White-winged Tern

The White-winged Tern is the smallest of the three Chlidonias marsh terns, measuring 20–27 cm in length with a wingspan of 63–67 cm and a weight of 54–66 g. In breeding plumage, adults are unmistakable: the head, neck, back, and belly are jet black, while the rump, undertail-coverts, and slightly forked tail are white. The upperwing is pale grey with a broad white leading edge formed by mostly white lesser and median coverts — the feature that gives the species its name. Crucially, the underwing-coverts and axillaries are strikingly black, a diagnostic feature clearly visible in flight and unlike any other tern.

The bill is short and stubby, measuring just 22–25 mm from the feathers — noticeably shorter than the head — and is reddish-black in breeding season. The legs and feet are red. The eyes are blackish-brown. The tail is slightly forked but often appears square-tipped, particularly in juveniles.

In non-breeding plumage, the transformation is near-total. The black is replaced by white and pale grey: the upperparts become pale grey, the head and underparts white. The crown turns brownish, and a distinctive dark auricular patch — often described as 'earmuffs' or 'headphones' — remains as the key identification feature. The bill becomes blackish and the legs dull reddish. Some birds retain a scattering of black underwing-coverts through winter. Moult back into breeding plumage begins in mid-March.

Male and female are identical in plumage — the species is not sexually dimorphic. The White-winged Tern is monotypic, with no recognised subspecies.

The White-winged Tern is a vocal species, particularly at the breeding colony and when alarmed. Its most characteristic call is a short, rapid 'kek-kek' or 'kik-kik-kik' — a buzzing series of sharp notes given in alarm or during social interactions within a flock. A harsher, creaking 'kesch' or 'kreek-kreek' is also frequently heard, particularly on the breeding grounds and riverbeds; New Zealand observers describe this rasping call becoming more frequent as birds moult into breeding plumage before spring migration. Additional calls include a loud 'kwek' or 'creek' and a more complex 'kvrr-kak' noted in Audubon's field guide.

The species is most vocal at the colony, where calls serve for communication between mates, alarm signalling against predators, and territorial interactions with neighbours. Both sexes vocalise similarly, and there is no evidence of a significant difference between male and female calls. The flight call — a short, sharp note — is audible at distance and can alert a birder to the presence of a bird passing overhead before it is seen.

Unlike passerines, the White-winged Tern has no complex song. Its vocal repertoire is functional rather than elaborate: sharp, carrying calls suited to open wetland environments where visual contact between birds may be intermittent. Recordings from Malaysia, Romania, and Poland (archived on Xeno-canto) confirm the consistency of the alarm and contact calls across the species' vast range.

In the UK, late May and June offer the best chance of encountering a White-winged Tern in breeding plumage — the jet-black body and white wings are unmistakable and unlike any other tern likely to be seen in Britain. Autumn birds (July–September) are in transitional or non-breeding plumage and require more care. The key feature to look for is the dark auricular patch ('earmuffs') on an otherwise white head, combined with a pale grey back and the absence of the dark shoulder bar shown by the similar Black Tern. Inland reservoirs, gravel pits, and coastal lagoons in East Anglia and the southeast are the most productive sites.

In Australia, the species arrives as a non-breeding summer migrant from around October and departs by April. Tidal estuaries, coastal lagoons, and sewage ponds in the north, east, and southeast of the mainland are the most reliable habitats. In New Zealand, coastal lagoons and estuaries from Northland to Canterbury are the best locations, with peak numbers in Bay of Plenty and Hawke's Bay. Numbers are small — fewer than 20 birds annually — so any sighting is notable.

In all regions, the flight style is the first thing to notice: buoyant and swallow-like, with shallow wingbeats and a habit of dipping gracefully to the water surface rather than plunge-diving. This immediately separates it from the larger Sterna terns. In breeding plumage, the black underwing-coverts visible from below are diagnostic — no other tern shows this combination of pale grey upperwing and black underwing lining. In winter, compare carefully with the Black Tern, which shows a dark shoulder patch that the White-winged Tern lacks.

