57^ PATAGONIAN EXPEDITIONS: ZOOLOGY. 



common here and Mr. Colburn obtained a series of four individuals, both 

 sexes being represented. All these additional birds, as well as a large 

 number seen, were in adult plumage. 



Arroyo Gio is over two hundred miles north of the Rio Gallegos country 

 and west of it; from the coast it is distant more than a hundred and 

 twenty miles in the foothills of the Cordillera ; these carrion hawks, hereto- 

 fore almost unknown, have a circumscribed distribution, so far as ascer- 

 tained, but are common where they occur. 



There is reason to believe that the immature plumage of Ibycter albogu- 

 laris closely resembles that of Ibycter megalopterus, but as this is as yet 

 hypothetical, the younger representatives of the species must remain for 

 the present undescribed. 



Darwin has to say of the type collected by him at Santa Cruz in April, 

 1845: "Mr. Gould, at the time of describing this species, entertained 

 some doubts whether it might not eventually prove to be the Phalcobcenus 

 montanus of D'Orbigny [=/. megalopterus\, in a state of change. I have 

 carefully compared it with the description of the P. montanus, and cer- 

 tainly, with the exception of the one great difference of M. albogularis 

 having a white breast, whilst that part in the P. montanus is black, the 

 points of resemblance are numerous and exceedingly close. The M. 

 albogularis, appears to be rather larger, and the proportional lengths of 

 the wing feathers are slightly different ; the cere and tarsi are not of so 

 bright a colour; the middle toe has fifteen scales on it instead of having 

 sixteen or seventeen. The black shades of the upper surface are pitchy, 

 instead of having an obscure metallic gloss, and the feathers of the 

 shoulders are terminated with brown, so as to form a collar, which is not 

 represented in the figure of P. montanus, given by M. D'Orbigny. 

 Although the main difference between the two birds is the colour of 

 their breasts, yet it must be observed, that in the M. albogularis there is 

 some indication of an incipient change from white to brown in the 

 plumage of that part. But as M. D'Orbigny, who was acquainted with 

 the young birds of P. montanus (of which he has given a figure), does 

 not mention so remarkable a modification in its plumage, as must take 

 place on the supposition of M. albogularis being an immature bird of 

 that species ; and as the geographical range of the two is so very different, 

 I am induced to consider them distinct. Moreover, on the plains of Santa 

 Cruz, I saw several birds, and they appeared to me similar in their colour- 



