Velocidad de maniobra

FUTURE POPULATIONS

This chapter is formatted for American Midland Naturalist and is coauthored by Will M. Inselman, Lora B. Perkins, Troy W. Grovenburg, and Jonathan A. Jenks

ABSTRACT

Knowledge of ungulate neonate survival allows for estimation of recruitment; crucial information for management decisions allocating harvest or cull rates, depending if the population is to remain stable, increase, or decline. However, survival rates for neonatal bison are mostly observational and anecdotal, which can be attributed to the lack of information on techniques to effectively capture and safely handle neonates. In May– July 2015, we initiated a study on Olson’s Bison Conservation Ranches, Pine River Ranch, Manitoba, Canada, to evaluate a new approach to effectively capture and handle neonate bison, monitor known-fate survival, and model future populations using both empirical and theoretical parameters. We captured bison neonates using a modified .308 caliber net–gun deployed from a utility terrain vehicle. We successfully captured and radio–tagged 10 male and 16 female neonate bison in 37 attempts (70.3% success). Over a period of four days, 16.0 man hours were spent pursuing and handling neonates, with an average capture rate of one bison neonate for every 0.6 man hours. Average handling time of bison neonates was 3.7±1.6 mins and ranged from 1.0−7.5 mins. Monitoring of neonate survival was limited to 77 days as all ear tags were dislodged to unknown circumstances. One mortality was observed resulting in an apparent survival of 96.7 % for neonates 0-2 months of age. Results of our study indicate that our approach was effective and efficient for capturing and handling bison neonates safely. No injuries or capture related mortalities were observed throughout the capture process and monitoring period. With the development of an effective transmitter for bison neonates, our capture approach will allow biologists to monitor neonate survival and collect cause–specific data on mortality of neonates in managed bison populations.

INTRODUCTION

Knowledge regarding neonate survival and cause−specific mortality rates are essential parameters to model populations (Lebreton et al., 1992). Understanding neonate survival rates allows for estimation of recruitment; crucial information for management decisions allocating harvest or cull rates, depending if the population is to remain stable, increase, or decline (Williams et al., 2002). Neonate ungulate survival rates can be low because of their vulnerability to predation (Barrett, 1984). Effective management decisions are difficult to make, if not impossible, lacking estimates of neonate survival for a given population. Although knowledge of survival rates for a population is essential, determining cause-specific mortality is equally important (Keller et al., 2013). Previous research suggests that maintaining a stable population with high neonatal mortality is difficult (Cook et al., 1971). Information regarding cause-specific mortality within a population allows for alterations in management practices to

potentially increase survival and recruitment rates.

Survival rates for bison < 1 year of age are mostly observational and anecdotal, which can be attributed to the lack of information on techniques to effectively capture and safely handle bison neonates (Fuller et al., 2007; Gates et al., 2010). To our knowledge, previous studies of bison neonate survival rates have been observational, primarily cow-calf pair counts, lacking information on known−fate mortality agents (Table 2.1). Additionally, most managers do not handle and tag bison neonates until ≥ 6 months of age because they are susceptible to injuries in corral systems (D. J. Lammers, personal communication).

Techniques to capture large ungulates and their offspring are similar for most species. Previous techniques employed to capture ungulates include: helicopter net– gunning (Barrett et al., 1982; White and Bartmann 1994; Jacques et al., 2009), chemical immobilization (Haigh and Gates, 1995; Fuller et al., 2007), clover traps (Clover, 1956), rocket nets (Beringer et al., 1996), drop–nets (White and Bartmann, 1994), drive nets (Kock et al., 1987), and hand–captures (Grovenburg et al., 2014; Smith et al., 2014). Clover traps, rocket nets, drop nets, and drive nets are non–selective techniques that require significant effort to complete. Conversely, hand–captures, net–guns, and

chemical immobilization are selective techniques to capture individuals being targeted by researchers.

