Islands provide important habitat for plants and wildlife and their seclusion helps support populations of a variety of threatened and endangered species. The dwarf lake iris, found on Plum Island, is listed on the Endangered Species list and is only found in select habitats in the Great Lakes region.

Removed from the federal Endangered Species list in 2007 due to rising populations, the recovery of the bald eagle is listed as one of the greatest conservation success stories in the nation. Eagles actively nest on Plum Island and are often visible to passing boaters as they sun in trees along the island perimeter. You can help protect bald eagles by maintaining a ¼ mile distance from their nests when hiking or boating, as they are often sensitive to disturbance.
 

Herring gulls are large gulls with stout bills. Adults have light-gray backs, black wingtips, and white heads and underparts. Juveniles are mottled brown. The legs are dull pink at all ages. Herring gulls breed on islands in the Great Lakes and can be found following fishing boats and feeding in habitats as diverse as open water, mudflats, plowed fields, and garbage dumps. They are loud and competitive scavengers, happy to snatch another bird's meal and are often found in large congregations.

These colonial nesting birds make nests of soft soil, sand, or short vegetation. To protect the nest from prevailing winds and hide it from predators, it is usually placed next to a rock or vegetation. This also hides it from the nearest neighbors. Crevices may be used as nest sites in rocky areas. After chicks hatch, both parents feed them day and night for up to 12 weeks, splitting foraging shifts to offer each chick up to half a pound of food per day as it nears fledging.

Young herring gulls are more migratory than adults. In the Great Lakes, most adults remain near their breeding grounds, but the nonbreeders move farther south in the fall.

Plum Island essentially functions as its own small ecosystem and retains natural characteristics absent on the nearby mainland. This habitat type contains a wide range of forest conditions, from those composed primarily of early successional species such as aspen and to forest dominated by sugar maple, basswood, and eastern hemlock. The interior of Plum Island is dominated by a sugar maple and basswood forest. White cedar is dominant near the coast, especially where dolomite rock formations are visible along the ground. The habitat provides valuable rest stops for birds migrating across open water. In early May, densities approaching 60 birds/hectare (up to 17 species/hectare) have been recorded. Seven species of wood warblers and up to 25 yellow-rumped warblers per tree, in some locales, have been observed.

Great Lakes islands provide essential habitat for colonial nesting waterbirds. The location of these islands, near forage fish habitat, combined with their relatively undisturbed condition during spring and early summer, offer these species of migratory birds the necessary protected habitat. Ring-billed gull, herring gull, black-crowned night heron, double-crested cormorant, great blue heron, and great egret use the islands as loafing and breeding sites. The colonial nesting species have slightly different habitat requirements. Herring gulls and ring-billed gulls nest on the ground while black-crowned night herons, great-blue herons and great egrets prefer to nest in trees. Double-crested cormorants nest in trees but will nest on the ground if no trees are available. Annual use of the same trees used by nesting cormorants result in destruction of the trees due to excessive levels of nitrogen from their guano.