GREATER PRAIRIE CHICKEN 249 



unusual disturbance about the nest may delay the start of incuba- 

 tion for several days, thus making the determination of the incuba- 

 tion period under normal conditions in the field a difficult task. This 

 accounts for discrepancies in the determinations made by different 

 observers, which vary from 21 to 28 days as the incubation period for 

 the prairie chicken. In the case of a nest under continuous observa- 

 tion, incubation began on May 22 and the eggs hatched on June 14, 

 establishing an incubation record of 23 days. The incubation period 

 for the eggs of the closely related heath hen, as determined by Dr. 

 George W. Field, is 24 days. 



After incubation is started the prairie chicken, under normal con- 

 ditions, remains faithful to her duties through the vicissitudes of 

 weather, storms, and dangers of attacks from enemies. Unless 

 flushed from the nest she leaves only for very short intervals to feed, 

 usually at dawn or late in the afternoon about sunset, times when the 

 eggs will not be exposed to extreme heat. Excessive heat is very 

 destructive to the embryos, and great care must be exercised in flush- 

 ing birds away from nests in which the protecting vegetation has 

 been removed for purposes of photography. The birds that left the 

 nest normally slipped off it quietly and made no attempt to cover the 

 eggs, as they did during the laying period when the nest was aban- 

 doned for a longer time. One bird, after nervously surveying her 

 surroundings, sneaked off the nest and walked briskly in a crouched 

 position until she had gone several yards from the nest. There she 

 hesitated, elevated her head, and looked about as if to determine 

 whether her movements had attracted any attention. She then casu- 

 ally nipped at the grasses as she walked along, and finally when 

 about 25 yards away from the nest she arose with a loud whir of 

 wings and disappeared in the scrub pines, where she probably found 

 at least a part of her meal. After an absence of half an hour she 

 flew into view, circled the nest, and alighted in the tall grass 15 to 

 30 yards away from the nest. At first she crouched in the grass 

 completely concealed from view, but after being assured all was well 

 she walked along stealthily though not directly toward the nest. It 

 was not possible to keep her in view at all times, but now and then 

 she would come to an open place and from this vantage point more 

 carefully scrutinize the surroundings. Sometimes she completely en- 

 circled the nest and blind with a wide radius and frequently retraced 

 her steps to make a careful inspection in order to satisfy herself that 

 no spying enemy was near. One could not be sure whether this be- 

 havior was prompted by apprehension of harm to herself, fear of 

 revealing the presence of the nest, or to both. After these maneu- 

 vers, which usually took about 20 minutes, were completed, she ap- 

 parently was assured, and then without hesitation she walked quickly 



