THE SWIMMING FOXES OF SMITH ISLAND *** A Pilot Study ***

Dennis G. Jorde and G. M. Haramis
Patuxent Wildlife Research Center

ABSTRACT

Intense predator pressure can influence waterfowl to select suboptimal nesting habitats resulting in lowered nest success. Black ducks breeding on Smith Island in the Chesapeake Bay nest extensively in low marsh habitat, especially black needlerush, rather than in upland or high marsh sites as expected. Nest success of black ducks using this habitat seemed unusually low during the 1995 breeding season (G. M. Haramis and D. G. Jorde, unpubl. data), which raised questions about habitat quality and habitat selection. If periodic high tides and unpredictable flooding by storm tides make low marsh habitats a poor choice for nesting sites, why do black ducks continue to nest in this habitat? After observing the presence of Red Fox on Smith Island and their intensive predation of terrapin nests on sandy beaches during summer 1995, we questioned whether avoidance of foxes might be influencing black ducks to select less favorable low marsh as nesting habitats. Because there is little information about activities of red foxes inhabiting small islands in the Chesapeake Bay or on barrier islands along the Atlantic coast, we began a pilot study to determine the potential influence of foxes on the nesting success of black ducks on Smith Island. Four red foxes (2 male, 2 female) were trapped and radio–collared on Smith Island in March and April 1996 to record movements and other activities during the 18–month life of the transmitters. These radio–marked foxes routinely swam tidal guts and often changed locations, but within separate well–defined territories. Few permanent den sites are available; holes dug in sandy substrates often collapse within 4 weeks. The need for a formal study will depend on interpretation of pilot study data collected through July 1997.

Smith Island is a compact archipelago about 8 miles long and 4 miles wide and is located mostly in the Maryland portion of the Chesapeake Bay with its southern tip extending into Virginia. Access to the island is restricted to boats traveling approximately 11 miles from Crisfield, Maryland. Martin NWR (4,423 acres) is located in the northern sector of Smith Island that is bisected by Big Thorofare navigation channel. The three small villages of Ewell, Rhodes Point, and Tylerton are located in the southern sector of Smith Island where the local economy is focused on harvesting of blue crabs. The primary locations of 4 radio–collared red foxes are distinguished by colored pins: blue Fox 5.324 Adult Male trapped 2-26-96 Fogpoint beach north of Cherry Tree Island green Fox 5.404 Adult Female trapped 3-13-96 Easter Point dredge spoil site yellow Fox 5.423 Adult Male trapped 4-23-96 Rhodes Point dredge spoil restoration site red Fox 5.384 Juvenile Female trapped 4-23-96 Rhodes Point dredge spoil restoration site

Smith Island is primarily saltmarsh (left photo) with numerous tidal creeks (guts) and ponds with salinities >12 parts per thousand. Uplands are characterized by hummocks dominated by Red Cedar, Loblolly Pine, Hackberry and Poison Ivy and include remnant hedgerows (i.e. ditch lines, stock ponds) abandoned man–made mounds and ridges previously associated with past cattle grazing.

Much of the saltmarsh (right photo), which is dominated by black needlerush interspersed with areas of salt grass and saltmeadow hay, is succeptable to flooding by high tides. Many tidal guts are >3 meters wide and >1 meter deep at high tide with soft mud substrates and strong tidal currents. Many navigation channels, which several foxes routinely cross, are >5 meters wide and >1 meter deep at low tide.

Holes and dens were located in sand dunes adjacent to beaches, in dredge spoil sites, and upland tree hummocks. Of 22 holes that foxes dug in sandy soils between February and May 1996, all had collapsed and the sites were abandoned by late summer. Old and new holes dug in clay soils at dredge spoil sites and tree hummocks remained intact and several were still occupied in August.

Foxes were trapped above the high tide line on sandy beaches (left photo) where fresh tracks were a sign of frequent activity. Padded leg–hold traps were placed in single and duel sets and baited with fox lure. Maryland DNR fur–bearer specialist Robert Colona assisted with the trapping. Trapped foxes (right photo: fox 5.423) were checked for trap injuries, fitted with a radio–collar, and released at the trap site.

Potential food resources of red foxes on Smith Island include oystercatcher eggs (top left); clapper rails (top right); black duck eggs (lower left); terrapin eggs (lower right), in addition to young herons and egrets displaced from nests, marsh nesting birds, injured birds, rodents (especially norway rats on spoil sites) and muskrats, carrion (fish, birds, mammals) washed up on beaches, persimmon fruits and berries of wild cherry, and possibly fiddler and blue crabs.