Mule deer overload. Hunt or move them?
What happens when populations of mule deer are too high?
The Panguitch Lake unit in southern Utah, is dealing with a unique set of issues that rarely occurs across the West these days. According to the Utah Division of Wildlife Resources (UDWR), the Panguitch Lake mule deer population is too high and is causing localized damage to winter range along the western boundary of the unit.
The study area
The western boundary of the Panguitch Lake Unit is Interstate 15. This man made boundary runs north to south through nearly the center of the state and has almost completely interrupted historic migration routes for mule deer. Deer that once migrated from high elevation summer ranges out into sagebrush winter ranges to the west are now confined to a very limited section between the foothills and the interstate. This problem is further compounded by the fact that an estimated 70% of this deer herd spends their winter off the west side of the unit where temperatures, snow depths and elevations are more suitable.
According to agency biologists, too many deer on too little winter range has negatively impacted habitat in this area. To deal with this problem and reduce habitat damage, the UDWR has historically issued a limited number of doe hunting permits. Although relatively unpopular with the public, hunting does was thought to be the most suitable option at the time.
In 2012, Sportsmen for Fish and Wildlife (SFW) started to express their concern with harvesting does and began to explore the option of trapping and relocating deer to surrounding units that had lower numbers of mule deer. Very little information was previously available in order to judge the efficacy of transplanting mule deer and the information that was available suggested that previous attempts at translocations had been very unsuccessful. Still, SFW was eager to try and continued to pursue the project proposal, eventually forming a partnership between SFW, Brigham Young University (BYU), UDWR and Utah State Parks to translocate deer and study the results.
The primary goals of the project were to evaluate the survival rate, causes of mortality, movements and reproduction of transplanted deer. Additionally, researchers were interested in using the results of the project to assist managers to determine if translocating deer is a viable option to address management issues, such as over utilized winter range or urban deer issues.
How did the study work?
In January and March of 2013, SFW funded the capture of 102 does along the western winter range of the Panguitch Lake Unit. Each doe was collared with either a GPS or VHF collar and moved by truck and trailer to the western slope winter range of the Pahvant Unit, which is approximately 95 miles north.
The Pahvant Unit was chosen specifically because it currently has a low deer population, but has had several large-scale habitat restoration treatments and shares similarities with the Panguitch Lake Unit like the north/south range and I-15 running as the western boundary. In addition to the deer that were moved, a control group of 50 does were caught and similarly collared on the Pahvant range. Researchers also evaluated each deer’s body condition by taking a rump fat and tenderloin measurement and recorded its weight and estimated age.
In January and March of 2014, another 95 deer were caught, collared and translocated from the Panguitch Lake Unit to the Pahvant. An additional 20 were caught and collared on the Pahvant and released again on the Pahvant as a control group.
What did the study uncover?
Through 2013 and 2014 the collared deer were closely monitored by BYU graduate student David Smedley and some interesting results began to emerge.
The transplanted deer had survival rates of about 50% the first year and there does not seem to be any statistical difference between the group that was transplanted in January or in March. The majority of that mortality was due to coyote and cougar predation that occurred during the summer and early fall months, not with complications or issues associated with the capture. The survival rate of resident deer was 86%.
Home ranges for transplanted deer in their first year were significantly larger than resident deer. This may correlate with the increase in mortality due to predation. A larger home range equals an increased likelihood of predator encounter.
Things get more interesting the second year. Site fidelity (transplanted deer returning to same wintering location where they were released) was very high at nearly 90%. Also, the average home range of transplanted deer seemed to decrease in year two. Home ranges were still larger than resident deer, but did reduce and it is hypothesized that they will continue to reduce in future years.
Of the approximate 50% of the transplanted deer that survived the first year, 90% of those also survived the second year. In other words, the transplanted deer that survived the first year had a very high probability of surviving the next year and survival rates for that second year were very close to resident and historic known rates of survival. The data suggests that there may be a correlation between the age of transplanted deer and their survival rate. Younger does had a higher percentage of survival than older does.
Deer caught on the Panguitch Lake Unit were ultimately in poorer body condition that deer caught on the Pahvant regardless of whether they were captured in 2013 or 2014. This may indicate that the wintering population of the Panguitch Lake Unit may be near or over carrying capacity. Another interesting portion of this study that should be noted is that some of the does that were caught on the Panguitch Lake Unit and moved to the Pahvant were recaptured in year two to reevaluate body conditions. Interestingly enough, those deer had similar or even slightly better body conditions than when they were originally captured, even though that had gone through a transplant and ranged greater distances that year.
The fact that body conditions were maintained or even improved may suggest that habitat restoration efforts that occurred on the Pahvant Range are indeed helping to improve the habitat. More forthcoming studies will further evaluate that correlation. Additionally, reproduction of transplanted deer seemed to be similar to resident herds. The data suggests that capturing and transplanting deer may be a suitable way to reestablish deer herds on unused or underutilized suitable winter ranges.