Mr. R. B. Sharpe's Catalogue of Accipitres. 417 



The great rarity in Northern India of Falcons in the 

 " milvipes" plumage, and the comparative frequency of 

 those in the ordinary " saker " dress, can, if both are 

 referable to the same species, only be accounted for by the 

 known fact that amongst some birds of prey immature indivi- 

 duals are usually more vagrant in their migrations than those 

 that are older. As a familiar instance of this I may mention 

 Archibuteo layopus, a species that in its first yearns plumage 

 is a frequent and often an abundant autumnal migrant to 

 Great Britain, whilst its occurrence in this country in its 

 most adult dress is an exceptional phenomenon of very great 

 rarity. So again, the autumnal migration oi Pernis apivarus 

 to our shores is always composed of young birds, the old 

 birds never appearing at that season, though some few in 

 adult plumage visit us in spring. 



The differences, whether specific or not, which exist between 

 G. saker and G. milvipes have a curious parallel in the 

 Gennaia Falcons of North America, which are thus divided 

 and defined by Mr. Ridgway'^ : — " Falco lanarius, var. poly- 

 agrus ; adult, above with obscure transverse spots of bluish ; 

 young, above with feathers bordered with rusty. Hab. 

 Western division of North America, eastward to Illinois, 

 Oregon to Lower California and Texas. 



" Falco lanarius, var. mexicanus : above uniform dark 

 brown with a faint plumbeous cast, the feathers without trace 

 of light or rusty edges, outer web of tail-feathers without 

 trace of light spots. Hab. Mexico." 



It would seem, however, that the two type specimens 

 of Lichtenstein's Falco mexicanus which are preserved at 

 Berlin, agree better with the phase of plumage which Mr. 

 Ridgway refers to F. pohjagrus than with that which he 

 refers to F. mexicanus ; for Professor Schlegel, who describes 

 these two specimens in his Museum d'Hist. Nat. des Pays- 

 Bas, vol. i. Falcones, p. 18, there says of them, " Queue avec 

 unedouzaine de bandes peu distinctes et composees detaches 

 d'un roux pale. Le male adulte . . . plumes de la tete et 



* Vide Baird, Brewer, and Kidgway, ' Land Birds of North America/ 

 vol. iii. pp. 109 and 124, 



2h 2 



