Land use and dispersal influence mortality in white‐tailed deer

Abstract

Restoring male age structure in white‐tailed deer populations has become an important objective for many state agencies aimed at improving herd dynamics. Limiting mortality in the yearling (1–2 yr old) age class is a primary consideration, and regional differences in climate, habitat characteristics, hunting regulations, and hunter behavior complicate the understanding of how specific factors influence the risk of mortality. We used Cox proportional hazard modeling to determine the effects of body size, mean distance to road, dispersal behaviors, use of forested land, and use of land open to public hunting on the risk of mortality for a population of radio‐collared, yearling males (n = 76) in Sussex County, Delaware, USA. Annual survival averaged 0.55 (95% CI = 0.45–0.68), with harvest accounting for 79% (26/33) of all mortalities. Measurements of body size (chest girth, shoulder height, and total length; cm) influenced dispersal probability but not dispersal distance. The best approximating model for mortality risk included a covariate for landownership, whereby mortality risk increased on public land. Among males who dispersed, longer‐distance dispersal was associated with reduced mortality, which contradicts previous research describing dispersal as a high‐risk behavior. The effect of landownership on mortality risk has not been previously identified, especially when regulations regarding harvest of yearling males are similar between landownership types. We observed annual survival rates of 0.69 (95% CI = 0.57–0.82) for deer apparently using private land exclusively during the hunting season, and 0.20 (95% CI = 0.11–0.48) for deer that used public land during the hunting season. Survival rates on private land were comparable to those of other regions actively managing male age structure. These results suggest survival of yearling males in the region is influenced by hunter harvest and the risks associated with dispersal may be minimal in areas where harvest pressure is low, although hunter harvest on public land may limit male age structure on a localized scale. © The Wildlife Society, 2019

Risky movements? Natal dispersal does not decrease survival of a large herbivore

“…In each case, the null model (circles) was more parsimonious than models that estimated survival of dispersers (triangles) and nondispersers (squares) separately Trewhella, 1988;Johnson et al, 2009;Jones, 1988). Although we did not detect a significant effect of dispersal distance on survival, Haus et al (2019) found decreased mortality with increasing dispersal distance in yearling male white-tailed deer. As in our study system, hunting was the largest source of mortality, and vehicular collision was relatively minor, although they did not specify if any of the observed vehicular collisions occurred during transfer.…”

“…Consistent with this, male dispersal movements in our study were quick (often <12 hr), direct, and relatively short (median dispersal distance in our system = 5.9 km; Long, 2005;Long et al, 2010), although dispersal movements in more agricultural landscapes are often longer in duration and distance (Anderson et al, 2015;Springer, 2017). These findings suggest that males have adapted efficient dispersal strategies, and like our study, Haus et al (2019) found no effect of dispersal on yearling male white-tailed deer survival in Delaware, USA.…”

“…As in our study system, hunting was the largest source of mortality, and vehicular collision was relatively minor, although they did not specify if any of the observed vehicular collisions occurred during transfer. Like other studies of white-tailed deer (McCoy et al, 2005;Shaw et al, 2006), Haus et al (2019 showed that dispersing males were larger than philopatric males, suggesting condition-dependent dispersal. In this way, it is possible that males in the best condition prior to emigration embarked on the longest dispersals, and the observed greater survival rate of longer dispersers reflected fitness-related factors predating transfer.…”

“…In whitetailed deer, dispersal has been predicted to increase mortality (McCoy et al, 2005;Nelson & Mech, 1986;Roseberry & Klimstra, 1974), but this prediction has rarely been tested. To our knowledge, only two prior studies of large mammals (both white-tailed deer) have compared mortality of dispersers and nondispersers: Nixon et al (2001), working in highly fragmented agricultural region of Illinois (USA), suggested that dispersal increased mortality risk, but Haus et al (2019), working in Delaware (USA), suggested that dispersal status was not a significant predictor of mortality for yearling male white-tailed deer.…”

Interannual Variability in Survival Rates for Adult Female White‐Tailed Deer

“…We used package survival in Program R for survival analysis (Therneau 2015). We used a study‐based time period (1 May [0]–30 Apr [364]) for all years (Fieberg and DelGiudice 2009, Haus et al 2019). We used the Kaplan‐Meier estimator (Kaplan and Meier 1958) to calculate a baseline annual survival curve with the Greenwood variance estimator to generate 95% confidence intervals.…”