The last place you'd expect to find a rare wildlife habitat is Philadelphia. But the Tinicum marshlands, located inside city limits near the International Airport, is a treasure trove of plants and wildlife not found anywhere else in Pennsylvania.

Although surrounded by the major metropolitan landscape, it isn't hard to get lost in the natural beauty of the marsh. Renamed the John Heinz National Wildlife Refuge at Tinicum, in memory of the environment-friendly senator killed in a 1991 mid-air crash, the refuge includes a tidal marsh, an impoundment pond, woodlands, meadows and other wetland habitats.

Tidal marshes are unusual because they are close enough to the coast to be influenced by ocean tides, but are far enough away that they remain freshwater ecosystems. The adjoining impoundment is protected from tidal forces by a dike between it and Darby Creek. A 3 1/2-mile foot trail around the impoundment is built on the dike, most of which dates from the 1930s.

Tinicum was a tidal marsh covering more than 5,700 acres when Swedish, Dutch and English settlers began diking the region to create pastureland in 1643. Rapid urbanization following World War I reduced the marsh to fewer than 300 acres.

The impoundment, a popular gathering spot for a variety of waterfowl, was slated to become a dumping ground for dredge from the Schuylkill River in the 1950s when Philadelphia conservationists and birders successfully campaigned to save it. The owner, Gulf Oil, donated the 145-acre parcel to the city as a wildlife preserve.

A decade later, the neighboring tidal marsh was threatened by plans for Interstate 95 and Folcroft Landfill. Again, local conservationists fought to save the habitat -- the last of its type in Pennsylvania -- and the highway was rerouted and the landfill closed. In 1972, the U.S. Fish & Wildlife Service assumed ownership of the preserve and began to purchase surrounding wetlands.

Now measuring about 1,200 acres, Tinicum is a unique juxtaposition of natural and urban environments. The calm marshland is riotous with birdsong, but the ever-present sounds of the city -- particularly highway traffic and the roar of passing planes -- provide a constant backdrop of sound. From many points on the trails, buildings and bridges are visible over the trees. After a while, however, city sounds fade into a background hum and your eyes focus away from the concrete jungle surrounding the marsh.

The trails are wide and flat, an easy stroll for novice hikers. There are narrow boardwalks built over the water to provide a close look at the marsh. There is a two-story observation deck a half-mile down the main trail, a good spot for bird-watching over the impoundment. A half-mile or so further on, a bird blind gives a nice view of the tidal marsh.

Birds vary by season, but Tinicum is considered an excellent locale for bird-watching. Birders have recorded 288 species, including great blue herons, northern harriers, least bitterns, great and snowy egrets, and a variety of swallows, warblers, ducks and terns. At least 25 species of butterflies have been photographed there. Muskrats, turtles and frogs abound in the water, and licensed fishers can take advantage of the well-stocked pond and creek. There are canoe launches in some locations.

Motorists trying to find Tinicum from Interstate 95 should exit onto Route 420 South, then make a left onto 291 East. A left onto Bartram Avenue gives you your first glimpse of the marshes. A left on 84th Street, and another on Lindbergh Boulevard, takes you to the Tinicum entrance.

[ by Tom Knapp ]