Assessing pronghorn translocation success, fawn survival and cause-specific mortality in Southeast New Mexico
Conant, Emily Ruth
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Translocations are a common component of pronghorn (Antilocapra americana) management across the western United States to augment declining or reestablish extirpated populations. However, post translocation monitoring has either been minimal or non-existent. In 2013, the New Mexico Department of Game and Fish entered into an agreement with a ranch located east of Cimarron, New Mexico to reduce winter crop depredation by translocating pronghorn to supplement declining populations in the southeast region of the state. A total of 159 adults were translocated over three years (61 male and 98 female) to Fort Stanton, New Mexico, where 37 were collared in both 2013 (7 male, 30 females) and 2014 (10 male, 27 female). Low fawn:doe (6:100) ratios were observed in late-summer 2013, which provided an opportunity to more closely examine fawn survival in subsequent years. Vaginal implant transmitters (VITs) were deployed in females translocated in 2014 (n = 26), and 2015 (n = 15) to more precisely estimate fawn survival. Specifically, the objectives of this research were to (1) estimate post-translocation adult pronghorn survival and cause-specific mortality, (2) estimate fawn survival and cause-specific mortality and (3) determine VIT efficacy and success in pronghorn. Collared adults were monitored from January – August 2013 and 2014. In both 2014 and 2015, adult monitoring from 1 April onwards focused on monitoring VITs, female status, and locating fawns for capture. Pronghorn fawns were located by (1) finding fawns or uncollared females without VITs opportunistically, (2) locating females with radio collars and no VITs, or (3) locating females with both radio collars and VITs. Fawns were captured and outfitted with ear-tag transmitters and then monitored to estimate fawn survival and cause-specific mortality in 2014 and 2015. A set of a priori models were developed based on adult pronghorn biology and ecology to assess the influence of a suite of covariates on translocated adult pronghorn survival on Fort Stanton. These covariates were total precipitation (mm), mean deviation from minimum temperature (°C), mean deviation from maximum temperature (°C), and mean vapor pressure deficit (VPD; mmHg). The known-fate model, with a logit-link function, in Program MARK was used to evaluate competing model plausibility and performance. Similarly, a set of a priori models were developed based on pronghorn fawn biology and ecology to assess pronghorn fawn survival at the site. Fawn survival models were estimated using the nest survival model, with a logit-link function, in Program MARK, with the following covariates: fawn mass (kg) at capture; total precipitation (mm), mean minimum and maximum temperature (°C) from date of capture to last day of individual fawn monitoring, and mean VPD (mmHg) from date of capture to last day of individual fawn monitoring. Adult survival was estimated for both year of translocation (2013 and 2014) and the year post translocation (2013 animals in 2014). Adult seasonal survival was high both years of translocation (0.68 + 0.08; 2013 and 0.95 + 0.05; 2014) and the year post translocation (0.74 + 0.23). No covariates were found to influence translocated adult survival in any model. Twenty nine fawns were captured in 2014 and 31 fawns were captured in 2015. Apparent fawn survival was 0.01 (+ 0.1) in 2014, and 0.04 (+ 0.3) in 2015, and no covariates were to found influence fawn survival in either year. In both years, most fawn mortality was attributed to predation, where most sites with fawn remains were “cached” in this study. Fawn survival in this study was some of the lowest estimated. Vaginal implant transmitters were only marginally useful in this study as related to assisting with fawn parturition sites. Most (n = 17) VITs signaled false expulsion, (i.e. VIT signaling “expelled” despite remaining in the female), resulting in significant time and effort exerted on tracking these false expulsions, rather than monitoring pregnant does for potential opportunistic fawn capture opportunities. Fawn capture from females with VITs (n = 12) was comparable to opportunistic (i.e., fawns located without VIT assistance) fawn captures (n = 13). High adult survival indicates that these translocation efforts were successful in establishing a viable adult population. However, poor fawn survival in both years suggests that future efforts should focus upon identifying and remedying potential limiting factors negatively impacting fawn survival in this localized population. We recommend modifications to VITs to limit false expulsions in future studies (specifically widening wings for better transmitter retention), so more time can be spent on fawn captures instead of spent determining transmitter status.