Question: What  is a 17 acre island separating Long Island and Block Island sounds, that has A ground-dwelling coastal beach grass herbivore endemic of the Meadow Vole ?
Context: Unity Island is an approximately 160 acre island separating the Niagara River and the Black Rock Canal, located within the city limits of Buffalo, New York.  The historic island is home to two public parks and a water treatment facility. Isla Vista virus (ILV) is an enveloped, single-stranded, negative-sense RNA hantavirus species of the Bunyaviridae family.  It is a novel New World microtine rodent hantavirus discovered in the California vole (M. californicus) in Santa Barbara County, California, near Isla Vista.  It is similar to Prospect Hill virus which has been isolated from a meadow vole (Microtus pennsylvanicus). Block Island Sound is a strait in the open Atlantic Ocean, approximately 10 mi wide, separating Block Island from the coast of mainland Rhode Island in the United States.  On the west, it extends to Montauk Point on the eastern tip of Long Island, as well as Plum Island, Gardiners Island, and Fishers Island, all in the state of New York. The gray-tailed vole ("Microtus canicaudus") also known as the gray-tailed meadow vole or gray-tailed meadow mouse, is a rodent in the genus "Microtus" (small-eared "meadow voles") of the family Cricetidae.  Voles are small mammals, and this species lies roughly in the middle of their size range.  First collected in 1895, it is endemic to the Willamette Valley, Oregon, and Clark County, Washington, in the Pacific Northwest region of North America.  Historically, they were found in the prairie areas of the Valley and, though many of these areas have been converted for agricultural purposes, these animals remain common.  For reasons that remain unclear, vole population densities in any area may fluctuate widely from season to season and year to year.  They are preyed upon by owls, hawks, and carnivorous mammals, and their parasites include fleas and ticks.  These voles build underground burrows and complex tunnel networks, which they sometimes share with other burrowing animals.  Relatively little is known about their behavior in the wild, because they are elusive and unlikely to enter traps. Great Gull Island is a 17 acre island separating Long Island and Block Island sounds, located approximately 0.4 mi southwest of Little Gull Island.  Both islands are located in Suffolk County, New York, and lie roughly midway between Plum Island and Fishers Island. United States v. Maine, 469 U.S. 504 (1985), also known as the "Rhode Island and New York Boundary Case", was a decision by the U.S. Supreme Court, which held that the Long Island and Block Island Sounds in part constitute a juridical bay under Article 7(6), Long Island being an extension of the mainland and the southern headland of the bay, and (b) that the bay closed at the line drawn from Montauk Point at the eastern tip of Long Island to Watch Hill Point on the Rhode Island shore, the waters of the bay west of the closing line being internal state waters, and the waters of Block Island Sound east of that line being territorial waters and high seas.  Maine is named in the title of the case because it is the northernmost of the thirteen defendant states with coastline on the Atlantic Ocean in a series of cases related to overlapping claims of state and federal jurisdiction over seas and the seafloor. The meadow vole ("Microtus pennsylvanicus"), sometimes called the field mouse or meadow mouse, is a North American vole found across Canada, Alaska and the northern United States.  Its range extends farther south along the Atlantic coast.  One subspecies, the Florida salt marsh vole ("M. p. dukecampbelli"), is found in Florida, and is classified as endangered.  Previously it was also found in Chihuahua, Mexico, but has not been recorded since 1998. The Gull Island vole ("Microtus pennsylvanicus nesophilus") is a subspecies of the Meadow Vole last collected in 1897.  A ground-dwelling coastal beach grass herbivore endemic to Great Gull Island, New York, it disappeared after habitat destruction for naval fortifications in August 1898 for the Spanish–American War.  Also, feral cats were also partly responsible in its decline.  It is known from fifteen specimens in Washington, D.C. East Beach State Beach is a state-operated recreation area in Charlestown, Rhode Island, encompassing 3 mi of oceanfront beach abutting Ninigret National Wildlife Refuge on Quonochontaug Neck, the barrier island separating Block Island Sound and Ninigret Pond.  The area offers a small, seasonal campground (20 units), salt-water fishing, ocean swimming, and beach activities. USS "Block Island" (CVE-21/AVG-21/ACV-21) was a "Bogue"-class escort carrier for the United States Navy during World War II.  She was the first of two escort carriers named after Block Island Sound off Rhode Island.  "Block Island" was launched on 6 June 1942 by Seattle-Tacoma Shipbuilding Corporation in Tacoma, Washington, under a Maritime Commission contract; sponsored by Mrs. H. B. Hutchinson, wife of Commander Hutchinson; transferred to the United States Navy on 1 May 1942; and commissioned on 8 March 1943, Captain Logan C. Ramsey in command.  Originally classified AVG-21, she became ACV-21 on 20 August 1942, and CVE-21 on 15 July 1943.  She was named after Block Island, an island in Rhode Island east of New York.
Answer: Great Gull Island