STERCORAEIUS PARASITICUS, PARASITIC JAEGER. 613 



region, and whole upper parts, as in the adnlt. The under parts white (as in the 

 adult), but clouded everywhere with dusky patches, most marked across the breast, on 

 the sides, the flanks, and under tail coverts, and leaving the middle of the belly and 

 throat nearly pure. Varying degrees of this dusky nnbilatiou approach in some ispeci- 

 mens nearly to the uniform dusky below characterized ; in others fade almost into the 

 pure white of the adult, connecting the two ages perfectly. The tarsi of the most 

 dusky specimens have small yellow blotches ; the others not. 



Dusky stafje (No. 20362). — With the size and proportions of the adult. Wholly deep 

 dusky; darker and more plumbeous superiorly; lighter, and with a fuliginous tinge, 

 inferiorly; the pileum quite black; the latero-uuchal region yellow; the remiges and 

 rectrice^ quite black ; feet black. 



Immature (No. 18652). — Size and general proportions nearly those of the adult. Bill 

 and cere perfectly formed ; feet mostly black, but with some yellow blotches. The 

 upper parts are unadulterated with any rufous bars ; the deep brownish-black pileum 

 has appeared, and the sides of the neck have obtained their yellow shade, which con- 

 trasts conspicuously with the fuliginous back-ground. Evidences of immaturity, 

 however, are found on the under parts, where the dark color is mixed with the illy- 

 defined transverse bars of ochraceous. Rufous is also found at the bend of the wing 

 and on the under wing and tail coverts. The primaries are still whitish at the out- 

 side, as are also the rectrices. The central rectrices project 2^ inches, and have the 

 tapering form of those of the adults. 



Yomujer (No. 2754). — The juvenility of the specimen is attested by its small size, 

 delicate bill and feet, little projection of the central rectrices, general molliisilose con- 

 dition of plumage, &c. The rufous of the veiy young bird, instead of giving way 

 everywhere to dusky, yields to this color only on the upper jiaits and crown ; on the 

 sides of the head, neck, and the Avhole under parts, whitish beiug the predominating 

 color ; the continuity of this last beiug interrupted by indistinctly marked dusky bars. 

 The yellow of the sides of the neck has not yet ai)peared. There is the same white 

 space on the bases of the wings and tail that exists on the very young. The central tail 

 feathers only project about 2% inches. 



Young-of-ihe-year in Angusi. — Size considerably less than that of the adult, form every 

 way more delicate. Wings more than an inch shorter; bill and feet much slenderer 

 and weaker. Bill in some specimens light bluish-horn ; in others greenish-olive, the 

 terminal portion brownish-black. Tarsi and greater part of the toes yellow. The 

 bird is everywhere rayed and barred with rufous and brownish-black. On the head 

 and neck the rufous has a very light ochraceous tinge, and is by far the predominating 

 color, dark only appearing as a delicate line along the shaft of each feather. There is 

 an aggregation of the l)rown into a spot at the anterior canthus of the eye. Proceed- 

 ing down the ueck to the back, the longitudinal lines become larger, and gradually 

 spread wider and wider, until between the shoulders they occupy the whole of each 

 feather, except a narrow border of rufous, which latter is of a detqier tiut than on the 

 head. Passing down the throat to the breast, the rufous becomes decidedly lighter — 

 almost whitish — while the brown, which on the throat exists ouly as a light longitud- 

 inal line, changes on each feather to transverse bars of about equal width with the 

 light rufous bars with which it alternates. This i)attein i)revails over the whole under 

 I^arts, the transverse bands being broadest on the Ihmks and under tail and wing 

 coverts, narrowest in the middle of the belly. The primaries are brownish-black, nar- 

 rowly tipped with rufous, tlierr shafts yellowish, their inner webs fading basally into 

 wliite. The tail lias the same coloration as the wings. The central feathers project 

 about three-fourths of an inch. 



In tliis .species we can favorably study the changes of plumage which are character- 

 istic of all the species. I am enabled by the extensive series at my command to trace 

 the various stages of the present sjiecies. 



Beginning witii the stage last described, that of the young-of-the-year, we find it 

 characterized essentially by the presence of rufaux or orltracrous, disposed chielly in 

 trdunnrnc bars, or spots, or waves, which alternate with similarly shaped dusky or 

 brownish-black markings. The birds are iiincli smaller than the adults, the bill and 

 feet more delicate. As ihe bird grows older the bill and feet become .stouter, the cere 

 better developed, and the rufous everywhere grows first lighter and then more re- 

 stricted, giving way ti> an encroachment of the blackish. This increase of the darker 

 color is parliculaily rapid on the upper parts, which become uniformly dusky before 

 the under parts ilo. When this has taken place tlu' lurd is in the plumage of No. Ic652. 

 The tarsi and feet are still mostly yellow; there is still the white space at the bases of 

 the primaries; the central rectrices still have only a partial development. By the 

 tinie the rufous mentioned in No. 18652 as existing on the alar coverts, under parts, 

 &c., liJis entirely di.sappeared, the bird has become half-grown, ami is now in tliat 

 peculiar state of plumage charaeteiized in the description of No. 2t):<(;2. This is a defi- 

 nite stage. But .someYew specimens in the collection do not .seem to pas.s througli tliia 

 dusky eiioeh in arriving at maturity. The rufous yields to black only on the upper 

 parts; on the under parts the blackish bars us well as the rufous ouos become changed 



