Using maternal mule deer movements to estimate timing of parturition and assist fawn captures

Abstract

ABSTRACTMovement patterns of maternal ungulates have been used to determine parturition dates and aid in locating fawns, which may be important for understanding reproductive rates (e.g., pregnancy and fetal), but such methods have not been validated for mule deer (Odocoileus hemionus). We first determined timing of parturition using vaginal implant transmitters (VITs) and then predicted timing of parturition using VITs in conjunction with Global Positioning System collar data in the Piceance Basin of northwestern Colorado, USA, during 2012–2014. We examined daily movement rate to determine differences in movement rate among days (7 days pre‐ and postpartum) and for movement patterns indicative of parturition. Mean daily movement rate (m/day) of 102 maternal deer decreased by 46% from 1 day preparturition ( = 1,253, SD = 1,091) to parturition date ( = 682, SD = 574), and remained at this low rate 1–7 days postpartum. We applied an independent data set to validate predicted parturition dates based on daily movement rate. We estimated day of parturition correctly (i.e., day 0), within 1–3 days postparturition, and ≥4 days postparturition of field‐reported dates for 10 (29%), 21 (60%), and 4 (11%) maternal females, respectively. For novel data sets, we predict that a mule deer female whose daily movement rate decreases by ≥46% and remains low ≥3 days postparturition particularly when preceded by a sudden increase in movement—has given birth. However, we caution that disturbance of deer by field crews should be minimized, and if birth sites are not found, neonatal mortality will be underestimated. Our results can help determine timing and general location of parturition as an aid in capturing fawns when the use of VITs is not feasible, with the ultimate objective of estimating pregnancy, fetal, and fawn survival rates if birth sites are found. © 2018 The Wildlife Society.