Distribution, Movements, and Space Use by Elk on the Idaho National Laboratory Site
Investigators and Affiliations
- Ryan A. Long, Ph.D. Candidate, Department of Biological Sciences, Idaho State University, Pocatello, Idaho
- Jericho C. Whiting, Ph.D., Wildlife Biologist, Environmental Surveillance, Education, and Research Program, Gonzales-Stoller Surveillance, LLC, Idaho Falls, Idaho
- R. Terry Bowyer, Ph.D., Professor, Department of Biological Sciences, Idaho State University, Pocatello, Idaho
- John G. Kie, Ph.D., Research Professor, Department of Biological Sciences, Idaho State University, Pocatello, Idaho
- U. S. Department of Energy-Idaho Operations Office
- U. S. Environmental Protection Agency
- The Berryman Institute
- The Rocky Mountain Elk Foundation
- Idaho State University
Background: Large mammals play important functional roles in many ecosystems, including sagebrush-steppe. Indeed, large herbivores often act as keystone species, and thus understanding the causes and consequences of their patterns of behavior can provide important insights into a variety of ecosystem processes. In addition, detailed data on movements of large mammals can provide land managers with critical information on ecological interactions between those animals and their environment. Such information is necessary for understanding past effects of anthropogenic disturbance on mammals and for predicting effects of future development, as well as for minimizing the negative effects of development on mammals. Such data may also provide important clues about the potential transport of nutrients and environmental contaminants by large mammals across landscapes. Nevertheless, the detailed data necessary to understand large-scale patterns of movement and resource selection by large mammals on the INL Site have never been obtained.
Previous research on large herbivores at the INL Site has focused primarily on documenting presence-absence or general locations of those animals through aerial surveys, with some notable exceptions. For example, Strohmeyer and Peek (1996), Strohmeyer et al. (1999), and Comer (2000) reported that elk (Cervus elaphus) on the INL Site foraged primarily in burned areas and agricultural fields at night, but strongly selected sagebrush habitat on lava located far from foraging areas during the day. Even in those studies, however, locations of individual elk were collected infrequently via very high frequency (VHF) radio-collars, and consequently a large number of important questions remain unanswered. For example:
- To what extent do elk on the INL Site utilize surrounding agricultural lands, and how does that use vary seasonally?
- What proportion of the elk population on the INL Site is resident (i.e., remains on the Site all year) versus migratory (i.e., leaves the Site for some portion of the year)?
- How do elk on the INL Site respond to anthropogenic factors already in place, such as roads and Site facilities?
- How do general patterns of movement and space use by elk on the INL Site change seasonally?
These and similar questions can be addressed using high-frequency location data, and answers to these questions will allow biologists and land managers to minimize the negative effects of future development on populations of elk and other large herbivores on the INL Site, and will also provide information useful for managers desiring to minimize depredation of crops surrounding the INL Site by large herbivores. In addition, detailed movement data for elk will provide insights into the potential role of this species in distributing environmental contaminants both on and off of the INL Site.
Objectives: The overall goal of our project was to document landscape-scale patterns of movement and space use by elk at the INL Site. Results of our study will be integrated into the Conservation Management Plan for the INL Site, and will provide the U. S. Department of Energy with important information for environmental planning purposes. In addition, our results will provide information useful for managers desiring to minimize depredation of crops surrounding the INL Site by large herbivores, and will provide insights into the potential role of large mammals in distributing environmental contaminants both on and off of the study site.
- Capture 20 elk per during 2010-2012 on the INL Site in order to collect data on body condition, morphology, disease, and pregnancy status, and to fit each of those animals with a GPS collar programmed to collect hourly locations between March and December.
- Determine the extent to which critical habitat (e.g., calving grounds) for elk occurs within the Development Zone
- Determine when, where, and to what extent elk move between the INL Site and surrounding agricultural lands to aid in quantifying potential depredation problems and potential transport of contaminants off of the INL Site by elk.
