Green Bay

Green Bay National Wildlife Refuge consists of five islands located in Lake Michigan off the tip of Wisconsin's Door Peninsula, established in 1912 by President William Howard Taft as the nation's 28th wildlife refuge and only the second in the Great Lakes region. The refuge islands, including Hog, Pilot, Plum, Spider, and Gravel Islands, serve as essential stepping stones for birds, bats, and butterflies migrating along the Niagara Escarpment across the open waters of northern Lake Michigan. This remote archipelago protects critical colonial nesting habitat for waterbirds and provides vital stopover sites where migrating species can rest and refuel during their perilous Great Lakes crossings.

The refuge islands support important colonial nesting populations of waterbirds, with Hog Island providing nesting habitat for great blue herons, black-crowned night herons, great egrets, and herring gulls. Pilot Island hosts a large colony of nesting double-crested cormorants along with herring gulls, while the other islands support varying combinations of nesting waterbirds. During migration, the islands serve as critical stopover sites where remarkable concentrations of passerine birds have been documented, with up to 25 yellow-rumped warblers observed in a single tree and seven species of wood warblers recorded simultaneously. Bats and monarch butterflies also use the islands as stepping stones during their migrations across Lake Michigan, underscoring the refuge's importance as a migratory corridor.

The vegetation on the refuge islands varies considerably based on each island's size, substrate, and exposure to Lake Michigan's harsh conditions. Larger islands like Plum and Hog support mixed hardwood and conifer forests with species including white cedar, balsam fir, paper birch, and sugar maple, while smaller, more exposed islands may support only grasses, shrubs, and stunted trees. Pilot Island's vegetation has been significantly impacted by double-crested cormorant nesting, with guano deposition altering soil chemistry and killing many trees. The islands' flora includes elements of both the boreal forest to the north and the deciduous forest to the south, reflecting their position at a biogeographic transition zone within the Great Lakes basin.

The Green Bay refuge islands are geological expressions of the Niagara Escarpment, a prominent dolomite formation that extends from New York through Ontario, Michigan, Wisconsin, and Illinois, creating the backbone of the Door Peninsula and the islands at its tip. The resistant Silurian-age dolomite bedrock, approximately 430 million years old, forms the foundation of the islands, while their current form was shaped by glacial erosion and the fluctuating water levels of post-glacial Great Lakes. The islands range in elevation from barely above lake level to modest heights of 30 to 40 feet, with rocky shorelines, cobble beaches, and limited soil development reflecting the harsh erosive forces of Lake Michigan waves and ice. The Niagara Escarpment's biological significance as a migration corridor adds geological context to the refuge's ecological importance.

The refuge islands experience a lake-modified climate that differs significantly from mainland conditions, with cooler summers, milder winters, and dramatically higher wind exposure than nearby Door County shores. Summer temperatures on the islands average in the mid-60s to low 70s Fahrenheit, while winter temperatures are moderated by the surrounding lake water, though fierce wind chills and ice accumulation create extremely harsh conditions. Lake Michigan's influence produces frequent fog, sudden weather changes, and persistent winds that challenge both wildlife and the occasional human visitor. The timing of lake ice formation and breakup, typically from December through April, governs access to the islands and influences the seasonal cycles of nesting and migrating bird populations.

The islands at the tip of the Door Peninsula have been significant to maritime navigation since the earliest days of Great Lakes shipping, with the treacherous passage between the islands known as Death's Door (Porte des Morts) for the many vessels wrecked in its swift currents and unpredictable storms. Native American peoples, including the Menominee and Potawatomi, navigated these waters for trade and fishing long before European contact. Plum Island housed a U.S. Life-Saving Service station beginning in 1895, later operated by the Coast Guard, which rescued countless sailors from the dangerous strait. Pilot Island's lighthouse, built in 1858, guided ships through the treacherous passage and its keepers endured extreme isolation on the windswept island.

Green Bay National Wildlife Refuge was established on February 21, 1912, by Executive Order of President William Howard Taft, making it one of the earliest wildlife refuges in the Great Lakes region during the nascent years of the national refuge system. The refuge was created primarily to protect nesting colonies of waterbirds that were being depleted by egg collecting, hunting, and human disturbance on the islands. Over the decades, the refuge has evolved to encompass a broader conservation mission that includes protection of migratory stopover habitat and management of colonial nesting species. The U.S. Fish and Wildlife Service manages the refuge from its field office in Baileys Harbor on the Door Peninsula, coordinating with the Coast Guard and other agencies that maintain facilities on some of the islands.

Plum Island is the only refuge island open to public access, available from Memorial Day through Labor Day during daylight hours, offering visitors the chance to explore the historic Life-Saving Station complex and observe the island's natural features. The remaining islands, including Pilot, Hog, Spider, and Gravel Islands, are closed to public access to protect nesting and migrating bird populations from disturbance. The historic Pilot Island Lighthouse, visible from nearby waters, is a notable landmark though the island itself is off-limits. Wildlife viewing from boats passing through the Death's Door passage provides opportunities to observe nesting waterbirds, and charter services from Door County ports offer excursions to the area.

Access to the Green Bay National Wildlife Refuge is by boat only, as the islands are located several miles offshore from the tip of the Door Peninsula. Public boat launches are available at Northport, Gills Rock, and Washington Island, with varying distances to different refuge islands depending on departure point. There are no developed visitor facilities on the refuge islands, and visitors to Plum Island should be self-sufficient with water, food, and appropriate gear for the variable lake conditions. Refuge information is available from the U.S. Fish and Wildlife Service field office in Baileys Harbor and the Door County Visitor Bureau. Weather conditions on Lake Michigan can change rapidly, and boaters should check forecasts carefully before attempting the crossing to the refuge islands.

The primary conservation challenge facing Green Bay National Wildlife Refuge is managing the ecological impacts of double-crested cormorant populations, whose expansion has significantly altered vegetation and soil chemistry on several islands, particularly Pilot Island where nesting cormorants have killed most mature trees. Balancing the protection of native colonial waterbird species with the ecological damage caused by overabundant cormorant populations requires careful management decisions informed by ongoing monitoring. Invasive plant species, including European swallowwort and garlic mustard, threaten native vegetation communities on the islands and require periodic removal efforts. The refuge also addresses the impacts of climate change on Great Lakes water levels and temperature regimes, which affect island habitats and the timing of bird migration and nesting cycles.