Stephens’ Kangaroo Rat Research and Monitoring Program Active
Western Ecological Research Center (WERC) scientists provide valuable support to management agencies as they work toward recovery of the threatened Stephens’ kangaroo rat (Dipodomys stephensi). The Stephen’s kangaroo rat (SKR) occupies a limited range of habitat within southern California. WERC’s long-term monitoring of SKR at several sites has revealed local trends in distribution and abundance. SKR continues to face threats including habitat loss and degradation, population isolation due to habitat fragmentation, and the cumulative effects of climate change.
Stephens’ kangaroo rat (Dipodomys stephensi) is a small-sized nocturnal rodent adapted for warm and arid conditions. Stephens’ kangaroo rats (SKR) primarily eat seeds, and collect seeds and other materials in exterior cheek folds lined with fur rather than in cheek pouches inside the mouth as do hamsters. This is because carrying the food in the mouth would involve wetting it and moisture needs to be conserved as much as possible in dry environments.
SKR hop on two hind feet, and require open habitat on gentle slopes for efficient movement. SKR also use their hind limbs to excavate sufficiently deep burrows which provide shelter from predators, areas for nesting or food storage, and protection from most fires and other surface disturbances. By removing and redistributing seeds, SKR can act as keystone species in their habitat . Stephens’ kangaroo rats are known to occur in western Riverside County, western San Diego County, and central San Diego County.
Due to extensive habitat loss, degradation, and fragmentation, SKR was listed as threatened by the California Fish and Game Commission in 1971 (CNDDB, California Endangered and Threatened Animals List, July 2023; https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=109405) and was subsequently listed as endangered by the U.S. Fish and Wildlife Service in 1988 (53 FR 38465 38469). The threat of habitat loss has been significantly reduced through the development and implementation of the Stephens’ Kangaroo Rat Habitat Conservation Plan and the Western Riverside County Multiple Species Habitat Conservation Plan in Riverside County, and management efforts by the Department of Defense on Naval Weapons Station Seal Beach Detachment Fallbrook, Marine Corps Base Camp Pendleton and at Navy Base Coronado’s Remote Training Site Warner Springs in San Diego County. These efforts were important in the Federal reclassification of SKR from endangered to threatened that was finalized in 2022 (87 FR 8967 8981; https://www.govinfo.gov/link/fr/87/8967). WERC’s research and monitoring efforts on SKR provide critical information in the continued efforts for recovering this species.
Research and Monitoring Program – 2005 to Present
The species recovery plan recommends the establishment of several ecosystem-based reserves, one of which includes parts of Marine Corps Base Camp Pendleton (MCB Camp Pendleton). SKR on MCB Camp Pendleton represent the westernmost population unit for species recovery. WERC scientists study SKR demography, threats, and effectiveness of conservation actions at the MCB Camp Pendleton site and Naval Base Coronado, Remote Training Site Warner Springs.
Marine Corps Base Camp Pendleton
A monitoring plan for MCB Camp Pendleton was implemented in 2005 following a scientific workshop between WERC researchers, statisticians, species experts, and many partners the previous year. This multi-tiered, habitat-based, adaptive monitoring program was designed to track annual trends in the total area occupied by SKR on base. The program was optimized in 2011 to increase the power to document population changes over time and gain a better understanding of the importance of habitat characteristics, environmental factors, fire, and military disturbance in the occupation and persistence of SKR.
Study Design
Monitoring occurs on 100-150 spatially-balanced 50m x 50m plots (100 permanent + 50 random/discovery) located throughout MCB Camp Pendleton every year. The two-phased sampling approach includes 1) sign surveys for burrows, tracks, and scat, and 2) live trapping for 2-3 nights per year at each plot. More than ten covariates are recorded that include soil texture and compaction, vegetation cover, dominants plants, disturbance, and more.
Live-trapping at spatially-balanced plots provides a snapshot of annual occupancy. Live-trapping is necessary as SKR frequently co-exist with sympatric and similar looking Dulzura kangaroo rats (DKR); therefore, burrow counts do not directly correspond to SKR abundance. Once kangaroo rats are captured, standard field measurements are taken, including cranial characteristics, which can be used to verify species identification. The animals are then given a unique ear tag and released. Live-trapping results are used to calculate trend metrics such as the total area occupied (or used) by SKR and relative density in occupied habitat each year.
