The Effect of Predator Removal on Pheasant Reproductive Success

Effects of nest predation on pheasant (Phasianus colchicus) production were studied on two areas in southern Minnesota during 1960-64. Principal nest predators were striped skunks (Mephitis mephitis), spotted skunks (Spilogale putorius), raccoons (Procyon lotor), and crows (Corvus brachyrhynchos). During the nesting seasons of 1960-62, 434 predators were removed from the 2,560acre Trapped Area; none were removed from the 4,080-acre Untrapped Area. Searches in at least a third of each area's potential nesting cover revealed 460 nests on the Trapped Area and 429 on the Untrapped Area. Nest densities on the two areas were similar each year, but declined during the 3 years. On the Trapped Area, hatching success progressively improved during the study, reaching 36 percent in 1962. On the Untrapped Area, by contrast, hatching success remained consistently low and was only 16 percent in 1962. Predation was highest on poorly concealed nests, especially those located in fencerows. Nest losses from other causes, chiefly haymowing, were comparable between study areas. Clutch size averaged higher on the Trapped Area and chick production per 100 acres was consistently higher than on the Untrapped Area, showing roughly a twofold difference in 1961 and 1962. Dummy nests placed in selected cover types supplemented information obtained from natural nests. Results from the former suggested (1) that predation, especially by crows, was highest early in the nesting season, (2) that predation was highest among poorly concealed nests, and (3) that there were no carryover benefits one year after predator removal. Late summer pheasant censuses were inconclusive, probably because of inadequate sampling and because ingress and egress obscured population responses on our small study areas. Costs of removing predators averaged $21.00 per predator taken and $4.50 for each chick hatched on the Trapped Area in excess of the number hatched on the Untrapped Area. It was concluded that, using presently available techniques, removal of nest predators would not be economically feasible for improving pheasant hunting on extensive agricultural lands, even if the increase in chicks was directly reflected in the fall population. The ring-necked pheasant is primarily a bird of agricultural lands, and production of pheasants is greatly influenced by farming practices. In recent years more intensive farming in Minnesota's primary agricultural range has adversely affected pheasants, most importantly by reducing undisturbed nesting cover. In addition, the availability of small grains has steadily declined because cropping patterns have gradually shifted toward row crops, especially corn and soybeans. Small grains have been a valuable source of nesting cover in Minnesota (Nelson and Chesness 1964). Along with deterioration of nesting habitat, pheasant nest losses have increased from both farming practices and predation (Nelson and Chesness 1964). The present study was carried out during 1960-64 to determine the effect of predator removal on pheasant reproduction in an area of intensive agriculture in the main pheasant range of south-central Minnesota. Conclusions of various authors on the effects of predator control upon game populations differ depending upon the kind and intensity of predation, the degree of predator control, and the prey species. Wagner et al. (1965:108) summarized some results of predator control studies in pheasant range. In general, little pheasant population response was noted either where predator control was limited to only one predatory species as in the New York fox studies (New York Conservation Department 1951) or where only avian predators were controlled (Lauckhart and McKean 1956:65). However, Einarsen (1950) reported in-