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COSEWIC Update Status Report on the Roseate Tern in Canada 1999

Evaluation of Proposed Status

 

I recommend that Roseate Terns be upgraded from “Threatened” to “Endangered” in Canada based on the following points:

1.   The Canadian Roseate Tern population is small. Only 88-137 pairs breed in the country.

2.   Ninety-four per cent of the Canadian Roseate Tern population is concentrated into only three main sites in Nova Scotia, making it extremely vulnerable to existing environmental threats.  Any major disturbance to these sites could lead to the extirpation of Roseate Terns from Canada.

3.   Of the three main breeding colonies, The Brothers Islands and Grassy Island are both near-shore sites that are vulnerable to human disturbance and terrestrial predators.  The third colony, on Country Island, is neither productive nor stable due to heavy predation on eggs and chicks by corvids and gulls.  Roseate Terns produced only 0.08 fledglings/nest on Country Island in 1996, and only one pair returned to breed in 1997 (Whittam 1997).

4.   The distribution of Roseate Terns in North America is limited by the number of predator-controlled colony sites in close proximity to good foraging sites.  In Canada, high-quality breeding habitat such as that found on Country Island continues to be lost due to displacement by Herring and Great Black-backed Gulls.  Until predator management is implemented, the amount of Roseate Tern breeding habitat available in Canada will not increase.

5.   Mortality during migration or at wintering areas is limiting adult survival.  Roseate Terns have the lowest survival rate of any seabird species measured to date (Spendelow et al. 1995).

6.   Roseate Terns in Canada constitute 3-4% of the northeastern North American population at the northern limit of their breeding range.  The remaining 96-97% of this population was listed as Endangered in the United States in 1987 and will retain this designation until the criteria for downlisting are met (see U.S. Fish and Wildlife Service 1998).  Leading authorities on the U.S. Roseate Tern population believe that the Canadian portion of this population should be listed as endangered based on its small size and limited distribution (I.C.T. Nisbet and J. Spendelow pers. comm.).

7.   In a recent review of the status of seabirds in eastern Canada, the Roseate Tern was designated “highest priority” for species at risk (Nettleship 1998).  Moreover, D. N. Nettleship (pers. comm.) asserts that Roseate Terns met the criteria for listing as “Endangered” in 1985, but “Threatened” status was recommended (Kirkham and Nettleship 1985) primarily to maintain access to important Roseate Tern breeding sites.  This allowed the monitoring of population status to proceed without the strict regulations associated with obtaining access to breeding sites of endangered species.  Now that more information has been gathered on Roseate Terns in Canada, an endangered listing is warranted (D.N. Nettleship pers. comm.).