Update for April 29, 2025The park has received a number of questions related to horse management over the last several months and is now responding to those questions. The questions received are shared below verbatim, so as to not misconstrue intent or interpretation. The original questions are in italics. Mares that were 8 months of age or older and that had not been previously vaccinated were selected. Mares that were vaccinated approximately two years ago were also given hand injections. Mares that were due to be darted in 2024 and 2025 were injected to reduce the workload in spring and summer 2025. 2. When we talked with Blake and Superintendent Finley, when it was decided that you would NOT be removing any horses from the park, you said that you would be hand injecting the non-responders with GonaCon. From your reports, it does not look like any of the non-responders where hand injected. Can you explain why this decision changed? It is assumed the term “non-responders” is referring to animals that have continued to have foals even though they have been treated with GonaCon. Many of the animals demonstrating a lesser response to the contraceptive had been darted (received GonaCon) during summer 2024, and therefore were not re-treated in the fall of 2024. There were a few animals in this same category that had not received doses prior to the roundup, and we chose a combination of those and other animals to defer contraception. 3. Please provide an updated list of GonaCon treatments to include ALL mares that were hand injected in 2009 and 2013, including any deceased mares. I am asking that the report also please give a month and year that GonaCon was administered and the dose that was given at each injection. This information is something that the park should have readily available because it is something that the park should already be utilizing in the day-to-day management of the horses. A spreadsheet is displayed below with all Colorado State University experimental group study animals, year, and horse identification. Park horses have been treated with 1.8 to 2.0 ml of GonaCon Equine.
4. Have you received an answer yet on if the park can give a list of the numbered horses along with their common name(s)? As we discussed, this is important so that the public can read these reports the way you intend us to so that we know we are all talking about the same horses. See the spreadsheet above with names in response to question 3. Going forward, the park will not be naming horses in official records. They will be referred by official park identification numbers in the future. 5. During the examination of the horses while they were captured, how many horses were found to be pregnant in October and who are they? The NPS did not physically evaluate pregnancy of mares during the roundup. However, progesterone levels in the blood samples from 132 female horses collected during that operation have indicated that 6 mares were likely pregnant. Another 12 mares may have been pregnant but showed values intermediate and less predictive of pregnancy. The lab did not report back individual animal IDs with the hormone level results. That information has been requested, but it has not been received it yet. Therefore an answer for “which horses were pregnant” cannot be answered at this time. 6. Since we know the park had DNA on 98% of the herd in 2022 and you collected more in October, can you confirm the sires of the following horses: Only 118 genotypes were acquired from the herd for the Thompson et al. 2024 publication. Since approximately 200 horses existed in the park going into fall of 2024, >80 animals had not yet been sampled. Though parentage could be calculated for those animals included in the Thompson et al. 2024 dataset, we have not done so. 7. How did you determine the mares that were taken off GonaCon? Your website states that it was because of their genetics, but a simple laymen’s look at the list calls a lot into question: 3 of the mares are from the Pale Lady/Copper lines (201310, 201420 & 202006) – how does having 3 mares from the same lines help genetic diversity, especially when you ONLY took 5 mares off GonaCon? Mare Skipper (aka 201432) is the daughter of Mare Dolly (aka 200620), a known non-responder to GonaCon and a mare that you considered removing, along with her offspring. Why would this oversaturated line be ONE of FIVE that we want to make sure we preserve? Animals were selected based on signatures of inbreeding in the herd, where animals with less inbreeding and higher diversity, or their offspring, were selected to be “released” from GonaCon treatments. 8. How were the collared mares chosen? Blake stated in our last meeting that these mares were recognized as lead mares of their bands. That is untrue for the majority of the mares. The intention was to collar lead mares, however in many cases that was not possible. Mares were chosen first by their known band association and likelihood of staying in the group over the study period. Selections were then refined by anatomical shape of the horses' neck to best fit the collar, resulting in some changes in collar assignments in the field. 