FIRST YEAR: 174 BREEDERS 

 1000 potential eggs Breeders 



Survivors, 105 



Overwinter loss, 8! 

 Hunter take, 38 — 



Brood loss, 337 



Apr-Sep loss, 24 



- — Hunter take, 26 



Overwinter loss, 54 



SECOND YEAR: 175 BREEDERS 



FIG. 15-1 Average life equation of a stabiliied ruffed grouse population in New York State (Bump ei al. 1947). 



tion on the age ratios of the hving population, pro- 

 vided it is stabilized ; or from data on a single cohort, 

 adequately identified, followed throughout its life's 

 span (Farner 1955). 



Curves of survival plotted from life tables may 

 be of three types (Pearl and Miner 1935, Deevey 

 1947). In type I, a cohort finds environmental con- 

 Factor respon- 



ditions ideal ; all members born at the same time, live 

 out the full physiological life span characteristic of 

 the species, and all die at about the same time. In 

 type II, the rate of mortality is fairly constant at all 

 age groups so that there is a more or less uniform 

 percentage decrease in the number that survive. Type 

 III shows extremely heavy mortality early in life, but 



Reproductivity and structure 213 



