This granite ?dome? island lies just over two miles southeast of Bar Harbor in Frenchman Bay. This island was once forested, but trees have long since died probably as a result of the guano from nesting birds.
The Thrumcap supports one of the states most significant colonies of Double-crested Cormorants, with a high of 430 pairs documented in 1994. Common Eiders, Herring and Great Black-backed Gulls, and Black Guillemots also nest there. The island is equally important during the winter months to most of these species as well as to wintering flocks of Purple Sandpipers
The island is fully in conservation ownership. The most obvious threat is likely from human disturbance, although the steep shoreline makes landing on this island tricky and consequently restricts easy access from recreationists. Potentially more damaging and of a longer-term nature are the threats (i.e., hazardous spill, overboard discharges, and direct disturbance) associated with the increasing number of cruise ships visiting Frenchman Bay, the multiple daily tours provided by commercial operators during the non-winter months, and the continuing high volume of recreational and commercial fishing boats.
The island is owned by Acadia National Park, but is managed as part of the Coast of Maine Wildlife Management Area. Therefore, the island is closed to public access during the seabird nesting season (April 15 ? July 31).