9. How is the park responding to the public request to stop the use of GonaCon? PZP native is known to be reversible and is widely used by the BLM. Why can’t this be used as a method of birth control, especially when you have significantly “halted the reproduction” of this herd already with your aggressive use of GonaCon the last few years. If nothing else, why can’t PZP native be used on the 2024 fillies who have yet to be treated with GonaCon according to park records? This has been previously responded to publicly to the issue of GonaCon use vs. PZP: 10. 200107 (aka Mare Pale Lady) and 202310 (aka Filly Willow) were the only 2 horses that were not microchipped either during this roundup or the one in 2013. Why does the park not feel the need to have these two specific horses microchipped? As it shows in the document provided to the public after roundup, 200107 was microchipped prior to 2013 and did not need another one administered. Horse 202310 was not captured, so therefore could not be given a microchip. 11. Are there any additional Categorical Exclusions that have been signed with relation to the management of the wild horses since 2020? A CE (tiering off the 1978 EA) for population management of feral horses was signed in September 2024, addressing work to be done at the roundup. A Memo to File was signed in March of 2023 to document ongoing use of contraceptive for management of the herd. A CE for removal of nuisance animals (wildlife and/or livestock) was signed in September 2022. Though this was not specific to horses, it would apply in circumstances where a horse needed to be euthanized. Otherwise, the Livestock Plan EA process occurred after 2020, but that plan was canceled in 2024. 12. What happened to 202302 Filly Aspen’s body after the park euthanized her? Superintendent Finley stated that the park would be shooting her. Normally when this has happened in the past, the body is left to “nature” after being removed from public view if need be. Why was her body removed from the park or the area where she died? Was a necropsy performed and if so, what were the results? Horse 202302 was not removed from the location. The animal was herded along the creek bottom away from the road before being euthanized and left to recycle. A necropsy was not performed. 13. Did every mare with the exception of 201418 and 202017 along with the 5 new fillies that were born in 2024 all receive injections of GonaCon in 2024? Yes – see the following clarification below:
Update for March 19, 2025Updated preliminary geospatial results from the GPS collar study on the horse herd are displayed below. The interactive graphic depicts the individual movements of 15 horses (colors) every two hours throughout the months of January and February 2025. Paths of travel are depicted by gray lines. Because collared individuals are known to travel in established groups of approximately 5 – 15 horses, movement patterns shown in the graphic represent over 70 percent of where the horse herd has traveled during this time period.Descriptive TranscriptThe interactive graphic illustrates the movements of 15 horses (represented by different colors) every two hours during January and February 2025. The paths of travel are shown as gray lines. Three horses primarily frequent the upper northwest area of the park, three are located in the central northern region, and the remaining horses are situated in the southeastern portion.
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The interactive graphic depicts the individual movements of 15 horses (colors) every two hours throughout the months of January and February 2025.
If you would like to increase your chances of viewing the horses, many of the groups can be seen on the Southeast area of the park by the Talkington trailhead located off of Exit 36 on I-94. Groups can also frequently be seen from common lookout points such as Painted Canyon, Buck Hill, or Wind Canyon.
Update January 31, 2025After a few months of data collection, Theodore Roosevelt National Park would like to share some preliminary geospatial results from our GPS collar study on the horse herd. The interactive graphic below depicts the individual movements of 15 horses (colors) every two hours throughout the months of November and December 2024. Paths of travel are depicted by gray lines. Because collared individuals are known to travel in established groups of approximately 5 – 15 horses, movement patterns shown in the graphic represent over 70 percent of where the horse herd has traveled during this time period.Descriptive TranscriptThe interactive graphic illustrates the movements of 15 horses (represented by different colors) every two hours during November and December 2024. The paths of travel are shown as gray lines. Three horses primarily frequent the upper northwest area of the park, three are located in the central northern region, and the remaining horses are situated in the southeastern portion.
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The interactive graphic depicts the individual movements of 15 horses (colors) every two hours throughout the months of November and December 2024.
