638 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



Two of the plumages in the adult stage seem to fairly correlate with 

 the sex of the birds, the adult male with clear slate color prevailing, the 

 adult female with a more or less rusty red back and otherwise much like 

 the male ; the third phase is that of adult birds that are nearly similar in 

 appearance, and while having the rusty back of the oldest females, are 

 more heavily barred and often rusty beneath ; in this dress the sexes are 

 alike or nearly alike, allowing for individual variation. The fourth 

 plumage presented by these birds correlates strictly with age. Of the 

 fifth, or dimorphic form, the material at present to hand does not warrant 

 generalization. 



These five presentations of this hawk are given below in all detail and 

 as field notes made by the naturalists from Princeton, who collected most 

 of the series, are available, we are in position to have precise ideas as to 

 the appearance of Bideo erythronotus. 



General description. 



Size. — No. 8307, adult male. P. U. O. C, Rio Chico, Patagonia, 10 

 March, 1898. 



Total length, about 20.50 inches. 

 Wing, 14.12 inches. 



Fig. 323. 



Biiteo crytJironotns. Adult male. P. U. O. C. 8307. About one-half natural size. 



Culmen, 1.2 inches. 



Tail, 8.0 inches. 



Tarsus, 3.25 inches. 



Three males in the perfectly adult plumage, all from Patagonia, do not 

 differ much in measurements; the longest wing is just under 15 inches 

 and the smallest is given above. These three birds are of almost exactly 

 the same length. 



Color. — Adult male cited above. 



