190 
SEXUAL selection: birds. 
Part II.. 
remarkable facts recorded by Mr. Blyth,® with respect 
to closely-allied species which 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- 
cillsc. 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 winter and summer, nearly the same plum- 
^ See his admirable paper ia the ‘ Journal of the Asiatic Soc. of 
Bengal/ vol. xix. 1850, p. 223 ; see also Jerdon, ‘ Birds of India,’ vol. i. 
introduction, p. xxix. In regard to Tanysiptera, Prof. Schlegel 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 j)revious 
paper, with an extract from a note by Mr. Blyth, in ‘ Ibis/ Jan. 1861, 
p. 52. 