If you would like to increase your chances of viewing the horses, many of the groups can be seen on the Southeast area of the park by the Talkington trailhead located off of Exit 36 on I-94. Groups can also frequently be seen from common lookout points such as Painted Canyon, Buck Hill, or Wind Canyon. The park has received some concerns associated with the placement of GPS collars on the 15 mares which we would like to acknowledge. These collars have been used on horses for many years in other studies and were carefully fitted upon placement. Biotechnicians are observing these 15 animals, evaluating for injury or disruption of their behavior. Though the collars will shift, these shifts do not impact the horse or the collection of data and should not cause concern. The collars provide important location information, allowing the park to see how horses use various habitats and how they move through the park during different times of year. This information will assist the park in understanding land use, forage preferences, and how horses interact with native species. Update January 13, 2025We have received concerns regarding the use of the immuno-contraceptive GonaCon in the feral horse herd at the park and wanted to provide some information about current management practices for population management.
The National Park Service (NPS) has a responsibility to manage park resources for the benefit of the entire ecosystem present, including many different species. Because Theodore Roosevelt National Park is fenced, the population of horses, bison, pronghorn, and elk must be managed for the health of all species that share the space. Periodic roundups and other studies help to collect data using a science-based process to determine how best to balance these resources. The park is committed to maintaining a healthy, genetically viable horse population. The administration of GonaCon, an immunocontraceptive, is one method that the park uses to control reproduction and manage the population. We will continue to evaluate other approaches to management as we assess the newly collected data, develop a population viability analysis, and draft an updated horse management strategy.
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| Birth Order ID | AVID RFID | Biomark RFID | Sex | Age | GPS Collar | Gonacon | Date Gathered | Date Handled | Date Released | Notes |
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Table 2: Horses Not Captured during 2024 Roundup at Theodore Roosevelt National Park
The table below denotes horses that the park had no contact with or that the park purposely did not bring into the South Unit Pasture. Specifically, a stallion in one band displayed a physical condition that would have resulted in the band being separated. The park determined it best to leave that band alone and did not make further contact with those animals. We did not bring in some individual horses (e.g. bachelor stallions) due to difficulty in herding single animals. We also provide information on horses historically recorded within the park, but no contact was made with these animals during the roundup. We have no other records indicating their status.Table Key
* Microchipped prior to 2013.** Microchipped in 2013.
| Birth Order ID | AVID RFID | Biomark RFID | Sex | Age | Notes |
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Table 3: Theodore Roosevelt National Park Horse Herd GonaCon Administration and Foaling History for all Mares Known to be Present in the Park as of 10/16/2024
The table below provides specific information on the years that GonaCon was administered to horses within the park. The purpose of GonaCon administration is to create a level of reproductive control. Each "G" represents the initial treatment followed by boosters. An “F” represents the years where the treated horses foaled. Some animals may have more foaling events than listed. As indicated in the table, mares have received multiple doses to address the differing responses to this immunocontraceptive. It should also be noted that mares have still reproduced when treated with GonaCon. During the October roundup, five mares were released from GonaCon treatment (not boosted), providing an opportunity for these horses to reproduce. These animals were selected based on their genetic diversity regardless of most recent GonaCon administration.Table Key
* Gonacon administered during roundup to avoid 2025 darting schedule.Note: "F" indicates known foaling events.
Note: "G" indicates Gonacon administration.
Note: Some animals may have more foaling events than listed.
