330 PREDATION 



almost invariably is absent at this season. In migration these birds pass through in moder- 

 ate numbers and a few remain to breed, at which time from one to two pairs per square 

 mile have been observed. Usually the latter species has been more plentiful. 



Among the predators of lesser importance to grouse on this area limited numbers of mink 

 (Mustela vison). opossum and barred owls fStrix van'a) are present the year around. Now 

 and then wandering house cats are encountered. During the winter goshawks a|)pear irreg- 

 ularly and snowy owls more rarelv. The Buteo hawks (red-tailed Buteo horealis. red-shoul- 

 dered B. Uneatiis. rough-legged B. lapopus s. johanni.s. and broad-winged B. plalvpterus) and 

 the marsh hawk (Circus hudsonius) are common in migration and a few breed. Crows (Cor- 

 vus hrachyrhynchos) are moderately numerous particularly in spring. 



In correlating these figures with the grouse population winter densities are most comparable. 

 For the years 1931-32 and 1933-34, when the above data for resident predators were obtained, 

 the mean winter density of grouse was 28 per square mile*. The corresponding figure for 

 the total period of study was the same although it has varied from 18 to 10 per square mile. 



To summarize it may be estimated that the ratio of grouse to their principal predators in 

 this area has averaged roughly as follows during the winter*^: 



grouse 28 per square mile 



fox 4 per square mile 



weasel 10 per square mile 



skunk 8 per square mile 



raccoon 4 per square mile 



great horned owl 5 per square mile 



Yet one must remember that these densities were by no means uniform over the tract and 

 that minor changes from year to year have constantly taken place. 



Obviously variations in this pattern in other localities over the State arc endless but spe- 

 cific data are largely lacking. Observations on the Adirondack area, however, indicate greater 

 populations of weasels and barred owls; about the same of foxes* and raccoons: and smaller 

 numbers of skunks, while great horned owls have not been obserxed. Cooper's and sharp- 

 shinned hawks are slightly more numerous there during the summer. Goshawks are more fre- 

 quent and breed sparingly in the region. The most common hawk is the broad-wing which 

 seems to be negligible as a grouse predator. Crows are much less abundant. Occasional bob- 

 cats (Lynx rufus) occur. 



Winter grouse densities on this area have averaged 31 birds per square mile, ranging from 

 17 to 39 per square mile in different years, .^t first glance this appears very similar to con- 

 ditions on Coniiccticul Hill. Considering that oidy about half of the latter area is grouse cover, 

 however, while all of liie other falls in this category, it becomes evident that the actual pop- 

 ulation density was much lower in the continuous coverts of the northern region. 



VlILNERABII,ITY 



It is logical to sujipose that birds atid animals which are crippled or suffering from disease 

 are more easily captured iiy pre<lators than those in the same habitat which are not so handi- 

 capped. In the experience of the Investigatioti. however, the occurrence of grouse in such 

 condition has been low^ In this connection (>l>servalions at the Research Center indicate that 



* The trouifl cover on ihit area occupies roughly half the total acreage, 

 A The akunk and rarroon hibernate For coniulerable pcriixls at ihii aeaaon. 

 t All fnxea on this area were of the red speriro. 

 t On the areas most intensively studied shooting has not been permitted. 