Accomplishments Through 2012:
- A total of 58 female elk were captured and fit with GPS collars in the winters of 2010, 2011 and 2012 by net-gun from a helicopter or by drive-netting. During the capture, data on body condition, morphology, and blood parameters were collected.
- We plotted all locations obtained from GPS-collared elk in ArcGIS 10 and calculated the proportion of locations occurring in agricultural fields (based on 2011 NAIP imagery) on a seasonal basis.
- We used the “near” tool in ArcGIS to calculate the distance from each elk location on the INL Site to the nearest Site facility, as well as to the nearest primary road. We then calculated the percentage of elk locations that occurred within 1 km of either INL Site facilities or primary roads on the Site.
We captured a total of 58 adult female elk on the INL Site during winters of 2010-2012. After accounting for post capture mortality and equipment failure (primarily during 2010), we obtained usable GPS data from 35 of those animals (Figure 10-8). A total of 55,998 hourly GPS locations were obtained for elk during spring (April-June; Figure 10-9), 39,907 locations were obtained during summer (July-September; Figure 10-10), and 35,671 locations were obtained during autumn (October-November; Figure 10-11). The proportion of elk locations occurring on the INL Site was 27 percent, 23 percent, and 63 percent during spring, summer, and autumn, respectively.
Figure 10-8. 131,576 hourly GPS locations obtained from 35 collared female elk (Cervus elaphus) on the INL Site from April-November, 2010-2012.
Figure 10-9. 55,998 hourly GPS locations obtained from 35 collared female elk Cervus elaphus) on the INL Site during spring (April-June), 2010-2012.
Figure 10-10. 39,907 hourly GPS locations obtained from 35 collared female elk Cervus elaphus) on the INL Site during summer (July-September), 2010-2012.
Figure 10-11. 35,671 hourly GPS locations obtained from 35 collared female elk Cervus elaphus) on the INL Site during autumn (October-November), 2010-2012.
Overall, elk spent very little time in agricultural fields surrounding the INL Site during spring through autumn, or within 1 km of Site facilities or primary roads (Table 10-3). The amount of time spent in close proximity to each of these areas (agricultural fields, facilities, and roads) increased, however, between spring and autumn (Table 10-3). A maximum of 9 percent of elk locations occurred in agricultural fields, 1 percent within 1 km of a Site facility, and 10 percent within 1 km of a primary road on the Site during autumn (Table 10-3). The majority of elk locations occurring within 1 km of a primary road on the INL Site were in the southwestern portion of the Site along U.S. highway 26/20 (Figure 10-12).
Table 10-3. Proportion of hourly GPS locations obtained from collared female elk (Cervus elaphus) on the INL Site that were in agricultural fields, or within 1 km of an INL Site facility or primary road, during spring (April-June), summer (July- September), and autumn (October-November), 2010-2012.
Figure10-12. Hourly GPS locations obtained from collared female elk Cervus elaphus) during 2010-2012 showing some use by elk of areas near major highways and INL Site facilities.
Our results indicate that use of the INL Site by many elk during spring-autumn is largely transient. Indeed, only a small proportion of our study animals remained on the INL Site throughout the entire year. Most elk that were captured and fit with GPS collars during late winter dispersed long distances during early spring, and home ranges of collared animals covered hundreds of square miles of the Big Desert. Nearly all of those animals, however, returned to the INL Site during winter, and many of them returned during autumn. One of the most likely explanations for the substantial increase in the proportion of elk locations occurring within the boundaries of the INL Site during autumn is that the Site provides a refugium from hunters. Most hunting seasons in units surrounding the INL Site occur during autumn and early winter, and it is likely that elk respond rapidly to hunting pressure by shifting their distribution, as well as the timing of various behaviors, such as foraging (Naylor et al. 2009).
