Age-Specific Survival and Space Use of White-Tailed Deer in Southern Michigan

Article excerpt

ABSTRACT

Assessments of age-specific space use and demographics are important for managing popular game species, such as the white-tailed deer (Odocoileus virginianus). Habitat management relies on knowledge of space use, and abundance estimation models (e.g., sex-age-kill) require estimates of age-specific data. Because these population characteristics often vary across landscapes, management is often based on specific land-unit areas. We captured and radiomarked 76 deer and aged them as fawn (<1 yr old; both sexes), yearling ([greater then or equal to] 1-< 2 yrs old; females) or adult ([greater then or equal to] 2 yrs old; females) to estimate survival, assess cause-specific mortality, and describe space use in southern Michigan. Annual survival varied by age class (fawn = 0.51, yearling = 0.94, adult = 0.56). Primary sources of mortality were canid predation, vehicle collisions (fawns), and hunter-harvest (fawns, adults). Age-specific space use varied seasonally (agricultural growing and non-growing seasons), with home-range sizes larger during fall for each age class. Yearlings generally had larger home ranges (growing season: [bar.x] = 201.8 ha [+ or -] 91.1 SE; non-growing season: x = 156.9 ha [+ or -] 28.2 SE) than fawns (60.2 ha [+ or -] HA; 116.3 ha [+ or -] 20.6) or adults (77.5 ha [+ or -] 9.6; 140.4 ha [+ or -] 23.4). Compared with other studies in Michigan, we observed several differences in survival and space use, suggesting that managers should consider landscape characteristics when setting objectives and implementing management programs.

INTRODUCTION

Regulated harvest and habitat management for game species are two primary management methods used by state wildlife agencies. Consequently, accurate descriptions of population characteristics such as estimates of age-specific demographics and space use are imperative during the development of harvest and habitat management plans for game species. For example, survival of cervids can be influenced by weather patterns (e.g., DelGiudice et al. 2006), predator-prey dynamics (e.g., Labisky and Boulay 1998), and hunter-harvest (e.g., Bender et al. 2000). Survival and other age-specific demographic estimates are also important parameters for managers using simulation modeling to predict species abundance.

Spatial and temporal changes in cover may affect species abundance and age and sex structure, and land-use or ownership changes may impact a state agency's ability to manage deer populations. Because home-range size varies by sex and age of the individual, as well as habitat and season (Demarais et al. 2000), specific information about space use may help guide management objectives and decisions. Increasing white-tailed deer (Odocoileus virginianus) and human populations coupled with land-use changes (e.g., urbanization) further add to the complexity of deer management across much of the United States (Demarais et al. 2000). Because population demographics and structure vary greatly across landscapes, management agencies often develop species-specific management units. Although management units are often based on non-ecological components, such as roads or county boundaries, these features are more apparent to hunters and other stakeholder groups.

Management of high deer populations through regulated hunting is probably the most cost-effective strategy (Demarais et al. 2000). Harvest objectives are often implemented at the management-unit level and may be age- and sex-specific for deer. For example, harvest objectives for antlerless deer (i.e., males < 1 yr old and females) are often adapted to achieve the agency's population goals, such as when the deer population is determined to be higher than desired. Thus, knowledge of area-specific survival and space use of female deer, under these circumstances is important as female deer are often the sex class of primary interest for managers desiring relatively large reductions in population densities through hunter-harvest (Carpenter 2000). …