Effects of Hunting and Mast Crops on a Squirrel Population

Abstract

A 10-year evaluation was made of the effects of hunting and mast crops on a population of gray squirrels (Sciurus carolinensis) and fox squirrels (S. niger) located on a 505.0-ha (1,250-acre) public shooting area in southeast Ohio. On a 95.7-ha (237-acre) research portion of the area, preseason squirrel densities averaged 1.91 squirrels per ha (0.77 squirrel per acre), hunting pressures averaged 4.5 gun-hours per ha (1.81 gun-hours per acre), and harvests averaged 0.89 squirrel per ha (0.36 squirrel per acre). The kill per ha each year was significantly correlated (P < 0.01) with preseason density per ha and with total gun-hours expended. Annual mortality averaged 80 percent for adult and subadult gray squirrels and adult fox squirrels but only 69 percent for subadult fox squirrels. Hunters recovered an average of 45.1 percent of the available marked population each year, and hunting accounted for 55.2 percent of the annual mortality. Fall-to-fall densities of squirrels were unstable, with significant changes in density occurring in 6 of 10 years. The squirrel population fluctuated mainly in response to the mast crop the preceding fall, but fall harvests also affected subsequent squirrel densities, particularly for adult gray squirrels. Both harvests and population densities affected the subsequent survival of adult female gray squirrels; survival was highest when densities were less than 70 squirrels per 40.4 ha (100 acres). Mortality and/or dispersal exceeded natality after 1966, and fall densities and kill became increasingly dependent upon immigration from surrounding forests. The response of individual squirrels to a good-to-heavy seed crop included: (1) improved survival of summer-born young, (2) a lower rate of emigration of both juvenile and subadult squirrels, (3) an increase in fecundity of breeding females, and (4) a higher rate of survival of adult gray squirrels in response to an increase in the size of the hickory (Carya spp.) seed crop. At least 58.9 kg (130 lb) of sound tree seed per 0.4 ha was needed to sustain reasonably high squirrel densities. A minimum of 3.2-3.7 m2 of basal area of mast-producing species per 0.4 ha (35-40 ft2/acre) is needed to produce this amount of tree seed, and 1.0-1.4 m' (10-15 ft2) of basal area should be hickory species of seed-producing size. J. WILDL. MANAGE. 39(1):1-25 This paper reports a 10-year evaluation of the effects of hunting and mast crops on a population of gray and fox squirrels located on a public hunting area in southeast Ohio. Annual hunting pressures are often several times higher on forests open to the general public than on privately owned forests (Allen 1954, Uhlig 1955, Fouch 1969, Nixon et al. 1974). Reported squirrel harvests from public forests have varied from lows of 13 percent (Uhlig 1955:26) and 15 percent (Kidd and Soileau 1965: 113) to highs of 45 percent (Nixon and McClain 1969:354), 46 percent (Chapman 1941:7), and 58 percent (Peterle and Fouch 1959, Nixon et al. 1974) of the estimated squirrel population. In most of these studies no evaluation was made of the subsequent effects of these harvests on the squirrel population. Mosby (1969:65) found that an average harvest of 37.4 percent of the estimated fall population of gray squirrels produced no significant difference in the average annual mortality rate compared with the rate on an adjacent unhunted area. The rate of population turnover, the annual mortality rate, and the rate of juvenile recruitment were somewhat higher under controlled hunting (Mosby 1969:71). In general, squirrel populations located in extensive forests and composed mainly of gray squirrels have been reported 1 A contribution of Federal Aid in Wildlife Restoration Projects, Ohio W-105-R and Illinois W-66-R. J. Wildl. Manage. 39(1):1975 1 This content downloaded from 157.55.39.30 on Fri, 27 May 2016 05:56:30 UTC All use subject to http://about.jstor.org/terms 2 EFFECTS OF HUNTING ON SQUIRRELS Nixon et al. to be underharvested (Allen 1954, Uhlig 1955) and to fluctuate in size in response to the availability of forest seed crops, particularly acorns (Allen 1954:61, Christisen and Korschgen 1955:350, Sharp 1959:383, Nixon and McClain 1969:353, Barkalow et al. 1970:499). The response of both gray and fox squirrels to fluctuations in tree seed crops has been reported to include changes in fecundity (Allen 1943, Uhlig 1955) and in the survival and/or dispersal rates for juveniles (Uhlig 1955, Barkalow et al. 1970). We acknowledge C. McKibben, J. Ely, R. Beal, R. Dicken, and R. Stoll, Ohio Division of Wildlife, who assisted with livetrapping, mast collections, and operation of the checking station. S. Havera, Illinois Natural History Survey, assisted with the statistical analysis, and H. C. Schultz, W. R. Edwards, and G. C. Sanderson, Illinois Natural History Survey, reviewed the manu-