Currently, a need exists for an approach to effectively capture neonate bison (Haigh and Gates, 1995). Methods for capturing adult bison are available (Haigh and Gates, 1995; Joly, 2001; Fuller et al., 2007) and could potentially be employed to capture neonates. Contrary to methods employed by Haigh and Gates (1995), Joly (2001)

recommended the use of a net–gun over chemical immobilization when capturing bison; reduced handling times decreased the chance of capture–related mortality. Lacking a chase vehicle for protection when handling neonates captured with a net–gun from a helicopter could predispose researchers to increased risk of injury from parturient female bison. Moreover, helicopter captures are expensive and may not be effective in a densely forested landscape. Therefore, an alternative approach to capturing neonates from a helicopter needs to be developed. The objectives of this study was to evaluate the effectiveness of capturing bison neonates with a net–gun from a utility terrain vehicle (UTV), calculate neonate survival and determine cause–specific mortality, and model

future populations. A successful approach to capture neonatal bison will allow managers to monitor marked bison neonates, providing data for estimating survival, cause-specific mortality, and recruitment for managed bison populations across North America. Moreover, these empirical parameters will help managers accurately model future populations and aid in determining proper cull rates depending on specific management objectives.

METHODS Neonate Capture

Neonatal bison captures were conducted 19–22 May 2015, within the South Pasture of the Olson’s Conservation Bison Ranch (Figure 0.2). The South Pasture encompasses 976 ha, of which 264 ha (27.1%) was considered open/grassland, with the remaining 712 ha (72.9%) characterized as forest or wetlands. However, only four open/grasslands totaling 165 ha (17.0%) were considered suitable for captures due to limited accessibility and terrain conditions (Figure 2.1).

Prior to capture, we baited bison into open fields by dispensing 800 kg of oats from a Trip Hopper Range Feeder trailer (T&S MFG., INC., Jermyn, TX, USA). The hopper, towed by a pick–up truck (hereafter bait–truck), dropped 3 kg of grain in 3 m intervals. This method dispersed the herd over a large area, which allowed the capture crew to identify target neonates. Target neonates were individuals with exposed umbilical cords, wet or dry, and were estimated to be < 7 days old (R. L. Metcalfe, personal

communication).

We mechanically restrained bison neonates using a modified .308 caliber net–gun (Wildlife Capture Equipment, Austin, TX, USA; Barrett, 1982) that deployed a 4.6 m2

net. The capture crew consisted of three individuals: a UTV driver, net–gunner/mugger, and bait–truck operator. Target neonate bison were singled out from the herd with the UTV until within range (< 15 m) for the net-gunner to deploy the net. After successfully restraining a neonate, the bait–truck operator would assist the mugger in retrieving the neonate while the UTV operator kept the mother from intercepting the crew. Neonates were placed into the bed of the bait–truck for safe handling. The UTV was parked parallel to the most exposed bumper of the bait–truck to deter protective female bison from injuring the capture crew during the handling process. Each calf was fitted with a model M3620 very high frequency (VHF) ear tag transmitter (Advanced Telemetry Systems (ATS), Isanti, MN, USA) to monitor for capture–related mortality. All three crew members remained vigilant for bison that posed a threat to the capture team.

Throughout the capture process, data for each bison neonate was collected; sex, maternal identification, and time spent pursuing and handling the calf. Any injuries to neonates occurring from capture were documented. Radio–tagged neonates were monitored for captured–related mortality at least once daily for 30 days (Beringer et al., 1996). The Institutional Animal Care and Use Committee at South Dakota State

University (Approval No. 15–038A) approved all animal handling methods for bison neonates.

Calf Survival and Cause−Specific Mortality

We used a handled receiver (R–1000, Communication Specialists, INC., Orange, CA, USA) and an H-antenna (ATS) to monitor neonate bison for captured–related

additional 47 days, or until individual ear–tags were recovered. A field necropsy was performed upon discovery of a deceased neonate to best determine cause of death.

Population Modeling

A complete census of the Pine River Ranch herd was conducted during the annual round–up in 2016 and partially in 2015. In 2016, we classified individuals as a brown calf (~ 8–10 months old), yearling heifer (2014 calf, 190-320 kg), two year old heifer (2013 calf, 320-410 kg), adult cow (3+ years old, 410+ kg), yearling bull (2014 calf, 180- 340 kg), young bull (2−5 years old, 340-500 kg), and breeding bull (5+ years old, 500+ kg; Berger and Peacock, 1988). We estimated age by analyzing tooth replacement, horn development, pelage, weight and/or rib separation (G. Clapham, personal

communication; Fuller, 1959). Referencing our 2015 capture data, we assumed calf and yearling sex ratios of 2:3, males to females, respectively. We conducted rectal palpation on all females ≥ 2.5 years old to test for pregnancy and estimate fetus development (Kirkpatrick et al., 1992). Additionally, we noted any 2015 calf with a ripped left ears with the assumption this resulted from an ear tag being dislodged during summer 2015.