| Birth Order ID | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 |
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If you have additional interest in this topic, please see:
Baker, D. L,, B.E. McCann, J.G. Powers, N.L Galloway. J.E. Bruemmer, M.A. Thompson and T.M. Nett. 2023. Reimmunization intervals for application of GnRH immunocontraceptive vaccine (GonaCon-Equine) in free-roaming horses (Equis ferus caballus) using syringe darts. Theriogenology Wild 3 (2023) 100061. https://doi.org/10.1016/j.therwi.2023.100061
Thompson, M.A., B. E. McCann, R.B. Simmons and T. Rhen. 2023. Major locus on ECA18 influences effectiveness of GonaCon vaccine in feral horses. Journal of Reproductive Immunology 155 (2023) 103779. https:/doi.org/10.1016/j.jri.2022.103779
Baker, D.L., J.G. Powers, J. I Ramson, B.E. McCann, M.W. Oehler, J. E. Bruemmer, N. L. Galloway, D. C. Eckery, and T.M. Nett. 2018. Reimmunization increases contraceptive effectiveness of gonadotropin-releasing hormone vaccine (GonaCon-Equine) in free ranging horse (Equus caballus): Limitations and side effects. PLOS ONE July 21, 2018. https://doi.org/10.1371/journal.pone.0201570
Ransom, J.A., J.G. Powers, H.M. Garbe, M. W. Oehler, Sr., T. M. Nett, and D. L. Baker. 2014. Behavior of feral horses in response to culling and GnRH immunocontraception. Applied Animal Behaviour Science. 157 81-92. http://dx.doi.org/10.1016/j.applanim.2014.05.002
Ransom, J.A., B.S. Cade, and N. T. Hobbs. 2010. Influences of immunocontraception on time budgets, social behavior, and body condition in feral horses. Applied Animal Behaviour Science. 124 (2010) 51-60. doi:10.1016/j.applanim.2010.01.015
Thompson, M.A., B. E. McCann, R.B. Simmons and T. Rhen. 2023. Major locus on ECA18 influences effectiveness of GonaCon vaccine in feral horses. Journal of Reproductive Immunology 155 (2023) 103779. https:/doi.org/10.1016/j.jri.2022.103779
Baker, D.L., J.G. Powers, J. I Ramson, B.E. McCann, M.W. Oehler, J. E. Bruemmer, N. L. Galloway, D. C. Eckery, and T.M. Nett. 2018. Reimmunization increases contraceptive effectiveness of gonadotropin-releasing hormone vaccine (GonaCon-Equine) in free ranging horse (Equus caballus): Limitations and side effects. PLOS ONE July 21, 2018. https://doi.org/10.1371/journal.pone.0201570
Ransom, J.A., J.G. Powers, H.M. Garbe, M. W. Oehler, Sr., T. M. Nett, and D. L. Baker. 2014. Behavior of feral horses in response to culling and GnRH immunocontraception. Applied Animal Behaviour Science. 157 81-92. http://dx.doi.org/10.1016/j.applanim.2014.05.002
Ransom, J.A., B.S. Cade, and N. T. Hobbs. 2010. Influences of immunocontraception on time budgets, social behavior, and body condition in feral horses. Applied Animal Behaviour Science. 124 (2010) 51-60. doi:10.1016/j.applanim.2010.01.015
Update October 18, 2024
Today we had a report of an injured animal. Upon investigation, we found a one-year-old female horse exhibiting lameness. The veterinarian examined the animal this evening and determined the humane course of action was to euthanize.
We have identified the animal as one that had been in the handling facility last Tuesday at which time the veterinarian evaluated a small cut on its front left leg. After the exam the animal was cleared to be released with its band Wednesday morning. Since then, the animal has traversed 5 miles with its band and the condition has worsened. The animal has been euthanized.
Update October 17, 2024
We have heard concerns associated with the health status of some animals that were recently rounded up this week. A total of 5 of the 178 horses rounded up were observed to have minor injuries and all were evaluated by a veterinarian. The veterinarian determined all animals were fit for release. We will continue to evaluate their status and will conduct follow-up evaluations if needed.
NPS Photos / P Clark
Update for October 16, 2024
The observation area at the south unit animal handling area is no longer available as roundups operations have concluded. We anticipate sharing data collected from the roundup toward the end of next week.
Microchipping horses provide a permanent and unique identifier for each animal, making it easier to identify them over time. Microchips do not provide locations, are just a tool to identify animals accurately through the course of scientific studies. Thanks to dedicated volunteers, each horse and their position in each band has been identified and recorded, aiding in effective population management.
Additionally, analyzing DNA is crucial for assessing genetic diversity. This information is essential to direct future management actions to maintain a genetically diverse population.
