252 BULLETIN 162, UNITED STATES NATIONAL MUSEUM 



The first eggs are pipped on about the twenty-second day after 

 incubation starts. The shell is slightly raised at the point on the 

 circumference between the blunt and pointed ends, but slightly 

 nearer the larger end. The embryo inside the egg can be heard to 

 " peep " at this time, an event that greatly excites the mother and 

 at once becomes a great stimulus in her behavior. It causes her to 

 reach under her breast feathers to turn the eggs every few minutes 

 and to exhibit a great deal of nervousness in her response to various 

 other stimuli. 



On the morning following the day on which the eggs are slightly 

 pipped, all the eggs destined to hatch are pipped. In those eggs 

 where there was but a slight elevation in the shell the day before, 

 there are now well-defined openings through which the tip of the 

 bill of the embryo can be clearly seen. At this stage the mother bird 

 may frequently roll the eggs with her body in addition to turning 

 them with her bill. I have even observed the old bird pick out bits 

 of shell from a pipped egg, as if attempting to facilitate the process 

 of hatching. After a few hours the calcareous shell is cracked for 

 its entire circumference, but the shell membrane may remain intact 

 for a longer time. The struggles of the young, however, soon fling 

 the cap open with a part of the shell membrane on one side serving 

 as a kind of hinge. After the embryo has kicked itself out of the 

 prison shell, the tension of the drying shell membrane pulls the cap 

 back in place and thus prevents the youngster from being cupped by 

 its own shell. 



The time of hatching of the various eggs of a set is remarkably 

 uniform, and in some instances the time elapsed from the time of 

 hatching of the first to the last egg is less than an hour. In cases 

 where incubation started before the last one or two eggs were laid, 

 the latter may be delayed, and in several cases under observation, 

 during the summer of 1930, they failed to hatch in time, and the con- 

 tained young were left behind when the brood left the nest. 



The precocious young of the prairie chicken are ready to leave the 

 nest as soon as their down is dry, and the mother bird often has 

 difficulty in preventing the first young from leaving the nest before 

 the last to hatch are prepared to go. The brood may leave in a few 

 hours after hatching, but if the hatching takes place late in the af- 

 ternoon the old bird, unless disturbed, will brood them on the nest 

 during the night, but leaves the next morning j ust as soon as the tem- 

 perature and weather conditions are suitable for the chicks to move. 

 The eggshells are never removed from the nest by the old bird. 



The chicks, as well as embryos in the eggs, are very sensitive to ex- 

 tremes of temperature. Young left exposed to the cool damp night 

 air will quickly perish, and brooding at such times is absolutely 



