Effects of Winter Conditions on Reproduction in a Northern Wild Turkey Population

Abstract

Nine aspects of the reproductive performance of female wild turkeys (Meleagris gallopavo) were measured in Minnesota during 1975, 1977, and 1978. Sixty-eight of 75 (90%) radio-tagged females attempted to nest, renesting was common, and eggs in nests of 67% of the females ultimately hatched. Clutch size averaged 11.7 eggs, hatching success was 82%, and 37% of the young produced survived to late summer. Winter severity, measured in terms of impacts of site-specific conditions on late-winter body weights of females and mortality rates, varied within 14 different winter flocks. Females weighing less than 4.3 kg were less likely to survive to breed, less likely to nest, and had a natality rate of 2.6 females/female in the breeding population. Heavier females had higher survival and nesting rates and natality was 4.3. Strong correlations were observed between survivorship within winter flocks and reproductive performance of females that survived to breed. Severe winter conditions appeared to reduce egg hatching success among yearling females and recruitment of young among adults. Population modeling demonstrated that winter mortality and impaired reproduction performance can result in a significant decline in the population. At least 2 breeding seasons are necessary for population recovery. Impacts on hunting harvest quotas are discussed. J. WILDL. MANAGE. 47(2):281-290 It is a basic ecological tenet that on the fringe of its geographic range the abundance of a species tends to be influenced primarily by physical aspects of the environment. This generality seems to hold true for species of the Phasianidae (pheasants, quail, and turkeys). It is commonly agreed that 1 of the most important physical factors influencing phasianid populations in the upper Midwest is winter severity. However, the mechanism by which winter severity acts to cause variation in population levels has been unclear. Leopold (1931) and Schorger (1966) noted that historical populations of wild turkeys in the upper Midwest ebbed and flowed depending on the severity of winter. Implicit was the hypothesis that the primary impact of severe winters was extensive mortality as a result of prolonged negative energy balances. Austin and DeGraff (1975) in New York, Wunz and Hayden (1975) in Pennsylvania, and Porter et al. (1980) in Minnesota reported data strongly supporting this hypothesis. The ultimate effect of severe winter on the population depends not only on the overwinter mortality incurred but also on the reproductive performance of those individuals that do survive. Under ideal conditions, the reproductive potential of the turkey could offset substantial winter losses. However, work with many species of birds has shown that nutritional variation in the wild can significantly impact breeding success (e.g., Lack 1966, 1968; Ryder 1970; Moss et al. 1974; Newton 1979). Prolonged periods of negative energy budget during the winter can result in poor nutritional condition of females in the spring. Work with ring-necked pheas'Research supported by National Institutes of Health Training Grant 5 T01 GM 01779, the University of Minnesota, the Minnesota Department of Natural Resources, the Minnesota State Archery Association, the Special Projects Committee of the Minnesota Big Game Club, and the State University of New York, College of Environmental Science and Forestry. 2 Present address: Institute of Ecology, University of Georgia, Athens, GA 30602. J. Wildl. Manage. 47(2):1983 281 This content downloaded from 157.55.39.35 on Mon, 29 Aug 2016 04:45:51 UTC All use subject to http://about.jstor.org/terms 282 WINTER CONDITIONS AND REPRODUCTION IN TURKEYS * Porter et al. ants (Phasianus colchicus) and northern bobwhite (Colinus virginianus) has led to the general hypothesis that the reproductive performance of these species can be impaired by severe winter conditions (Breitenbach et al. 1963, Edwards et al. 1964, Gates and Woehler 1968, Labisky and Jackson 1969, Roseberry and Klimstra 1971, Gates and Hale 1975). If such a cause-and-effect relationship exists within turkeys as well, proper management should consider a time lag in the recovery of a population following a severe winter in northern regions. The reproductive ecology of the wild turkey in the upper Mississippi Valley has not been examined previously. As part of a larger investigation (Porter 1978), data were acquired to document reproductive performance. The objectives of this paper are to report on the reproductive performance of wild turkeys in southeastern Minnesota and to evaluate the effects of severe winter on reproduction and population dynamics. We acknowledge D. B. Siniff of the University of Minnesota and H. Shepperd, N. Gulden, R. Johnson, and G. Meyer of the Minnesota Department of Natural Resources for support of this project. D. Hamilton, S. Erickson, B. Neil, and R. Tangen provided extensive field assistance. D. DeMaster, J. Ludwig, J. Tester, H. Tordoff, and an anonymous reviewer provided especially helpful comments during preparation of this paper.