AVES FALCONID>E. 575 



For many years, from the 2Oth of April, 1834, till the i6th of June, 

 1883 (when M. Lcbrun obtained a single bird on the Rio Gallegos) the 

 type collected by Darwin was the sole representative of this bird in any 

 collection. Both of these birds are adult and each is referred to below. 



The Naturalists of the Princeton Expeditions were so fortunate as to 

 discover localities where this must now be considered as at least a common 

 bird. In late May and during early June, 1896, Mr. Hatcher secured 

 specimens in the region about Rio Gallegos ; where M. Lebrun collected 

 his single bird in June, 1883. The particular points in this territory where 

 a stay was made at this time were Killik Aike and Guer Aike, both near 

 the mouth of the Rio Gallegos ; Killik Aike on the estuary and Guer Aike 

 on the river proper, some sixty miles from the coast. 



Mr. Hatcher writes in the Narrative: "There are three species of car- 

 rion hawks in southern Patagonia. These pertain to three different 

 genera, Polyborus tharus, Ibycter albigularis, and Milvago chimango. [An 

 additional species Ibycter megafapterus also occurs. W. E. D. S.] I 

 could not detect that they had any distinguishing names for the different 

 species, which, though of almost identical habits, were so unlike in color. 

 Although frequently seen mingled together and feeding from the same 

 carcass, it can not be said that such social relations were entirely har- 

 monious, since they indulged almost continuously in most spirited per- 

 sonal conflicts, though I cannot assert that such engagements were any 

 less frequent between individuals of the same species than between those 

 belonging to different species." (Narrative, Princeton Exped. p. 57, 1903. 

 Hatcher.) 



From the foregoing the conclusion must be drawn that Ibycter albogu- 

 laris was about as common as the rest of the carrion hawks which 

 abounded in this region, even though no large series of the birds was col- 

 lected. And the economy of the species, as would be expected, is so like 

 that of its congeners as to lead to no comment Of its breeding habits 

 thus far we know nothing, and its several phases of plumage, correlating 

 with age, for there are such plumages without doubt, have still to be 

 studied by future field workers. 



Mr. A. E. Colburn was conducting the work of the Princeton Expedi- 

 tions during the season of 1898 at a point on the headwaters of the Rio 

 Deseado, known as Arroyo Eke and later placed on the Hatcher map as 

 Arroyo Gio. During the last days of April the bird in question was 



