Statistical analysis
We monitored neonates daily for mortality during the first 30 days using
aerial telemetry, omnidirectional whip antennas, and handheld telemetry
equipment and then monitored them 2-3 times per week thereafter. We
investigated mortalities immediately after detecting a mortality signal
and transported carcasses to the North Dakota Game and Fish Department
Wildlife Health Laboratory in Bismarck, North Dakota, USA to confirm
proximate cause of death.
We summarized weekly neonate mortality from telemetry data (Grovenburg
et al., 2014). We estimated 3-month (capture to 12 weeks) survival rates
using the Kaplan-Meier method (Kaplan & Meier, 1958) for non-staggered
entry and 6-month (capture to 24 weeks) survival rates using staggered
entry (Pollock et al., 1989) via known fate models in Program MARK
version 6.0 (White & Burnham, 1999; Cooch & White, 2016). We
considered models within 2 ∆AICc of the top model as
competing (Burnham & Anderson, 2002).
We developed up to 19 models to describe factors that most affected
neonate survival (S) at 3- and 6-months of age. Response variables
included age interval 1 (2-stage age interval: 0-2 weeks, 3+ weeks), age
interval 2 (3-stage age interval: 0-2 weeks, 3-8 weeks, 9+ weeks),
capture type (VIT or opportunistic), distance from capture site to
nearest road (km) and distance from capture site to nearest water body
(stream or stock pond, km), percent canopy cover at neonate capture
site, precipitation during age intervals (0-2 weeks, 3-8 weeks, 9-12
weeks, 13-24 weeks), sex, birth mass, and capture age (Table 1). We used
hoof measurements to estimate capture age for all neonates (Haugen &
Speake, 1958). We back-calculated birth mass for individuals we
estimated to be >1 day old using estimated age and assumed
neonates gain 0.215 kg per day (Verme, 1963). We assigned mean mass (n =
27) and mean hoof measurements (n = 33) of neonates captured within the
same week to neonates that were too wet or too large to weigh or take
hoof measurements (i.e., only sex was obtained and a radio-collar was
placed on the individual). Finally, we assigned capture mass as birth
mass for individuals estimated to be ≤1 day old. We refer to all body
mass measurements obtained at capture and estimated body mass for
neonates as body mass. We only investigated the age interval using the
3-month model set because we used non-staggered entry for 3-month models
(Grovenburg et al., 2014). We assessed if capture method affected
derived survival estimates, model selection, and our subsequent
interpretation of ecological covariates by including capture method in
our candidate model set for all neonates. We then excluded capture
method from our candidate set and further assessed how model selection
and interpretation varied by analyzing a data set that included neonates
captured via VITs, neonates opportunistically captured, and all neonates
combined regardless of capture method. Finally, we compared birth mass
and capture age between neonates captured from VITs and neonates
captured opportunistically using analysis of variance (ANOVA) in Program
R (R Core Team 2016 version 3.3.1; Themeau, 2015). We considered all
variables important if their 95% confidence intervals (95% CI)
excluded zero.