THE BTEDS OF MONGOLIA ETC. 149 



found nests. But this happening about the end of July, they were empty. 

 Judging, however, by their size and structure, they evidently belonged to 

 Eagles. 



Excepting the Hoang-ho valley, we at times met with this species in 

 Kan-su, and during spring and autumn observed it also about Koko-nor. 



This bird departs for the winter, and returns again in March. I believe 

 I observed it in the vicinity of Urgey in September 1873. 



13. Falco hendersoni, Hume. Socol Hendersona, 



Falco hendersoni, Henderson & Hume, Lahore to Yarkand^ pi. i. 



The various stages of plumage, according to age and local varieties, make 

 it very difficult to distinguish the different species of Falcons — so much so, 

 that even the best ornithologists differ in this respect in their opinions. To 

 one of such disputed species belongs Falco sacer, which forms several varieties 

 in Eastern Europe and throughout Asia. In the region of our travels we did 

 not observe (or, at least, did not obtain) the true Falco sacer, Schl., which is 

 so beautifully figured by Schlegel in his ' Traite de Fauconnerie,' pi. v., and 

 by Gould in his ' Birds of Asia,' part xx. Everywhere we found only the 

 species described by Hume, in ' Lahore to Yarkand,' under the name of Falco 

 hendersoni. 



We obtained only four specimens (two males and two females), of which 

 three (two males and one female) completely correspond with Hume's 

 description, with only insignificant differences. The second female, which is 

 rather younger than the three former specimens (this is to be distinguished 

 by the blue, and not yellow legs), differs from them by the absence of a fully 

 striped tail, as only incomplete reddish-yellow bands are perceptible on the 

 inner webs of the tail-feathers, whilst the outer webs are marked with spots 

 of the same colour as the bands. Again, the yellow streaks of the female 

 F. hendersoni are replaced in the present specimen by spots of the same colour. 

 The breast is pied, on account of the large dark brown spots, just like the 



