in xv/u'ch Changes of Colour are effected in Moulting. 305 



and, on the other hand, in males of other species which differ 

 in uniform from their mates and young, every amount of diver- 

 sity is apparent, in a series of species (or, perhaps, genera), from 

 all but resemblance, to very considerable dissimilarity. So, in 

 the females, as already stated, there is every gradation towards 

 the assumption of the typical plumage; and this not only as 

 exhibited in a series of distinct species, but as shown in a 

 greater or less tendency to obtain it at a later period of life 

 than in the males, or analogously to what is seen in the adult 

 male oriole, when compared with other species. The Lanius 

 Collurio, and more especially the L. rufus, would seem to 

 exemplify what has been just asserted.* 



Indeed, in the latter species, I have chanced to notice a fact 

 which is particularly worthy of mention here; namely, that, 

 although the young, in their nestling plumage, almost always 

 considerably resemble in their markings those of L. Collurio, 

 exhibiting a series of transverse bars on the upper parts, yet 

 specimens do sometimes occur, even at this age, in very nearly 

 the livery of the adultf, but which are, of course, readily dis- 

 tinguished by the much looser texture of their feathers. A 

 more striking instance of this disposition to advance, or, ra- 

 ther, of the vacillation (so to speak) occasionally discernible in 

 species of an intermediate character, can scarcely be imagined 

 possible. To apply such facts, we are naturally led to infer, 

 that, as the sexes of the common sparrow, for instance, are 

 constantly dissimilar, while those of the tree sparrow are 

 always the reverse, in intermediate species, such as the Pas- 

 ser cisalpinus, some inconstancy in the plumage of the old 

 females might be expected ; also, whereas, at the one ex- 

 tremity of the scale, it would not seem unlikely for species to 

 exist of which even the adult male plumage was analogous to 

 that of the female and young of the common sparrow, at the 

 other it is equally probable for even the nestlings to present 

 corresponding markings to those of the adult male of the 

 same bird : indeed, I could prove as much by reference to 

 known species in several groups. I will content myself, 

 however, by citing an additional instance illustrative of the 

 gradation noticeable in species of intermediate character, as 

 observable in the assumption of the male livery by the female 

 dwarf-bitterns (Ardeola). Alexander Wilson, who was well 

 aware of the usual similarity of the sexes in this tribe of 

 birds, much more so than contemporaneous European 



* In connexion with these facts may be cited Mr. Gould's figure, in his 

 Birds of Europe, of a male Circus rufus with its plumage partly grey. 



t An example of this may be seen in the Museum of the Zoological 

 Society. 



