Boston Harbor Islands National Recreation Area ⓘ

Between the horn of Cape Ann to the north and the defiant, jutting arm of Cape Cod to the south and east, the Boston Harbor forms a giant crescent in the central coast of Massachusetts, and is the beating heart of the New England shoreline. The harbor sits within an ancient feature, known as the Boston Basin, which predates the formation of North America. Over the course of over 400 million years, it has seen tropical latitudes, multiple advances and recessions of the sea, and multiple periods of glaciation—the latter couple of which deposited and then carved many of the hills that currently dapple its surface. Today, within a vibrant metropolitan area, the Boston Harbor Islands provide a dynamic assembly of ecosystems, ranging from rocky, windswept shores to dense forests to developed and filled land—all with a long and complicated history of human use.

Stand at the dock and find a cloud of comb jellyfish drifting through the pilings; watch a double-crested cormorant drying its wings atop a navigational buoy; find trees that rise clear out of the asphalt—there are few places where the intersection of urban and coastal ecology are so well illustrated.

Discover Boston Harbor's vital ecological hotbed of rocky and sandy shores, salt marshes, sea grass beds, tidal mudflats, and more.

The flora of the islands reflects a long history of human alteration, including introduction of a large number of invasive exotic species. The islands' drumlins are thought to have been covered with mature forests of hemlock, maple, oak, pine, and hickory, which were cleared to support agriculture and pasturage, and to supply firewood for fuel. In addition, the construction of the islands' massive fortifications severely disrupted much of the native flora.

Thorough documentation of the characteristics of the terrestrial environment is just beginning, but successional species including aspen, pine, birch, and white poplar are clearly evident on most of the islands. Farming is known to have been carried out by Native Americans as well as later colonial settlers. Most of the fertile sites found on the islands have been converted to agriculture. The remnants of attempts at subsistence farming are evident in the appearance of apples, pears, grapes, chives, garlic, asparagus, and horseradish. Today, patches of undisturbed native flora are rare on the islands, and vegetation on most of the islands is dominated by grasses and sumac. The owners of Worlds End and Thompson Island have continued to manage expansive grasslands that are part of the cultural landscape. Worlds End and Thompson Island have communities of mixed oak forest; on Thompson they cover approximately one-tenth of the island.

The Massachusetts Natural Heritage Program lists two species of plants within the park: sea beach dock and American sea blite. There are no island species listed by the U.S. Fish and Wildlife Service.

From the densely settled downtown of Boston, extending over eleven miles seaward into the open Atlantic, the Boston Harbor Islands represent a remarkable diversity of natural features. As one of only three partially flooded drumlin fields in the world, and the only one in North America—with glacially carved hills rising above the sea as islands—the region provides insight into urban ecology, coastal ecosystems, and offers a critical perspective into adaptations to sea level rise and climate change.

Once considered the dirtiest harbor in the United States, Boston Harbor has been rejuvenated and remains a vital ecological hotbed, containing rocky shores, sandy shores, salt marshes, sea grass beds, tidal mudflats and more. These ecosystems are important in sustaining local food webs and biodiversity, mitigating flood and storm impacts, and establishing the unique appeal and beauty of the area to all who live and visit here.

Boston Harbor sits within Boston Bay, a feature of the forty-mile long Massachusetts Bay that extends from Cape Ann to Plymouth Harbor.

The Boston Harbor Islands National and State Park encompasses over 35 miles of coasts and shoreline on thirty islands and four peninsulas.

Terrestrial Animals The diversity of upland and marine habitats provides good nesting and feeding opportunities for a number of bird species. A few species of terrestrial mammals, including exotic species, have occured throughout the islands, such as cottontail rabbits, raccoons, skunks, gray squirrels, mice, muskrats, voles, and Norway rats. Some species have been known to devastate populations of small vertebrates and nesting birds. Although formal surveys are in initial stages, Eastern garter snake, Northern brown snake, and Eastern smooth green snake are known to occur on the islands.

An inventory was completed in 2007 to document mammal, reptile, and amphibian species expected to be found on the Boston Harbor Islands. "Due to logistical and budgetary constraints, and the lack of existing data relevant to the islands of Boston Harbor, this project was limited to islands isolated from the mainland...." Please contact us for a copy.

Wetland and Aquatic Marine Animals The Boston Harbor Islands provide shelter and food-rich habitats for marine birds, mammals, fishes and invertebrates, as well as nurseries for their young. Much of the Gulf of Maine fauna can be found in Boston Harbor, especially around the Brewsters. Lobsters, crabs, and clams inhabit submerged portions of the islands. Mussels and barnacles cling to the intertidal zone. Jellyfish live in the surrounding waters. Several species of fish, including striped bass, bluefish, and winter flounder, live in waters surrounding the islands. Little Brewster, Nixes Mate, Shag Rocks, and other islands characterized by bedrock outcroppings contain rocky intertidal communities of rockweed and barnacles. Harbor seals haul out on some of the outer islands. Because their feeding grounds or migratory routes are nearby, humpback, fin, minke, and North Atlantic right whales and white-sided and striped dolphins are potential, though rare, visitors, as are harbor porpoises.

The US Fish and Wildlife Service reports several federally listed endangered and threatened species of fish, turtles, birds, and mammals near or in coastal waters of Massachusetts, but not known to be found among the Boston Harbor Islands. There are no island species on the federal list.

Park visitors have can contribute to bird conservation science and management in two significant ways: submitting observations through eBird or joining the annual Coastal Breeding Bird Monitoring project.

The Park needs your help to discover more about the birds that inhabit the Boston Harbor Islands. The collaborative and interactive database eBird provides birdwatchers with the tools to track and learn more about birds in one's community. You can help with data collection anytime you visit the park. Your records, when combined with those of other observers, become a powerful tool for bird conservation by supplying scientifically useful data on species distribution and movement patterns in Massachusetts and across the continent.

Boston Harbor Islands National and State Park was designated a Massachusetts Important Bird Area (IBA) because the park provides habitat for a significant number of colonial-nesting waterbirds. The National Park Service identified these birds as indicator species of the overall health or condition of the park. The National Park Service, in conjunction with University of Rhode Island, developed a long-term volunteer-based monitoring protocol to improve our understanding of these breeding waterbirds, the effects of habitat changes, and management actions.

Volunteers work with a researcher and park staff to implement this protocol, which focuses on obtaining information on the relative abundance of thirteen coastal breeding species by estimating or directly counting nests, incubating adults, or territorial nesting pairs. Visit the link below to learn more about these efforts, and check out the 2021 summary report "Long-term Coastal Breeding Bird Monitoring in the Boston Harbor Islands, 2007–2019" by Trocki, Weed, Kozlowski, and Broms, published in Northeastern Naturalist 25 (Special Issue 9): 235-257.

Please check out Boston Harbor Island Volunteer Opportunities , or email volunteers@bostonharbornow.org