28-3-2025 BUNDALA NAT PARK, SRI LANKA - RUDDY TURNSTONE (Arenaria interpres)

The ruddy turnstone (Arenaria interpres ) is a small wading bird, one of two species of turnstone in the genus Arenaria.

It is now classified in the sandpiper family Scolopacidae but was formerly sometimes placed in the plover family Charadriidae. It is a highly migratory bird, breeding in northern parts of Eurasia and North America and flying south to winter on coastlines almost worldwide. It is the only species of turnstone in much of its range and is often known simply as turnstone.

Ruddy turnstones are small highly migratory wading birds. In all seasons, their plumage is dominated by a harlequin-like pattern of black and white. Breeding birds have reddish-brown upperparts with black markings. The head is mainly white with black streaks on the crown and a black pattern on the face. The breast is mainly black apart from a white patch on the sides. The rest of the underparts are white. The females are slightly duller than the males and have a browner head with more streaking. Non-breeding adults are duller than breeding birds and have dark grey-brown upperparts with black mottling and a dark head with little white. Juvenile birds have a pale brown head and pale fringes to the upperpart feathers creating a scaly impression.

The ruddy turnstone breeds in northern latitudes, usually no more than a few kilometres from the sea. The subspecies A. i. morinella occurs in northern Alaska and in Arctic Canada as far east as Baffin Island. A. i. interpres breeds in western Alaska, Ellesmere Island, Greenland, Norway, Denmark, Sweden, Finland, Estonia and northern Russia. It formerly bred on the Baltic coast of Germany and has possibly bred in Scotland and the Faroe Islands.

In the Americas, the species winters on coastlines from Washington and Massachusetts southwards to the southern tip of South America although it is scarce in southern parts of Chile and Argentina and is only an unconfirmed vagrant in the Falkland Islands. In Europe, it winters in western regions from Iceland, Norway and Denmark southwards. Only small numbers are found on Mediterranean coasts. In Africa, it is common all the way down to South Africa with good numbers on many offshore islands. In Asia, it is widespread in the south with birds wintering as far north as southern China and Japan (mainly in the Ryukyu Islands). It occurs south to Tasmania and New Zealand and is present on many Pacific islands. Some non-breeding birds remain year round in many parts of the wintering range, with some of those birds still taking on breeding plumage in the spring and summer.

The ruddy turnstone has a varied diet including carrion, eggs, fish and plant material but it feeds mainly on invertebrates. Insects and their larvae are particularly important in the breeding season. At other times it also takes crustaceans, spiders, molluscs, and worms. It often flips over stones and other objects to get at prey items hiding underneath; this behaviour is the origin of the name "turnstone". It usually forages in flocks.

They have also been observed preying on the eggs of other bird species such as gulls, terns, ducks, and even other turnstones, though this behaviour is uncommon. In the majority of observed cases, turnstones typically go after undefended or unattended nests, puncturing the shells with their beaks to get at the contents within.

Ruddy turnstones engage in a variety of behaviours to locate and capture prey. These behaviours can be placed into six general categories:-

Routing: The turnstone manipulates piles of seaweed through flicking, bulldozing, and pecking to expose small crustaceans or gastropod molluscs hidden underneath.

Turning stones: As suggested by its name, the turnstone flicks stones with its bill to uncover hidden littorinids and gammarid amphipods.

Digging: With small flicks of its bill, the turnstone creates holes in the ground substrate (usually sand or mud) and then pecks at the exposed prey – often sandhoppers or seaweed flies.

Probing: The turnstone inserts its bill more than a quarter-length into the ground to get at littorinids and other gastropods.

Hammer–probing: The turnstone cracks open its prey's shell by using its bill as a hammer, and then extracts the animal inside through pecking and probing.

Surface pecking: The turnstone uses short, shallow pecks (less than a quarter bill-length) to get at prey at or just below the ground's surface.

There is evidence that turnstones vary between these feeding behaviours based on individual preference, sex, and even social status with respect to other turnstones. In one studied population, dominant individuals tended to engage in routing while preventing subordinates from doing the same. When these dominant individuals were temporarily removed, some of the subordinates started to rout, while others enacted no change in foraging strategy.