Type: report

Article abstract: In 2005, we implemented a new monitoring program for the endangered Stephens’ kangaroo rat (Dipodomys stephensi) 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. 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 the Stephens’ kangaroo rat and/or the Dulzura kangaroo rat (D. simulans). In order to provide continuity with previous monitoring efforts, we also live-trapped 10 SKR grids that were historically monitored biennially from 1996 to 2002. Overall, the estimates of SKR occupancy in 2006 on MCB Camp Pendleton were similar to the previous year. Within the high suitability stratum, we estimated SKR occupied 70.8 ha (SE=29.7) in 2006 compared to 60.0 ha (SE=24.2) in 2005. At the spatial scale of 50x50m grids, occupied habitat is approximately 20% of that expected and reported before the onset of this program. In areas occupied by SKR, density was estimated at 5.5 SKR/ha (SE=2.3), which is considered “medium” for this species (O’Farrell and Uptain 1987) or “low” (Tetratech and SJM Biological Consultants 1999) and were comparable to 2005 estimates of 4 to 7 SKR/ha in occupied habitat. At this time, we are not finding support for SKR existing at multiple densities across habitats, but in similar densities in a patchy framework, often co-occurring with DKR. We are also finding that DKR are much more prevalent in the pre-identified SKR habitat (or high suitability stratum) than are SKR. These results continue to indicate that SKR are likely much rarer on MCB Camp Pendleton than previously thought, greatly increasing the importance of active management for this species. In the high suitability stratum, our estimates of proportion of area occupied (PAO) over the past two years have been less than 0.10 (or 10%). At this low level, we have very little power to model habitat suitability and have low precision for our occupancy estimates. These are of utmost importance 1 2 to MCBCP for assessing the status and trends of SKR as well as understanding the importance of habitat, environmental, and disturbance variables