306 Reconciliation of apparent Discrepancies in the Mode 



writers, in the instance of the American A. exilis, describes 

 them separately ; and, although Mr. Selby, in his British 

 Ornithology, asserts that those of the European A. mimita 

 differ in no respect, this is contrary to my own experience of 

 several individuals, some of which contained eggs consider- 

 ably advanced, and would certainly have bred in their existent 

 state of plumage. I have since learned that this is the case, 

 and that the proportion such females bear, at the breeding 

 season, to others which have assumed the perfect livery of the 

 male, is much the same as has been already noticed of the 

 other sex of the oriole. The herons never propagate but in 

 mature plumage; and the affinities of the tiny dwarf-bitterns 

 are in no way more beautifully exemplified than by the 

 simple fact which has been just detailed. 



The young of the different species of Strigidae exhibit some 

 remarkable nonconformities in the character of their first 

 plumage, which, if duly investigated, would, doubtless, help to 

 enlighten us a good deal respecting their mutual affinities, 

 which are at present very obscure. Those of the common 

 barn owl, for instance, remain extremely long in the nest, 

 wherein they slowly elaborate a plumage adult in its appear- 

 ance and texture, which, as in the Falconidae, is not moulted 

 till the second autumn. The young of the Aluco stridula, 

 on the contrary, are clothed, at an early age, with rather flimsy 

 downy feathers, which are entirely moulted, including all the 

 primaries, before the first winter. 



It is hoped the announcement of these and analogous diver- 

 sities will serve to awaken the attention of practical observers 

 to the investigation of all such particulars. But, without 

 descending, on the present occasion, into the details of every 

 group, let us endeavour, rather, to deduce the general laws 

 which prevail in the abstract, and in which all seeming dis- 

 crepancies and merely apparent anomalies will, most probably, 

 be found eventually to merge, however useful a correct know- 

 ledge of them has been shown to be in tracing out the physio- 

 logical relations of species. We have seen that the amount 

 of constitutional vigour is a very important modifier; and in 

 no instance is this more strikingly exemplified than in the 

 case of species which ordinarily require a number of years 

 to attain their fixed or perfectly adult livery. The loons 

 (Colymbus), for example, commonly advance through several 

 intermediate stages ere they exhibit the complete markings of 

 maturity ; yet I know of one preserved specimen of C. glacial is, 

 which was killed while exchanging its first or greyish plumage 

 for the nearly or quite perfect garb, thus omitting the inter- 

 mediate gradation. We also know that eagles, and analogous 



