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Ross's gull (Rhodostethia rosea): recovery strategy: chapter 1


1. Background

1.1 Species assessment information from COSEWIC

Date of Assessment: April 2007

Common Name: Ross's Gull

Scientific Name: Rhodostethia rosea

COSEWIC Status: Threatened

Reason for Designation: In Canada, this species is known to occur in small numbers in very few locations. Threats include disturbance in some breeding areas and changes in ice and snow patterns associated with climate change.

Canadian Occurrence: Nunavut, Manitoba

COSEWIC Status History: Designated Special Concern in April 1981. Status re-examined and confirmed in April 1996. Status re-examined and designated Threatened in November 2001 and in April 2007. Last assessment based on an update status report.

1.2 Description

Ross's Gull (Rhodostethia rosea) is a small gull with a wedge-shaped tail and a black collar. During the breeding season, Ross's Gull develops a deep pink hue on its breast.

Figure 1. Ross's Gull (Rhodostethia rosea)
© Her Majesty the Queen in Right of Canada
(Mark Mallory, Environment Canada).

Figure 1. Ross’s Gull (Rhodostethia rosea) © Her Majesty the Queen in Right of Canada (Mark Mallory, Environment Canada).

Ross's Gulls breed mainly in the Eurasian Arctic, but a few breeding locations are known from Canada. They do not migrate south like most North American birds but instead are thought to move around the North Pole to the edge of the ice pack in the Bering Sea (Alvo et al. 1996).

Their nests can be a depression in the ground or a moss cup, or they can be located in sedge tussocks (Chartier and Cooke 1980; Macey 1981). Ross's Gull eggs are olive with faint reddish-brown markings (Ehrlich et al. 1988) and measure approximately 30 mm × 43-46 mm (Béchet et al. 2000). Clutch size is generally three, but a clutch may contain one or two eggs. Nests are incubated by both parents (Macey 1981) for 21 to 22 days, and chicks fledge at 20+ days after hatch (Chartier and Cooke 1980; Ehrlich et al. 1988). In Canada, chicks hatch approximately mid-July (Macey 1981).

1.3 Populations and Distribution

1.3.1 National and Global Status

Ross's Gull is an arctic species with a circumpolar distribution (Macey 1981). The main breeding grounds are found in northeastern Siberia (Macey 1981), with additional breeding locations on Spitsbergen Island in Svalbard (Norway), a few islands in Greenland, and in northern Canada (Béchet et al. 2000; Mallory et al. 2006).

There is little information on the abundance of this species, either in Canada or globally. The global population of Ross's Gull is estimated at 50 000 breeding adults (Degtyaryev 1991) and is considered vulnerable/apparently secure (G3G4). The global population appears to be stable, based on accounts of birds migrating by Point Barrow, Alaska (Divoky et al. 1988).

In Canada, the Ross's Gull has likely always persisted at low population numbers scattered throughout the Low Arctic and the High Arctic. A few small colonies comprise a total known population of 0-10 pairs in any year. The Ross's Gull is listed as Threatened on Schedule 1 of the Species at Risk Act at the federal level and is considered rare nationally (N2B) (NatureServe 2004).

1.3.2 Canadian Distribution

In Canada, there are four known nesting areas: Prince Charles Island, Nunavut; Cheyne Islands, Nunavut; an unnamed island in Penny Strait, Nunavut; and Churchill, Manitoba (Figure 2). Occasional sightings of Ross's Gulls are also made south of the breeding grounds in British Columbia, Ontario, Nova Scotia, and Newfoundland and Labrador (Macey 1981).

Figure 2.  Known breeding distribution of Ross’s Gull (Rhodostethia rosea) in Canada

 

Figure 2
Churchill

Churchill is the breeding site most used by Ross's Gulls in Canada, although breeding has become sporadic in recent years (COSEWIC, in prep). Observers have recorded Ross's Gulls around Churchill since 1978, with the first breeding record in 1980 and more than 10 birds observed in 1982 (Appendix A). It is difficult to assess breeding, in part because of the remoteness of the current breeding location at Churchill and in part because of their vulnerability to human disturbance. Thus, birders and biologists have avoided surveying the area (B. Chartier, pers. comm.). Ross's Gulls are also seen in the company of other gull species at Prince of Wales Fort National Historic Site near Churchill but are not known to breed there.

