524 Field Museum of Natural History — Zoology, Vol. IX. 



Adult female: Similar, but without white tail band, and the throat, 

 tawny instead of white. 



Length, about 9; wing, 8; tail, 4.55; bill, .25. 



The Nighthawk is a common summer resident throughout Illi- 

 nois and Wisconsin, arriving in May and leaving again in September. 

 As soon as the sun goes down, it may be observed flying about in 

 pursuit of insects, uttering at frequent intervals a loud, harsh " peei, " 

 the cry being immediately preceded by two or three hurried strokes 

 of the wings. During the mating season the male makes a peculiar 

 "booming" sound preceded by a downward' rush or drop from a 

 considerable height. 



The majority breed in June and July. The eggs are two in number 

 and are deposited on the ground or flat rock, occasionally on the roof 

 of a house, without any attempt at a nest. They are dull white, 

 speckled and marked with pale brownish gray, and measure about 

 1. 18 X .85 inches. 



200a. Chordeiles virginianus sennetti (Coues). 

 Sennett's Nighthawk. 



Distr.: Great Plains region, from Texas to the Saskatchewan. 



Sennett's Nighthawk differs from the eastern form in having the 

 upper parts paler and the under parts showing more white. Most of 

 the specimens of the Western Nighthawk, C. v. henryi, which have 

 been recorded as taken in Illinois and Wisconsin, are probably sennetti, 

 although the variation in plumage is such that individuals occur 

 which might be referable to either form. The range of the Western 

 Nighthawk, C. v. henryi, is supposed to be from the Rocky Mountains 

 to the Pacific Ocean, but prior to the year 1888 its range extended to 

 Illinois, as the "plains" form, now known as sennetti, had not been 

 recognized as separable from it. 



In 1875 Nelson found what he considered to be C. V. henryi breed- 

 ing in considerable numbers among the sand hills near Waukegan 

 (111.), but Ridgway (Cat. Bds. 111. 1881) states they were "merely 

 somewhat pale examples of the eastern bird." 



The late Captain Charles Bendire gives henryi as the prevailing 

 form throughout the prairie regions of northern and central Illinois 

 (Life Hist. Am. Bds., 1895, p. 168) but as he does not recognize sen- 

 netti, the statement is open to question. 



Kumlien and HoUister give henryi as occurring in Wisconsin, stat- 

 ing that there were three specimens in the Kumlien collection, one 

 of which was sent to Dr. Coues for identification and pronounced 

 typical henryi, but at that time sennetti was not recognized. 



