A handsome, little-known gull that lives along the Atlantic coast of southern South America. It’s named after Claes Olrog, the Swedish-Argentinian biologist who described it, and it has a very “clean” look: white head, neck, and underparts; inky black back and wings edged with white; and a white tail tipped with a bold black band. Its bill is yellow with a dark band and a red tip, its legs are yellowish, and a thin red ring circles the eye. It’s a fairly large gull, a bit stockier than many familiar seagulls, and often stands very upright when it’s scanning the shoreline.

This species is a real local specialist. It breeds only along a short stretch of coast in northern Argentina, mainly in and around the Bahía Blanca estuary, with a few colonies farther south. Outside the breeding season, it ranges more widely along the coasts of Argentina, Uruguay, and southern Brazil, but it still stays close to shallow coastal waters, estuaries, lagoons, and tidal flats. It nests in colonies on low islands and sand or shingle banks just above the high-tide line.

What really makes Olrog’s gull stand out from most gulls is its very focused diet. While many gulls behave like generalists and scavengers, Olrog’s gull is a crab specialist, especially during the breeding season. Adults spend a lot of time working the muddy edges of estuaries between high and low tide, stalking small shore crabs in very shallow water or on exposed flats. They use a mix of walking, wading, and short swims, then snap up crabs from the surface or dip just under the water to grab them. In Spanish, it’s often called gaviota cangrejera—“crab-eater gull”—which fits it perfectly. Outside the breeding season, it becomes a bit more flexible and will also take shellfish, worms, fish, and even scraps from fishing boats and harbours, but crabs still make up an important part of its diet.

Distribution

Country

Population est.

Status

Year

Comments

Argentina

2018

Breeding

Brazil

2018

Non-Breeding

Chile

2018

Seasonality Uncertain

Uruguay

2018

Non-Breeding