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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).
Our objectives were to describe age-specific survival, cause-specific mortality, and space use of male and female fawns and female yearling and adult white-tailed deer in south central Michigan, and to compare our findings with past research on deer in Michigan. We focused primarily on female white-tailed deer for our analyses, as south central Michigan currently has a relatively high deer density (~27/[km.sub.2] during fall 2005; Michigan Department of Natural Resources [MDNR] 2005), and southern Michigan deer numbers generally exceed the goals of the MDNR (Clute 2006).
STUDY AREA
Our study was conducted in eastern Jackson, western Washtenaw, and southwestern Livingston counties in south central Lower Michigan (Figure 1; Hiller et al. 2008). The study area (82,636 ha) included publicly owned lands, including the MDNR Waterloo (8,410 ha; 10.2% of study area) and Pinckney (4,276 ha; 5.2%) recreation areas, and privately owned lands. Although the study area was primarily rural (98% of total land area), the human population increased 16% and housing units increased 22% between 1990 and 2000 (U.S. Census Bureau 2003). Land-use activities in much of southern Michigan and other areas of the Midwest are expected to show increases similar to those seen in the study area (Madill and Rustem 2001).
[FIGURE 1 OMITTED]
The physiographic regions of this area are Hillsdale-Lapeer Hilly Upland, South Central Rolling Plain, and Southeastern Rolling Plain with alfisols as the major soil order (Sommers 1977). Elevation of the study area is approximately 180 to 300 m with limited relief (Sommers 1977). Annual precipitation was about 81 cm during 1971-2000 (based on conditions in Chelsea, Michigan; Midwestern Regional Climate Center 2008a). During 1971-2000, average annual snowfall was 99.3 cm and mean monthly temperatures ranged from -5.4 [degrees]C (Jan) to 21.8 [degrees]C (Jul) in Jackson County (Midwestern Regional Climate Center 2008b, 2008c). Total annual snowfall during our study was highly variable (90.9 cm in 2004, 149.9 cm in 2005, and 40.0 cm in 2006; conditions in Chelsea, Michigan; Midwestern Regional Climate Center 2008d).
Much of the study area is well suited for agriculture, with a 150-day growing season that generally occurs from 10 May to 7 October (Sommers 1977). In 2002, agriculture in Jackson and Washtenaw counties (total area = 366,483 ha) included corn (37,840 ha), soybeans (34,200 ha), hay (17,200 ha), winter wheat (7,970 ha), and oats (930 ha; Michigan Department of Agriculture 2002).
We generalized land-use, land-cover data (Michigan Center for Geographic Information 2001) using Arc View GIS v3.2 software (ESRI,...
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