304 The Ruffed Grouse 



disastrous. While the immediate causes of death of these chicks re- 

 main obscure, the relationship of high population density to poor 

 recovery, and vice versa, is probably the guiding consideration. 



The normal curve of infant loss is steep during the first month 

 of life, levels off considerably during the second month, and then 

 drops a little more abruptly for a time in the third month (see 

 Fig. 15 ) . The causes of the early season losses are somewhat obscure. 

 Certain facts are quite clear, and these help to delimit the prob- 



GROUSE CHICKS LOST 



80 



- 20 



June 1 June 15 July 1 July 15 Aug. 1 Aug. 15 Sept. 1 



SUMMER GROWINGUP PERIOD 



Fig. 15. Normal Grouse Infant Mortality Curve June to September 



lem. Predation is of little significance at this season. Diseases and 

 parasitic infestations apparently are not of great significance in nor- 

 mal years. And man has little direct effect on brood survival. 



When a mother grouse brings off an average brood of about ten 

 chicks she has a big problem of family control on her hands. Ten 

 active little birds are no simple group to keep well fed, brooded, and 

 husbanded together. In the first place, there will be considerable 

 variability in the vitality of the individual youngsters. Even as with 

 us mortals, some grouse will be born weaker than others. These 