Cheyne Islands

Ross's Gulls bred at the Cheyne Islands in 1976 and 1978, and it is possible that they nested here for several years, with up to seven pairs of gulls found in a single year (MacDonald 1978; MacDonald, pers. comm. in Alvo et al. 1996). No gulls were found at the Cheyne Islands in 1986 (Alvo et al. 1996), 2002, 2003, or 2004, nor was there evidence of nesting in these years (Mallory et al. 2006) (Appendix A). However, four pairs of birds were observed at the site in July 2006, with at least three of these pairs nesting (Mallory et al. 2006).

Prince Charles Island and Air Force Island

A single pair of breeding Ross's Gulls was discovered on Prince Charles Island in 1997 (Appendix A) (Béchet et al. 2000); it is not known if they have nested here at other times. Despite intensive aerial and terrestrial surveys, no additional birds were found on Prince Charles and Air Force islands during 1996 and 1997, nor have Ross's Gulls been reported from aerial surveys in earlier years (see Béchet et al.2000). Yet, it is still possible that Ross's Gulls could be a regular breeder in this area, as independent but unconfirmed observations of Ross's Gulls were made on the southeastern coast of the island in 1984 (Béchet et al. 2000).

Unnamed island in Penny Strait

A small colony of approximately five breeding pairs was found on an unnamed island in Penny Strait in July 2005 (Mallory et al. 2006) about 80 km from the Cheyne Islands. This island had not supported Ross's Gulls in 2002-2004. The appearance and disappearance of nesting birds at sites in Penny Strait suggest that Ross's Gulls in the High Arctic may use colonies intermittently, perhaps moving to avoid predators that have cued in on nesting locations.

1.4 Needs of the Ross's Gull

1.4.1 Habitat and Biological Needs

Breeding habitat

The majority of Ross's Gulls breed in Siberia, where the habitat consists of shrub tundra with sedge meadows and numerous ponds (Densley 1991). In Canada, Ross's Gulls breed in a variety of habitats; the only common nesting requirement among sites appears to be the presence of open water, such as lakes, ponds, or open leads in the pack ice (Macey 1981). The most common habitat is marshy wetland in subalpine and boreal tundra (Blomqvist and Elander 1981), but the gulls also use high arctic tundra and gravel reefs (Macey 1981; Béchet et al. 2000; Mallory et al. 2006).

Churchill, Manitoba -- The Churchill breeding location is at the most southerly latitude for nesting Ross's Gulls in the world (Chartier and Cooke 1980). The Churchill Special Conservation Area was established to protect Ross's Gull breeding sites around Churchill. The habitat at the original breeding site consisted of vegetated hummocks elevated above wet grass or sedge tundra, small pools, or shallow lakes. The hummocks were dominated by grasses, lichens, and willows (Salix sp.) (Chartier and Cooke 1980; Macey 1981; Alvo et al. 1996). The three nest sites described by Chartier and Cooke (1980) were located beside water and usually in Carex aquatilis marsh. This original breeding location was temporarily flooded in 1984, and the Ross's Gulls have since relocated upstream, where they nest with Little Gulls (Larus minutus) and Arctic Terns (Sterna paradisaea) (R. Koes, pers. comm. and B. Chartier, pers. comm.). There is no road access to this area. There are no habitat descriptions for the new nesting location. The new nesting location is also within the Churchill Special Conservation Area (G. Suggett, pers. comm.). Additional suitable nesting habitat may exist elsewhere in the Hudson Bay Lowlands (Alvo et al. 1996).

Prince Charles Island, Nunavut -- At Prince Charles Island the nest was located on an elevated hump covered with moss and willow. The area surrounding the nest consisted of a network of medium-sized lakes in an area of poorly vegetated, dry tundra and gravel, although the area immediately surrounding the nest was completely covered with vegetation (Béchet et al. 2000). Ross's Gulls nested here with Arctic Terns (Béchet et al. 2000).

Cheyne Islands in Penny Strait, Nunavut -- Ross's Gulls nested within a colony of Arctic Terns on small gravel reefs approximately 400 m long and 1 m high (MacDonald 1978).