This approach advances our understanding of how drivers influence SKR abundance and distribution and allows researchers to model and assess threats to SKR, such as vegetation succession, non-native grasses, and disturbance. This powerful monitoring framework is currently being used as a template for monitoring SKR across its range (“Stephens’ Kangaroo Rat Rangewide Management and Monitoring Plan”, address: https://consbio.org/publications/stephens-kangaroo-rat-rangewide-management-and-monitoring-plan/).
Naval Base Coronado, Remote Training Site Warner Springs
Following successful monitoring at MCB Camp Pendleton, in 2010 the Navy requested WERC to implement a long-term monitoring program for SKR on Naval Base Coronado, Remote Training Site Warner Springs (RTSWS). A combination of cattle grazing, hunting, and military training have created unique factors which affect habitat at this site. Considering these factors, WERC researchers developed a monitoring program based upon that which was previously developed for MCB Camp Pendleton.
Significant Findings
Marine Corps Base Camp Pendleton
Increased area occupied has been correlated with increases in the density index, indicating SKR population growth occurs by expansion into suitable habitat patches as well as by increases in numbers within occupied patches. Although total area occupied has remained stable in recent years, results have demonstrated that SKR are extremely dynamic and move frequently among habitat patches based upon changes in habitat suitability.
Models have shown that on MCB Camp Pendleton, SKR are more likely to colonize and occupy areas with low slopes, compact soils, moderate to high levels of open ground and forbs, and low shrub cover.
In contrast, lower proportion of open ground and high levels of non-native grasses are associated with an increased risk of localized extinctions among years.
Additionally, SKR have demonstrated a positive response to all but the most extreme military training, as these disturbances often open up the habitat and increase habitat suitability for SKR.
Naval Base Coronado, Remote Training Site Warner Springs
Similar to MCB Camp Pendleton, monitoring results from 2010 to 2020 have indicated SKR have been stable or increasing during this time period. Consistent with findings from previous studies, low slopes, high forb cover, and low shrub cover were most predictive of areas occupied by SKR at this site. Additionally, there has been no evidence that military activity or cattle grazing have significantly affected SKR populations.
Hopping Toward Recovery
The program objectives are more than just monitoring SKR – the scientifically-robust sampling framework not only facilitates monitoring of long-term trends for SKR over time but also improves researchers’ knowledge of processes affecting SKR persistence. Understanding SKR associations with habitat and landscape features, responses to changes in habitat and climate, and responses to threats and stressors allows land managers to make informed management decisions and undertake recovery actions that may benefit SKR populations.
In fact, WERC research has shown that SKR benefit from activities that promote ideal habitat conditions suggested from occupancy modeling. Management strategies that encourage higher forb cover, native grasses, and more open habitat include vegetation thinning, non-native grass control, and prescribed burns. As documented on MCB Camp Pendleton, frequent fires decrease cover of shrubs and non-native grasses and maintain the open ground and forb-dominated habitat that is suitable for SKR. The probability of occupancy or colonization is greater in more recently burned habitat.
The benefits of habitat management have also been documented by researchers in other SKR population areas (such as by Riverside County Habitat Conservation Agency, San Diego Zoo Wildlife Alliance). Department of Defense and these partners are striving to use knowledge gained by WERC and others to assist recovery efforts for SKR and find ways to increase population sizes and improve the resiliency of SKR to other threats and stressors.
Continued research will allow WERC and our partners to gain further insight into SKR conservation needs and inform strategies to meet goals for recovery and long-term persistence of this iconic species.
What's New?
New and current research components include:
- Diet analysis of SKR and co-occurring species (such as DKR) in relation to available resources using genetic analysis of scat. Results could inform habitat restoration efforts with specific plant species that may be linked with reproductive success and greater resilience of local SKR populations.
- Radiotelemetry to better understand SKR movement dynamics on RTSWS. This would directly inform the effect of military training on SKR by documenting movement in relation to training activities.
- Advances in modeling to estimate the total number of SKR annually (spatially explicit abundance models) and to better understand competition dynamics with DKR (interactive two-species occupancy models).
