other places would be 

 valuable. 



But let us pass to other particulars. It will be remembered that 

 we want facts for the support or otherwise of what is commonly 

 called the Darwinian theory, viz., that every species of animal 

 has been derived from a preceding one, through the instrumentality 

 of causes acting slowly over a long period of time. Now any plain 

 facts speaking to an alteration of character or habit will have a 

 certain weight one way or the other in this argument. In the case 

 of birds, any variation of plumage or song, or mode of nidification, 

 or of food, which sometimes affects the colour of the plumage,t 

 should be especially noted. Plumage we know varies in certain 



* Nat. Hist, of Selb. Letters xvi. and xxxix. to Dairies Barrington. 

 t WMte has remarked that " bullfinches, when fed on hempseed, often 

 become wholly black." [Letters xv. and xxxix. to Pennant.] See other 

 instances of " the effects of diflbrent kinds of food on the colours of birds," 



