The Delmarva fox squirrel, a beefy grey squirrel with an unusually fluffy tail that used to dominate the Eastern Shore of Maryland, has been hanging on to its population hold by a single paw for decades. Thanks in part to new research on the squirrel’s risk of extinction by University of Maryland Center for Environmental Science researchers, the U.S. Fish and Wildlife Service is proposing to delist the squirrel from the federally endangered list.
Once found throughout the Delmarva Peninsula, the fox squirrel today occurs in only four counties in Maryland, less than 10 percent of its historical range. It underwent significant decline from historic levels, largely due to loss of the mature pine and hardwood forests where it lives, and was listed as Federally endangered in 1967.
During the past 47 years, the U.S. Fish and Wildlife Service, state and local partners and private landowners, have taken a coordinated, collaborative approach to recover the species across the Delmarva Peninsula. It has long been a goal to delist the Delmarva squirrel by increasing its population through reintroduction and protecting its habitat so it can persist as a viable, self-sustaining component of the ecosystem.
A missing piece has been determining just how much habitat is needed for the squirrel to continue its comeback. That’s where UMCES scientists come into the picture. Bob Gardner and Bob Hilderbrand of the UMCES’ Appalachian Laboratory, and Todd Lookingbill of the University of Richmond, did a mathematical simulation of the squirrel populations using several new techniques to see how much land the squirrels needed to make a comeback.
They compared data on how much the population is currently surviving year to year, how much the environment is expected to change year to year, and the maximum amount of squirrels a habitat can support, They also factored in how likely the squirrels are to move from one patch of forest to another across the landscape. By using computer models to calculate the extinction risk for different population sizes, they were able to identify a reasonable level of risk.
“For any target population size we can back calculate to how much habitat is necessary for the squirrel population,” said Bob Hilderbrand. “This gives government agencies a management tool. How many wood lots are big enough to maintain viable populations of fox squirrels? By modeling the extinction risks for different population sizes, we can identify a reasonable level of risk.”
They figured out that 400 hectares—close to 1,000 acres--of land were needed for any given population to survive—and it turns out there are quite a few large patches of trees on the Eastern Shore that can sustain the squirrel population.
For more on the research: http://www.umces.edu/al/extinction-risk-delmarva-fox-squirrel
Photos by Guy W. Willey Sr.