Wildlife & Habitat

Wildlife and Habitat

  • Caspian Tern

    Caspian Chick thumbnail

    Gravel Island supports the largest Caspian tern colony in the Great Lakes Region. Caspian terns are the world’s largest terns. Adult birds have black legs, white head with black cap, thick reddish-orange bill with black tip and grey wings. As fish eaters, they hover and then dive for their food.

    These colonial nesting birds make depressions in the ground for nests and use nesting material sparingly - such as a few twigs or feathers in sand or gravel. One to three eggs are laid on the ground in gravel or sand.

    Young Caspian terns often stay with their parents for long periods. Some are even still fed by their parents when they reach their wintering grounds.  

  • Double-crested cormorant

    Double-crested cormorant

    The Great Lakes population of double-crested cormorants was devastated during the 1960s, primarily by the effects of chemical contamination from heavy metals such as mercury, organochloride pesticides like DDT, and other chlorinated compounds like PCB’s and dioxins. Cormorants are fish-eating birds at the top of the food chain and can live up to 20 years old. These two factors caused adults to accumulate large amounts of pesticides and other toxins from their prey. The chemicals did not kill the birds outright, but caused reproductive failure or extreme deformity in young that hatched. Cormorants were listed on the Wisconsin list of threatened and endangered species and then also listed for federal protection in 1972.

    Today, the Great Lakes population of double-crested cormorants is at historic highs. The abundance of this species in the Great Lakes region has become a concern due to the destruction of vegetation at some nesting sites, and perceived competition with humans for fish resources. Biologists do not expect the population to grow continuously. Instead, the number of birds should decline eventually, and then stabilize due to limiting factors of available nesting habitat.

  • Migratory bird habitat

    Shorebird Habitat thumbnail

    The limestone and dolomite rocks that make up the base of Gravel and Spider islands formed from compacted sediments of marine life that were deposited over 500 million years ago, when the area was covered by an ancient ocean. These unique geologic formations have many shallow depressions that hold water after rain or high waves. In the sun, they warm to perfect temperatures for supporting aquatic life. The aquatic insects in these shallow depressions are an important food source for migrating shorebirds as they stopover on the islands.

  • Colonial nesting bird island

    Colonial nesting bird island

    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. The birds that nest on Great Lakes islands face a range of threats including nest washouts, human disturbance, and toxic chemicals. Most birds tend to build their nests on the higher portion of the nesting islands to protect them from storm waves. Human disturbances range from purposeful actions to destroy eggs to inadvertent damage caused by curious visitors approaching islands in kayaks and boat. Some species such as the Caspian tern and double-crested cormorant are more sensitive to disturbance whereas the gulls are much bolder and less willing to move away from nest and will often eat or destroy eggs and young from unattended tern and cormorant nests.