Unnamed island in Penny Strait, Nunavut -- Ross's Gull nests were found in mossy gravel on a gravel reef island 3 km long (Mallory et al. 2006). Ross's Gulls nested with Arctic Terns and Sabine's Gulls (Xema sabini) at this location.

Non-breeding birds in summer

During the summer, non-breeding and immature Ross's Gulls use areas of drift ice in the Eurasian Arctic Ocean up to the North Pole (Hjort et al. 1997). In particular, the edge of the continental shelf (the shelf break) is associated with high numbers of birds due to high food productivity resulting from upwelling nutrients (Hjort et al. 1997).

Migration

In the fall, Ross's Gulls briefly head to the Arctic Ocean, but within a few weeks the ocean freezes over and they return westward and south via the Bering Strait to winter in the Bering Sea and Sea of Okhotsk (Degtyarev et al. 1987; Zubakin et al. 1990). Ross's Gulls seem to prefer feeding in loose ice at the edge of the Arctic ice pack, as these areas are very productive and prey is abundant and relatively easily to locate (Macey 1981; Alvo et al. 1996; Stirling 1997).

Diet

Little is known about the diet or foraging behaviour of Ross's Gulls. On the nesting grounds in Siberia, the main food of Ross's Gulls is insects; on occasion, they have taken fish and small molluscs (see Macey 1981). Blomqvist and Elander (1981) suggest that the main food of the Ross's Gull is small fish and invertebrates. In Alaska, Arctic cod (Boreogadus saida) comprised the majority of the diet of Ross's Gulls (Divoky 1976). At Prince Charles Island, breeding birds have been observed foraging either by hovering above the water surface or by walking along the shoreline; the birds were suspected of feeding on small crustaceans or insects (Béchet et al. 2000). At Churchill, birds were observed taking small items from below the surface of ponds, and at the Cheyne Islands, Ross's Gulls were observed flying to the edge of the pack ice to feed (Macey 1981). In the fall and winter, the Ross's Gull relies on the abundance of food found along the pack ice. This abundance of food likely accounts for the large concentration of birds in the Chukchi Sea in the fall (Macey 1981).

1.4.2 Ecological Role

The ecology of the Ross's Gull and its role in arctic ecosystems are very poorly known. Based on diet and breeding locations, we assume that it plays a role similar to that of Sabine's Gull, Ivory Gull (Pagophila eburnea), and Arctic Tern. All four species feed principally on invertebrates and small fish, although Sabine's Gulls may feed more in freshwater habitats. However, Sabine's Gulls and Arctic Terns fly far south (tropics or southern high latitudes) for the winter, while Ivory and Ross's gulls are well adapted to polar, ice-covered regions all year. Both Ivory and Ross's gulls will apparently scavenge carrion (Ivory Gulls are much more likely). In the absence of detailed study of Ross's Gulls, a further examination of their ecological role is not possible at this time.

1.4.3 Importance to People

The Ross's Gull appears to have had a minor role in the traditional life of aboriginal inhabitants of Arctic Canada (although Ross's Gulls are sought by aboriginal hunters in Alaska; Macey 1981). The Inuit harvest eggs of many birds, including gulls (Priest and Usher 2004). However, aboriginal harvest of this species (adults or eggs) in Canada is probably low. A Ross's Gull was harvested near Arctic Bay in the 1980s, and an adult was shot in the spring of 2006 near Pond Inlet (Mallory, unpubl. data). Due to their exceptionally small numbers, unpredictable presence, and the remoteness of their colonies, subsistence harvest of this species has probably been negligible.

The Ross's Gull does have considerable importance among the bird-watching community because of its rarity (Macey 1981; Alvo et al. 1996), aesthetic value, and contribution to biodiversity.

1.4.4 Limiting Factors

Ice cover and weather conditions likely play a critical role in the breeding success and survival of Ross's Gulls (Stirling 1997). Weather events such as floods and long, cold springs can decrease reproduction substantially (Macey 1981). For example, in Siberia in 1986, a heavy rainstorm killed five of six hatched chicks (Densley 1988). Although the effects of climate change are unknown, it is possible that preferred breeding locations for Ross's Gulls will shift.

