ROLE OF PR ED AT I ON 323 



Predator Fluctuations 



Someone has said that the only constant quahty of life is change. All living organisms 

 continually fluctuate in numbers to a greater or lesser degree. Among wildlife such phe- 

 nomena have long been recognized. Many observers have commented on the marked periodic 

 abundance and scarcity of certain birds and animals. Perhaps the best-known in North 

 America pertain to the ruflfed grouse, the varying hare and the lemming (Lemmus trirnii- 

 cronatus). Among predators behavior of this kind has been reported in a number of species, 

 particularly the arctic fox ( Alopex lagopus) and the lynx (Lynx canadensis)'". 



Such fluctuations appear to be more pronounced among populations inhabiting the boreal 

 and arctic regions than in New York and other temperate sections. The reasons for this are 

 not entirely clear. Undoubtedly the difference in climate is important. One of the principal 

 necessities for sustaining life in any animal is the maintenance of body heat. When food be- 

 comes scarce this is more difficult where the axerage environmental temperature is lower. In 

 the North also the variety of food available to predators especially in the winter is less and. 

 during lows in their cycles, the numbers of small mammals, their staple, drop lower than 

 farther south. These and other less well understood influences contribute to the marked vari- 

 ations in survival reported. An outstanding example of the response of a predator to its food 

 supply is the relationship between the lynx and the varying hare in Canada''". 



It has been generally believed that these recurrent tides of abundance represent continent- 

 wide conditions. Recent evidence, however, points to a regional pattern. For exam])le Cross" 

 found this to be true for the red fox in Ontario, as did Macl,ulich"'° for the varying hare. 

 It is interesting that the latter concept agrees with the conclusions of the Investigation with 

 respect to grouse in the Northeast*. 



During the Investigation there has not been opportunity to undertake specific censuses of 

 predator species. Nevertheless data recorded in connection with the regular grouse survey 

 and other field work have afforded a means of appraising their relative abundance from year 

 to year. 



The most complete picture pertains to the Connecticut Hill study area. Here, populations 

 of resident species especially, ^uch as fox, weasel (Mustela noveboracensis and M. cicognanii), 

 skunk (Mephitis mephitis), raccoon (Procron lolor) and great horned owl. have, in general, 

 remained relatively stable during the years involved"^. Unquestionably the populations of 

 these predators have varied but the changes have not been great. Certainly nothing approach- 

 ing the fluctuations reported in Canada has taken place. 



The gradual northward spread of the gray fox in southern New York has had little effect 

 on the study area since, as in many grouse coverts of the Northeast, reds predominate. Over 

 its range in this State, however, the great horned owl regularly becomes somewhat more nu- 

 merous during the winter as a result of a southward movement of wandering individuals 

 from farther north. The degree of this influx seems to have been quite constant from year 

 to year. 



Among the migratory hawks, particularly the Buteos. some indication has been noted for 

 their abundance during spring and fall to vary from year to year. The numbers remaining 

 during the summer, however, have been quite stable. Likewise, breeding populations of the 

 Cooper's hawk and sharp-shinned hawk have been very similar each year. 



» Sp,- Chaplcr XUI. p. 567. 



A On thngr pnrliiins of Connecticut Hill where predator control was carried on between 1930 and 1934 the trapping appeared to 



have little effect on the abundance of predators except during the season immediately involved. Weasels, however, recuperated 



more slowly than the others. 



