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...."
» An Inventory of Amphibians, Reptiles, Nonvolant Mammals, and Select Bird Species On Islands In Boston Harbor (Technical Report NPS/NER/NRTR--2007/094)
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.