The bird with a lopsided beak that hunts by slicing through the water

Nature · Published 3 October 2026 Swipe more like this →

In short: The genus Rynchops, or skimmers, are the only birds on Earth with uneven bills. By flying low over water with their elongated lower mandibles slicing the surface, they catch fish with a snap. This unique hunting style is paired with vertical slit-shaped pupils, a feature found in no other bird.

The skimmers are a trio of species found across Africa, South Asia, and the Americas. Belonging to the family Laridae, they are closely related to terns and noddies. Their name, Rynchops, is derived from the Ancient Greek words for beak and face. While the Swedish naturalist Carl Linnaeus introduced the genus in 1758, he used the spelling Rynchops, which remains the standard despite later arguments for the more etymologically correct Rhynchops. Similarly, while originally treated as feminine, the genus is now typically classified as masculine, leading to the designation of the black skimmer as Rynchops niger.

The most striking feature of these birds is the lower mandible, which is significantly longer than the upper. This anatomy allows them to skim the surface of lakes, streams, and lagoons at high speeds. Because their bills fall within their binocular field of vision, they can precisely position themselves to snap up prey. Beyond their specialized beaks, they are the only birds known to possess vertical slit-shaped pupils, an adaptation that likely assists in their unique hunting environment. They are agile fliers that congregate in large flocks on coastal sand banks and riverbeds.

These tropical and subtropical birds nest on sandy beaches, laying clutches of three to six eggs. The female is responsible for incubation, but their reliance on specific nesting habitats makes them highly sensitive to environmental disruption. The Indian skimmer is currently listed as endangered by the IUCN, a status driven by the degradation of the rivers and lakes they depend on for survival. As their nesting sites are often restricted, human disturbance and habitat loss remain significant threats to the continued existence of these remarkable, scissorbilled creatures.

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