Together, microchipping and DNA analysis enhance our understanding of horses and support management practices.
NPS Photos / P Clark
Update for October 14, 2024
On Monday, October 14, a subset (4 of the 15 slated to receive collars) of horses were fitted with GPS collars.
The park collaborated with the US Geological Survey and volunteers experienced in horse handling to place the collars.These collars allow us to track where horses roam both day and night, revealing the areas that horses frequent. By pinpointing their locations, we can better understand their range and use of the park environment.
Designed in a teardrop shape, these collars fit comfortably around their necks and are equipped with both Global Positioning System (GPS) and Very High Frequency (VHS) technology. The combined technology allows for detection of a signal when terrain or distance interferes with one of the methods. These collars feature a remote release safety mechanism for added security.
Our ultimate goal? To gather valuable insights on how horses interact with park wildlife and understand their foraging range. The data collected from these collared horses will support the development of a proactive strategy for horse management, ensuring a balance within the ecosystem.
NPS Photo / P Clark
Update for October 13, 2024
On Sunday, October 13, Theodore Roosevelt National Park successfully rounded up approximately 144 horses, bringing them into the South Unit pasture. We now allow horses time to rest, water and feed in our pastures prior to initiating the genetics sampling, administration of immunocontraception and health evaluations etc. We will also be fitting 15 animals with GPS collars. The GPS collars will be very helpful in allowing the park to understand how the horses use the park environment. In addition, we have committed to releasing some animals from the immunocontraception to allow reproduction in the herd beyond those that have already demonstrated successful reproduction.
These roundups provide invaluable opportunities to gather data on horse health and genetics which will inform our future management. By evaluating general health, demographics (like age classes and sex ratio), and genetics, we aim to create a long-term management strategy that ensures a genetically viable and healthy horse population in the park.
Overall, this strategy will strike a balance between ensuring a viable and healthy horse population while protecting the broader park ecosystem.
Update for October 12, 2024
While the operational area of this week’s horse roundup remains closed to the public to ensure animal and public health and safety, a nearby viewing area has been designated to allow public observation of the gather from a safe distance. Helicopter operations are currently set to begin October 13 and will continue no later than October 18. (The roundup operations may end sooner. Schedule changes will be posted on this page.)
- Due to limited staff resources and the need to maintain safety and security of the site, two observation windows will be available each day from 9:30 am – 11:30 am and 1 pm – 2:30 pm.
- Interested individuals should park at the South Unit Wildlife Handling Facility. Maps to the facility will be available each morning beginning at 9 am at the South Unit Visitor Center located at 201 East River Road N., Medora, ND 58645.
- Staff on site will direct visitors where to park and how to access the designated viewing area, which will be clearly marked. To protect the health and safety of both the horses and the public, visitors will not be allowed outside of the designated area.
- No more than 15 people can be accommodated at any time.
- Visitors are not required to stay for the entire observation window. Individuals who leave the designated area will not be allowed back in during the same observation window to minimize disruption to the work zone during active operations.
- The road leading to the facility will be closed intermittently throughout each day’s roundup when the helicopter is in flight.
- Public restrooms are not available at the viewing area.
A copy of the superintendent’s record of determination granting limited temporary public access to the designated viewing area is available online and at the South Unit Visitor Center.
Update for October 11, 2024
Theodore Roosevelt National Park appreciates the engagement and interest we have received in both the bison and horse roundups. Some changes will be implemented to the horse roundup to address this feedback. We want to reaffirm our commitment to ensuring a viable and healthy horse population that is manageable based on the park’s natural resource and ecosystem needs.
The park has completed bison roundup operations in the North Unit, with 196 bison transferred to their new homes, largely with Tribes. Bison were also evaluated for general health, genetics, and population demographics (age, sex ratio, etc.). This data provides important information to the manage the bison population. As a result of this operation, the bison herd size has been reduced by nearly half.
The park is currently shifting operations to the South Unit to prepare for the horse roundup early next week. NPS has decades of experience with these roundups and as such, staff safety and the health and wellbeing of the horses is our top priority. We also seek to minimize disruption to the park ecosystem from these operations. To ensure both animal and public health and safety, the roundup operation is not open to the public.
