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Effect of Birth Date on Development

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The Yearling Disadvantage in Alabama Deer:Effect of Birth Date on DevelopmentWilliam N. Gray II, Alabama Division of Wildlife and FreshwaterFisheries, 64 N. Union Street, Montgomery, AL 36130Stephen S. Ditchkoff, School of Forestry and Wildlife Science,Auburn University, AL 36849M. Keith Causey, School of Forestry and Wildlife Science, AuburnUniversity, AL 36849Christopher W. Cook, Alabama Division of Wildlife and FreshwaterFisheries, 64 N. Union Street, Montgomery, AL 36130Abstract: Male white-tailed deer are subjected to a variety of factors that influence bodyand antler development when they are yearlings. Nutrition and genetics have receivedconsiderable attention as factors that influence this development; however, date of birthhas yet to be adequately investigated and theoretically could dramatically influence de-velopment in later years. To determine how date of birth influences development ofantler and body characteristics at 1.5 years of age, we collected data from yearling malewhite-tailed deer (Odocoileus virginianus) harvested on 23 Alabama Wildlife manage-ment Areas (WMAs) during the 1998–99 and 1999–2000 hunting seasons. We foundthat early born males had greater body mass, number of antler points, antler beamlength, and antler beam circumference than their late born counterparts. Mean birth dateof fork-antlered yearlings was earlier (26 Jun) than spike-antlered yearlings (23 July).Yearling males from the Lower Coastal Plain had shorter main beam lengths and lessantler points that those from the Appalachian Plateau, Piedmont Plateau, and UpperCoastal plain, but body mass and main beam circumference did not differ. There wasalso a lower proportion of fork-antlered yearlings harvested on the Lower Coastal Plainthan in other physiographic regions. Antler development in the yearling age class hasbeen proposed as a predictor of an animal’s potential for antler quality. Because of vari-ability of fawning periods in Alabama and subsequent effects on physical development,as well as differences in physical development among physiographic regions, selectiveharvest programs based on physical characteristics of yearling males may not be suit-able as a means to improve genetic quality of deer populations. Proc. Annu. Conf. Southeast. Assoc. Fish and Wildl. Agencies 56:255–264Most white-tailed deer (Odocoileus virginianus) populations across NorthAmerica breed in late fall (Nov–Dec) and give birth in May and June (Verme and Ull-rey 1984). In Alabama, peak breeding for most deer populations occurs in January.However, summary data from statewide reproductive surveys indicate nearly one-2002 Proc. Annu. Conf. SEAFWAfifth (16.8%) of conceptions occur in February (Gray, unpubl. data). These breedingpatterns result in fawns being born during late summer/early fall (Leuth 1955, 1967).In extreme cases, breeding may be extended as late as March and fawning as late asOctober (Leuth 1967). Late breeding and fawning periods also have been document-ed for other Gulf Coast deer populations including Mississippi (Jacobson et al.1979), Louisiana (Roberson and Dennett 1966), and Florida (Morgan, pers. com-mun.).Excessive harvest of males and inadequate harvest of females in many areas ofAlabama have resulted in deer populations with a very young male age structure andbiased adult sex ratios heavily skewed towards females. These unnatural herd struc-tures have been reported to delay and prolong breeding and fawning periods (Gruveret al 1984). Further protraction of an already late fawning period in much of Alabamahas resulted in a high variability of age (e.g., several months’ difference) amongfawns. Consequently, when many male deer enter the hunting season in their secondyear, they may only be 15–16 months of age.Differences in body mass and antler development among yearling male deer areattributed to differences among subspecies, nutrition, and genetic potential (Frenchet al. 1956, Harmel 1982, Sauer 1984). However, late and extended fawning periodslikely are as important as well, but their effects have been poorly researched. Datacollected in northwest Florida suggested later-born yearlings had less antler develop-ment than earlier-born yearlings (Shea et al. 1991). Similarly, Vanderhoof (1991)found that later-born yearlings in northwest Florida had smaller antler characteristicsthan earlier-born yearlings from the Everglades region of Florida, a smaller sub-species. In South Carolina, Knox et al. (1991) reported differences in both weightand antler development between yearlings 17 months and yearlings 19 months.Jacobson (1995) reported that deer raised in captivity showed a relationship betweenbirth month and antler size when they were yearlings. In contrast, Causey (1990)found that earlier born captive fawns fed ad libitum did not have greater body mass orantler characteristics than late born fawns at 16 months of age.Prohibiting harvest of yearling males is commonly prescribed in managementstrategies designed to improve age structure among male deer. However, in some re-gions, yearling bucks with small antlers (e.g., spikes) or other “undesirable” antlercharacteristics may be harvested as part of the management approach. Such manage-ment schemes are based on the belief that yearling antler development is a strong in-dicator of genetic potential for antler production (Brothers and Ray 1975, Harmel1982). Many Alabama hunters and landowners selectively “cull” spike-antlered year-lings on areas where the efficacy of such a strategy may be questionable. Becausemany factors such as birth date may influence physical development of yearling maledeer, selective harvest of yearling males in Alabama may not be appropriate. Consid-ering that in many areas of Alabama over 85% of all yearling bucks may be spike-antlered (Cook 2001), such an approach could further compound problems associat-ed with poor age structures resulting from over-harvest of young males. Thus, thegoal of our study was to determine if birth date influenced body mass and antler de-velopment of yearling male white-tailed deer. 256 Gray et al.2002 Proc. Annu. Conf. SEAFWAThe Alabama Division of Wildlife and Freshwater Fisheries (DWFF) and theAuburn University School of Forestry and Wildlife Sciences provided support forthis project. We are grateful to the many biologists and field staff of DWFF who as-sisted with data collection, and A.L. Silvano and the GAP Analysis Project (Ala.Coop. Fish and Wildl. Res.


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