Productivity and Populations 287 



Sexual Relations. The ruflFed grouse breeds at the age of about ten 

 months. Practically all birds breed each year/ This matter has not 

 been checked perfectly since it is impossible to locate all grouse 

 nests on a sizable area, or to determine that every grouse has bred. 

 However, all the evidence indicates that a failure in the breeding 

 of grouse, at least in good grouse range, is rare. 



The species is promiscuous in its sexual relations, which fact helps 

 prevent mimated birds. Audubon (1856) recognized the species as 

 being polygamous while Baird, Brewer, and Ridgeway ( 1905 ) sug- 

 gested that both sexes were promiscuous. There is no doubt a 

 fairly high proportion of grouse that mate with only a single bird 

 in a breeding season but this is apparently more a matter of expe- 

 diency than character. 



A factor that tends to limit the breeding efficiency of the species 

 is the sexual-readiness cycle which occurs in both male and female, 

 and called "sexual rhythm" by Allen ( 1934 ) ( see page 30 ) . It ap- 

 parently works out very satisfactorily in nature since infertility is 

 very low, although it gives rise to serious problems with birds in 

 captivity. 



Size of Egg Clutches. The size of the egg clutch has been gener- 

 ally known for the ruffed grouse for well over a century. Wilson 

 (1812) recorded tlie range as from nine to fifteen, while Audubon 

 (1856) gave it as from five to twelve. Forbush (1929) gives the 

 general range as from seven to fourteen eggs with occasionally up 

 to sixteen or seventeen, and he notes one case of a grouse nest con- 

 taining twenty-three eggs. Smith (1921) also records a nest of 

 twenty-three eggs and notes that it was probably the product of 

 two hens. 



The average number of eggs per clutch for six hundred thirty-four 

 first nests ( that is, not including renests following a destroyed first 

 clutch) in New York from 1935 to 1941 was eleven and four tenths. 

 The commonest size was twelve eggs; the next commonest was 

 eleven eggs, and these two sizes made up over half the total. Nests 

 with nine, ten, thirteen or fourteen eggs made up most of the bal- 

 ance, although there were cases from three to twenty-four. Only 

 in one year was any number of eggs other than eleven or twelve 

 most prevalent; in that year there were more nests with thirteen 



^ King did not find this to be true in his Minnesota studies. 



