Rootin’ for the Birds: Restoring Marshes at the Stone Harbor Bird Sanctuary
Freshwater wetland in the process of being restored.
The Stone Harbor Bird Sanctuary is a truly a remarkable place with a distinguished history. You may remember when it hosted one of the largest rookeries for colonial waterbirds in the United States, or you have heard the stories. Unfortunately, development, invasive plants, and predators ultimately drove the nesting wading birds to offshore islands, where they still can be found. Today, the sanctuary remains an important refuge on Seven Mile Beach, is heavily used by a wide array of wildlife, and is home to many native plants.
This 21-acre site boasts a mature North Atlantic Coastal Plain maritime forest and both fresh and tidal wetlands. Atlantic maritime forests were once widespread on barrier islands and mainland coasts but now are relatively rare. Coastal development has reduced them dramatically, and they now make up less than 1% of the habitat in New Jersey. These forests are defined by their proximity to the sea and the great forces that shape them. Harsh winds, salt spray, and sandy soil combine to make these unique and special places worth exploring, no matter the season.
During spring and fall, the sanctuary is an important migratory stopover for songbirds, dragonflies, and butterflies. Large flocks of sparrows, robins, thrushes, and woodpeckers make the sanctuary their winter home. In the summer, the sanctuary is home to dozens of species of nesting songbirds – especially those that eat insects and berries (warblers, catbirds, mockingbirds, robins, flycatchers, swallows, and many others). At present, black-crown night herons use the site as a roosting area, and you can find great and snowy egrets feeding in the tidal marsh. Ospreys are common sights here as they gather sticks and branches to fortify their nests, but the proximity of the sanctuary to coastal development and the continual threat of predators has made treed islands in the back bays their favored nesting sites. The sanctuary also provides an important habitat for eastern box turtles and several species of frogs and toads, and bats can be seen around dusk – especially during migration.
Keeping the Stone Harbor Bird Sanctuary’s habitats viable and valuable requires a lot of management, and the Borough of Stone Harbor and The Wetlands Institute have partnered to manage and restore the sanctuary for several years. Over the past four years, a major focus has been on the restoration of both the tidal and freshwater wetlands at the sanctuary.
A number of non-native, invasive plants – common reed (Phragmites australis) and purple loosestrife (Lythrum salicaria) in particular – have become established in the wetlands and transition areas located within the sanctuary. These have crowded out native vegetation, reduced species diversity, and degraded habitat functions and values for the sanctuary’s wildlife. If you walked by the sanctuary along Third Avenue between 117th and 114th streets a few years ago, you would have seen a solid stand of 12-foot common reed. To manage these invasive species, the Borough of Stone Harbor implemented the Stone Harbor Bird Sanctuary Habitat Restoration Project. The objective of the project is to restore native vegetation and wildlife habitat within the sanctuary for colonial wading birds, migratory and resident songbirds, the endangered Cope’s gray treefrog (Hyla chrysoscelis) population, and other wildlife.
Step one was to manage the invasive plants. This was done in the fall of 2021 via application of an herbicide specifically shown to have relatively low toxicity to birds, mammals, and fish. In addition, studies indicated that this herbicide is excreted by mammalian systems rapidly with no bioaccumulation. Licensed professionals conducted this work under permit from New Jersey Department of Environmental Protection. The invasive plants were treated using a Marsh Master (a low ground pressure vehicle that can work in marshes), a hose sprayer, or a backpack sprayer depending on the area being treated.
The initial management of invasive plants was highly successful, leaving tall stands of dead reeds, but the restoration team was concerned about the millions of seeds of the invasive plants still in the marsh soils and sought a way to prevent them from germinating and repopulating the marsh with more common reed. To tackle this problem, in the spring of 2022 the restoration team mulched the dead reed stalks and left them covering the soil for one full growing season to prevent seed germination.
We were surprised by the increase in water in the freshwater marsh and in Paul’s Pond following the treatment. It was unanticipated but easily explained. The dense stands of invasive common reed were utilizing all the water and had effectively dried up the marsh. Once they were eradicated, the water returned to much higher levels, restoring the marsh water cycle.
In the spring of 2023, we decided to remove some of the mulch from a few small wet areas to test if the seedbank would sprout. A small group of restoration ecologists hand-raked and removed a few small patches of mulch in late March. The invasive plants did not sprout during the growing season of 2023, thus clearing the way for the restoration to proceed.
We are pleased to report that this approach is working very well. This spring, restoration experts planted 500 native broad-leaf cattails in the wetter areas of the freshwater marsh. Cattails were selected because they are the favored plants for the Cope’s gray treefrog that makes its home in the marsh and adjacent forest. They also spread 20 pounds of seeds around the three-acre wetland. These flourish over a range of water conditions, and include a number of native grasses, flowering plants, pollinator favorites, and plants that provide food and cover for wildlife. Our fingers are crossed that these plants take hold and continue to flourish and spread on their own. This fall, more than 45 native shrubs will be planted on the slightly higher hummocks in the marsh.
The effective management of invasive vegetation at the bird sanctuary required a multiyear treatment program that shifted from control to management to maintenance. We will continue to monitor the site for plant establishment and adaptively manage as needed, but the goal is to have a self-sustaining ecosystem reestablished at the sanctuary. We do expect that the common reed will need to be continually managed but have been successful at eradicating purple loosestrife from the sanctuary. The Borough has included it on the Do Not Plant List and we are hopeful that residents will not plant purple loosestrife and, if they already have it in their gardens, will remove it. Asking landscape contractors to not plant it is also really important. It aggressively spreads via wind-borne seeds, so its return to the sanctuary is likely without the help of the island’s residents. Everyone can have a role to play in protecting the sanctuary and helping to facilitate the biodiversity that thrives there.
The Stone Harbor Bird Sanctuary is a special place for plants and animals. A walk on the sanctuary trails transports you to another time and place and provides a wonderful respite from the busy days of summer, and all year-round. To learn more, check the bird sanctuary website, stoneharborbirdsanctuary.com.
