One of the primary threats to the recovery of the Federally threatened Mojave desert tortoise is raven predation of hatchling and juvenile tortoises, which are vulnerable until they are at least 8 years old (USFWS 2011). In general, as human communities grow, raven populations increase, taking advantage of resource subsidies that humans inadvertently provide (e.g., food, water, nesting opportunities, etc.) (Boarman 2014). Predation by ravens has increased because of resource subsidies provided by humans (Kristan and Boarman 2007). Ravens obtain resources such as food from landfills and trash containers, water from reservoirs and human-made sources, and nesting substrates on billboards, utility towers, bridges, and buildings (Boarman et al. 2006). Predation by subsidized predators can adversely impact native prey populations because human-provided subsidies allow such predator populations to increase and remain high even when natural prey becomes rare (Courchamp et al. 2000). The Red Cliffs Desert Reserve (Reserve) was established in Washington County in 1996 as a part of the Washington County Habitat Conservation Plan (HCP) to protect Mojave desert tortoises and their habitat in an area with rapid development. The Reserve protects over 45,000 acres of tortoise habitat in the Upper Virgin River Recovery Unit and lands are managed by the Bureau of Land Management (BLM), Utah School Institutional Trust Lands Administration (TLA), Utah Department of Natural Resources (UDNR), Washington County, and private landowners. Tortoise densities of 17-28 tortoises per sq km in the Reserve (McLuckie et al. 2020; Bandy and Rognan 2022) are higher than any other Mojave desert tortoise population range-wide (1.7 to 14.2 tortoises per sq km; USFWS 2020). However, within the Reserve, tortoise populations have experienced an annual decline of 3.2%, like other tortoise populations across the range (Allison and McLuckie 2018). From 2015 through 2025, County HCP staff and local BLM have conducted raven nest surveys within and adjacent to the Reserve. They have documented more than 40 juvenile tortoise carcasses that were attributed to raven predation (Schijf 2024). These observed carcasses likely represent only a small portion of the actual number of tortoise carcasses deposited because carcass persistence rates can be very low in desert habitats. Through 2020, 53 total raven nests had been documented inside and adjacent to the Reserve, including 20 nesting territories (Schijf 2024). Beginning in 2021, the HCP began a pilot study using a USFWS draft protocol for raven population surveys and techno tortoise decoy station deployments. Decoy stations showed that ravens were predating on juvenile tortoises higher than is sustainable for juvenile recruitment. In 2022, in collaboration between the County, BLM, Snow Canyon State Park, and the USFWS Desert Tortoise Recovery Office, spring point-count surveys were conducted to document raven population estimates. In these surveys, 89 individual ravens and 55 raven clusters were identified. Using these data, raven density was estimated to be 2.7 raven/square kilometer (km2) across Washington County (Schijf 2024). The USFWS estimates that 0.89 raven/km2 is a sustainable and manageable ecological threshold for tortoise-raven conflicts (Holcomb et al. 2021). Local population estimates were conducted again in 2024 and found to be 2.3 ravens/square km (Schijf et al 2024). These numbers remain unsustainably high, likely contributing to tortoise population declines that may contribute to localized to widespread function extinction due to low 1 to 10-year-old annual survival rates. Sources Cited: Allison LJ, McLuckie AM. 2018. Population trends in Mojave desert tortoises (Gopherus agassizii). Herpetological Conservation and Biology 13:433-452. Bandy, M. and Rognan C. (2022). Drone and pedestrian desert tortoise surveys in Zone 6 of the Red Cliffs Desert Reserve. Technical report 2022-001-01, Resi Solutions. Submitted to the Washington County Habitat Conservation Plan. Boarman, W.I., Patten, M.A., Camp, R.J., and Collins, S.J., 2006. Ecology of a Population of Subsidized Predators: Common ravens in the central Mojave Desert, California. Journal of Arid Environments 67 (2006) 248-261. Boarman, W.I. 2014. Measuring Raven and Coyote Predation of Desert Tortoises: Phase 1. Conservation Science Research & Consulting. Brussee, B. E., and P. S. Coates. 2018. Reproductive success of Common Ravens influences nest predation rates of their prey: implications for egg-oiling techniques. Avian Conservation and Ecology 13: 17. Courchamp F., M. Langlais, and G. Sugihara. 2000. Rabbits killing birds: Modelling the hyperpredation process. Journal of Animal Ecology 69:154--164. Holcomb, K. L., Coates, P. S., Prochazka, B. G., Shields, T., & Boarman, W. I. (2021). A desert tortoise--common raven viable conflict threshold. Human--Wildlife Interactions, 15(3), 14. Kristan, W. B., III, and W. I. Boarman. 2007. Effects of anthropogenic developments on common raven nesting biology in the west Mojave Desert. Ecological Applications 17: 1703--1713. McLuckie, A.M., Fronk, N.L., and Fridell, R.A. (2020) Regional Desert Tortoise Monitoring in the Red Cliffs Desert Reserve , 2019. Publication 20-06, Utah Division of Wildlife Resources, Salt Lake City, UT. Schijf, M., Compton R., and Rognan C. 2018. Raven Predation and Tortoise Monitoring in the Red Cliffs Desert Reserve. Washington County Habitat Conservation Plan. Schijf, M., Martinez C., and Rognan C. 2019. Tortoise Predation and Raven Monitoring in the Red Cliffs Desert Reserve. Washington County Habitat Conservation Plan. Schijf, M. Holcomb K. and Rognan C. 2024. Draft Analysis of Common Raven Densities and Desert Tortoise Predation Rates in the Upper Virgin River Recovery Unit. Washington County Habitat Conservation Plan. U.S. Fish and Wildlife Service [USFWS]. 1994. Desert tortoise (Mojave population) recovery plan. U.S. Fish and Wildlife Service, Portland, Oregon, USA. U.S. Fish and Wildlife Service. 2011. Revised recovery plan for the Mojave population of the desert tortoise (Gopherus agassizii). U.S. Fish and Wildlife Service, Pacific Southwest Region, Sacramento, California. 222 pp. U.S. Fish and Wildlife Service. 2022. Range-wide Monitoring of the Mojave Desert Tortoise (Gopherus agassizii): 2020 Annual Reporting. Report by the Desert Tortoise Recovery Office, U.S. Fish and Wildlife Service, Reno, Nevada.