Aquatic and terrestrial insects form the backbone of the White-winged Tern's diet. The species takes Dipterans (flies), Odonata (dragonflies and damselflies), and Coleopterans (beetles) in large numbers, along with spiders, small fish, tadpoles, crabs, and shrimp. In southern Africa, wintering birds have been recorded eating sardines (Limnothrissa miodon) and fish trapped in drying pools during the dry season. The species is also opportunistic around fishing boats, taking discarded fish from the water surface.

Unlike the 'white' terns of genus Sterna, the White-winged Tern never plunge-dives. Instead it employs three main foraging techniques. Hawking involves catching insects in flight, often in flocks that use rising air to gain height before swooping. Dipping sees birds flying 2–4 metres above the water surface and dropping down to snatch prey from the surface film or just below it. Occasional shallow plunges are also recorded, though these are the exception rather than the rule.

Prey is sometimes carried to a secluded perch to be killed and eaten, particularly larger items such as dragonflies. Between feeding bouts, birds often rest on emergent branches or floating vegetation. The feeding style — graceful, buoyant, and surface-oriented — is far more reminiscent of a swallow or hirundine than a seabird, and it is this quality that makes the species so distinctive to watch over a freshwater marsh in summer.

The breeding season runs from April to August, with peak activity in June. White-winged Terns nest in small colonies, typically of 20–40 pairs, occasionally reaching 100 pairs. Colonies are usually monospecific but may include other terns, gulls, or grebes nesting nearby. Both sexes defend a small territory within the colony, responding aggressively to neighbours and intruders.

Courtship involves aerial displays and courtship feeding, in which the male flies with a fish held in the bill to attract a female — a behaviour that functions as a direct assessment of the male's foraging ability and quality as a provider. Copulation typically follows a fish-transfer between the pair. Pair bonds may be re-established with previous partners or new pairs formed each season.

The nest is a shallow cup constructed from small reed stems and other aquatic vegetation, placed on a mound of floating plant material over water 30–120 cm deep. Occasionally nests are placed on dry shore or in very shallow water. The female lays 2–3 eggs (occasionally 4), creamy-white with dark brown markings. Both adults share incubation, which lasts 18–22 days. At hatching, the downy chicks have buffy upperparts with black streaks and paler underparts; the eye is surrounded by a pale patch. Both parents feed the young, and chicks fledge 20–25 days after hatching. The species can breed from 2 years of age.

In New Zealand, all four confirmed breeding records have involved single pairs nesting on braided riverbeds — often in association with Black-fronted Tern colonies — a strikingly different habitat from the floating-vegetation marshes used across Eurasia. The most recent confirmed breeding was in 2015.

The White-winged Tern's flight is its most immediately distinctive quality in the field. The wingbeats are shallow and leisurely — almost casual compared to the powerful, direct strokes of the larger Sterna terns — and the overall impression is of a bird that floats rather than drives itself through the air. The body is held relatively horizontal, and the slightly forked tail is often held closed, giving a square-tipped appearance. The combination of buoyancy and manoeuvrability is genuinely swallow-like, and birds can change direction rapidly when hawking insects in flight.

In breeding plumage, the flight pattern is unmistakable from above and below. From above, the broad white leading edge of the upperwing contrasts with the pale grey flight feathers and the jet-black body. From below, the pale grey underwing is bisected by the strikingly black underwing-coverts and axillaries — a diagnostic feature visible at considerable distance. The white rump and tail flash conspicuously against the black back as the bird banks and turns.

In non-breeding plumage, the flight silhouette remains distinctive: compact and buoyant, with a relatively large head and short, stubby bill compared to other terns of similar size. When feeding, birds typically fly 2–4 metres above the water surface before dipping down to snatch prey — a technique that produces the characteristic 'bouncing' flight path over marshes and lagoons. During migration, flocks may travel at greater height, using thermals and wind assistance to cover the vast distances between breeding and wintering grounds.

Specific longevity data for the White-winged Tern is limited in the published literature — the species has not been as intensively ringed as some of the larger, more accessible terns. Based on the biology of comparable Chlidonias marsh terns, a typical lifespan of around 5–10 years in the wild is plausible, with older individuals likely reaching their teens. The closely related Black Tern has a confirmed maximum recorded age of around 17 years from European ringing data, which provides a reasonable upper reference point for the White-winged Tern.

