Productivity and Populations 293 



does indicate, however, tliat the nest density is very close to a 

 one-to-two correlation with breeding bird density. 



Individual distances between nests has varied greatly. In one 

 instance, two nests were only twenty-five feet apart, but only one 

 nest was in use when observed, and hence both may have been made 

 by the one bird. In another instance, two females nested seventy- 

 five feet apart. In still another instance, two females were incubat- 

 ing concurrently in nests just fifty feet apart. In other years the 

 closest nests were from one hundred feet to over three hundred 

 feet apart. As an average, of course, nests are much farther apart, 

 even though they are relatively concentrated in the outer fringe 

 of the woodlands and brush areas. Most nests are more than six 

 hundred feet from the next nearest grouse nest even when the 

 density is high. 



Densities of Grouse Broods. The density of grouse broods is lower 

 than the nest density by the proportion of nest failure that is not 

 adjusted by successful renesting. In comparison with the rather 

 incomplete determination of nest density, the brood statistics can 

 be very accurate, based as they are on observations taken over a 

 whole summer period. 



In most years, the density will range between forty and seventy 

 acres of cover per brood in good range. 



The number of broods seems to vary less by a notable degree than 

 either the density of grown grouse or the survival of the young birds 

 in these broods. There appears to be somewhat of a correlation be- 

 tween nesting success, i.e., number of broods, and breeding density: 

 the greater the breeding density, the lower the nesting success ratio; 

 and the lower the breeding density (within optimum bounds) the 

 higher is likely to be the success ratio. Thus an equalizing efi^ect 

 tends to stabihze the number of broods on an area. 



Somewhat correlated with brood densities is the area needed by 

 broods. Since grouse brood territories overlap, in contrast to breed- 

 ing territories, the territorial requirement does not in itself limit the 

 brood density. The area actually used by broods, as indicated by 

 location of a series of observations, varies greatly. Of considerable 

 significance is the minimum area of cover that may support a grouse 

 brood. Evidence indicates this to be in the neighborhood of nine 

 acres, or slighdy less. I know one isolated covert of nine acres that 



