National Wildlife Refuge
Door County, WI
Phone Number: 920-387-2658
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|Double-crested cormorants nest on both Gravel and Spider islands.|
Gravel Island National Wildlife Refuge
Gravel (4 acres) and Spider (23 acres) islands comprise the Gravel Island National Wildlife Refuge. These islands are located in Lake Michigan, approximately 1 mile east of the northern tip of the Door County peninsula, Wisconsin.
The islands were set aside by Executive Order in 1915 as a preserve and breeding ground for native birds.
Gravel Island National Wildlife Refuge and Hog Island, one component of Green Bay National Wildlife Refuge, comprise the Wisconsin Islands Wilderness Area, which, at 29 acres, is one of the smallest wilderness areas in the country. The refuge is managed by staff at Horicon National Wildlife Refuge, in Mayville, WI. Public use is not allowed due to ground nesting by migratory birds and limited access.
Neither Gravel nor Spider Island have an overstory vegetation layer. Learn More>>
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. Learn More>>
Public use not permitted to ensure necessary protection of ground nesting migratory birds.
Resource values are maintained by natural processes. The refuge is monitored to ensure that these values have not been compromised.
Several studies involving double-crested cormorants, red-breasted mergansers, and black-crowned night herons have used Gravel Island Refuge as a study site. Activities have included sampling eggs, embryos, adults, and juveniles for various toxicants; counting nests; sampling blood for genetic purposes; and banding.
The most recent study was initiated in 2001. Through banding and re-sighting efforts, researchers are trying to better understand the population of double-crested cormorants and its growth. The study continued through 2006.