Evaluating expandable global positioning system collars for white‐tailed deer neonates

Abstract Recent advances in biotelemetry allow monitoring of large mammals with varying neck sizes across multiple ecological phases (e.g., summer survival, dispersal, winter habitat use). Current collar technologies allow for use on neonatal ungulates such as white‐tailed deer ( Odocoileus virginianus ). However, assessment of the function and overall retention of recent technology is warranted. Our objectives were to evaluate the retention rates of collar designs, determine factors affecting retention (e.g., mass, sex), and assess global positioning system (GPS) collar function (e.g., fix success rate, mean linear error) on wild neonatal deer in grassland and forested habitat types. We fit 75 (39 females, 36 males) and 82 (33 females, 49 males) white‐tailed deer fawns with expandable GPS collars of 2 different collar designs 2021 (V1) and 2022 (V2), respectively. Collar retention issues included caught on fences, broken collar, and premature expansion. Collar retention at 3 months of age was 88% and 91% in 2021 and 2022, respectively, declining to 41% and 59% by 1 year of age. Older fawns at capture were less likely to retain their collar, such that for every 1 day increase in fawn age at capture, the odds of collar failure increased by 52%. We found no evidence that sex or birth size affected retention. Fix success rate was high (~97%) and showed no evidence of variation by canopy cover. However, location error was greater (β = −7.7, 95% CI = −5.92–−9.39) in forested ( = 12.7 m) versus grassland ( = 5.1 m) habitat type. Both collar designs (V1, V2) functioned well and would allow for assessing spring and summer survival and cause‐specific mortality for fawns collared at birth. However, collar failures often occurred after 6 months of age, which may reduce sample sizes necessary to examine dispersal, migration, and first year survival. We recommend researchers consider their specific ecological questions (e.g., summer survival, dispersal) and account for potential retention issues (e.g., barbed‐wire fences, thick cover) when determining sample size. We also recommend continued interaction with collar companies to refine collar designs and enhance function of neonatal expandable collars.