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AUTHORS: Justin R. Dion, Jacob M. Haus – Department of Entomology and Wildlife Ecology, University of Delaware; Joseph E. Rogerson, Delaware Division of Fish and Wildlife; Jacob L. Bowman, Department of Entomology and Wildlife Ecology, University of Delaware
ABSTRACT: Survival and cause-specific mortality of neonate white-tailed deer has been the focus of recent research, particularly in regards to predation mortality. An understanding of the true impact of predation on survival rates requires a predator-free population to serve as a control. We captured 109 neonates using opportunistic capture (n = 55) and vaginal implant transmitters (VIT; n = 54) in Sussex County, Delaware, USA during 2016 and 2017 (Fig. 1). Predators (i.e., black bear, bobcat, and coyotes) were functionally absent from the study area. We calculated 30-day survival using a Kaplan-Meier estimator and determined the importance of covariates on survival using Cox proportional hazard models. The overall 30-day survival estimate was 0.61 (95% CI = 0.51 – 0.72). The survival estimate for neonates captured using random searches (0.76) was greater (P < 0.01) than those for VIT neonates (0.53; Table 1). Natural causes (n = 34) accounted for all of our observed mortality, including one potential predation by red fox. The top supported models included covariates for birth weight, doe maturity, and precipitation (Table 2). Survival estimates for the functionally predator-free study area were comparable to those found in other studies where predators were present and predation was identified as the primary source of mortality. Predation could be less of a limiting factor for survival than many studies have suggested. Data derived from opportunistically captured neonates may inflate estimates of survival and misrepresent cause-specific mortality due to inobservance of early-life mortalities [1,2]. Although the influence of birth weight on survival has been reported previously [3,4], the impact of doe maturity and precipitation has not been readily documented in this environment. The current emphasis on predator management and the impact on deer abundance in this ecosystem may be misplaced.
