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Delmarva Peninsula Fox Squirrel

Left: Fox squirrel. Right: Squirrel in handling cone.Federally Listed Endangered Species

Beginning in spring, visitors to the Refuge are often treated to good views of Delmarva Peninsula fox squirrel (Sciurus niger cinereus) as they find tempting truffle treats (underground fungi that grows on tree roots) along the roadsides. Enjoy these views, but please SLOW DOWN, especially in the short drive between the fee booths and the Bateman Center. Sadly, a number of squirrels are killed each year by cars. The Delmarva fox squirrel (DFS) is an endangered species inhabiting the refuge's loblolly pine forests. Their coloring is similar to the gray squirrel, but the fox squirrel is larger and more terrestrial than the gray squirrel.

The DFS original range stretched from central New Jersey south through eastern Pennsylvania and down the length of the Delmarva Peninsula. As woodland has been cleared for farming and altered by forestry, available fox squirrel habitat has dwindled, The DFS was listed as federally endangered in 1967 (Federal Register 1967). To encourage species recovery, 34 DFS from Blackwater NWR and Eastern Neck NWR, Maryland were translocated to Chincoteague NWR. DFS release sessions were conducted in 1968, 1970, and 1971. Gray squirrels (Sciurus carolinensis) were trapped and removed from the refuge to reduce interspecies competition.

To monitor DFS population numbers, refuge biologists conduct DFS population assessments every two years. Biologists catch the squirrels in a trap, mark the squirrels with a tag, and then release the squirrels. Staff can statistically compare the number marked squirrels captured with the number of unmarked squirrels captured to determine the population’s size.

DFS population trapping began on the refuge in 1990 in three major locations. In each location, 30-40 traps are placed on the ground in a grid pattern, spaced about 100 meters apart. The “trap line” is marked with orange flagging because traps are small, like a bread container, and hard to see in the underbrush. The traps are “pre-baited” with pecans for at 5 days prior to a trapping session. Meaning they are left open and the squirrels can enter, take the pecan, and exit the trap without being caught. Once the trapping session begins, the traps are checked twice daily: once in the morning and once in the afternoon. At the end of the day, traps are closed so squirrels are not trapped overnight.

When a squirrel is captured, biologists take the weight, determine the sex and age, and then with a scanner (Mini Portable Reader, Destron Fearing) check to see if the squirrel is marked with a Passive Integrated Transponder (PIT tag). PIT tags are the staff’s method of marking individual squirrels with a unique number. Each PIT tag contains a 10 digit reference number associated with a particular squirrel. The scanner sends radio waves that create a response from the microchip in the Pit tag. If the squirrel doesn’t have a PIT tag, biologists insert a tag under the skin. The PIT tag is about the size of a grain of rice and is similar to “microchips” used for house pets like dogs and cats. Trained refuge staff performs the Pit tagging, but many refuge volunteers assisted in recording data and setting trap lines.

Biology staff, with the aid of many volunteers, monitored the Delmarva fox squirrel population on the refuge during October and November 2008. Within the three areas studied (Lighthouse Ridge, White Hills, and Woodland Trail), a total of 58 unique, individual squirrels were captured. Of these, fifteen squirrels had been captured and tagged during previous studies, one as long as eight years ago! New “unmarked” squirrels received PIT tags, which identifies each squirrel as a unique individual.

By consulting a mathematical model which uses the ratio of “marked” to “unmarked” squirrels and capture probabilities, we can come up with a population estimate. The 2008 population estimate of Delmarva Fox Squirrels in the three areas sampled was 155. This compares to population estimates of 148, 107, and 144 in years 2004, 2003, and 2001, respectively. The total population for the entire refuge is estimated at 200. We therefore conclude that this endangered species continues to do well forty years after they were transplanted to the island.

USFWS Chesapeake Bay Field Office DFS Website
Delmarva fox squirrel factsheet (pdf)

Page Photo Credits — Left: Delmarva fox squirrel - John White. Right: Squirrel in handling cone - Emma Kerr/USFWS.
Last Updated: Feb 24, 2014
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