We would like to engage with affected stakeholders and expand local outreach efforts to reduce raven and other wildlife subsidies--e.g., food, water, and nesting substrates near the Reserve. The largest subsidy affecting the study area is suspected to be the Washington County landfill, where large clusters of ravens are commonly present. Additional subsidies that need to be reduced include, but are not limited to, municipal garbage, anthropogenic water sources, power/communication/transportation infrastructure, animal feeding operations, and roadkill. Our primary goal for raven population control is through egg-addling (or oiling) to prevent raven eggs from hatching within tortoise habitat. These efforts will help us reach the goal of reducing the raven density to 0.89 ravens / km-2 and increase the median distance between tortoise populations in the Reserve and active raven nests to >2.5 km. These management objectives are expected to increase the annual survival probability of juvenile tortoises above the 0.77 threshold for sufficient tortoise recruitment (Holcomb et al. 2021). The effectiveness of oiling efforts will be measured by reducing raven densities towards the 0.89 ravens / km-2 goal. Our success will also be evaluated in terms of the proportion of known active nests treated each year as well as the number of active nesting territories within the Reserve plus 2.5 km buffer area during subsequent nesting seasons.

Washington County encompasses nearly 317,000 acres of Mojave desert tortoise habitat. Approximately 68,000 acres of lands within the Red Cliffs Desert Reserve are managed by the BLM, TLA, UDNR, Washington County, and private landowners. Our primary target area will be the Reserve and a 2.5 km buffer. However, as time and funds allow, we will target other raven nests found in tortoise habitat throughout the County. Our first population control efforts began in 2024 when we successfully addled 64 eggs at 12 raven nests. These efforts were expanded in 2025 to 158 eggs at 31 nests, of which 8 were re-nest attempts. Due to additional surveys in 2025, we also expanded the number of known nesting sites. This should allow us to continue treatment efforts at a similar or elevated amount in 2026-2028. It may take several years of continued active management to see a noticeable change in raven or tortoise density. To this end, we continue plans to monitor both tortoise and raven populations to determine if our management actions are reducing the raven density and distribution to our target management goals, and consequently increasing tortoise recruitment

