Deer and Elk Ecology within the Trans-Pecos and Panhandle CWD Zones
Request for Proposals November 2020
Shawn Gray, Mule Deer and Pronghorn Program Leader
In July 2012, CWD was initially detected in Texas in mule deer residing in the Hueco Mountains. Since then the disease has also been detected in the Franklin Mountains. These mountain ranges are located in far west Texas within El Paso and Hudspeth counties. The Hueco Mountains extend from southern New Mexico approximately five miles north of the state line about 20 miles into Texas along the El Paso/Hudspeth County line. The southern end of the Franklin Mountains is located within the city of El Paso and spans north approximately 23 miles into New Mexico. Most of the Franklin Mountains are within the Texas Parks and Wildlife Department (TPWD) Franklin Mountains State Park. Because of CWD detections in New Mexico near our state line and the north/south orientation of the Hueco/Franklin Mountains, TPWD staff believe it is likely that the disease spread from New Mexico.
Texas Parks and Wildlife Department and Texas Animal Health Commission (TAHC) implemented a disease-management strategy intended to determine the geographic extent and prevalence of CWD and reduce risks of the disease spreading out of the area in which it is known to exist upon detection of the index case in 2012. The initial step in the plan was to develop CWD Management Zones to eliminate or limit the movement of live susceptible species and certain carcass parts out of those zones. CWD Management Zones (Containment and Surveillance) were delineated using the best available science at that time regarding susceptible species’ densities and movements as well as habitat within the affected areas. However, mule deer movement, dispersal, home range and habitat use are poorly understood within this region of the state.
Another part of the CWD management plan was to increase surveillance by creating mandatory hunter check stations where hunters bring their harvested animals (mule deer, white-tailed deer and elk) for sample collection. The more intensive sampling efforts have produced 549 CWD test results within the Trans Pecos Containment Zone during the past eight hunting seasons. Of these, 158 CWD test results have come from the Hueco Mountains area with 17 CWD positive mule deer being detected since 2012. Almost all samples are from mule deer bucks as there is no doe harvest within this area of Texas. Therefore, it appears that CWD prevalence among mature mule deer bucks within the Hueco Mountains area is about 10%. In the Franklin Mountains the disease was first detected in the summer of 2018. Following the index case in the Franklin Mountains four more positives have been detected for a total of five detections. There is no hunting allowed within the Texas side of the Franklin Mountains because the mountains are located within the city limits of El Paso and are mostly within the TPWD Franklin Mountains State Park. The CWD positives found in the Franklin Mountains were either mule deer euthanized by TPWD officials or roadkills. From 2012–2019, thirty-one mule deer have been sampled within the Franklin Mountains and surrounding area. Based upon current data, the CWD prevalence rate in and around the Franklin Mountains is slightly higher than in the Hueco Mountains area at approximately 15%.
The disease has also been detected in free-ranging mule deer, white-tailed deer and elk in Dallam and Hartley counties, located in the northwest Panhandle. The first case of CWD in the northwest Panhandle was detected in a mule deer buck during the 2015 hunting season. Subsequently, 1,127 deer and elk have been sampled within the Panhandle Containment Zone with 18 animals (13 mule deer, 4 white-tailed deer and 1 elk) testing positive for CWD. So far, the CWD prevalence (all species combined) within the Panhandle Containment Zone appears to be about 1.5%. However, because of the detection of CWD in 3 species of cervids, perceived lack of movement barriers and the relatively close distance of the CWD positives to the Canadian River Breaks (a major wildlife travel corridor across the northern Panhandle), this area is also of significant concern to TPWD. Based upon ongoing research regarding mule deer ecology in other portions of the Panhandle, adult deer movements may not be as extensive as once thought. However, data from the same study documented several young mule deer dispersed long distances (e.g., one buck dispersed 70 miles and one doe dispersed 35 miles from their natal ranges).