Our results do not support the hypothesis that elk have been successful in occupying the Big Desert ecosystem largely as a result of the high quality forage provided by agricultural fields. Although agricultural fields did appear to provide an increasingly import source of forage for elk as quality of native forages presumably declined between spring and autumn, elk still spent only a small amount of time utilizing those fields, and many elk never used agricultural fields at all. Consequently, we conclude that the combination of burned habitat and native sagebrush-steppe in the Big Desert provided forage of sufficient quality and abundance to support a substantial number of elk during spring through autumn, even in the absence of agriculture. This conclusion is also supported by results of other studies of elk conducted in similar sagebrush-steppe ecosystems (e.g., McCorquodale 1991).
It is not clear from our study how elk in the Big Desert obtain the water necessary for their survival. Although we did document some use of guzzlers by elk, many collared animals never utilized a known water source throughout the duration of our study. This included waste water ponds associated with many INL Site facilities. Collared elk in our study were almost never found within 1 km of a Site facility, and only a small number of GPS locations occurred near waste water ponds. As a result, we conclude that the probability of elk transporting environmental contaminants off of the INL Site as a result of drinking contaminated water is likely very low.
Numerous studies of elk and other large herbivores have documented strong avoidance of primary roads and other forms of human disturbance (e.g., Rowland et al. 2000, Naylor et al. 2009). Our results are consistent with the hypothesis that elk generally try to avoid areas with substantial disturbance (this included both roads and INL Site facilities in our study). Nevertheless, because 10 percent of the GPS locations we obtained from elk that were on the INL Site during autumn were located within 1 km of a primary road, the potential for vehicle collisions with elk does indeed exist. Our results indicate that the highest potential for a vehicle collision with elk exists in the southwestern corner of the INL Site along highway 26/20, and this potential is greatest during October-November. Consequently, we recommend that any efforts made by the Department of Energy to reduce dangerous interactions between humans and elk be focused along that stretch of highway. Such efforts could include the placement of warning signs along the highway to indicate that elk frequently cross in that area. In addition, during the hunting season, it may be useful to place temporary electronic signs along that stretch of highway to draw further attention among motorists to the potential for a collision with elk crossing the highway.
Data collected during the course of this project were useful for quantifying the seasonal distribution of elk on the INL Site, as well as how that distribution was influenced by agriculture, roads, and INL Site facilities. Like many large mammals, however, the distribution of elk is highly fluid, and can vary with seasonal and annual changes in factors such as habitat, anthropogenic disturbance, or risk of predation. For example, during the course of this study several large wildfires on and around the INL Site resulted in a substantial change in the abundance and distribution of sagebrush and grassland habitat. This change affected the distribution of elk on the INL Site almost immediately, and in 2012 many collared elk never left the boundaries of the Jefferson Fire during the entire spring-autumn period. Consequently, we recommend that high frequency (e.g. hourly) location data be collected for at least 30 elk on the INL Site every 3-5 years in order to keep track of changes in the distribution of elk that may influence potential conflicts with humans near roads, agriculture, or INL Site facilities. Such data could also be of great importance if wolves take up residence on the INL Site in the near future. Recent confirmed sightings of wolves on the INL Site highlight the potential for such a shift in distribution of these predators, and if such a shift occurs, it will undoubtedly influence the movement and distribution of elk on the INL Site. Indeed, some researchers have reported that elk select areas that are closer to human disturbance when in the presence of wolves, because it reduces the risk of predation. If this occurred on the INL Site, then conflicts with elk near roads or Site facilities could increase dramatically. In addition, it would be useful to collect similar data for other species of large mammal on the INL Site (e.g., pronghorn and mule deer) in order to determine how those species interact both with the environment on the INL Site, as well as with each other.
Plans for Continuation:
The field work for the project has been completed and is in the data analysis and writing phase.
Publications, Theses, Reports:
This project is ongoing (i.e., field data are still being collected), and thus no publications have been completed at this time. Several peer-reviewed publications and a Ph.D. dissertation will be forthcoming when the project is completed in 2013.