We developed an interactive model using Microsoft Excel (Microsoft, Redmond, WA, USA) to predict a 15 year population growth using empirical and theoretical data on population dynamic parameters for bison (Van Vuren and Bray, 1986). Our exponential “no cull” model includes survival estimates for calves (0.915), yearlings (0.955), two year old heifers (0.960), young bulls (0.950), cows (0.960), and breeding bulls (0.950), pregnancy rates for two year old heifers (0.531) and cows (0.714), and no cull rates. Our stable model suggests cull rates for two year old heifers (0.180), young bulls (0.340), cows (0.250), and breeding bulls (0.970), while the survival and pregnancy rates

remained the same as the no cull model. Our 15 year goal was to manage the bison population between the estimated carrying capacity of 2,000-2,200 individuals (Chapter 1) and to approximately manage for a cow:bull ratio of 8:1, to maximize reproductive success (D. J. Lammers, personal communication). Additionally, we estimated projected sales given our suggested cull rates for the stable population model. We estimated rail weight by taking 50% and 60% of the average live weights of female and male cull bison, respectively, from March 2016 roundup. Projected sales were calculated given current estimates of $8.47 US dollars*kg−1 for cull cows, $9.57 US dollars*kg−1 for 2 year old heifers, and $9.79 US dollars*kg−1 for young and breeding bulls (D. J. Lammers, personal communication).

RESULTS Neonate Capture

We successfully captured and radio–tagged 10 male and 16 female neonate bison in 37 attempts (70.3% success). Over a period of four days, 16.0 man hours were spent pursuing and handling neonates, with an average capture rate of one bison neonate for every 0.6 man hours. Average handling time of bison neonates was 3.9±1.6 mins and ranged from 1.0−7.5 mins. Unintentionally, two neonates were captured in one net. This capture was removed from our handling time analysis as we cut holes in the net to release the neonates. No injuries or mortalities were observed throughout the capture process. Moreover, no capture–related mortalities occurred during the 30 day monitoring period. All ear tag transmitters detached and were recovered by day 77. However, our 30 day post capture survival was 100% (N=21).

Calf Survival and Cause−Specific Mortality

Survival monitoring was limited to 77 days as all ear tags dislodged by 30 July 2015. We documented one mortality on day 44 (27 June 2015) with cause of death being starvation/drowning. This individual was mired in mud and was too weak to get out, resulting in death by drowning. She was weak and stunted when captured because her mother was unhealthy. Her mother died the same fate 2 days prior on 25 June 2015. It is likely the neonate received minimal nutrition, if any at all, in the form of milk from her mother throughout her life, which resulted in her weak state. Therefore our apparent survival for 0-2 months of age was 96.7 %.

Population Modeling

The March 2016 census produced a total population of 1,834 bison. The

population distribution comprised of 542 calves, 331 yearlings, 147 two year old heifers, 168 young bulls, 591 mature cows, and 55 breeding bulls. Rectal palpation resulted in 78 pregnant two year old heifers and 422 pregnant cows. We observed 23 brown calves with ripped left ears of the 227 individuals checked. Therefore, our 10 month survival estimate is 76.7% (23/30).

The March 2015 annual round-up documented 263 pregnant female bison that should have given birth May−August 2015. These individuals would be documented as brown calves during the March 2016 round-up as their pelage transitions from orange to brown at approximately 3 months-of-age (R. Metcalfe, personal communication). However, only 227 brown calves were observed in March 2016, resulting in an 86.3% parturition/10 month survival rate.

Our theoretical “no cull” model produced a population of 21,211 bison by 2031 (Figure 2.2). Our “best model” yielded a population of 2,099 bison in 2031 while remaining a stable 7:1 cow:bull ratio throughout (Figure 2.3), satisfying both management goals. Moreover, the projected revenue given the suggested cull rates stabilizes at approximately $880,000, annually (Figure 2.4).