USGS SKR Research and Monitoring Team
Western Ecological Research Center (WERC) scientists provide valuable support to management agencies as they work toward recovery of the threatened Stephens’ kangaroo rat (Dipodomys stephensi). The Stephen’s kangaroo rat (SKR) occupies a limited range of habitat within southern California. WERC’s long-term monitoring of SKR at several sites has revealed local trends in distribution and abundance. SKR continues to face threats including habitat loss and degradation, population isolation due to habitat fragmentation, and the cumulative effects of climate change.
Stephens’ kangaroo rat (Dipodomys stephensi) is a small-sized nocturnal rodent adapted for warm and arid conditions. Stephens’ kangaroo rats (SKR) primarily eat seeds, and collect seeds and other materials in exterior cheek folds lined with fur rather than in cheek pouches inside the mouth as do hamsters. This is because carrying the food in the mouth would involve wetting it and moisture needs to be conserved as much as possible in dry environments.
SKR hop on two hind feet, and require open habitat on gentle slopes for efficient movement. SKR also use their hind limbs to excavate sufficiently deep burrows which provide shelter from predators, areas for nesting or food storage, and protection from most fires and other surface disturbances. By removing and redistributing seeds, SKR can act as keystone species in their habitat . Stephens’ kangaroo rats are known to occur in western Riverside County, western San Diego County, and central San Diego County.
Due to extensive habitat loss, degradation, and fragmentation, SKR was listed as threatened by the California Fish and Game Commission in 1971 (CNDDB, California Endangered and Threatened Animals List, July 2023; https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=109405) and was subsequently listed as endangered by the U.S. Fish and Wildlife Service in 1988 (53 FR 38465 38469). The threat of habitat loss has been significantly reduced through the development and implementation of the Stephens’ Kangaroo Rat Habitat Conservation Plan and the Western Riverside County Multiple Species Habitat Conservation Plan in Riverside County, and management efforts by the Department of Defense on Naval Weapons Station Seal Beach Detachment Fallbrook, Marine Corps Base Camp Pendleton and at Navy Base Coronado’s Remote Training Site Warner Springs in San Diego County. These efforts were important in the Federal reclassification of SKR from endangered to threatened that was finalized in 2022 (87 FR 8967 8981; https://www.govinfo.gov/link/fr/87/8967). WERC’s research and monitoring efforts on SKR provide critical information in the continued efforts for recovering this species.
Research and Monitoring Program – 2005 to Present
The species recovery plan recommends the establishment of several ecosystem-based reserves, one of which includes parts of Marine Corps Base Camp Pendleton (MCB Camp Pendleton). SKR on MCB Camp Pendleton represent the westernmost population unit for species recovery. WERC scientists study SKR demography, threats, and effectiveness of conservation actions at the MCB Camp Pendleton site and Naval Base Coronado, Remote Training Site Warner Springs.
Marine Corps Base Camp Pendleton
A monitoring plan for MCB Camp Pendleton was implemented in 2005 following a scientific workshop between WERC researchers, statisticians, species experts, and many partners the previous year. This multi-tiered, habitat-based, adaptive monitoring program was designed to track annual trends in the total area occupied by SKR on base. The program was optimized in 2011 to increase the power to document population changes over time and gain a better understanding of the importance of habitat characteristics, environmental factors, fire, and military disturbance in the occupation and persistence of SKR.
Study Design
Monitoring occurs on 100-150 spatially-balanced 50m x 50m plots (100 permanent + 50 random/discovery) located throughout MCB Camp Pendleton every year. The two-phased sampling approach includes 1) sign surveys for burrows, tracks, and scat, and 2) live trapping for 2-3 nights per year at each plot. More than ten covariates are recorded that include soil texture and compaction, vegetation cover, dominants plants, disturbance, and more.
Live-trapping at spatially-balanced plots provides a snapshot of annual occupancy. Live-trapping is necessary as SKR frequently co-exist with sympatric and similar looking Dulzura kangaroo rats (DKR); therefore, burrow counts do not directly correspond to SKR abundance. Once kangaroo rats are captured, standard field measurements are taken, including cranial characteristics, which can be used to verify species identification. The animals are then given a unique ear tag and released. Live-trapping results are used to calculate trend metrics such as the total area occupied (or used) by SKR and relative density in occupied habitat each year.
