Pygmy rabbits are extreme habitat specialist living only in areas of tall, dense sagebrush with loose soils appropriate for digging burrows (Green and Flinders 1980) and are therefore threatened by the loss and/or deterioration of sagebrush habitats. The rabbits face the same threats faced by the more high-profile greater sage-grouse, but with more specialized habitat requirements within a smaller range. Pygmy rabbits were petitioned in 2023 citing disappearing habitat, emerging disease (rabbit hemorrhagic disease), and lack of regulatory mechanisms. There is currently no announced timeline for addressing the petition. Several studies have documented the short-term response of pygmy rabbits to sagebrush thinning designed to benefit sage-grouse and other habitat disturbances including pipeline and oil and gas infrastructure. Those studies included research by BYU and USU in Rich County and the Parker Moutain/Grass Valley area. In general, research has shown that pygmy rabbits no longer used the disturbed areas and shifted their habitat use away from the disturbance edge. All work stressed the importance of conserving the areas of tall, dense sagebrush that pygmy rabbits inhabit. From the research, BYU developed guidelines for sagebrush treatment projects in pygmy rabbit habitat. The recommendations resulting from that study included: 1) provide a 100m (or more) buffer around occupied pygmy rabbit habitat and 2) preserve long and wide swaths of undisturbed mature big sagebrush among narrow treatments. A key knowledge gap is the extent to which pygmy rabbits will recolonize a previously disturbed site. Twenty years ago, habitat projects aimed at reducing sagebrush cover were quite common management actions primarily designed to improve brood-rearing habitat for sage-grouse. Since the studies were conducted, there has been an increased understanding of the importance of areas where sagebrush is available above the snow throughout the winter for food and cover for sage-grouse, and thus much less sagebrush thinning work has occurred. In some areas, habitat managers report that sagebrush has returned to pre-treatment densities, however, there has been no work to determine pygmy rabbit response. Where the recommended buffers were used, there has also been little follow-up to determine the long-term efficacy of those management actions.

This research aims to answer key questions related to pygmy rabbits and disturbance. In disturbed sites, does sagebrush return to conditions suitable for pygmy rabbits? If so, do the rabbits reoccupy the areas? Do pygmy rabbits persist in sites buffered from treatment edges? We may also investigate if juniper removal projects can increase pygmy rabbit use of the landscape.

Western Watersheds project submitted a petition to list the pygmy rabbit under the ESA in March of 2023. The UDWR and partners are currently conducting inventory and monitoring work throughout the pygmy rabbit's range in Utah. This research is need to help refine and develop conservation actions to ensure the persistence of the species.

This project directly addresses threats to pygmy rabbits identified in the Wildlife Action Plan, namely continued monitoring of populations to update species status, habitat treatment recommendations, assessing impacts of development and the recommended mitigation. Pygmy rabbits occur within Sage Grouse Management Areas and we will address how habitat management for sage grouse, as outlined in the Sage Grouse Management Plan, might affect rabbit populations. Additionally, BLM Manual 4680 directs the BLM to "determine, to the extent practicable, the distribution, abundance, population condition, current threats, and habitat needs" for sensitive species.

Data collected in the research will help determine how pygmy rabbit populations respond to and recover from disturbances, such as fire. Pygmy rabbits occur in older, denser stands of sagebrush, which can be wiped out in fires. This project can help inform areas of priority protection from fuel breaks and fire suppression.

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UDWR has jurisdictional authority for this species and will provide researchers with any needed permits.

Study sites in the Rich County and Grass Valley investigated between 2005-2012 (Lee 2008 and Edgel 2013) will be revisited to assess vegetative status, presence or absence of pygmy rabbits, and habitat use patterns of pygmy rabbits. Methodology will follow that employed by researchers during initial studies so that results will be directly comparable. We have the exact coordinates and corresponding data from the earlier studies. Depending upon the site, we will use remote cameras, pellet plots, walk transects, burrow surveys, and snow tracking to measure pygmy rabbit presence and/or abundance. In Grass Valley, we will attempt to revisit 383 burrows that were within 500m of a treatment edge and were used to develop the 100m disturbance buffer guideline. Reference sites in in a large continuous sagebrush area adjacent to and directly south of the treatments in Grass Valley will also be revisited. We will rank burrow activity according to the 1-4 classification described by Rachlow and Whitam (2004). Remote cameras will be placed to document pygmy rabbit and terrestrial predator activity, and pellet plots will be monitored as an index of habitat use (Pierce et al. 2011). We will compare the proportion of active pygmy rabbit burrows to the data collected in 2004-2008 to determine how pygmy rabbit activity and habitat condition changed over the last 20 years. In Rich County, we will use similar methods focusing on the area within and adjacent to the Ruby Pipeline right-of-way from Edgel 2013. To assess vegetative changes, at each occupied and unoccupied site, we will collect habitat measurements that including vegetative cover, horizontal obscurity, percent understory composition, and shrub density. For vegetative cover, we will use the line intercept method along 15 m transects in each cardinal direction from the burrow or random point in unoccupied habitat. For horizontal obscurity measurements, we will use a cover board with 36 squares (Bunnell et al. 2004). We will place the cover board at the burrow or random site, and then read the number of squares obscured by vegetation while kneeling down (to simulate height of a predator such as a coyote) from distances of 2.5 m, 5 m and 10 m in each cardinal direction. To determine percent composition of the understory, we will use a ¼ m square quadrat (Daubenmire 1959) placed at the center point (burrow or random location) and 1 random point along the 15 m transect in each cardinal direction (5 quadrats per site). Within each quadrat, we will make an ocular estimate of percent moss, bare ground, rock, litter, grasses, shrubs, trees, and forbs. We will then calculate percent understory composition for each component at each site as the average of the five values from each plot. We will these measurements collected at each site with remote sensing-based metrics including Landfire landcover metrics, slope, aspect, and terrain ruggedness.

