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COSEWIC Update Status Report on the Roseate Tern in Canada 1999

Population Size and Trend


Canada represents the northern limit of the Roseate Tern’s range in northeastern North America.  Determining trends in size and distribution of this population therefore requires a review of data from both the U.S. and Canada.


United States

The numbers of “peak period” and “total season” breeding pairs in the U.S. have been increasing slowly since 1988, except between 1991 and 1992 when they dropped by 17% (Table 1).  In 1997, 3382 pairs bred in the U. S. during the peak period.  “Total season” pairs, estimated at 3980 in 1997, are generally 10-20% higher than peak period pairs (U.S. Fish and Wildlife Service 1998), and probably include failed and late breeders.

Roseate Terns have bred in 44 colonies from Maine to New York since 1988 (U.S. Fish and Wildlife Service 1998).  In any given year, however, only 16-20 of these colonies are used by Roseate Terns. Some colonies are occupied annually, while others are used occasionally by small numbers of Roseate Terns.  Since 1988, some historic colonies in the U.S. have been recolonized (e.g. Eastern Egg Rock, ME; Kress 1983; Ram Island, MA; Nisbet and Spendelow 1998) while others have declined (e.g. Nauset-New Island, MA) or been completely abandoned (e.g. East Inlet Island, NY and Cedar Beach, NY). Currently the five largest colonies in the United States are Great Gull Island, NY (1455 pairs in 1997), Bird Island, MA (1179 pairs in 1997), Ram Island, MA (253 pairs in 1997), Eastern Egg Rock, ME (138 pairs in 1997) and Falkner Island, CT (136 pairs in 1997).  The population has declined at Bird and Falkner Islands, but has remained stable at Great Gull Island, and increased at Eastern Egg Rock and Ram Island over the last ten years (U.S. Fish and Wildlife Service 1998).

Ninety-three per cent of the U.S. population currently nests in the five largest colonies, and 78% nests in the two largest colonies (Table 1).  This concentration makes the species extremely vulnerable to disturbance and was the primary reason for the designation of this population as endangered (U.S. Fish and Wildlife Service 1987, 1998).

Table 1.  1988-1997 estimates of “peak period” nesting pairs of Roseate Terns in the northeastern U.S.by state (reprinted from U.S. Fish and Wildlife Service 1998).
See text for the names and locations of the five largest colonies. The “total season” numbers are generally 10-20% higher than “peak period” numbers, and can be found in U.S. Fish and Wildlife Service (1998)
New York1122107411591380110411491265134511311555
Total Pairs2995283329963430274327752872310231703382
Total colonies in use19201618161917181720
Concentration in largest colonies
      % in 2 colonies86868685858583746578
      % in 5 colonies96949695949492909693


Estimates of breeding pairs in 1996 and 1997 place the Canadian Roseate Tern population between 88 and 137 pairs breeding in six locations (Table 2).  These estimates are based on a combination of “total season” numbers for The Brothers Islands and Country Island, and primarily “single-visit” numbers for all other sites.  This estimate is similar to Kirkham and Nettleship’s (1985) estimate of 101-125 pairs breeding in nine locations.  Roseate Terns have therefore remained stable in Canada since 1985 (Table 2).  Three per cent of the northeastern population currently nests in Canada. 

The distribution of Roseate Terns in Canada has changed since the early 1980s (Table 2, Fig. 1).  Roseates currently nest in only three of nine sites noted in the original status report.  These are Sable Island, NS, The Brothers Islands, NS, and the Magdalen Islands, QC (Table 2).  Several new sites have also been colonized (Table 2).  Changes in distribution by province are described below.

Table 2.  Estimated number of Roseate Tern pairs breeding inCanadain 1982-85 (from Kirkham and Nettleship 1985) and 1997 (see Table 3 for sources)
The presence or absence of nesting gulls at each site is also indicated
Site1982-85 estimate1997 estimateGulls nests
Several colonies on the Magdalen Islands, QC1 - 51 - 5yes
Machias Seal Island, NB01 - 2no; gulls are discouraged
Peter’s Island, NS10yes
The Brother’s. NS55 - 6054no; nests are destroyed
Mud Island, NS20yes
Tusket Island, NS15 - 200?
Westhaver Island, NS80?
Grassy Island, NS012 - 30no
Wedge Island, NS60yes
Sambros Island, NS30?
Country Island complex*, NS018 - 45yes
Sable Island, NS10 - 201yes
TOTAL101 - 12587 - 137 
*includes birds breeding on Country Island, Charlos Cover, Fisherman’s Harbour and Inner West Bird Island in 1997 (see text)

Nova Scotia 

At least 95% (86-130 pairs) of the Canadian Roseate Tern population nests in Nova Scotia. Roseate Terns breed at four sites in this province, two of which (Sable Island and The Brothers) were noted by Kirkham and Nettleship in 1985 (Table 2). Roseates have nearly disappeared at Sable Island, whereas the number currently breeding on The Brothers is almost the same as the 1982 estimate (Table 3).  This makes The Brothers the only large colony (i.e. greater than 20 pairs) in Canada known to have maintained a stable population of Roseate Terns for the last 15 years (Table 3).