This project is in support of several local, state and federal management plans listed below: 1) Utah Wildlife Action Plan (UDWR 2023) - Threat -- Problematic Animal Species -- Native (pp 151-153) 2) Washington County Management Plan 2022 - Threatened and Endangered Species (pp 55-67) - Predator Control (pp 49-51) - Wildlife (pp 81-83) 3) Washington County's Amended Habitat Conservation Plan (2020). - Biological Goals and Objectives 6.1.2 - Adaptive Management Program 6.3.3.1 - Raven Monitoring 6.3.3.2.2 - Its also in support of a local Raven Management Plan being developed by the County HCP, UDWR, USFWS and BLM. 4) Snow Canyon State Park Resource Management Plan (1998) - Biology -- Fauna (pp 26-27) 5) Revised Recovery Plan for the Mojave Population of the Desert Tortoise (USFWS 2011) - 2.14 Minimize excessive predation on tortoises - 4.1 Monitor desert tortoise population growth - 5.1 Determine factors that influence the distribution of tortoises 6) Recovery Action Plan for the Mojave Desert Tortoise in the Upper Virgin River (USFWS 2014) - Decrease predator access to human subsidies - Targeted predator control 7) Red Cliffs NCA Resource Management Plan (2016) - Special Status Wildlife Species, Management Actions (pp 35-47)

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The project is in compliance with Washington County HCP and at the recommendation of its Technical and Advisory Committees. Additionally, as a lead partner, USFWS holds an active depredation permit through its Migratory Bird Office, authorizing egg addling and other control measures. The County, UDWR, and BLM are listed as sub-permittees to carry out project activities.

Up to 50 potential raven nests are authorized for egg-oil treatment. These nests are primarily located in the Red Cliffs Desert Reserve and 2.5-km buffer area, or within other tortoise habitat in the County. Prior to treatment, nest activity will be monitored by the HCP and other partners to ensure that the timing of egg oiling occurs when eggs are present. Vegetable oil or similar food-based oil will be gently distributed on the eggs by hand, extended pole, or through a drone applicator developed by OrniLogic. Most nests will be accessed by climbing or rappelling, however we may utilize the drone with OrniLogic for more difficult to access nests if deemed necessary. Some nests may hatch prior to oil treatment. In these cases, depending on the threat to tortoises, we may seek authorization from USFWS or contract with wildlife services for lethal control of the hatchlings or parent ravens.

Washington County HCP has been monitoring raven nest, predation, and raven populations annually since 2015. Monitoring each nest prior to treatment is necessary to ensure proper timing when the eggs are likely to be present. Post-monitoring of the project effects will occur annually by the HCP and other partners. This will include annual nest monitoring in and around the Reserve and comprehensive raven density estimates via point counts every third year. We will also conduct tortoise predation studies every-third year through techno-tortoise decoys and motion-triggered cameras. This effectiveness monitoring will allow us to adapt our strategy, if necessary, and will also help us determine if and when we have reduced the raven density to the desired target threshold of 0.89 / sq km and pushed raven nests beyond 2.5 km of the Reserve.

Washington County has been engaged with several partners on this project including UDWR, USFWS, BLM, Snow Canyon State Park, Wildlife Services and OrniLogic. All of these entities have a vested interest in promoting recovery of the Mojave desert tortoise and each play a role in planning, implementing, and monitoring the project results.

To address raven predation on desert tortoises in Washington County, we have formed a working team comprised of the local USFWS, BLM, UDWR, Snow Canyon and HCP. This team is committed to developing and implementing a long-term raven management strategy that employs both lethal and non-lethal management. Our goals include: 1. Engaging with the local landfill manager to implement more deterrent measures, such as additional covering, use of lasers, and containing open water sources. 2. Coordinating with the local airport on migratory bird management strategies. 3. Developing design features for transmission lines such as perch/nest deterrents, replacing lattice towers with mono-poles, and requiring raven monitoring along new lines. 4. Identifying areas in the Reserve and throughout the County where wildlife-proof dumpsters could be installed. 5. Increasing community engagement and outreach through the HCP's full-time outreach coordinator and developing raven-specific materials such as a "Let's Talk Trash" campaign. 6. Implementing the monitoring plan to annually determine where/whether lethal measures are needed each year.

While the raven control measures we would like to implement are aimed at benefiting tortoises, reduction of ravens will also have a positive effect on agricultural use in the County and likely have a positive effect on other species. Ravens are known to be detrimental to many crops in the County and they are opportunistic predators on many species of reptiles, birds, and mammals.