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Grassy Island Complex (NS026)


Grassy Island Complex (NS026)

Mahone Bay and Margaret's Bay, Nova Scotia

Latitude 44.501°N
Longitude 64.134°W
Altitude 0 - 10m
Area 9.96km²

Site Description

The three islands of the Grassy Island complex are on the south coast of Nova Scotia east of Halifax. Over the last 20 years, these three islands within Mahone Bay and St. Margarets Bay have regularly supported nesting Roseate Terns at alternate time-periods. The three islands are: Grassy Island, a small islet located between Big Tancook and Flat Island at the mouth of Mahone Bay; Westhaver Island, on the west side of Mahone Bay, about 500 m offshore and about 15 km to the west of Grassy Island; and Wedge Island, on the east side of St. Margarets Bay, about 1 km off the mainland shore, and about 15 to 20 km east of Grassy Island.

Grassy Island and Westhaver Island are treeless. Wedge Island has a rocky foreshore that slopes up into raspberry, nettle, and low spruces. All of the islands are small (10 ha or less), and rise only about five to ten metres above sea level. Of the three islands, Grassy is the most exposed and experiences frequent fog and wind. All of the islands are uninhabited.


Roseate Terns (identified by COSEWIC as nationally endangered) were not reported on Grassy Island until 1993. At that time, 20 pairs were estimated among a mixed colony of about 500 terns (other species were Common and Arctic Terns). Since then, relatively large (but fluctuating) numbers of Roseate Terns have been reported at this site (the Canadian population is estimated at between 87 and 137 pairs). For example, 30 pairs were reported in 1995, but only 12 pairs were reported in 1997. In 1998, no tern species nested on Grassy Island, possibly because of a storm early in the breeding season which over-washed the entire island.

Westhaver Island supported Roseate Terns in the early 1980s but this species has not been reported there since, even though the colony can be easily surveyed from shore. There is some speculation that the Roseate Terns from Westhaver Island may have relocated to Grassy Island. In 1997, 168 pairs of Arctic and Common Terns nested at this site, and Roseate Terns were observed foraging in the area, but nesting was not confirmed.

Wedge Island supported Roseate Terns throughout the 1970s and early 1980s with a peak of 45 pairs being recorded in 1970. In 1985, 12 adults were recorded, and when the colony was re-surveyed in 1995 no Roseate Terns were recorded. In 1998, however, Roseate Terns were again present on Wedge Island, with five pairs being recorded. Both Common and Arctic Terns also nest on Wedge Island.

Conservation Issues

These three islands appear to function as a complex of nesting sites with Roseate Terns shifting locations depending on local conditions. During the 1990s, Grassy Island has consistently supported the largest number of nesting Roseates. This island is owned by the Province of Nova Scotia, and since 1994 nesting shelters have been placed to encourage nesting Roseate Terns. A Nova Scotia Department of Natural Resources Tern Colony sign was also erected to discourage human disturbance.

Both Westhaver and Wedge Islands are relatively accessible to the mainland; unfortunately, uninhabited islands attract human visitors, many of whom do not recognize nesting terns as vulnerable to disturbance. As with all tern colonies in the Maritimes, predation of eggs and young by Herring and Great Black-backed Gulls is a concern. In general, human activities have sustained gull populations at high levels that have had a negative effect on tern populations.

IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status
Roseate Tern
Number Year Season