Good News for Stephens' kangaroo rat
The US Fish and Wildlife Service recently reclassified the Stephens’ kangaroo rat (Dipodomys stephensi, or SKR) from the direst classification under the Endangered Species Act of Endangered to the lesser category of Threatened. Although one might think that an organization called the Conservation Biology Institute (CBI) might lament such a decision or charge that it is political, our kangaroo rat expert and Chief Scientist, Dr. Wayne Spencer, wrote a public letter in support of the Service’s decision. As a conservation science organization, it is imperative that CBI always stands for objective and rigorous interpretation of the available science, whichever side of a decision it may support—and in this case the available scientific evidence strongly suggests that conservation actions have reduced threats to the SKR to where it is no longer in danger of extinction.
In other words, this down-listing of an Endangered Species is a conservation success story worthy of celebration. Moreover, reclassifying the species as Threatened actually benefits conservation efforts intended to even further recover the species. This is because Threatened status allows the Service to invoke the Endangered Species Act’s special “4(d) Rule,” which allows for greater flexibility in implementing conservation actions that were, perhaps counter-intuitively, hindered by Endangered status. The 4(d) Rule for SKR allows the Service and other conservation partners greater freedom to conduct genetic research and monitoring, species translocations and reintroductions, habitat management experiments, noxious weed control, and other “activities conducted as part of a Service- or State-approved plan that are for the purpose of Stephens’ kangaroo rat conservation” (USFWS 2020b).
With funding provided by the Bureau of Land Management (BLM) and leadership of the Riverside County Habitat Conservation Agency (RCHCA), CBI has headed up a multi-agency, multi-stakeholder SKR Working Group* to develop a Rangewide SKR Management and Monitoring Plan. The plan is intended to standardize and better coordinate management, monitoring, and research efforts across the SKR’s geographic range, and the diverse entities having some form of responsibility for the species and the land it occupies.
The down-listing of the species and the preparation of this new conservation plan come on the heels of 30+ years of conservation efforts by federal, state, and local agencies and organizations, including CBI. Since 1992, Dr. Spencer has contributed significantly to the body of knowledge related to SKR (as well as other kangaroo rat species). Dr. Spencer currently serves as the technical lead for the SKR Working Group; and with others at CBI, including Deanne DiPietro, Gwynne Corrigan, Heather Rustigian-Romsos, Craig Thompson, and Rebecca Degagne, CBI has developed new mapping tools and approaches in support of the effort based on the latest available science.
Below, Dr. Spencer summarizes some key information that was unavailable at the time the Service prepared the SKR Status Assessment Report (USFWS 2020a) and the proposed rule to Reclassify SKR from Endangered to Threatened (USFWS 2020b).
Updateable SKR Habitat and Biogeography Working Map. Over the past few months, the SKR Working Group has created, tested, and refined a high-resolution SKR habitat quality map across the species’ range, which represents the best available information on SKR habitat quality, distribution, and abundance. We developed spatial models of SKR habitat quality across the range based on SKR detection data and an array of environmental variables (e.g., climate, terrain, vegetation, and soil variables) using maximum entropy (Maxent) statistical methods. A clear advantage of the new habitat map is that it uses variables derived at relatively fine resolution (20m) from freely available satellite imagery, which can be regularly updated (e.g., annually) to track habitat changes due to management or other influences. The habitat value map is also far more nuanced, detailed, and scientifically defensible than previous SKR habitat maps based on GIS overlay methods.
The SKR Working Group has integrated new and available spatial information into a dynamic SKR Biogeography Working Map (illustrated below), which uses the SKR habitat suitability layer as a foundation. The working map can be updated, refined, and used by Working Group members or others for planning, monitoring, or other purposes.
Illustration of SKR biogeography working map on Databasin.org. The live SKR Biogeography Working Map is available to SKR Working Group members for viewing, commenting on, updating, or downloading data. Other interested parties can also request access to the map.
The plan uses this new SKR habitat modeling system as a foundation for monitoring and management decisions. It can be used to map and track how habitat quality varies across space and time in response to management, weather, and other factors. By establishing correlations between predicted habitat quality and field-based SKR population estimates, the system can also be used to estimate and track population abundance.
