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.