Project Details

One of the primary threats to the recovery of the Federally threatened Mojave desert tortoise is extensive raven predation of juvenile tortoises, which are vulnerable to raven predation 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 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 become 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 (SITLA), 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% similar to other tortoise populations across the range (Allison and McLuckie 2018).

From 2015 through 2021, County HCP staff conducted raven nest and powerline surveys within and adjacent to the Reserve. They documented a total of 40 juvenile tortoise carcasses that were attributed to raven predation (Schijf 2024). These 40 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). The current raven density of 2.7/km2 is more than triple the threshold and is 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.

Provide evidence about the nature of the problem and the need to address it. Identify the significance of the problem using a variety of data sources. For example, if a habitat restoration project is being proposed to benefit greater sage-grouse, describe the existing plant community characteristics that limit habitat value for greater sage-grouse and identify the changes needed for habitat improvement.

We would like to reduce the raven population to within the range that is sustainable for tortoise recruitment and long-term sustainability (0.89 raven/km2). To meet this goal, we will need to reduce the current population through direct control measures, subsidy management and outreach efforts.

As a top priority in our plan, we would like to implement egg oiling to reduce raven nest success in tortoise habitat. Egg oiling (addling) is a common method for wildlife managers to manage bird populations (USDA 2022), whereby eggs are made non-viable (commonly done by coating the egg in vegetable or silicon oil) and remain in the nest. By keeping the non-viable eggs in the nest, the parent birds will often continue to care for the eggs instead of producing a new clutch of eggs (Humane Society of the United States 2009). This reduces predation of tortoises at the time they are most vulnerable in the spring and prevents other ravens from moving into the territory. Egg oiling has been found to be more effective in preventing successful nesting than direct removal of eggs or nests because nesting birds continue incubation often beyond the typical nest period It also discourages future nest attempts in the area. Addling of raven eggs has been shown to be a viable, localized method to reduce raven reproduction, which can reduce predation and increase the reproductive performance of their prey (Brussee and Coates 2018). Nest removal can be a viable management tool when conducted at the appropriate time (e.g., close to the end of the breeding season), as ravens are less likely to attempt re-nesting in that season.

We have targeted 18 raven nests in or near the Red Cliffs Desert Reserve which should be treated to reduce raven predation. Some of these nest can be treated with manually by climbing or reached by an extended pole, others will require a specialized contractor (HardShell Labs Inc) which has experience in addling eggs with a drone and oil-applicator.

Washington County and HCP partners will continue to work with landfill managers to reduce subsidies available to ravens. The outreach program will also focus on educating the public on raven-tortoise issues and how they can keep their trash secured to reduce raven growth in the county.

Provide an overall goal for the project and then provide clear, specific and measurable objectives (outcomes) to be accomplished by the proposed actions. If possible, tie to one or more of the public benefits UWRI is providing.

LOCATION: Justify the proposed location of this project over other areas, include publicly scrutinized planning/recovery documents that list this area as a priority, remote sensing modeling that show this area is a good candidate for restoration, wildlife migration information and other data that help justify this project's location.

TIMING: Justify why this project should be implemented at this time. For example, Is the project area at risk of crossing an ecological or other threshold wherein future restoration would become more difficult, cost prohibitive, or even impossible.

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)

List management plans where this project will address an objective or strategy in the plan. Describe how the project area overlaps the objective or strategy in the plan and the relevance of the project to the successful implementation of those plans. It is best to provide this information in a list format with the description immediately following the plan objective or strategy.

If applicable, detail how the proposed project will significantly reduce the risk of fuel loading and/or continuity of hazardous fuels including the use of fire-wise species in re-seeding operations. Describe the value of any features being protected by reducing the risk of fire. Values may include; communities at risk, permanent infrastructure, municipal watersheds, campgrounds, critical wildlife habitat, etc. Include the size of the area where fuels are being reduced and the distance from the feature(s) at risk.

Describe how the project has the potential to improve water quality and/or increase water quantity, both over the short and long term. Address run-off, erosion, soil infiltration, and flooding, if applicable.

Description of efforts, both completed and planned, to bring the proposed action into compliance with any and all cultural resource, NEPA, ESA, etc. requirements. If compliance is not required enter "not applicable" and explain why not it is not required.

Describe the actions, activities, tasks to be implemented as part of the proposed project; how these activities will be carried out, equipment to be used, when, and by whom.

Describe plans to monitor for project success and achievement of stated objectives. Include details on type of monitoring (vegetation, wildlife, etc.), schedule, assignments and how the results of these monitoring efforts will be reported and/or uploaded to this project page. If needed, upload detailed plans in the "attachments" section.

List any and all partners (agencies, organizations, NGO's, private landowners) that support the proposal and/or have been contacted and included in the planning and design of the proposed project. Describe efforts to gather input and include these agencies, landowners, permitees, sportsman groups, researchers, etc. that may be interested/affected by the proposed project. Partners do not have to provide funding or in-kind services to a project to be listed.

To address raven predation on desert tortoises in Washington County, we have formed a working team comprised of the local USFWS, BLM, UDWR, and HCP. This team is committed to developing and implementing a long-term raven management strategy that employs both lethal and non-lethal management. While a long-term strategy is still being developed, this team has identified several immediate measures that can be taken. These 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. Developing a monitoring plan to annually determine where/whether lethal measures are needed that year.

Detail future methods or techniques (including administrative actions) that will be implemented to help in accomplishing the stated objectives and to insure the long term success/stability of the proposed project. This may include: post-treatment grazing rest and/or management plans/changes, wildlife herd/species management plan changes, ranch plans, conservation easements or other permanent protection plans, resource management plans, forest plans, etc.

Potential for the proposed action to improve quality or quantity of sustainable uses such as grazing, timber harvest, biomass utilization, recreation, etc. Grazing improvements may include actions to improve forage availability and/or distribution of livestock.