The Delmarva fox squirrel (DFS, Sciurus niger cinereus) was one of 14 mammal species included on the first U.S. Endangered Species List, March 10, 1967. A subspecies of the eastern fox squirrel, the DFS once ranged from southeastern Pennsylvania and New Jersey southward through Maryland and Delaware to the southern tip of the Delmarva Peninsula in Virginia. It typically occupies mature closed-canopy forests of mixed pine and hardwoods with sparse understory. By the mid-1950s its range was reduced by 90% through hunting, land clearing for agriculture and regional conversion from sawtimber forestry to pulpwood pine plantations. This “old-growth” squirrel couldn’t cope with forest fragmentation and the introduction of short-rotation forest management.
Results/Conclusions
The DFS Recovery Team identified 5 critical recovery tasks. (1) Determine population status –A 2001 resurvey of 101 presence/absence sites studied in 1971 confirmed subpopulation persistence, colonization and extirpation rates of 92%, 31% and 8%, respectively. Seven benchmark subpopulations exhibited variable but stable fluctuations over 7 years, and 3 timber-harvested sites demonstrated subpopulation persistence and slow recovery after 20 years. (2) Extend occupied range – Sixteen translocations created 11 new colonies by 1992, each of which expanded beyond the release site. Natural and translocated subpopulations exhibit comparable levels of genetic variability. (3) Determine habitat availability – LiDAR surveys detected ~175,656 and 55,280 ha of mature forest in Maryland and Delaware, respectively. Not all may be suitable, but there is still considerable habitat available for range expansion, with suitable connectivity. (4) Reduce obvious threats – Once the DFS was listed, legal, regulatory and land ownership changes significantly reduced threats from residential development, sawtimber conversion and hunting. Landscape simulations indicate that the DFS can largely escape the effects of sea-level rise by moving upslope into available habitat. Two subpopulations in Delaware and Virginia may have fewer options. (5) Foster public awareness – Citizen scientists provided hundreds of DFS reports and evidence of 8 previously undocumented subpopulations on the periphery of the range. As of 2011 we estimated there to be between 17,000 and 22,000 squirrels occupying ~54,633 ha in Maryland, Delaware and Virginia. Furthermore, ~29% of this range occurs on protected land. This is ~50 times the required acreage to support a minimum viable population (95% probability of persisting for 100 years). Based on findings of population viability, range expansion, available unoccupied habitat and reduced threats, the DFS was removed from the endangered species list November 16, 2015.