Mahone Bay Roseate Tern Recovery Project


BCAF’s RTRP crew completed bay-wide surveys throughout the islands in Mahone Bay from May to August 2010. Attempts to survey the bay three times per week were made; however, due to boat inaccessibility and weather conditions attempts were not always successful. Bay-wide surveys were completed with the intention of monitoring tern and gull distribution, abundance, productivity, and reproductive success, as well as tern predation in Mahone Bay. While bay-wide surveys were conducted, islands with a tern presence were monitored for anthropogenic disturbances.

Fifteen islands were monitored in 2010 in order to determine tern distribution, abundance, and reproductive success. Terns were observed in proximity of Birch, Crow, Goat, Grassy, Gully, Hobson, Mash, Mason, Meisners, Pearl, Quaker, Rafuse, Saddle, Spectacle, and Westhaver Islands. “Seabird Nesting Area – Do Not Disturb” signs were placed on all islands where terns were known or suspected to be nesting (2 signs per island), warning boaters to maintain their distance and refrain from disturbing nesting seabirds. Nesting took place on Crow, Goat, Grassy, Gully, and Westhaver Islands. Fledglings were only noted on Crow and Westhaver Island in 2010. Only Common and Arctic terns were observed in Mahone Bay, with no Roseate terns being observed.

Tern nest and egg counts were conducted in early June and when compared with 2008 and 2009 data, showed an increase of 59 nests from 2008 to 2009 and a decrease of 37 nests from 2009 to 2010. As in 2008 and 2009, Gully and Westhaver Islands hosted the largest tern colonies in Mahone Bay in 2010, with 107 and 126 nests respectively. RTRP staff also reported 4 nests on Goat Island, 56 on Grassy Island, and 46 on Mash Island. To determine the reproductive success of tern colonies, fledgling counts were conducted in late July and mid-August. Surveys carried into August as some colonies re-nested throughout the season, creating later hatching dates. The only fledglings observed were on Crow and Westhaver Island, with 4 and 1 observed respectively. Low reproductive success rates are attributed to a severe thunder and lightning storm event which caused colony abandonment in mid-June.

The Grassy Island Stewardship Program was initiated this year and incorporated gull deterrence and tern attraction activities. In late April, RTRP staff armed with the necessary permits from the Canadian Wildlife Service and NS Department of Natural Resources began deterring Great Black-backed and Herring gulls from the island. This entailed RTRP staff remaining on the island for up to an hour’s time as well as removing any gull eggs. These activities were necessary to reduce the number of gulls nesting on the island and overtime to deter the gulls from the island permanently. By the end of the field season, RTRP staff effectively reduced the gull colony on Grassy Island from approximately 100 to 25 individuals. After a decrease in gulls was established on the island, RTRP staff introduced nesting boxes, tern decoys, and a sound system playing tern calls to the island. By mid-July, the tern presence on Grassy Island peaked at 180 individuals, indicating that terns were easily attracted to the island for nesting purposes. While terns did attempt to nest on the island, predation and storm events prevented reproductive success. Efforts will be continued in 2011 with hopes that Grassy Island will provide a secure nesting site for terns with a lowered gull population.

A remote monitoring system was established on Westhaver Island in order to monitor the tern colony without causing disturbance. The system proved to be non-intrusive and allowed RTRP staff to determine the cause for colony abandonment, such as in the case of the severe storm event that hit Mahone Bay in mid-June. The remote system proved to be extremely useful and will be utilized again in during the 2011 field season.