While it seems like an unlikely spot for a wildlife refuge, John Heinz National Wildlife Refuge at Tinicum sits in the shadow of Philadelphia International Airport. Here at American’s First Urban Refuge, you will find open water, a freshwater tidal marsh, woodland, and mudflats, all of which entice hundreds of species to stop and rest in their migration, or even to make it a permanent home. Tinicum Marsh is the largest tidal marsh in the commonwealth. It provides nesting grounds for 90 species of birds, and hundreds more have been seen passing through. Visitors can explore the refuge via a ten mile network of trails, including the 3.5-mile Wetland Loop…