Assessing factors affecting adult female white-tailed deer survival in the Northern Great Plains

Abstract

Context Documenting cause-specific mortality and deriving survival estimates for a population are both vital to understanding potential restrictions to population growth. Survival varies among populations of the same species and depends on several factors, including climatic events, density-dependent and density-independent factors, observed predator composition and whether recreational hunting occurs. Therefore, understanding factors affecting adult survival and estimating survival rates at biologically important times will help refine management of these populations. Aims We aimed to assess cause-specific mortality, estimate survival rates, and determine at what part of the winter (January to April) most mortalities occurred for female white-tailed deer located in the Northern Great Plains region of the USA. Methods We captured 165 adult female white-tailed deer (Odocoileus virginianus) located in western North Dakota and north-western South Dakota, USA, during the winters of 2014 and 2015. We fitted individuals with Very High Frequency (VHF) radio-collars and located them 1–3 times per week to monitor survival. We investigated all mortalities to establish proximate cause of death. Key Results Survival was lowest during our Hunt time period (S=0.93), although hunter harvest was not the leading cause of mortality. Predation was the greatest source of mortality, particularly during our Post-hunt time period. Additionally, almost 90% of mortalities occurring during the Post-hunt time period happened during late winter before spring green up. Conclusions and Implications Predation was the main source of mortality for adult females in our study, with coyotes (Canis latrans) being the sole predator capable of depredation in our study area. Predation by coyotes may indicate that potential factors, including winter severity and nutritional restrictions, have decreased female body condition, making individuals more susceptible to predation. Although we report relatively high survival, managers should consider the possibility that coyotes may impact adult populations, particularly in regions where other large-sized predators occur, or in regions where coyotes are newly established. Managers should also acknowledge that overwinter density estimates may need to be adjusted during severe winters to account for mortalities that occur after population surveys are conducted.

Habitat selection of white-tailed deer fawns and their dams in the Northern Great Plains

“…Although there are several predators of white-tailed deer, coyotes are the main predator of adult white-tailed deer in the Northern Great Plains (Moratz et al 2018) and are also an important predator of white-tailed deer neonates in the Northern Great Plains (Brinkman et al 2004;Grovenburg et al 2011) and throughout their range (Gingery et al 2018;Kautz et al 2019;Warbington et al 2017). Furthermore, coyotes are reported to have substantial impacts on white-tailed deer neonate populations at local scales (Chitwood et al 2015;Kilgo et al 2012).…”

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

“…The low mortality rate and absence of observed hunter harvest as a mortality source in 2016 was unexpected and difficult to account for. We are not aware of any study documenting a greater rate of annual survival for adult females than we observed in 2016 (0.96), but rates ≥0.88 have been reported in New Brunswick, Canada (0.92 and 0.89; Whitlaw et al 1998), West Virginia (0.88; Campbell et al 2005), South Dakota (0.88; Moratz et al 2018), and Kentucky, USA (0.91; Haymes et al 2018). Following the hemorrhagic disease outbreak in summer 2012, annual harvest of adult females in Sussex County declined by approximately 30% in 2012 and 2013, began to increase in 2014–2016, and appeared to stabilize in 2017 and 2018 at a level slightly above pre‐2012 annual harvest (E. W. Ness, Delaware Division of Fish and Wildlife, unpublished data).…”

“…Hunter harvest accounted for 86% of mortality in exurban Illinois, USA (Storm et al 2007), 46% of mortality in an agricultural region in Minnesota, USA (Brinkman et al 2004), and 70% of mortalities in agricultural regions of South Dakota, USA, and Minnesota (Grovenburg et al 2011). In contrast, separate research in South Dakota reported natural causes (i.e., disease, starvation, predation) were a more prominent source of mortality than hunter harvest in adult females (DePerno et al 2000, Moratz et al 2018).…”

“…Survival rates of adult females are of particular interest to managers because population changes are disproportionately influenced by adult females relative to other demographics (Gaillard et al 1998, Robinson et al 2014, Chitwood et al 2015). Annual survival rates can fluctuate spatially and temporally as a function of habitat, population structure, disease outbreaks, resource availability, management regulations, and hunting pressure (Grovenburg et al 2011, Moratz et al 2018). Although extensive literature compares spatial differences among regions and ecotypes, temporal variation in annual survival rates within regions is less understood because of the cost and logistical constraints of long‐term monitoring (Gaillard et al 1998, DelGiudice et al 2006, Clutton‐Brock and Sheldon 2010).…”

White‐Tailed Deer, Weather and Predation: a New Understanding of Winter Severity for Predicting Deer Mortality

“…could provide a reprieve from nutritional bottlenecks during winter related to snow depth. Few studies explicitly examine effects of winter variables on deer survival in agricultural areas, although Moratz et al (2019) did report elevated mortality during March-April of years with relatively harsher winters in the Northern Great Plains.…”