RED-BACKED SHRIKE. 213 



cases, and others wliicli might he cited, will be seen to hear 

 no real analogy to the numerously-ohserved instances of the 

 assumption of the male plumage hy the females of many 

 gallinaceous birds, in which it is accompanied if not induced 

 l)y a peculiar condition of the ovaries, while in the former 

 those organs are in full vigour. Some writers have assumed 

 that it is only the very old hen of this Shrike which acquires 

 the cock's plumage, but Mr. Blyth's statement as to the age 

 of the example he describes shews that the fact is not to be 

 thus explained. In the absence of any mode of account- 

 ing for the curious fact, it may be here suggested that this 

 is perhaps a case of what has become of late known to zoo- 

 logists under the name of " sexual dimorj)hism," and has now 

 l)een frequently observed in many groups of animals. 



Knowing that the adult females of the Grey Shrikes and 

 that of the Woodchat, next to be described, closely resemble 

 their respective males, while (setting aside the exceptional 

 cases just cited) the hen Red-backed Shrike without doubt 

 most generally differs greatly from the cock, it is worth con- 

 sidering whether any laws which govern the assumption by 

 birds of peculiar styles of plumage according to their several 

 ages and sexes can be discovered. Cuvier long ago made 

 two assertions on this subject (Regne Animal. Paris : 3 817, 

 i. p. 29G), which were no doubt true so far as his experience 

 went, and they have been dignified by the name of "laws." 

 These are : first, that when, as is most often the case, the 

 female differs from the male by its less lively colours, the 

 young of both sexes resemble her ; and secondly, that when 

 the adult males and females are of the same colour, the 

 young have a livery peculiar to themselves. To these two a 

 third " law " has been added in former editions of the present 

 work : namely, that whenever adult birds assume a plumage 

 during the breeding season decidedly different in colour from 

 that which they bear in the winter, the young birds of the year 

 have a plumage intermediate in the general tone of its colour 

 compared with the two periodical states of the parent birds, 

 and bearing also indications of the colours to be afterwards 

 attained at either period. 



