Sabine's Gull

Sabine's Gull arrives on the Arctic tundra in early June, sometimes before snow and ice have fully melted. Pairs form long-term monogamous bonds and typically return to the same territory with the same mate in successive years — a level of site and partner fidelity more typical of albatrosses than small gulls.

Nests are shallow depressions in vegetation or gravel, averaging around 13.7 cm across and 1.8 cm deep, and are seldom lined — occasionally a few strands of grass, algae, or feathers are added. Nest sites are typically at the edge of small tundra ponds, on islands within ponds, or on marshy ground near the coast. Colonies are small and loose, with 16–31 breeding pairs recorded annually at one well-studied Canadian High Arctic colony.

The clutch is typically 2–3 eggs (range 1–4), olive-green to olive-brown with darker greenish-brown irregular markings. Both sexes incubate for approximately 23–25 days. Chicks hatch covered in well-camouflaged down and may leave the nest cup within a day of hatching, though they typically remain on the nest platform for several days before parents lead them to freshwater or brackish ponds where fly and midge larvae are abundant.

Young birds are able to fly short distances before their flight feathers are fully grown — a developmental pattern more typical of terns than gulls. Both parents defend the nest vigorously, either by direct mobbing of intruders or by performing a distraction display, feigning injury to draw predators away. This injury-feigning behaviour is standard among plovers and sandpipers but is genuinely rare among gulls, reflecting Sabine's Gull's unusual position within the family.

The oldest recorded Sabine's Gull was 8 years and 1 month old, based on banding records compiled by the Cornell Lab of Ornithology. This is a relatively modest maximum for a gull — the Herring Gull, for example, can exceed 30 years — though the remote and pelagic lifestyle of Sabine's Gull makes it difficult to track individuals over long periods, and the true maximum lifespan may be higher.

Typical lifespan in the wild is estimated at 5–10 years. Annual survival rates are not well documented, but the species faces mortality risks at multiple stages of its annual cycle: predation on the Arctic breeding grounds (from Arctic Foxes, Glaucous Gulls, and other predators), the hazards of two long ocean crossings each year, and the risks of marine pollution and food scarcity on the wintering grounds.

First-year birds face the highest mortality, as is typical for gulls. Juveniles must navigate their first southbound migration — often crossing the interior of continents or vast stretches of open ocean — without the experience of adults. Those that survive to breeding age (typically two years) have a much improved chance of reaching several years of age. The long-term pair bonds and site fidelity shown by breeding adults suggest that experienced birds can maintain successful breeding for multiple consecutive seasons.

Sabine's Gull is listed as Least Concern on the IUCN Red List (assessed 2020), reflecting a large global range and a population estimated at 330,000–700,000 individuals. Partners in Flight puts the figure at around 340,000. The species scores 11 out of 20 on the Partners in Flight Continental Concern Score, indicating low overall conservation concern.

Population trends are not well known, largely because the species breeds in remote Arctic terrain and spends the non-breeding season far offshore. The global population is considered broadly stable. However, the Russian breeding population may be declining, and the species has been nominated for inclusion on Russia's Red Book. It is also listed as a Species of European Conservation Concern.

The remote Arctic breeding range and highly pelagic non-breeding habits provide some natural buffer against human disturbance, but several threats are recognised. Climate change is the most significant long-term concern: warming Arctic temperatures are reshaping tundra ecology, and shifts in ocean upwelling systems could reduce food availability on the wintering grounds. Oil spills and marine pollution pose risks during migration and on the wintering grounds, where birds concentrate in coastal upwelling zones. Bioaccumulation of pesticides and other marine pollutants is a concern for a species that feeds high in the marine food web. Overfishing of small fish and crustaceans along migration routes could reduce prey availability, and Arctic development — oil, gas, and mining — has the potential to disturb tundra breeding habitat.

The Greenland population was estimated at up to 2,000 pairs earlier this century. The Atlantic wintering population of approximately 10,000 birds is small enough that a significant oil spill in the Benguela Current could have a measurable impact on the global population.

Sabine's Gull's courtship behaviour is more typical of terns than gulls, and it sets the species apart from virtually every other member of the family. The male initiates courtship by giving a long call while arching his neck and bowing — a display that is broadly similar to the 'long call' displays of other gulls. But the key distinction comes in what happens next.

Rather than regurgitating food as most gulls do during courtship feeding, the male Sabine's Gull presents whole, intact prey items directly to the female — carrying fish in the bill and holding it upright as an offering. The female pecks at the partner's bill precisely where the yellow tip meets the black base. A receptive female then tosses her head several times, mirrored by the male, and often rubs her head and body against the male's breast as an invitation to mate. This direct prey-presentation behaviour is characteristic of terns and is genuinely unusual among gulls.

Pairs return to the same territory and the same mate in successive years, suggesting that pair bonds are maintained through the winter despite the two birds potentially wintering in different ocean basins — as geolocator studies have confirmed can happen. How pairs re-establish contact after months apart in different hemispheres remains an open question. Nest defence is equally atypical for a gull: both sexes perform injury-feigning distraction displays to lead predators away from eggs or chicks, a behaviour standard in shorebirds but rare in the Laridae.

Sabine's Gull was formally described to science on 25 July 1818, when Sir Edward Sabine — an Irish astronomer and geophysicist serving as scientific officer on Captain John Ross's Arctic expedition in search of the Northwest Passage — shot several specimens at Melville Bay on the west coast of Greenland. He sent the skins to his older brother Joseph Sabine in London, who formally described the new species and named it Xema sabini in his brother's honour. The genus name Xema was coined by William Elford Leach and has no clear etymology, though it has been suggested to derive from a Greek word for a type of seabird.

The species is the sole member of the genus Xema, reflecting its genuinely unusual combination of characters — the forked tail, yellow-tipped black bill, and tricoloured wing pattern are found in no other gull. For many years, its closest relative was assumed to be the Swallow-tailed Gull (Creagrus furcatus) of the Galápagos, which shares the forked tail and yellow-tipped bill. However, mitochondrial DNA studies overturned this assumption: Sabine's Gull's true sister taxon is the Ivory Gull (Pagophila eburnea) of the High Arctic. The two diverged from a common ancestor approximately 6 million years ago, with this clade splitting from the kittiwakes around 8 million years ago.

Four subspecies are recognised by some authorities: the nominate X. s. sabini (Canadian Arctic to Greenland), X. s. palaearctica (Svalbard to Taimyr Peninsula), X. s. tschuktschorum (Chukotsk Peninsula), and X. s. woznesenskii (Gulf of Anadyr to Alaska). Alaskan birds are slightly darker and perhaps larger than the nominate, though the differences are subtle and the validity of all four subspecies is not universally accepted.