190 SEXUAL selection: birds. Part II. 



remarkable facts recorded by Mr. Blyth,^ with respect 

 to closely-allied species wliich represent each other in 

 distinct countries. For with several of these represen- 

 tative species the adult males have undergone a cer- 

 tain amount of change and can be distinguished ; the 

 females and the young being undistinguishable, and 

 therefore absolutely unchanged. This is the case with 

 certain Indian chats (Thamnobia), with certain honey- 

 suckers (Nectarinia), shrikes (Tephrodornis), certain 

 kingfishers (Tanysiptera), Kallij pheasants (Gallopha- 

 sis), and tree-partridges (Arboricola). 



In some analogous cases, namely with birds having 

 a distinct summer and winter plumage, but with the 

 two sexes nearly alike, certain closely-allied species 

 can easily be distinguished in their summer or nuptial 

 plumage, yet are undistinguishable in their winter as 

 well as in their immature plumage. This is the case 

 with some of the closely-allied Indian wag-tails or Mota- 

 cillse. Mr. Swinhoe^ informs me that three species of 

 Ardeola, a genus of herons, which represent each other 

 on separate continents, are *' most strikingly different " 

 when ornamented with their summer plumes, but are 

 hardly, if at all, distinguishable during the winter. The 

 young also of these three species in their immature 

 plumage closely resemble the adults in their winter 

 dress. This case is all the more interesting because 

 with two other species of Ardeola both sexes retain, 

 during the Avinter and summer, nearly the same plum- 



' See his admirable paper ia the ' Journal of the Asiatic Soc. oi 

 Bengal,' vol. xix. 1850, p. 223 ; see also Jerdon, • Birds of India,' yol. i. 

 introduction, p. xxix. In regard to Tanysiptera, Prof. Sehlegel told 

 Mr. Blyth that he could distinguish several distinct races, solely by 

 comparing the adult males. 



^ See also Mr. Swinhoe, in 'Ibis,' July, 1863, p. 131 ; and a previous 

 paper, with an extract from a note by Mr. Blyth, in ' Ibis,' Jan. 1861, 

 p. 52. 



