348 P RED AT I ON 



TABLK 18. COMPARISON OF ADULT MORTALITY ON AREA SUBJECTED TO PREDATOR 

 CONTROL AND ON CHECK AREA— CONNECTICUT HILL-IOIU-IQSS 



♦Different method of computation used, see text. 

 ^Cotktrul liiiiitnl to foxes and weasels. 



The figures given in this table represent the differential from September to September of 

 the years indicated. In computing them complete census data have been available except 

 for the fall of 1933 when only a portion of the area was surveyed. It has been necessary, 

 therefore, to use some other means of evaluating the populations at this time on the two sub- 

 areas. Since the whole tract was surveyed during the winter and sprinp census estimates were 

 present for May 31, 1934. By adding to these the known mortality in dead birds actually 

 picked u|) conservative figures for the preceding fall have been secured. While the ratio 

 between these is considered representative it must be remembered that lioth are low with respect 

 to the actual degree of loss which took place. 



It is interesting to consider these data. If predation is, as it appears to be. the major cause 

 of mortality at this season, then it would seem logical that control of predators should 

 increase survival. Yet the trials conducted have not had such an effect. Certain relation- 

 ships have been noted, however, which may account, in part at least, for the results. 



In no instance has the differential between losses on the trial and on the check portions been 

 great regardless of which was higher. Even in 1933-31 llu- difference cannot be considered 

 important since, as pointed out above, the actual mortality in each case was some 20 per 

 cent more. It is sigiiifuant, too, that this similarity extends to 1934-35 when only foxes and 

 weasels were controlled. 



On Connecticut Hill the great horned owl has been the outstanding predator of adult grouse. 

 In 1934-3.S it was not affected except in the one covert where com|)lete control was under- 

 taken. A possible inference from this is that the operations carried on during the other years 

 were unsuccessful with respect to this species, allowing il Ici niainlaiM its domination of the 

 situation. That the number of these owls taken may not have acconiplished the desired reduc- 

 tion invoKcs the fact that the great majority of those present on this area during the winter 

 are transients. Under such conditions replacements would constant!) lend to offset the effect 

 of control. 



Another influence which may have been involved stems from the fact that the two plots 

 were adjacent as well as being surrounded by grouse coverts. Thus the "spring shuffle"* each 

 yar would liml In have equalized both populaticms. 



Data from the unit on which a fall density of a grouse to 2.5 acres of cover was reached in 

 1934 indicate several things. In the first place dispersal to surrounding coverts as a result 

 of the bird's intolerance of crowding took place innnediatel\. Beyond this, in spite of an 

 intensive attempt to completely eliminate predators iri(li\ iclual> from adjacent territory quickly 



* See Chapter V, |i. 256. 



