The Twin Islands are located in central James Bay, approximately 70 kilometres west of mainland Quebec. There are two islands, North Twin and South Twin, that are separated by 11 kilometres of open water. South Twin is about half the size of its counterpart to the northwest. The two islands are similar in landscape, reaching maximum elevations of 60 m above sea level, and being composed mostly of unconsolidated sand and gravel. Lakes and marshland are scattered throughout the islands, and sand dunes and wide tidal flats surround them. There are small stands of trees composed of White Spruce, Dwarf Birch, juniper and willows, although shrubs and heaths are more common. In general, South Twin Island has fewer trees and more mossy tundra than North Twin. These islands are important for Polar Bears as they use them for maternity denning and as a summer retreat. Numerous earth pits and dens are noticeable along the east ridge of North Twin Island.
In 1973, surveys showed that 1,500 Canada Geese of the Southern James Bay population were nesting on North Twin Island. It was noted that similar densities were found on South Twin Island, bringing the total population for the two islands to approximately 2,300 birds. This number represents at least 3% of this population. The geese tend to arrive at the start of May and leave the islands by the end of September.
During the same surveys, it was estimated that 1,200 Semipalmated Plovers nested on North Twin Island(perhaps 2% of the world population). If similar densities existed on the southern island, the estimated total population would be 1,800 birds.
The site supports numerous other species of breeding birds. Oldsquaw, Lesser Scaup, Northern Pintail and Green-winged Teal are the dominant nesting waterfowl. Other nesting shorebirds include Semipalmated Sandpipers (an estimated 2,000), Red-necked Phalarope, Least Sandpiper, Dunlin and Purple Sandpiper. In addition, an estimated 800 Willow Ptarmigans (resident) and 500 Arctic Terns, breed along with over 8,000 individual passerines, mostly Horned Larks, American Pipits, Savannah, American Tree and White-crowned sparrows, and Lapland Longspurs.
BirdLife International (2021) Important Bird Areas factsheet: Twin Islands. Downloaded from http://www.birdlife.org on 24/06/2021.