Introduction
Understanding the variability and elasticity of vital rate parameters is
important to better understand population dynamics for ungulate species
(Tuljapurkar & Caswell, 1997). Although adult female survival generally
has the greatest effect on population growth rates for ungulate
populations, adult survival tends to be stable; conversely, offspring
survival has less impact on population growth but is more variable
(Gaillard, Festa-Bianchet & Yoccoz, 1998; Gaillard et al., 2000;
Raithel, Kauffman & Pletscher, 2007; Chitwood et al., 2015).
Manipulating offspring survival to achieve various management and
conservation goals is therefore a viable method to increasing population
size (Crouse, Crowder & Caswell, 1987; Coluccy et al., 2008; Johnson et
al., 2010). However, better understanding what specific variables affect
offspring survival will likely increase effectiveness of management and
conservation efforts.
Intrinsic variables such as birth mass (Cook et al., 2004; Lomas &
Bender, 2007; Shuman et al., 2017) and capture age (Grovenburg et al.,
2014) as well as extrinsic variables including weather (Ginnett &
Young, 2000; Warbington et al., 2017; Michel et al., 2018) and landscape
composition and configuration (Gulsby et al., 2017; Gingery et al.,
2018; Michel et al., 2018) affect ungulate offspring survival. Other
factors such as maternal body condition may also affect offspring
survival as ungulate mothers in better body condition are more likely to
produce larger, healthier offspring with greater chances of survival
than those in poor body condition (Carstensen et al., 2009; Duquette et
al., 2015; Shallow et al., 2015). Additionally, predation is generally
the largest natural cause of offspring mortality for several ungulate
species (white-tailed deer, Odocoileus virginianus , Grovenburg et
al., 2011; Chitwood et al., 2015; elk, Cervus canadensis , Griffin
et al., 2011; Brodie et al., 2013; moose, Alces americanus , Keech
et al., 2011, Severud et al., 2019; pronghorn, Antilocarpa
americana , Jacques et al., 2007, 2015); however, the number of
predators an ungulate population is exposed to does not necessarily
equate to increased mortality (Kautz et al., 2019). Consequently,
factors affecting offspring survival can be area specific (Grovenburg et
al., 2011); therefore, understanding which factors most influence
offspring survival for a given ungulate population is warranted.
Although there are several ecological variables that affect ungulate
offspring survival, field methodology can also affect derived survival
estimates for a population. Derived survival estimates tend to be
greater for opportunistically captured neonates compared to those
captured via vaginal implant transmitters (VITs) due to increased left
truncation in the opportunistically captured datasets (black-tailed
deer, O. hemionus sitkensis , Gilbert et al., 2014; white-tailed
deer, Chitwood et al., 2017; Dion et al., 2020). This variation can
affect management and conservation efforts when survival estimates are
needed to model population growth rates and abundance as these metrics
are often used to determine the number of individuals that can be
sustainably harvested from a population. Model selection and
interpretation of the effects of ecological covariates on ungulate
neonate survival can also vary by capture method (Gilbert et al., 2014).
Therefore, assessing how capture method affects both derived survival
estimates and interpretation of the relationship between ecological
covariates and survival will further understanding of the population
dynamics for a given species within an ecosystem.
Our objective was to assess variation in survival estimates and
subsequently assess potential variation in model selection and
ecological covariate interpretation related to capture method for
white-tailed deer neonates captured from three study areas in North
Dakota and South Dakota, USA. We also assessed how intrinsic (capture
age, birth mass, sex) and extrinsic (percent canopy cover,
precipitation, distance to road, distance to water) ecological
covariates affected neonate survival through 3-months (neonates) and
6-months (juveniles) of age. We predicted neonates captured via VITs
would display decreased survival compared to opportunistically captured
neonates (Gilbert et al., 2014; Chitwood et al., 2017; Dion et al.,
2020). We also predicted survival would increase with increased birth
mass (Cook et al., 2004; Lomas & Bender, 2007; Shuman et al., 2017),
age (Nelson & Woolf, 1987; Rohm, Nielsen & Wolf, 2007; Grovenburg et
al., 2011), canopy cover (Rohm, Nielsen & Wolf, 2007; Sternhagen,
2015), and increased distance from the nearest road (Rost & Bailey,
1979; Stankowich, 2008). We predicted that survival would decrease with
increased precipitation (Warbington et al., 2017, Dion et al., 2020) and
increased distance from water (Adams & Hayes, 2008; Long et al., 2009;
Ditchkoff, 2011). Finally, we predicted survival would be lower for
females compared to males (Shuman et al., 2017).