Ross’s gull (Rhodostethia rosea) COSEWIC assessment and status report: chapter 9
Population Sizes and Trends
The discovery of two of the known breeding sites in Canada of Ross’s Gulls (the Cheyne Islands and Churchill) was not a result of systematic and organized searches for the species but rather fortuitous discoveries. The pair that nested on Prince Charles Island in 1997 was found during intensive terrestrial and aerial surveys of Prince Charles and Air Force Islands during the summers of 1996 and 1997 (Bechet et al. 2000). A.J. Gaston (pers. comm. 2006), who surveyed parts of Prince Charles Island in the 1980s, indicates “(t)he discovery of the breeding site on Prince Charles Island was made on the first serious land bird survey of an island the size of Prince Edward Island. Other islands in Foxe Basin with much the same sort of terrain have never been surveyed on the ground, or at most only a small proportion has been surveyed.” Ross’s Gulls were twice identified on a different part of Prince Charles Island by aerial surveys in 1984 (A.J. Gaston, pers. comm. 2006), although reports from other aerial surveys and visits to Prince Charles Island did not mention the species (Ellis and Evans 1960, Reed et al. 1980, Morrison 1997). Such information underscores the uncertainty about the status of this species in Canada.
The fourth known site, the unnamed island in Penny Strait, was a result of research and monitoring surveys of marine birds in High Arctic Canada (Mallory et al. 2006). The Canadian Wildlife Service, as part of research and monitoring of marine birds in High Arctic Canada, have conducted surveys for Ross’s Gulls at known and potential nesting locations in Nunavut from 2002 through 2006 (Mallory et al. 2006). Surveys were carried out on islands in Penny Strait on one day each year between 1 and 16 July, from a Bell 206 L4 helicopter. In Penny Strait, 16 small islands were surveyed, and in 2003 – 2006 Seymour Island and the Cheyne Islands were resurveyed (Mallory et al. 2006). These surveys did not result in any sightings of Ross’s Gulls between 2002 and 2004, but surveys in 2005 resulted in the discovery of the colony on the small unnamed island east of Crozier Island in Penny Strait, a location also surveyed between 2002 and 2004. In 2006, nesting pairs were relocated on the unnamed island and on the Cheyne Islands, the first time since the late 1970s (G. Gilchrist, pers. comm. 2006).
There is little information during the last 15 years to indicate if the global population is stable. Censuses of Siberian breeding grounds during the 1980s indicate that the population was about 50 000 individuals (Degtyaryev 1991), considerably higher than the estimate of 10 000 sexually mature birds in the 1970s (Borodin et al. 1978, cited in Macey 1981). In the late 1980s, the Ross’s Gull population in Alaskan waters in September-October was estimated to be at least 20 000 (Divoky et al. 1988) and the eastern movement at Point Barrow in 1984 was estimated at a minimum of 15 000 (Alvo et al. 1996). The pelagic population at the pack ice edge in the Chukchi Sea in 1970 was estimated at between 20 700 and 38 000 (Divoky 1988). A maximum of 4300 individuals was observed feeding in a flock at Point Barrow on 29 September 1976 (Kessel and Gibson 1978). The global population was considered stable based on accounts of birds migrating by Point Barrow, Alaska in the 1980s (Divoky et al. 1988, Alvo et al. 1996).
In Canada, the Ross’s Gull occurs at low population numbers, scattered throughout the low and high Arctic region. The total known breeding population has ranged from 0 to10 pairs per year. However, as A.J. Gaston (pers. comm. 2006) points out, “the species might actually number in the hundreds of breeders, given the huge areas of unexplored habitat available; on the other hand, we cannot possibly pretend to know anything about its current population trends on the basis of the very scattered localities where populations have been followed to any extent – really just Churchill. ….. Given the potential breeding habitat in Canada and the apparently rather peripatetic nature of the species, I think it certain that there are quite a few more that we have not yet found.”
Churchill, Manitoba
Sightings of Ross’s Gulls have been reported more often and more continuously in the area around Churchill than other known sites in Canada (R. Koes, pers. comm. 2006). Since the initial sighting in 1978, a photographed adult that occurred between 18–23 June (Manitoba Avian Research Committee 2003), the species has been recorded almost annually, with nestings documented at the Akudlik site in the 1980s and further up the Churchill River in recent years (Alvo et al. 1996, Manitoba Avian Research Committee 2003, R. Koes, pers. comm. 2006, IBA Site MB 003). The Churchill population has ranged from one to five pairs since 1980; themaximum number of known nests was five in 1982.