Mule deer density in the Hueco/Franklin Mountains of El Paso and Hudspeth counties is around 100 acres/mule deer as documented by TPWD helicopter surveys in February 2020; however, long-range dispersal or seasonal movements can be primary causes of spreading diseases such as CWD into new areas. Management practices that concentrate deer to specific areas can also exacerbate the spread of CWD. Mule deer, white-tailed deer and elk exist within the High Plains and Rolling Plains ecological regions of the northwest Texas Panhandle at higher densities (especially when mule deer and white-tailed deer are combined) than in the Hueco/Franklin Mountains. They occupy a variety of rangeland habitats in the northwest Panhandle from breaks, cottonwood draws, sand hills and short grass and mixed prairies. These herds in the northwest Panhandle also have access to agriculture such as winter wheat, corn, alfalfa, cotton and beans, which act as attractants because of the added nutrition they provide. Elk do occur in the northwest Panhandle, but in very low numbers within the Panhandle CWD Containment Zone. A much larger population of elk exists within the Panhandle CWD Surveillance Zone, near the Canadian River. These elk could be dispersing north into the CWD Containment Zone.
To date, data are lacking on cervid movements within these areas, and the extent and influences on their movements are educated inferences, at best. Some researchers have reported that bucks have a higher incidence of CWD compared to does, and buck movements can be more extensive, especially during breeding season. In addition, elk are known to disperse at much further distances than even mule deer in other states. Formulating and implementing reasonable CWD management actions is difficult when basic movement and habitat preference or avoidance are largely unknown as they relate to the ecosystems in question. Habitat components that act as attractants such as waters, feeders, agricultural fields, etc. also need to be evaluated as they relate to cervid movements and spatial and temporal use.
The 2015 Land and Water plan contains four specific goals. Research to further our knowledge of CWD prevalence as it relates to cervid movements and dispersal, habitat and habitat component use and survival in the Hueco/Franklin Mountains and northwest Panhandle would fall within goal one and associated strategies:
- Practice, encourage and enable science-based stewardship of natural and cultural resources.
- TPWD will be an exemplary steward of the public’s lands and waters by using the best available science for ecosystem-based management.
- TPWD will maintain the highest level of scientific validity and credibility.
The study design should address these main objectives:
- Evaluate sex- and age-specific (< 9 months old) common CWD-susceptible species movements to determine if cervid populations found within the Hueco/Franklin Mountains (mule deer) and northwest Panhandle (mule deer, white-tailed deer and elk) are isolated and which habitats are being selected for or avoided yearly and seasonally (e.g., breeding, gestation, parturition and lactation);
- Document which habitat components may cause animal concentrations yearly and seasonally (e.g., breeding, gestation, parturition and lactation), thus potentially increasing the prevalence of CWD;
- Monitor the incidence of CWD in radio-collared cervids through ante-mortem tests during annual captures;
- Investigate adult cervid mortality and determine cause of each mortality.
Ranches located within and near the Hueco/Franklin Mountains in El Paso and Hudspeth counties and in Dallam and Hartley counties will be the main study sites. The TPWD Franklin Mountains State Park can also be a study site. Since some deer and elk may be coming from New Mexico, New Mexico Game and Fish may also be a partner on the project. Focus will be on collaring mostly young deer and elk (< 9 months) because of their tendency to disperse farther distances than mature animals and to improve the researchers’ ability to determine CWD infection chronology within individuals. The use of satellite GPS radio-collars are essential to get data that are more reliable for fine-scale movements and habitat use as well as the improved ability to get to mortality events as quickly as possible. We predict that such research must be conducted for a minimum of 3 years to collect meaningful data.
Expected Management Implications
This project will provide new and essential information regarding yearly and seasonal movements, habitat preference/avoidance, and habitat component attractants in relation to CWD prevalence of cervids existing in the Hueco/Franklin Mountains and northwest Panhandle. Most importantly, results obtained from this research will assist TPWD in refining CWD management strategies for these areas.