EASTERN NIGHTHAWK 213 



millimeters. The largest egg of the series measured 33.53 by 22.86 

 and the smallest 27.68 by 20.57 millimeters. The average capacity 

 of nighthawk eggs, accoi'ding to Walter Hoxie (1887), is 0.448 

 cubic inch. 



The eggs do not necessarily remain in the position in which they 

 are first laid, especially when the nesting site is on a comparatively 

 level surface such as that provided by graveled roofs. During the 

 period of incubation of two nests under daily observation, the eggs 

 were gradually moved for a distance of 5 to 6 feet. This shift in 

 position comes about by the habit of the female pulling or pushing 

 the eggs under her breast, thus moving them a short distance each 

 time she settled on the eggs. As the direction of the bird's ap- 

 proach was more or less constant, the eggs were moved in the same 

 general direction. This resulted in a distinct trail being formed, 

 giving an appearance that one would expect to see if a giant snail 

 had traveled over the graveled surface and forced the larger pebbles 

 to one side. B. H. Warren (1890) writes that the eggs of a night- 

 hawk in one instance were moved 200 feet by the bird, which car- 

 ried them in her mouth. I have never been able to verify this ex- 

 traordinary behavior of a nighthawk transporting an object as large 

 as an egg in its mouth. 



The following experiment is of interest as it suggests an interpre- 

 tation of the manner in which a nighthawk locates its eggs. One 

 evening when the female nighthawk was away feeding I moved the 

 eggs to a place on the graveled roof about 6 feet from their original 

 position. When the bird returned she alighted in the accustomed 

 place and waddled up to the spot where she had left the eggs. No 

 eggs being there, she went by a few inches, turned around, and re- 

 crossed the spot. This was repeated several times, and finally much 

 bewildered she flew away. The eggs were in plain view yet were 

 not discovered. Fearing she might desert her nest, I returned the 

 eggs. In about 10 minutes the female returned, alighted in the usual 

 position and without hesitation went directly to the eggs. This 

 experiment was repeated on this and other birds with essentially the 

 same results. It is evident that some factor such as a hypothetical 

 sense of location or orientation is important, whereas sight plays a 

 minor role for the nighthawk in locating its eggs. The same factor 

 is probably important to the nighthawk in finding its way over thou- 

 sands of miles during migration and its ability to arrive punctually 

 not only in the same State and the same town but to the identical 

 nesting site. 



Incubation. — Both the male and female have been reported as 

 sharing the duties of incubation. George H. Selleck (1916) states 

 that the male nighthawk incubated the eggs during the daytime, 