The species can breed from 2 years of age, which is relatively early for a tern. Annual survival rates are influenced by the hazards of long-distance migration — the species crosses multiple ecological zones between its Palearctic breeding grounds and its wintering areas in sub-Saharan Africa, South Asia, and Australasia. Predation at the colony (Peregrine Falcons are documented predators), nest failure during dry breeding seasons, and wetland drainage on the breeding grounds are the primary mortality factors. The species' adaptability to artificial wetlands and its large global population of 3.1–4 million individuals suggest that overall survival rates are sufficient to maintain a stable population.

The White-winged Tern is listed as Least Concern on the IUCN Red List. The global population is estimated at 3.1–4 million individuals (2015 estimate), with the European breeding population alone comprising 133,000–347,000 mature individuals. The overall population trend is stable, though regional declines have been noted in Russia and Ukraine, linked to dry breeding seasons causing nest failure and the ongoing drainage of freshwater wetland habitats.

The primary threats within the European breeding range are the destruction and drainage of freshwater marshes, water regulation in wetlands, and recreational disturbance at breeding colonies — the last of these particularly documented in Poland. Dry summers can devastate entire colony seasons when water levels drop below the threshold needed to support floating nest platforms.

The species benefits from protection under an unusually wide array of international instruments. It is listed under the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), which coordinates conservation across its African and European flyways. It is also listed under the Japan-Australia Migratory Bird Agreement (JAMBA), the China-Australia Migratory Bird Agreement (CAMBA), and the Republic of Korea-Australia Migratory Bird Agreement (ROKAMBA). In Australia, it is protected under the Environment Protection and Biodiversity Conservation (EPBC) Act as both a listed migratory and marine species. The breadth of these treaty listings reflects the species' extraordinary geographic range — it has been recorded in over 180 countries and territories.

In breeding plumage, the White-winged Tern is straightforward to identify: no other small tern combines a jet-black body with white wings, white rump, and black underwing-coverts. The short, stubby reddish-black bill and red legs are additional confirmatory features. The key pitfall is confusion with the Black Tern in breeding plumage, which has a dark grey (not black) body, dark grey (not white) wings, and lacks the white leading edge to the upperwing. The Black Tern's underwing-coverts are pale, not black — a reliable distinction in flight.

In non-breeding and transitional plumage, identification requires more care. The White-winged Tern's 'earmuff' auricular patch is typically more compact and well-defined than the Black Tern's, and the White-winged Tern lacks the dark shoulder patches (carpal bars) that are a prominent feature of non-breeding Black Terns. The rump of the White-winged Tern is white in all plumages, contrasting with the pale grey rump of the Black Tern — a useful feature when a bird is flying away. The bill of the White-winged Tern is noticeably shorter and stubbier than that of the Black Tern.

Juvenile White-winged Terns show a dark brown saddle (mantle and scapulars) contrasting with pale grey wings — a 'saddle-back' pattern that is distinctive and unlike the more uniformly dark juvenile Black Tern. In all plumages, the buoyant, swallow-like flight style and the habit of dipping to the water surface (rather than plunge-diving) are behavioural features that confirm the bird is a marsh tern of genus Chlidonias.

Courtship in the White-winged Tern centres on aerial displays and a behaviour known as courtship feeding, in which the male flies with a fish held prominently in the bill. This fish-flight serves as a direct signal of the male's foraging ability — a female assessing a prospective mate can gauge his competence as a provider from the quality and size of the fish he presents. The display is performed over the colony and in the vicinity of the female, and copulation typically follows a successful fish-transfer between the pair.

Aerial displays involve both members of a pair flying in close formation, with the male often pursuing the female in swooping, twisting flights above the marsh. These displays are accompanied by frequent calling, and the colony as a whole becomes noticeably more vocal during the peak of courtship activity in May and June. Pair bonds may be re-established with previous partners from earlier seasons, or new pairs formed — the fish-transfer ritual appears to function as a quality assessment mechanism regardless of whether the birds have bred together before.

Territory defence within the colony is vigorous. Neighbouring pairs interact frequently at territory boundaries, and both sexes participate in aggressive posturing and calling directed at intruders. The combination of dense colony activity, persistent calling, and the dramatic breeding plumage of the adults makes an active White-winged Tern colony one of the more visually and acoustically striking spectacles of a European freshwater marsh in early summer.