A small treeless island located about five miles south of Cundy?s Harbor on the eastern edge of Casco Bay.

Ornithological Summary

This island has a mixed heronry with a large number of Great Blue Herons. It also hosts a sizable breeding population of Common Eiders. At one time, this island had one of the largest numbers of nesting Black-crowned Night Herons. The population of Snowy Egrets has declined slightly since the late 1990?s.

Conservation Issues

Fortunately this site is in conservation ownership. Overboard discharge from boats as well as the threat of an oil spill, in or around the bay, are the greatest threats.


Mark Island is owned by the Maine Dept. of Inland Fisheries and Wildlife and is closed to public access during the seabird nesting season (April 15 through August 31 each year).

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