350 P RED AT I ON 



densities of chicks as compared with the check unit are not entirely clear. A few, however, 

 may be suggested. In 1931. for example, the density of the breeding population on the check 

 area was higher than on the other, thereby tending to offset the greater nest loss. In 1932 

 there was some indication that renesting accomplished a similar result. .Again in 1935 grouse 

 were considerably more plentiful in the spring on the check area which may he traced to the 

 lack of effectiveness of control in preventing a high adult mortality on the test |)l()t during the 

 preceding winter. 



But even densities at hatching time are not indicative because during two of the four vears 

 brood losses were higher on the controlled area than on the check area. In 1931 a relatively 

 larger number of chicks on the managed tract suffered a lower mortality and produced a 

 greater abundance in the fall. In 1935 the reverse was true on the unit where selective con- 

 trol was practiced. In 1932 and 1934 both June and September densities as well as brood 

 losses were very nearly the same on both areas. 



It will be noted that the greatest apparent effectiveness occurred at a time when the general 

 population le\el was low and rising. The suggestion has been made that lower brood densities 

 may be subje<l to lower losses. While, other things being equal, there may be some truth to 

 this during the same season, it certainly does not apply when different vears are involved. For 

 example in 1931 and 1935 when the greatest differences in mortality at this time were recorded 

 the higher loss occurred on the area when the chicks were less numerous. Therefore, one can- 

 not conclude from these data that it is futile to attempt to produce increased fall surpluses 

 among high populations. 



Unquestionably, these experiments did not result in a markedly greater abundance of grouse 

 on the areas from which predators were removed in relation to the check areas used. But 

 this does not necessarily mean that they were not effective. Hather. it seems likely that the 

 method of trying to judge such effectiveness by comparing two ]jliits i> inadequate for that 

 ])urp()se. On the other hand there is a strong probabilit\ that the resultant fall density on 

 the managed tracts themselves was greater than it would have been otherwise. .Assuming 

 the same brood mortality would have taken place anyway, the increased nest survival could 

 have no other result. And. after all. that is what the game manager is interested in. 



Turning to the question of progressively increasing the breeding population through pre- 

 dator control the data are more clear. Outstanding is the record* of the covert which held 

 an average of a grouse to 2.5 acres in the fall of 1934. Incidentally, tliis high level was 

 reached in spite of a normal number of predators. On this unit, as well as on others in sub- 

 sequent years, the grouse soon reduced their own density 1>\ (lis|>crsing a portion of the sur- 

 plus'^ to less well populated surrounding coverts. Following this, in spile of efforts to ram- 

 plelely control predators, the coincident influx of these species was suniciciit In cause a high 

 overwinter loss just the same. Neither were these practices successful in the olln-r trials 

 undertaken, particularly that on \ ali nur Island. 



True, if complete elimination of prcdation were actualK accomplished. sur\i\al unnid at 

 first be greatly increased. That it would last long before being limited in some other way is 

 highly improbabli'. Furthermore, control of such an inlcrisilN would seldom, if ever, be 

 feasible. Thus the principal value of this type of management seems largely restricted to 

 the reduction of nest mortality and then only on areas where the hunting pressure is great 

 enough to utilize any additional surpluses created. Furthermore, these data indicate that 

 control of foxes and weasels alone can be effective for the latter |)urpose in habitats similar 

 to those studied by the Investigation. 



* Spr iliHrllKHinn <t{ llir KntllltH Durinic Ailutl Prriod. p. 317. 

 A Such movempnlt ■rrm ti> involve bir»i« of itir ypar mainlv. 