Two new relatively large Roseate Tern colonies, Country Island and Grassy Island, were discovered in 1987 and 1993, respectively (Field notes from Erskine 1992, Boates et al., 1993).  Each colony has been known to support one-third of the Canadian Roseate Tern population (Table 3).  Grassy Island may prove to be a stable breeding site, but more information on both population size and productivity of terns at this site needs to be collected.  Numbers on Country Island have fluctuated considerably since the colony was discovered, as illustrated by the drop from 25 pairs in 1987 to one pair in 1997 (Table 3).  Some of the birds that abandoned Country Island in 1997 are believed to have moved to three sites that were previously not confirmed as Roseate breeding sites.  These were Charlos Cove, Fisherman’s Harbour, and Inner West Bird Island (Whittam 1997).  I have not included these sites as current Roseate Tern colonies (i.e., in Table 2) because it remains to be seen whether Roseate Terns will continue to use them, or whether the birds will instead return to Country Island.  These three sites, along with Country Island, are referred to as the “Country Island complex” (Table 2) because of the likelihood that birds at these sites came from the same large colony on Country Island (Whittam 1997).  Interestingly, in 1987 several pairs of Roseate Terns were suspected nesting at one of the Bird Islands, and at two sites in Tor Bay (Cooks Island and Hog Island; Table 3, Fig. 1), suggesting that the “Country Island complex” has been in existence for some time.


Figure 1.  The locations of recent Roseate Tern colonies inCanada, including sites occupied in 1997 (filled circles) and sites occupied at least once in the 1980s or 1990s (open circles). Details, including colony names, are given in Table 3.  See Kirkham and Nettleship (1985, Fig 2) for colonies occupied prior to 1980.

Figure 1.  The locations of recent Roseate Tern colonies inCanada, including sites occupied in 1997 (filled circles) and sites occupied at least once in the 1980s or 1990s (open circles). Details, including colony names, are given in Table 3.  See Kirkham and Nettleship (1985, Fig 2) for colonies occupied prior to 1980.

Peter’s, Mud, Wedge, and Sambro Islands were noted as Roseate Tern breeding sites by Kirkham and Nettleship (1985), but have since been abandoned by all species of terns (Lock et al. 1993, Boates and Sam 1996, D. Currie - Nova Scotia Bird Society - pers. comm.).  Westhaver Island, also in Nova Scotia, was reported to have 8 pairs of Roseates in 1985 (Kirkham and Nettleship 1985), but none have bred since. Approximately 168 pairs of Arctic and Common Terns nested at this site in 1997 (Gregoire 1998), and Roseate Terns were observed foraging in the area, but nesting was not confirmed (D. Currie pers. comm.).  Grassy Island is only 16 km from Westhaver Island, so terns seen foraging near Westhaver may have been breeding at Grassy Island.

New Brunswick

Machias Seal Island is the only known breeding site for Roseate Terns in New Brunswick, and only 1-2 pairs breed in this colony annually.  Roseates were first discovered breeding in 1979 and again in 1982, but they did not breed in 1983-85 (Kirkham and Nettleship 1985).  A single pair was observed in 1988, and a nest was identified in 1994. In 1995-97 two nests were suspected based on courtship feeding and flying displays, but breeding was not confirmed (K. Amey pers. comm.).


The Magdalen Islands is the only known breeding location for Roseate Terns in Quebec. Fewer than five pairs of Roseate Terns breed in this area annually (Shaffer and LaPorte 1996).  Roseates were first reported on the islets off Pointe-aux-Loups, then at the tip of Dune du Sud and on Baie du Havre aux Basques, although the latter two sites have not been occupied since the early 1970s and 1980s, respectively (Shaffer and Robert 1996).  Since 1987 Roseate Terns have been confirmed breeding in small numbers (1 to 3 pairs) at three colonies, one on île aux Cochons, one on the islets off Pointe-aux-Loups (Deuxieme îlot), and one on an artificial islet (îlot C) off Grande-Entrée.  Not every colony is occupied annually (Shaffer and Robert 1996, Shaffer and LaPorte 1996).