Type: report

Article abstract: In 2005, we implemented a monitoring program for the endangered Stephens’ Kangaroo Rat (Dipodomys stephensi, SKR) on Marine Corps Base Camp Pendleton (MCBCP). It is a relatively simple, multi-tiered, habitat-based, adaptive monitoring program designed to track yearly trends in the total area occupied by SKR on base. We revised the program in 2011 after a five-year review and program evaluation to increase our 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. We focused our sampling and monitoring efforts within the recently revised SKR habitat boundaries totaling 628 hectares. Seventeen percent of our sample effort is for discovery of SKR within potentially suitable habitat outside of these boundaries. There is a two-phased approach for sampling. The first phase involves a complete search for any potential kangaroo rat sign and measurement of habitat and environmental variables. If any potential sign is observed, two to four days of live-trapping are conducted for the second phase. Live-trapping is necessary to determine if plots are occupied by SKR and/or the Dulzura Kangaroo Rat (D. simulans, DKR). Within the SKR Monitoring Area in Fall/Winter 2017/18, SKR occupied an estimated 231 ha which was an insignificant 6.6% decrease in comparison to 2016/17. Long term results indicate the amount of habitat occupied by SKR steadily increased from a low estimate of only 60 ha in 2005 to 248 ha in 2016/17, a four-fold increase, and has remained relatively stable for the past 7 years. SKR density estimates in occupied areas (11 SKR/0.25 ha) were also high in relation to historic values (1-10 SKR/0.25 ha) and have been stable and/or increasing for the past 6 years. SKR have often been associated with open forb- dominated areas and have historically been shown to respond positively to habitat disturbance. Occupancy models showed that open ground was a significant predictor of all parameters of SKR dynamics (occupancy, colonization, extinction). The greatest probability of SKR occupancy was with between 40 to 80% open ground. Additionally, forb 2 cover > 40%, more compact soils and flat slopes were also top predictors of SKR occupancy. Forbs are the primary seed resource for SKR, while firmer soils may increase seed foraging efficiency for SKR and better support their burrow structures from disturb