The upcoming horse roundup will provide a significant amount of data that will inform a long- term management strategy to create a genetically viable, and healthy population at the park. At this time, we have determined that no horses will be transferred out of the park in this year’s roundup effort, due to concerns about the ability of horses to be adopted in a limited amount of time.
Animal health is a priority for the horse roundup. Timing was selected because horses are in optimal health after a long grazing season and cooler temperatures prevent heat related stress during the movement of animals.
A helicopter will be used for roundup operations, which are set to last through October 18. The NPS has extensive experience using helicopters and aviation to support safe and effective animal captures incorporating park staff as observers on the ground and moving animals slowly. We also incorporate low stress livestock handling techniques after animals are brought in. Animals with known mobility constraints will not be rounded up. The park works with livestock veterinarians and subject matter experts to conduct these operations safety and humanely.
The roughly 200 horses will be brought into the South Unit corrals and evaluated for general health, genetics, and population demographics (age, sex ratio, etc.). A subset of horses will be fitted with GPS collars so the NPS can better understand their range and use of the park environment. The park intends to work with volunteers that have experience with the park’s management program and the handling of horses.
A small number of mares that did not successfully respond to previous contraception will be retreated with GonaCon, an immunocontraceptive. The park wants to ensure that these few mares are not skewing the population’s genetics by their breakthrough reproduction. Additional mares may receive a scheduled booster.
Another subset of horses previously identified as having above average genetic diversity will be released from GonaCon treatment, anticipating that they will contribute this diversity to the population through reproduction.
The horse herd population in the future will likely be less than it is today to ensure a healthy herd that is manageable in context of the park’s ecosystem and natural resources. The data gleaned from the roundup will be used to develop target options for the herd’s size using a Population Viability Analysis approach. There is no set number at this time. Once available, we will communicate our results and the recommended management approach for maintaining a viable and healthy population.
We are committed to sharing timely social media updates for those interested in the roundup progress. Updates will be posted on the park’s social media accounts and website throughout the process and when data collection for the roundup is complete. Like our community and visitors, we are committed to ensuring a viable and healthy horse population at the park that is manageable based on the park’s natural resource and ecosystem needs.
Update for October 9, 2024
As of this morning, Theodore Roosevelt National Park has successfully brought in 179 bison and begun the return of many to the north unit of the park. Thus far, the park provided 113 bison to partners, see the history of bison transfers at the park here: https://www.nps.gov/thro/learn/nature/bison-transfer-map.htm. Bison were be evaluated for general health, genetics, and population demographics (age, sex ratio, etc.).
Bison roundup operations are concluding today. We will be mobilizing equipment and personnel to the South Unit over the next few days to initiate the horse roundup operations early next week.
Update for October 1, 2024
Theodore Roosevelt National Park will begin operations to roundup bison on October 5 and horses on October 10 in the park and transfer them to Tribes or new homes. The park will transfer up to 200 bison and up to 15 horses to new homes as part of ongoing efforts to support healthy herds as well as park ecosystems.
Bison roundups are needed to ensure the park’s bison population, which is contained within a fenced environment, is appropriately sized. The horse roundup will support the development of a proactive strategy for horse management to create a healthy viewable population at the park that is manageable and minimizes impacts to park resources.
Animal health is a priority for the bison and horse roundups. The timing of these roundups was selected because animals are in optimal health after a long grazing season and cooler temperatures cause less heat related stress during the movement of animals.
The park will share regular updates regarding the bison and horse roundup progress. To ensure human and animal health and safety, the roundups are not open to the public. The park will work with volunteers who are familiar with the area and handling of horses at key times throughout the roundup. Please check our social media for updates over the next week.
September 27, 2024 News Release: Theodore Roosevelt National Park to Conduct Strategic Bison and Horse Operations
Learn about the history and management of the herd, and the park's adoption program.
Last updated: May 5, 2025