Threats Assessment. Although rangewide threats to SKR are already well known (USFWS 2020, Spencer et al. 2017), this plan refines our understanding using comprehensive threats assessments completed by preserve managers across eight SKR preserve areas. The threats assessment format was developed by the SKR Working Group to systematically address all possible threats to individual SKR and subpopulations at the reserve level, including both existing known threats and potential future threats (e.g., under climate change). The preserve- level assessments also address current management and mitigation strategies as well as factors that constrain management actions, such as lack of sufficient funding or guidance for how best to manage a threat. The results of these preserve-level assessments were summarized across the species’ range to better understand the pervasiveness and importance of various threats and thus aid prioritization of management, monitoring, and research actions.
Because habitat and population fragmentation represent major threats to SKR, the strategy uses the habitat maps and recent population genetic information to help identify where habitat restoration or other actions could improve habitat and demographic connectivity, or where active population management may be needed to counter risks of demographic and genetic isolation-- such as by translocating individual SKR between reserves or reintroducing them where they may have been eradicated.
New Scientific Recommendations for Management. The Management Plan identifies and promotes effective tools for managing SKR habitat, populations, and threats both within and among preserves based on the collective knowledge of SKR experts and reserve managers. It provides for coordinated species management across ownership boundaries by helping prioritize which management investments will best promote species conservation and recovery goals at the rangewide scale. Among the various pertinent sources of information are recent and ongoing population genetics analyses by researchers at the San Diego Zoo’s Institute for Conservation Research, which characterize genetic diversity within and among known populations and demonstrate where population interventions, such as translocations, reintroductions, or genetic augmentations, are most needed to promote genetic diversity, demographic connectivity, and population recovery.
New Scientific Recommendations for Monitoring. The SKR Monitoring Plan will provide a framework and standardized sampling strategy to track changes in SKR habitat and populations over time and across the range, based on previous work by the US Geological Survey (USGS) designing, testing, and refining sampling protocols on Marine Corps Base Camp Pendleton. The updateable habitat quality map provides a spatial foundation for quantifying habitat quality, quantity, and distribution; and by correlating field measures of SKR occupancy and density with habitat quality, the map can be used to track rangewide patterns in SKR abundance. The plan also recommends genetic monitoring to track status and trends in genetic diversity, relatedness, inbreeding, structure, and effective population size using hair samples extracted from SKR captured during population monitoring.
New SKR Reserve Areas. New areas supporting SKR habitat and populations continue to be conserved. We know of several new preserve areas established subsequent to the SKR Status Assessment Report, including the Montecito Ranch Preserve (owned and managed by the Endangered Habitats Conservancy) and several other parcels in the Ramona Grasslands SKR population area (owned and managed by the San Diego Habitats Conservancy and County of San Diego Department of Parks and Recreation); and the Paradise Valley Reserve, a new addition to San Diego County’s Hellhole Canyon Preserve that supports SKR on the edge of the large Rancho Guejito SKR population area.
Data Management. The SKR Data Management Strategy will provide a framework and guidance for developing an integrated SKR Data Management System, which will build on existing SKR data bases and provide guidelines for consistent data collection, collation, analysis, reporting, and sharing protocols. The strategy will facilitate quality assurance, data availability, and analysis to assist reserve managers and other users
Please join us in celebrating conservation success and pursuing an even better future for rare species!
Dr. Wayne Spencer with a San Quintin kangaroo rat. Photo by: Darian Spencer.
Spencer, W.D., S.J. Montgomery, P.R. Behrends, and D.M. Shier. 2017. Stephens’ kangaroo rat. Pages 60-66 in S. Tremor, D. Stokes, W. Spencer, J. Diffendorfer, H. Thomas, S. Chivers, and P. Unitt (editors). San Diego County Mammal Atlas. Proceedings of the San Diego Society of Natural History No. 46.
U.S. Fish and Wildlife Service. 2020a. Species Report for the Stephens’ kangaroo rat (Dipodomys stephensi). Version 1.1, July 30, 2020. U.S. Fish and Wildlife Service, Pacific Southwest Region, Sacramento, California. xi + 125 pp.
*The Stephens’ Kangaroo Rat Working Group includes representatives from US Fish and Wildlife Service, California Department of Fish and Wildlife, Bureau of Land Management, the San Diego Zoo Institute for Conservation Research, US Geological Survey, the counties of San Diego and Riverside, Marine Corps Base Camp Pendleton, Fallbrook Naval Weapons Station, and other scientists, conservationists, and land managers with interest in SKR conservation. Funding has been provided by Bureau of Land Management.
*Photos by Moose Peterson unless otherwise noted.