Evaluating antipredator strategies and ecological mechanisms that affect neonatal white-tailed deer (odocoileus virginianus) predation risk in Minnesota’s agricultural prairies

Abstract

Neonatal survival is a key driver of annual variation in ungulate population growth. Neonatal ungulates are vulnerable to many factors, but predation is often the leading cause of mortality. A key logistical challenge in studying neonatal survival is locating and collaring individuals, prompting us to evaluate new technologies to meet our study objectives. We found the use of a thermal infrared (TIR) equipped drone to be an efficient method under good conditions (e.g., cloudy, nighttime) to locate fawns in open habitats and outperformed other capture methods (e.g., vaginal implant transmitters, ground searches, monitoring doe behavior). Drones show immense promise in the future of wildlife research. Recent advances in biotelemetry enable monitoring of large mammals with varying neck sizes across multiple ecological milestones (e.g., summer survival, dispersal, winter habitat use). Radiocollars are instrumental in tracking home range size, dispersals, migrations, resource use, behavior, and causes of mortality. However, we identified that collar failures (e.g., broken, premature expansion, fence-related) often occurred after 6 months of age, which may reduce sample sizes necessary to examine dispersal, migration, and first-year survival. These findings emphasize the importance of aligning study design with specific ecological questions (e.g., summer survival, migration) and accounting for potential retention issues (e.g., barbed-wire fences, thick cover) when determining sample size. We deployed expandable global positioning system (GPS) collars on neonatal white-tailed deer (Odocoileus virginianus) fawns and modeled their activity patterns using piecewise regression models to determine more refined timing of antipredator strategies and how transitions changed with age by individual fawns. On average, fawns ended their hider strategy at 10.9 days old and entered the transitioner strategy for a duration of 25.5 days, and then initiated the follower strategy at 37.0 days old. Males were 1.8x more likely to die from predation than females. We also found fawns in the hider strategy had a 4.9x higher risk of mortality than those in transitioner strategy. These findings suggest that as fawns increase mobility via neuromuscular development, they shift from hiding to fleeing behaviors. This increased mobility enhances antipredator strategies, with more “fidgety fawns” demonstrating improved predator evasion tactics. We hope future researchers use our framework to examine other neonatal ungulates to further develop a robust antipredator ethogram (e.g., hider, transitioner, follower) with varying predator cohorts to examine interspecific ungulate variation that will yield insight into neonatal risk and ungulate population dynamics. Evaluating bedsite selection is a key component of neonatal risk and predator avoidance. Fawns are most susceptible to predation early in life and better understanding predisposing factors may be important to juvenile recruitment. Therefore, proper bedsite selection to avoid predator detection likely plays a critical role in survival. We compared mortality sites of fawns predated by coyotes with paired and capture bedsites of surviving fawns to assess variation in habitat characteristics that may be important to predation risk. We also compared bedsite characteristics by neonatal antipredator strategy (e.g., hider, follower) to further examine variation in selection. Our results revealed no differences with fawn sightability or lower canopy cover at paired and capture bedsites compared to mortality sites. We also found no differences with concealment cover, suggesting that concealment was adequate throughout the study area. Finally, we investigated habitat selection of fawns by antipredator strategies (e.g., hider, transitioner, follower) using an integrated step selection analysis (iSSA), and evaluated 3 predator reduction hypotheses: prey hiding hypothesis (PHH, selection for habitats with increased cover), predator escape hypothesis (PEH, selection for habitats with increased visibility), and landscape of fear hypothesis (spatial avoidance of predators, LFH). We found distinct differences in habitat selection across strategies, with hiders and transitioners favoring cover-rich habitats like grasslands and forests, aligning with the PHH. In contrast, followers exhibited behaviors consistent with the LFH by avoiding coyote travel corridors, such as roads and croplands. These insights provide a deeper understanding of the behavioral adaptations neonatal ungulates use to reduce predation risk and contribute to a broader understanding of predator-prey dynamics.