The low productivity of the Ross's Gull may limit its ability to recover. Ross's Gulls are probably similar to other arctic seabirds in that they are long-lived with slow reproductive rates; populations would therefore recover slowly after successive reproductive failures (Macey 1981).

1.5 Threats

Because Ross's Gulls are known from only four locations in Canada and each population is very small in size, any factor affecting reproductive success or survival could severely affect the persistence of Ross's Gulls in Canada. Threats to the survival of Ross's Gull are discussed below, in order of importance.

1.5.1 Human Disturbance

Churchill is a well-known location for bird watchers to visit, and the opportunity to observe Ross's Gulls here contributes to the popularity of Churchill as a destination (Hamel 2002). However, disturbance by bird watchers, photographers, and tourists is a threat to the Ross's Gull in Canada (Macey 1981). The presence of humans disrupts Ross's Gulls and may lead to lower breeding success. At least one nest was abandoned because a photographer was too close to it (Alvo et al. 1996). Observers within 100 m of a nest will disturb the gulls (Béchet et al. 2000); approaching to within less than 200 m of nests is therefore discouraged.

The remoteness of the breeding sites in Nunavut offers some protection to the birds. The initial breeding site in Churchill used to be the most readily accessible to humans, but since Ross's Gulls have moved further away from the centre of Churchill, the threat of human disturbance has decreased. However, the potential for disturbance still exists: airboats and helicopters, operated by tour companies, have on occasion been close to Ross's Gull nests around Churchill (B. Chartier, pers. comm. in Hamel 2002).

1.5.2 Predation

Gulls (Larus spp.), jaegers (Stercorarius spp.), Arctic fox (Alopex lagopus), weasels, and polar bears (Ursus maritimus) are known predators of Ross's Gull (Alvo et al. 1996). In Russia, gulls and jaegers are the major predators of the Ross's Gull (Densley 1991), and at the Cheyne Islands, Glaucous Gulls (Larus hyperboreus) are suspected predators of Ross's Gull chicks (Alvo et al. 1996).

Predators were thought to be partially responsible for the low breeding success at Churchill between 1980 and 1987 (Densley 1988), and Herring Gulls (Larus argentatus) continue to be a major factor affecting Ross's Gull populations around Churchill today (B. Chartier, pers. comm.). It is believed that Herring Gull numbers increased around Churchill due to the large open garbage dump, which attracted the birds. In the last 15 years, Herring Gulls have begun nesting on small islands in ponds, effectively increasing their success because other predators cannot reach the nesting locations (B. Chartier, pers. comm.).

Although Ross's Gulls and Arctic Terns share nesting colonies, Ross's Gulls appear to be more susceptible to predation by Herring Gulls. When avian predators fly overhead, Arctic Terns quickly leave their nests, while Ross's Gulls are slower to take off, resulting in Herring Gulls being able to spot where the eggs and chicks are (B. Chartier, pers. comm.).

1.5.3 Habitat Loss and Destruction

Loss and destruction of habitat can threaten the Ross's Gull. In 1984, the Akudlik Marsh was flooded, resulting in the submergence of all previous nesting sites (Gallop 1984). Temporary habitat loss of this nature can result in reduced reproduction and may lead to a shift of breeding locations in future years (Hamel 2002). The shift in breeding location following the flooding at Churchill, and the subsequent increased remoteness of the breeding colony, may partly explain the decline in nest records observed at this location since 1984 (Hamel 2002).

Oil drilling and disposal of waste products from mining activities at fall migration stop-over areas are potential threats to the Ross's Gull. During fall migration, Ross's Gulls congregate in high concentrations and thus are susceptible to pollution events, such as oil spills, that affect the availability of prey (Divoky 1988). Although this threat is generally located in areas beyond Canadian jurisdiction, it can affect the Canadian and global population.

1.6 Actions Already Completed or Underway

1.7 Knowledge Gaps

Many life history characteristics, including nesting and fledging success, adult and juvenile survival, causes of mortality, predation rates, philopatry to natal and breeding sites, and habitat and food preferences, are unknown for the Ross's Gull worldwide. As well, there is very little information on wintering grounds and migration paths, or on the effects of weather and climate change on survival.

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