NTCTIDEOMUS.— CHORDEILES. 395 



size. The bird from the Lower Eio Grande Valley has been recently separated by 

 Mr. Sennett as Nyctidromus albicollis merrilli^'^, and this course was endorsed by 

 Mr. Hartert ^^. But on re-examining the large series of specimens in the British 

 Museum we do not think such a distinction can be maintained. Rio Grande birds are, 

 perhaps, rather greyer on the upper plumage, especially on the head, and they are 

 rather large ; but they can be matched almost exactly by birds from many other places. 

 Moreover, the range of this species is no doubt quite continuous, and the Rio Grande 

 birds only represent it at its extreme northern boundary. 



Nyctidrom,us albicollis is by far the commonest species of Goatsucker in Mexico and 

 Central America. Its distribution is nearly universal in the low-lying districts up to 

 an elevation of about 5000 feet in the mountains. It affects the more open thinly 

 wooded districts rather than the dense forests, though it occurs in open glades. 

 After nightfall its presence is made known to the traveller by its habit of flitting in 

 front of the horseman and settling from time to time in the middle of the track. Its 

 familiar note, which resembles the words "Who are you]" may be heard throughout 

 the night. 



This bird makes no nest, but lays its two eggs on the bare ground. These are of a 

 pinkish-buff colour with darker spots. Salvin found an egg on bare ground about the 

 middle of May near Obispo Station on the Panama Railway, close to the edge of the 

 forest ; and Mr. Merrill also took a nest near Hidalgo in Southern Texas on 15th 

 May ; but Mr. Sennett met with one in the same district as early as 20th April. 



b. Rictus glaher, setts elongatis nullis. 



CHORDEILES. 



Chordeiles, Swainson, Fauna Bor.-Am. ii. p. 496 (1831); Hartert^ Cat. Birds Brit. Mus. xvi. 

 p. 609. 



Chordeiles is the only Central-American genus of Caprimulgidse which is destitute of 

 the strong, long, rictal bristles so characteristic of the foregoing genera. Three other 

 genera, Nyctiproqne, Podager, and Lurocalis, all of them belonging to South America, 

 have the same character ; and two Old World forms, Lyncornis and Eurystopodus, are 

 also destitute of rictal bristles. Amongst other characters distinguishing Chordeiles 

 from Central- American forms is the forked tail. 



Of the four definite species recognized by Mr. Hartert, divisible into nine imperfectly 

 segregated forms, two only occur within our limits. One of these is the well-known 

 C. virginianus and its modification C. henryi, and the other, C. texensis, a, northern 

 form of the South-American C. acutipennis. Both, after the usual habit of their kind, 

 are probably more or less migratory. 



50* 



