Female White-Tailed Deer Survival across Ecoregions in Minnesota and South Dakota

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ABSTRACT.-

Survival and cause-specific mortality of female white-tailed deer (Odocoileus virginianus) have been well documented in forested and agricultural landscapes, but limited information has been collected in grassland habitats typical of the Northern Great Plains. Our objectives were to document and compare survival and cause-specific mortality of adult female white-tailed deer in four distinct ecoregions. We captured and radiocollared 190 (159 adult, 31 yearling) female white-tailed deer and monitored (including deer from a previous study) a total of 246 (215 adult, 31 yearling) deer from Jan. 2000 to Dec. 2007. We documented 113 mortalities; hunting (including wounding loss) accounted for 69.9% of all mortalities and vehicle collisions accounted for an additional 15.0%. Natural causes (e.g., disease, predation) of mortality were minor compared to human-related causes (e.g., hunting, vehicle collisions). We used known fate modeling in program MARK to estimate survival rates and compare ecoregions and seasons. Model {S^sub season (winter=summer)^} had the lowest AIC^sub c^ value suggesting that survival differed only between seasons where winter and summer survival was equal and differed with fall season. Annual and seasonal (summer, fall, winter) survival rates using the top model {Sseason (summer=winter} were 0.76 (95% CI = 0.70-0.80), 0.97 (95% CI = 0.96-0.98), 0.80 (95% CI = 0.76-0.83) and 0.97 (95% CI = 0.96-0.98), respectively. High human-related mortality was likely associated with limited permanent cover, extensive road networks and high hunter density. Deer management in four distinct ecoregions relies on hunter harvest to maintain deer populations within state management goals.

INTRODUCTION

Knowledge of survival rates, cause-specific mortality, and temporal and spatial patterns of survival is essential to understanding white-tailed deer (Odocoiieus virginianus) population dynamics (Dusek et al, 1992; DePerno et al, 2000; Brinkman et al, 2004). Survival rates vary regionally with sex, age and density of deer (Gavin et al, 1984; Dusek et al, 1992; Whitlaw et ed., 1998; DelGiudice et ed., 2002). Common causes of mortality include human-related factors (e.g., legal and illegal hunting, vehicle collisions; Fuller, 1990; Nixon et al, 1991; Brinkman et al, 2004), weather (e.g., winter severity; DePerno et al., 2000; DelGiudice et al, 2002), predation (Mech, 1984), and disease (Matschke et al, 1984). In most areas, hunter harvest is the primary cause of deer mortality and is the factor most amenable to management efforts (DelGiudice et al, 2002). Hunter harvest accounted for 43% of mortality in southwestern Minnesota (Brinkman el ed., 2004), 60% in Illinois (Nixon et al, 2001), 43% in north-central Minnesota (DelGiudice et al, 2002) and 74% in eastern Montana (Dusek et al, 1992). Conversely, harvest accounted for only 23% of mortality in the central Black Hills of South Dakota (DePerno el ed., 2000).

Deer have readily adapted to the mosaic of habitats that characterize the Midwest and Northern Great Plains (Nixon et ed., 2001; Brinkman et al, 2004) and high deer densities commonly occur in this intensively fanned region despite limited patches of permanent cover (Naugle et ed., 1996). Survival rates and cause-specific mortality of white-tailed deer have been well documented in forested habitats (Van Deelen et al, 1997; Whitlaw et al, 1998; DePerno et al, 2000; DelGiudice el al, 2002) and intensively farmed areas (Nixon et al, 2001; Brinkman et al, 2004); however, information in grassland habitats with limited forested cover is lacking. Region specific practical data is important to predict spatial and temporal changes in deer populations (Brinkman et ed., 2004). Therefore, our primary objectives were to quantify survival and cause-specific mortality rates of adult female whitetailed deer. Additionally, our secondary objective was to compare survival rates between ecoregions with differences in land cover characteristics. …