The ability to capture and monitor neonate ungulates has been enhanced by vaginal implant transmitters (VITs). Improving capture methodology when using VITs will further increase the likelihood of capturing neonates. We analyzed data from 55 attempted captures of neonate elk (Cervus canadensis) in Utah, USA, during 2019-2020 to determine when searches for neonate elk should begin to maximize likelihood of capture while minimizing disturbance. Reducing the time elapsed between parturition and search initiation resulted in a decreased search length, decreased distance traveled by the neonate, and increased likelihood of capture. We initiated searches as early as 3.6 hours post-parturition with no evidence of maternal abandonment. Probability of capture was near or above 90% when searches were initiated within 10 hours of parturition. We recommend that researchers initiate searches 3.6-10 hours post-parturition to allow for capture attempts that are effective, efficient, and minimally disruptive.

The capture of neonate ungulates allows for the collection of valuable ecological data, including estimates of litter size. However, varied methods used to capture neonate ungulates can result in sampling biases. Our objective was to determine if opportunistic captures of neonate ungulates (i.e., locating neonates by visually scanning for adult females displaying postpartum behaviors) bias relative estimates of litter size and investigate potential causes if a bias does exist. We analyzed data from 161 litters of mule deer (Odocoileus hemionus) sampled using three different capture methods during 2019–2021 in Utah, USA. Estimates of litter size derived from opportunistic captures were smaller than estimates derived from movement-based captures or captures completed with the aid of vaginal implant transmitters (VITs). Age at capture was inversely related to estimates of litter size and likely influenced the detection bias associated with opportunistic captures. Neonates captured opportunistically were not older than neonates captured using movement-based methods, but were older than neonates captured with the aid of VITs. Distance between neonates from the same litter did not influence estimates of litter size. Researchers should be aware of the biases associated with different capture methods and use caution when interpreting data among multiple capture methods. Estimates of litter size derived from opportunistic captures should not be compared to estimates of litter size derived from alternative capture methods without accounting for the detection bias we observed.