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COSEWIC Update Status Report on the Roseate Tern in Canada 1999


Summary of information from original status report (Kirkham and Nettleship 1985)

The Roseate Tern (Sterna dougallii) occurs on six continents where it breeds colonially on small marine islands that are generally free from terrestrial predators (Gochfeld 1983).  In North America, Roseate Terns breed on the Atlantic coast in two distinct locations.  The northeastern population breeds from the Magdalen Islands in the Gulf of St. Lawrence south to New York.  These birds always nest in association with other tern species, especially Common Terns (S. hirundo, Nisbet 1981).  The second population breeds from Florida and the Bahamas to the Lesser Antilles (Cramp 1985). Both populations winter in South America, from Colombia to eastern Brazil (Nisbet 1984, Hays et al., 1997). 

Roseate Terns were listed as threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1986. This designation was a result of the decline in the northeastern population, from approximately 8,500 pairs in the 1930s to 2,600 pairs in 1976 (Kress et al., 1983).  This decline was accompanied by a contraction of the species’ range, a decrease in the number of breeding sites, and a concentration of more than 90% of the population into a small area between Long Island, NY and Cape Cod, MA (Nisbet 1981).

The Canadian population of Roseate Terns was formerly estimated at 101-125 pairs between 1982-1985 breeding almost exclusively in Nova Scotia (Kirkham and Nettleship 1985).  This constituted 3% of the northeastern population (~ 3100 pairs; Kress et al., 1983).  While the number of Roseate Terns in Canada had probably always been small, it appeared as though the population had declined since the 1930s, based on historical observations of numbers breeding on Sable Island, Nova Scotia (Kirkham and Nettleship 1985).  The most rapid period of decline on Sable Island occurred between 1971 (130 pairs) and 1976 (18 birds).  This corresponded to a major period of decline in the U.S. from 4800 pairs in 1972 to 2600 pairs in 1976 (Kress et al., 1983). The largest Roseate Tern colony in Canada at the time of the original status report was located on The Brothers Islands, NS, with 55-60 pairs breeding in association with several hundred Arctic and Common Terns (Kirkham and Nettleship 1985).

The two most important factors limiting the distribution and abundance of Roseate Terns in northeastern North America were thought to be trapping of adults on the wintering grounds for sale at local markets (Hamilton 1981), and predation and displacement by gulls on the breeding grounds (Nisbet 1981).  Increases in the numbers of Herring (Larus argentatus) and Great Black-backed (L. marinus) Gulls in North America (Kadlec and Drury 1968) were closely associated with declines in tern numbers (Kress et al., 1983).  Gulls are known to prey on tern eggs, chicks, and occasionally adults (e.g. Hatch 1970), and to displace terns from traditional breeding sites (Nisbet 1981).  Little, however, was known about the effects of gulls on the breeding biology or success of Roseate Terns in Canada.


Purpose of revised status report

After the species was designated threatened in Canada in 1986, the Roseate Tern Recovery Team and RENEW (Recovery of Nationally Endangered Wildlife) developed a Roseate Tern Recovery Plan (Lock et al. 1993).  The two objectives of this plan were: 1) to increase the Canadian population of Roseate Terns to 200 pairs by the year 2010; and 2) to maintain colony productivity at greater than one fledgling per pair per year. These goals would be met by providing a sufficient number of predator-free sites for Roseate, Arctic, and Common Terns, protection for Roseate Terns on their wintering grounds, and long-term reductions in gull populations.

Since the original COSEWIC designation, a number of studies (e.g. D’Eon 1991-1997, Boates et al., 1993, Boates and Sam 1996 and Whittam 1997) have provided new information on Roseate Terns in Canada.  In the U.S., the “Cooperative Long-Term Roseate Tern Metapopulation Project”, with co-investigators from Massachusetts, Connecticut and New York (see appendix), was begun in 1987.  Co-investigators have coordinated comprehensive studies of chick growth, productivity, dispersal, recruitment, survival, feeding, and behaviour of this species in the northeastern U.S. over the last 10 years (reviewed in Nisbet and Spendelow 1998).  In addition, the American portion of the northeastern population was designated endangered in 1987 (U.S. Fish and Wildlife Service 1987).

In this report I review recent information on the population size, distribution, and habitat of Roseate Terns in northeastern North America.  I also review any progress that has been made toward fulfilling the goals of the Canadian Roseate Tern Recovery Plan, and re-evaluate the threatened status of this species in Canada.