Productivity and Populations 305 



weaknesses may arise from unequal incubation, excessive chilling 

 during embryonic development, through some accident of develop- 

 ment in the egg, or they may be carried through the egg from some 

 weakness in the mother. We have no proof for any of these hy- 

 potheses other than the inference that may be drawn by the elimina- 

 tion of other factors and by parallels with the known facts of do- 

 mestic animals. There is little question but that a considerable por- 

 tion of the early deaths of grouse chicks arises from these weeklings' 

 dropping by the wayside when diey fail to keep up with the travels 

 of the family. 



An interesting sidelight on grouse psychology is the reaction of 

 mother giouse to the size of their broods. Evidence gathered time 

 and again indicates that they have little cognizance of numbers. 

 Following a disturbance when the brood is flushed and dispersed, 

 the chicks reassemble at the call of the mother when the coast is 

 clear. If some of the birds fail to arrive with the majority, the brood 

 will go its way with no apparent concern on the part of the parent. 

 She seems to be quite satisfied as long as she still has some chicks 

 with her. It is apparent that this characteristic will result in the 

 abandonment and consequent loss of quite a few chicks. Accidents 

 of other types will occasionally result in losses: chicks that stray and 

 become lost, little ones that tumble into some cavity from which they 

 cannot escape, and otlier similar chances sometimes cause the death 

 of young grouse. 



Probably the most vital immediate cause of early brood losses is 

 the weather. Young grouse are not always able to withstand the 

 drenchings of a cold June thunderstorm or the chilling of an ab- 

 normally cold night. If well brooded during these emergencies little 

 trouble is likely to occur. But with many chicks to care for, the like- 

 lihood of some of them getting chilled or soaked is considerable. 

 As the size of the brood decreases the mother's ability adequately to 

 brood them in adverse weather improves and the chicks themselves 

 are more hardy as they grow older. Thus the losses from exposure 

 are usually over in the first few weeks. 



It must be recognized that these heavy losses to baby grouse soon 

 after hatching are a normal expectancy if they do not exceed about 

 thirty-five per cent in the first three weeks. But occasionally an ab- 

 normal combination of adverse weather in June or early July will 

 result in far greater losses. In 1935 a period of excessive rains in early 



