THE NIGHTHAWK. 167 



Only two eggs are laid to a set (on alternate days) and incubation begins 

 with the first one deposited. The shell is strong, close-grained, and generally 

 moderately glossy; in shape they vary from elliptical ovate to elliptical oval, the 

 former prevailing in the majority, one end being a trifle smaller than the other. 

 Their ground color is quite variable, and ranges from a pale creamy white 

 through different shades of cream, olive buff, and olive gray, and the}' are pro- 

 fusely blotched and speckled with different shades of slate black, drab, smoke 

 and lilac gray, and tawny olive, mixed with lighter shades of pearl gray, lav- 

 ender, and plumbeous. In some specimens the markings are fine and uniform 

 in size, almost obscuring the ground color; in others they are less numerous, 

 but large and prominent. There is an endless variation in their markings. 

 Scarcely any two sets resemble each other closely, and I consider the egg of the 

 Nighthawk one of the most difficult ones known to me to describe satisfactorily. 



The average measurement of eighty-one specimens in the United States 

 National Museum collection is 29.97 by 21.84 millimetres, or 1.18 by 0.86 

 inches. The largest egg of this series measures 33.53 by 22.86 millimetres, or 

 1.32 by 0.90 inches; the smallest, 27.68 by 20.57 millimetres, or 1.09 by 0.81 

 inches. 



The type specimen, No. 9813 (PL 3, Fig. 1), from a set of two taken 

 near Dubuque, Iowa, on May 28, 1865, by the Messrs. Blackburn, represents one 

 of the larger and heavier marked specimens. No. 24968 (PI. 3, Fig. 2), Ralph 

 collection, from a set of two taken by Dr. William L. Ralph in Herkimer County, 

 New York, on June 24, 1891, represents a small specimen with an olive-gray 

 ground color and rather dark markings; while No. 20457 (PL 3, Fig. 3), like- 

 wise from a set of two, Bendire collection, was taken by the writer near Fort 

 Klamath Oregon, on July 6, 1882, and represents one of the lighter-colored 

 types. 



59. Chordeiles virginianus henryi (Cassin). 



WESTERN NIGHTHAWK. 



Chordeiles henryi Cassin, Illustrations of the Birds of California, Texas, etc., I, 1855, 233. 

 Chordeiles virginianus var. henryi Coues, Key, 1872, 181. 



(B 115, O 267a, E 357a, C 400, TJ 420a.) 



Geographical range: Western North America; north to central British Columbia 

 to about latitude 55° and through the prairie districts of southern Alberta, Assiniboia, and 

 western Manitoba; east in the United States to western Minnesota, Iowa, northern and 

 central Illinois, Kansas, the Indian Territory, western and southern Texas ; south over 

 the tabledauds of Mexico, and in winter through Central America, over the greater part 

 of South America to Patagonia. 



The Western Nighthawk, a lighter-colored subspecies than the preceding, is 

 a common summer resident throughout a considerable portion of western North 

 America, hut its range is likewise a rather irregular one. On the whole, it is 

 more of a prairie bird than the former, but it is by no means confined to the 

 plains alone; it appears to be equally at home on the more open, barren 



