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Location Canada, Ontario
Central coordinates 80o 4.19' West  44o 57.06' North
IBA criteria A4i, A4iii
Area 18 ha
Altitude 176 m
Year of IBA assessment 2008

Bird Studies Canada/Nature Canada

Site description The Watchers are located on the Great Lakes in the southeastern corner of Georgian Bay, Lake Huron. They consist of two islands, North and South Watcher, which are located at the mouth of Severn Sound, about five to seven km northwest of Giants Tomb Island. South Watcher is a small, slightly elevated cobblestone shoal with very limited shrubby vegetation. North Watcher is comprised of a low-lying limestone outcrop with several tall trees, and a well-developed shrub understory. Cormorants have killed most of the limited vegetation on South Watcher Island.

Key Biodiversity The Watchers support a significant concentration of nesting Caspian Terns. In all, 785 pairs were recorded in 1989: 747 nests on South Watcher, and 38 nests on North Watcher. The colony was re-censused in 1998, with 571 nests being recorded on South Watcher, and none on North Watcher. The average of 678 nests represents about 2% of the North American Caspian Tern population. During both the 1989-1990 survey, and the 1998 survey, the Caspian Tern colony on South Watcher was the largest recorded in the Canadian portion of the Great Lakes. Caspian Terns were designated by COSEWIC as nationally vulnerable in the late 1970s, but since their populations have increased during 1980s and 1990s, leading to the delisting of the species by COSEWIC in 1999.In addition to Caspian Terns, nationally significant numbers of Ring-billed Gulls nest on the islands with almost 8,000 pairs being recorded in 1989. This represents just over 1% of the estimated national population. Other colonial waterbirds nesting on the islands include Double-crested Cormorants of the interior population, with an average of about 1428 pairs in the early to mid 1990s and Herring, Gulls with 116 pairs in 1989.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Caspian Tern Hydroprogne caspia breeding  1998  571 nests  A4i  Least Concern 
A4iii Species group - waterbirds breeding  1989  9,524 breeding pairs  unknown  A4iii   


IUCN habitat Habitat detail Extent (% of site)
Wetlands (inland) Freshwater lakes and pools  -
Coastline Cliffs, rocky shores, islets, freshwater  -

Land use

Land-use Extent (% of site)
nature conservation and research major
not utilised major

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: The Watchers. Downloaded from on 22/10/2016

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