The purpose of this project is to monitor the impact of past disturbances on the long-term persistence and recovery of pygmy rabbit populations.

UDWR, BLM, USFS, and BYU

A goal of this project is to provide data necessary to develop area-specific management recommendations for pygmy rabbits.

Data will be used to support grazing permit renewals, fuels projects, and aid in pygmy rabbit conservation efforts.

07/01/2024

06/30/2025

2025

The areas investigated between 2005 and 2012 are located in Rich County, Grass Valley (near Richfield), and Hamlin Valley (in southern Utah). To date, we have revisited 438 historical burrow sites and assessed each site for presence of pygmy rabbits and vegetative status in these three study sites. Upon arriving at a historical burrow, we surveyed the area up to 60 meters away from the historical burrow. If a burrow was located within this distance, we ranked activity using a two-level ranking system (Ellis et al. 2017), documented its location, and placed a remote camera within 2 meters of the burrow entrance. If we did not find a burrow within the 60-meter buffer, we placed a remote camera in a random location within 60 meters of the historical burrow. Remote cameras remained active, continuously taking pictures when triggered without delay, for four weeks. After a minimum of four weeks, we removed the camera and analyzed the photos for evidence of pygmy rabbits to assess occupancy. To assess vegetative changes, at each occupied and unoccupied site, we collected habitat measurements that included vegetative cover, horizontal obscurity, percent understory composition, and shrub density. For vegetative cover, we used the line-intercept method along 15 m transects in each cardinal direction from the burrow or random point in unoccupied habitat. For horizontal obscurity measurements, we used a cover board with 36 squares (Bunnell et al. 2004). We placed the cover board at the burrow or random site and then documented the number of squares obscured by vegetation while kneeling (to simulate height of a predator such as a coyote) from distances of 2.5 m, 5 m and 10 m in each cardinal direction. To determine percent composition of the understory, we used a ¼ m square quadrat (Daubenmire 1959) placed at the center point (burrow or random location) and 1 random point along the 15 m transect in each cardinal direction (5 quadrats per site). Within each quadrat, we made an ocular estimate of percent moss, bare ground, rock, litter, grasses, shrubs, and forbs. We then calculated percent understory composition for each component at each site as the average of the five values from each plot. To estimate shrub density, we used the T-square method (Besag and Gleaves 1973). From 10 random points located near the center point (burrow or random location), we determined the distance to the nearest shrub. We then created two planes, split perpendicular to the selected shrub. We then determined the distance to the next nearest shrub located in the plane that excludes the randomly selected point. This combination of measurements will allow for detailed evaluation of habitat components where pygmy rabbits occur and where they are not found in conjunction with comparison to historical data.

The pygmy rabbit (Brachylagus idahoensis) is a species of conservation concern that has declined throughout its geographical range due to fragmentation and loss of essential sagebrush-steppe habitat (Green and Flinders 1980a; Knick et al. 2003; Grayson 2006). Pygmy rabbits were petitioned for listing under the Endangered Species Act (ESA) in 2023 and additional information on current occupancy rates and patterns of habitat-use within their range would be helpful. Several studies, taking place between 2005 and 2012, have documented the historical occupancy and short-term response of pygmy rabbits to habitat disturbance in Utah (Ellis et al. 2017; Edgel et al. 2018). To compare the documented historical pygmy rabbit occupancy with current occupancy, we revisited historical pygmy rabbit burrow locations and assessed the presence of pygmy rabbits and vegetative status.

In the next two years, we will continue to visit historical burrow sites to assess presence of pygmy rabbits and vegetative status. We also plan to estimate an occupancy rate for pygmy rabbits in each study site by comparing historical occupancy with current occupancy. Furthermore, we will assess the long-term response of pygmy rabbits to habitat disturbance, specifically in relation to disturbance of sage-brush systems.