either of two species of shorebirds (genus Arenaria) that constitute the subfamily Arenariinae (family Scolopacidae). The birds use their short, flattened bills, which are slightly recurved (upturned at the tip), to overturn pebbles and shells in search of food. Turnstones grow to a length of about 20 cm (8 inches).

The ruddy turnstone (A. interpres), pied black, white, and reddish, is a notable migrant: it breeds chiefly in the Arctic and migrates south to winter on seacoasts in Argentina, Chile, South Africa, Australia, and New Zealand. (A banded bird is known to have traveled 720 km 【450 miles】 in a single day.) On their wintering grounds, ruddy turnstones feed primarily on small crustaceans and other invertebrates but have been known to eat berries and terns' eggs. On the breeding ground the male may make many false nests, while the female makes a single true nest, in which she lays four eggs. The male incubates by day; the female, at night. As soon as the young are fledged, the female departs alone for the wintering ground; the male remains with the young nearly two weeks longer and then departs, to be followed by the young.

The black turnstone (A. melanocephala), which breeds in Arctic Alaska and winters as far south as Mexico, has a black and white wing pattern but is otherwise dark.