This approach advances our understanding of how drivers influence SKR abundance and distribution and allows researchers to model and assess threats to SKR, such as vegetation succession, non-native grasses, and disturbance. This powerful monitoring framework is currently being used as a template for monitoring SKR across its range (“Stephens’ Kangaroo Rat Rangewide Management and Monitoring Plan”, address: https://consbio.org/publications/stephens-kangaroo-rat-rangewide-management-and-monitoring-plan/).
Naval Base Coronado, Remote Training Site Warner Springs
Following successful monitoring at MCB Camp Pendleton, in 2010 the Navy requested WERC to implement a long-term monitoring program for SKR on Naval Base Coronado, Remote Training Site Warner Springs (RTSWS). A combination of cattle grazing, hunting, and military training have created unique factors which affect habitat at this site. Considering these factors, WERC researchers developed a monitoring program based upon that which was previously developed for MCB Camp Pendleton.
Significant Findings
Marine Corps Base Camp Pendleton
Increased area occupied has been correlated with increases in the density index, indicating SKR population growth occurs by expansion into suitable habitat patches as well as by increases in numbers within occupied patches. Although total area occupied has remained stable in recent years, results have demonstrated that SKR are extremely dynamic and move frequently among habitat patches based upon changes in habitat suitability.
Models have shown that on MCB Camp Pendleton, SKR are more likely to colonize and occupy areas with low slopes, compact soils, moderate to high levels of open ground and forbs, and low shrub cover.
In contrast, lower proportion of open ground and high levels of non-native grasses are associated with an increased risk of localized extinctions among years.
Additionally, SKR have demonstrated a positive response to all but the most extreme military training, as these disturbances often open up the habitat and increase habitat suitability for SKR.
Naval Base Coronado, Remote Training Site Warner Springs
Similar to MCB Camp Pendleton, monitoring results from 2010 to 2020 have indicated SKR have been stable or increasing during this time period. Consistent with findings from previous studies, low slopes, high forb cover, and low shrub cover were most predictive of areas occupied by SKR at this site. Additionally, there has been no evidence that military activity or cattle grazing have significantly affected SKR populations.
Hopping Toward Recovery
The program objectives are more than just monitoring SKR – the scientifically-robust sampling framework not only facilitates monitoring of long-term trends for SKR over time but also improves researchers’ knowledge of processes affecting SKR persistence. Understanding SKR associations with habitat and landscape features, responses to changes in habitat and climate, and responses to threats and stressors allows land managers to make informed management decisions and undertake recovery actions that may benefit SKR populations.
In fact, WERC research has shown that SKR benefit from activities that promote ideal habitat conditions suggested from occupancy modeling. Management strategies that encourage higher forb cover, native grasses, and more open habitat include vegetation thinning, non-native grass control, and prescribed burns. As documented on MCB Camp Pendleton, frequent fires decrease cover of shrubs and non-native grasses and maintain the open ground and forb-dominated habitat that is suitable for SKR. The probability of occupancy or colonization is greater in more recently burned habitat.
The benefits of habitat management have also been documented by researchers in other SKR population areas (such as by Riverside County Habitat Conservation Agency, San Diego Zoo Wildlife Alliance). Department of Defense and these partners are striving to use knowledge gained by WERC and others to assist recovery efforts for SKR and find ways to increase population sizes and improve the resiliency of SKR to other threats and stressors.
Continued research will allow WERC and our partners to gain further insight into SKR conservation needs and inform strategies to meet goals for recovery and long-term persistence of this iconic species.
What's New?
New and current research components include:
- Diet analysis of SKR and co-occurring species (such as DKR) in relation to available resources using genetic analysis of scat. Results could inform habitat restoration efforts with specific plant species that may be linked with reproductive success and greater resilience of local SKR populations.
- Radiotelemetry to better understand SKR movement dynamics on RTSWS. This would directly inform the effect of military training on SKR by documenting movement in relation to training activities.
- Advances in modeling to estimate the total number of SKR annually (spatially explicit abundance models) and to better understand competition dynamics with DKR (interactive two-species occupancy models).
USGS SKR Research and Monitoring Team