Effectiveness of a redesigned vaginal implant transmitter in mule deer

Abstract

Our understanding of factors that limit mule deer (Odocoileus hemionus) populations may be improved by evaluating neonatal survival as a function of dam characteristics under free‐ranging conditions, which generally requires that both neonates and dams are radiocollared. The most viable technique facilitating capture of neonates from radiocollared adult females is use of vaginal implant transmitters (VITs). To date, VITs have allowed research opportunities that were not previously possible; however, VITs are often expelled from adult females prepartum, which limits their effectiveness. We redesigned an existing VIT manufactured by Advanced Telemetry Systems (ATS; Isanti, MN) by lengthening and widening wings used to retain the VIT in an adult female. Our objective was to increase VIT retention rates and thereby increase the likelihood of locating birth sites and newborn fawns. We placed the newly designed VITs in 59 adult female mule deer and evaluated the probability of retention to parturition and the probability of detecting newborn fawns. We also developed an equation for determining VIT sample size necessary to achieve a specified sample size of neonates. The probability of a VIT being retained until parturition was 0.766 (SE = 0.0605) and the probability of a VIT being retained to within 3 days of parturition was 0.894 (SE = 0.0441). In a similar study using the original VIT wings (Bishop et al. 2007), the probability of a VIT being retained until parturition was 0.447 (SE = 0.0468) and the probability of retention to within 3 days of parturition was 0.623 (SE = 0.0456). Thus, our design modification increased VIT retention to parturition by 0.319 (SE = 0.0765) and VIT retention to within 3 days of parturition by 0.271 (SE = 0.0634). Considering dams that retained VITs to within 3 days of parturition, the probability of detecting at least 1 neonate was 0.952 (SE = 0.0334) and the probability of detecting both fawns from twin litters was 0.588 (SE = 0.0827). We expended approximately 12 person‐hours per detected neonate. As a guide for researchers planning future studies, we found that VIT sample size should approximately equal the targeted neonate sample size. Our study expands opportunities for conducting research that links adult female attributes to productivity and offspring survival in mule deer. © 2011 The Wildlife Society.

Dead before detection: addressing the effects of left truncation on survival estimation and ecological inference for neonates

“…Of the 49 deployed VITs, 81% resulted in confirmed birth sites and 62% in captured fawns at the birth site, representing very high retention and fawn detection rates in comparison with other VIT‐based studies (Bishop et al . ). In addition, 8% of females fitted with VITs expelled the devices before parturition, identified by VITs found at sites lacking the characteristics of birth sites.…”

Landscape‐scale habitat characteristics and neonatal white‐tailed deer survival

“…We measured new hoof growth, recorded hoof and umbilicus characteristics, and noted behavior during capture to use when estimating the age of neonates not found with a VIT (Sams et al , Brinkman et al ). For neonates found through the use of a VIT that was not expelled prematurely, date of birth was the date the VIT was expelled (Bishop et al , Hasapes and Comer ). We estimated birth mass by regressing neonate mass at capture (nearest 0.01 kg) on age at capture separately for each study area and sex, and used the estimated regression coefficients to predict birth mass (Smith et al , Eacker et al ).…”

Timing of precipitation in an arid environment: Effects on population performance of a large herbivore

“…Vaginal implant transmitters used during this study were similar to those described by (Bishop et al, 2011). In addition to the temperature sensor traditionally equipped in VITs used in previous studies (Bishop et al, 2007;Carstensen, DelGiudice, & Sampson, 2003;Johnstone-Yellin, Shipley, & Myers, 2006), VITs in this study also had a programmed photo sensor.…”