Since the mid-1990s, the traditional breeding sites at Churchill appear to have been abandoned. There have been persistent reports of nesting pairs upstream from the end of the Hydro Road (R. Koes, pers. comm. 2006), and apparently there were five nests there in 2002. After the mid-1980s locations of nests have usually been kept secret (if any were found), therefore an incomplete picture of the status each year at Churchill has emerged.Only a single bird has been reported in some years, and up to four in others (R. Koes, pers. comm. 2006); for example, four were reported in 2005. Other records in suitable habitat in northern Manitoba include two adults seen by J.D. Reynolds on June 10, 1984, at La Perouse Bay, flying inland from Hudson Bay (Alvo et al. 1996).
Specimens from the Churchill site are in the Canadian Museum of Nature (CMNAV 70983, 71120 and 71121, adults in July 1980 and 1981, and E4311 and E4781, eggs collected in 1981 and 1988; M. Gosselin, pers. comm. 2006). Two downy chicks were collected in 1982, and one in 1983, and are now in the Manitoba Museum collection (R. Koes, pers. comm. 2006).
Cheyne Islands, Nunavut
Three pairs nested on the island in 1976, and six pairs nested in 1978 with an additional eight unpaired birds also present, hence a maximum of 20 birds present (Macey 1981), and it is possible that they had nested here for several years (MacDonald 1978, Alvo et al. 1996). Although no nests were found at the Cheyne Islands in 1977 or in 1979, birds were seen there in 1974 and 1979 (Macey 1981). Further surveys did not find Ross’s Gulls on the islands in 1986 (Alvo et al. 1996), nor between 2002 and 2005 (Mallory et al. 2006). However, in 2006, three pairs were found in locations where they had nested previously (G. Gilchrist, pers. comm. 2006).
Although all three islands were used for nesting, Ross’s Gulls have not bred regularly in any one location within the islands. Ross’s Gulls, apparently already paired, arrived in early June and nesting was usually completed by mid-July. Breeding attempts appeared to have been unsuccessful, although a juvenile bird was seen flying over Bathurst Island in 1979 (MacDonald 1978, Macey 1981, Alvo et al. 1996). The polynyas present on the eastern side of Penny Strait appeared to provide an important feeding area for the gulls (Canadian IBA Site Catalog 2006).
Unnamed Island in Penny Strait
A previously undiscovered small colony of four and possibly five breeding pairs was located on an unnamed island in Penny Strait in 2005 (Mallory et al. 2006), and one pair was found nesting there in 2006 (G. Gilchrist, pers. comm. 2006). This location is only 80 km from the nesting sites on the Cheyne Islands. The island was also surveyed in 2002 through 2004, with no birds being located. Mallory et al. (2006) note that colony occupation by Ross’s Gulls in the Canadian High Arctic appears to be intermittent, and the birds may move nesting locations in response to predation or annual snow and ice conditions.
Prince Charles Island
Bechet et al. (2000) reported a breeding pair of Ross’s Gulls at the northwest corner of Prince Charles Island on 8 July 1997, a locality only 200 km from the first collected specimen in 1823 on the east coast of the Melville Peninsula. No additional birds were found on Prince Charles or nearby islands during aerial and terrestrial surveys in 1996 and 1997, and there is no information on occupancy by Ross’s Gulls of Prince Charles Island in recent years.
The low numbers of Ross’s Gulls that occur at any one site in Canada precludes analysis of fluctuations and population trends. The nesting occurrences in the High Arctic appear not to be consistent from year to year, presumably as a result of variables such as predation pressure or snow and ice conditions. The North American Waterfowl Conservation Plan (2002) lists the species as showing an apparent decline, although no details are given.
The known breeding population of Ross’s Gulls in Canada and Greenland represents less than 1% of the total global breeding population. The current status of the global Ross’s Gull population is unknown; reports documenting global populations in the 1980s indicate that the world’s population of Ross’s Gulls was about 50 000 and had not changed significantly since the end of the 1800s (Alvo et al. 1996). Rescue from the Siberian population is clearly possible, although it is not known whether the population breeding in Canada is part of the total global breeding population, or if it constitutes a distinct breeding population separate from the major nesting areas in Siberia.
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