DISCUSSION

Neonate Capture

Results of our study indicated that our approach was effective for capturing and handling bison neonates safely. We captured 26 neonates with minimal effort, a small capture crew, and few man hours. Data collection was limited to reduce handling time and to limit potential capture myopathy and abandonment, which increases in ungulates as handling time increases (Firchow et al., 1986; Beringer et al., 1996). However, no previous research has been conducted handling bison < 7 days old and thus, potential for capture myopathy and abandonment was unknown. No mortalities were reported during handling in contrast to studies of neonate ungulates (Ballard et al., 1981; Bertram and Vivion, 2002), but we recommend maximum handling times < 7.5 mins to reduce chance of capture–related mortality.

Although our study was conducted on a private, captive herd, we believe this approach can be implemented across ecosystems where bison currently inhabit. Few populations of bison are considered “wild” and of those, most are confined to boundaries in which they roam, similar to our study. Our study site was heavily forested (65.6%), limiting our suitable capture areas to open/grassland totaling 165 ha (17.0%). Our

approach will be most effective in habitats with a higher proportion of open/grasslands as bison spend up to 80% of their time inside or within 25 m of meadows (Fortin et al., 2003).

Manually restraining bison neonates via net–gun was chosen over alternative techniques because it has the lowest combined risk to ungulate health when compared to use of chemical immobilization, or drop–nets and drive nets (Kock et al., 1987).

Additionally, drop–nets, drive–nets, and rocket nets are mass capture techniques and were not practical in our circumstance as we were selectively targeting neonates. Conversely, chemical immobilization has the highest combined risk as cow–calf pairs would need to be immobilized to safely handle neonates (Kock et al., 1987). Upon darting, the potential for bison to run is high and in heavily forested landscapes could increase risk of injury to bison and capture crew members. Moreover, drugs required for chemical immobilization add cost and require training and permitting.

Processing the herd through a corral system could be effective for neonate capture but it is likely handling time would be greater, consequently increasing the likelihood of capture–related mortality (Firchow et al., 1986; Beringer et al., 1996). Likewise,

neonates may be more susceptible to injury and endure more stress over a longer period of time in corrals. Nevertheless, research should be conducted to evaluate the

effectiveness of alternative techniques to capture bison neonates less than a week old.

Population Modeling

We potentially missed up to 3 calves as we forgot to check a few individuals early on in the process. If so, our survival estimate would be 86.7% (26/30 calves), which is

similar to our predicted survival from the annual round-up data (86.3%). However, our 10 month survival of 76.7-86.7% is significantly lower than the 0-2 month survival of 97%, which is unusual as one would assume that survival would increase with age. The harsh winters endured by the older age class of calves could explain the decreased survival rates. Additionally, wolves tend to associate with the bison herd in the winter months more than any other time of the year (R. Metcalfe, personal communication), likely predating on vulnerable calves in deep snow. Moreover, calves unaccounted for can be explained by error from both pregnancy testing in March 2015 and identification of brown calves in March 2016. Some yearlings in the 180−230 kg range may actually be brown calves, but were mistakenly identified as yearlings due to their advanced horn development. We did observe at least two additional non-tagged neonate mortalities during June−July 2015 that were a result from infections of injuries incurred at a young age. Although our model is designed specifically for the Pine River Ranch, similar models for other ranches can be produced given management goals, empirical data, and/or life history tables.

CONCLUSIONS

Bison reintroductions across North America are becoming widely implemented (ADF&G, 2015; Banff National Park, 2015; Steenweg et al., 2016), thus increasing the need for effective monitoring techniques. Our approach allows biologists to capture and safely handle bison neonates at a young age. However, development of a more reliable VHF transmitter to attach to bison neonates is necessary to monitor survival > 2 months of age. Knowledge on mortality agents affecting bison neonates allows for

herds. Additionally, our technique provides bison ranchers a low-cost means to safely and efficiently capture and mark their bison earlier in the year.

ACKNOWLEDGMENTS

We thank R. Metcalfe for logistical and field support throughout our study. We also thank C. N. Jacques and J. B. Smith for providing comments on earlier drafts of our manuscript. Funding was provided in part by Olson’s Conservation Bison Ranches, South Dakota State University’s Department of Natural Resource Management, and South Dakota Agricultural Experiment Station.

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