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Order CAPRIMULGIFORMES 



Family STEATORNITHIDAE : Oilbirds ; Guacharos 



The one peculiar species of this family, while grouped in an order 

 with the typical goatsuckers, is so different in its anatomy that it is 

 segregated in a separate suborder Steatornithes. The large, strong 

 bill, with its elongated, curved tip, and toothed margin on the maxilla, 

 and the firm body plumage are striking external differences from the 

 related families of the order. Equally striking is the manner of life 

 in which the oilbird nests in colonies in the shelter of caverns. Where 

 these are dark, the birds in flight are guided by a system of acoustic 

 orientation in which they produce sharp, clicking sounds. The slender 

 vibrissae that project forward from the base of the maxilla perhaps 

 may serve some tactile sense. This is suggested as the longer ones, 

 10 to 12 in number on either side, measuring 50 mm. or slightly more 

 when complete, often are shorter so that they seem subject to abrasive 

 wear. 



STEATORNIS CARIPENSIS Humboldt: Oilbird, Guacharo 



Figure 30 



Steatornis caripensis Humboldt, Bull. Sci. Soc. Philom. Paris, 1817, p. 52. 

 (Caverns of Caripe, Monagas, Venezuela.) 



Body form of a large goatsucker, but with powerful bill ; rusty 

 brown, spotted with white on under surface, wings and head. 



Description. — Length 410-460 mm. Adult male, above rusty brown, 

 paler, more buffy on secondaries and inner primaries, which, with 

 their coverts, are barred and faintly mottled with dull slate ; tail with 

 narrow bars and numerous dots of sooty black ; lower surface, includ- 

 ing under wing coverts, pale rusty ; under surface, crown, and middle 

 wing coverts spotted with white, each spot bordered narrowly with 

 sooty black ; outer primaries and outer tail feathers spotted with white 

 on outer webs ; edge of wing white. 



Adult female somewhat paler and more rufous. 



Immature, sooty brown on crown, back, and rump; wings and tail 

 dark brown, except the uppermost lesser coverts, which are rusty, 

 edged with white ; darker, slaty brown below ; spotted with white as 

 in adult. 



Iris dull yellow ; bill light reddish brown ; tarsi and feet light reddish 

 brown. 



Measurements. — Males (10 from Ecuador and Trinidad), wing 



