Ruddy turnstone

The ruddy turnstone has a varied diet including carrion, eggs, fish[7] and plant material but it feeds mainly on invertebrates. Insects and their larvae[7] are particularly important in the breeding season. At other times it also takes crustaceans, spiders,[7] 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.[8]

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.[9]

Ruddy turnstones engage in a variety of behaviours to locate and capture prey. These behaviours can be placed into six general categories:[10]

• 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.[11]
• 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.

When foraging, turnstones adopt different postures indicative of their level of dominance. A lowered tail and a hunched stance is associated with chasing and aggression, and thus a dominant individual. Dominance in aggression is age-related, with juveniles assuming the subordinate role a disproportionate amount of the time.[12]

The plumage patterns of ruddy turnstones exhibit an unusual amount of variation in comparison with other shorebirds. Turnstones use these unique plumage patterns to recognize individuals and discriminate intruders in their territory from neighbours occupying an adjacent territory. When a fake fiberglass turnstone model is placed in a turnstone's territory, the occupant is less likely to respond aggressively if the model is painted to have the plumage pattern of a neighbouring turnstone.[13]

Ruddy turnstones can survive in a wide range of habitats and climatic conditions from Arctic to tropical. The typical breeding habitat is open tundra with water nearby. Outside the breeding season, it is found along coasts, particularly on rocky or stony shores. It is often found on man-made structures such as breakwaters and jetties. It may venture onto open grassy areas near the coast. Small numbers sometimes turn up on inland wetlands, especially during the spring and autumn migrations.[8]

In terms of wintering sites, ruddy turnstones are particularly faithful to specific locations. A study published in 2009 examined turnstones wintering along a stretch of coastline in the Firth of Clyde. It found that 95% of birds resident to the area at the end of winter returned the following autumn. The same study also confirmed ruddy turnstones as one of the longest lived wader species, with annual adult mortality rates of under 15%.[11] Their average lifespan is 9 years with 19 years and 2 months being the longest recorded.

Breeding-plumaged adult on nest

It is a monogamous bird and pairs may remain together for more than one breeding season. The nest is a shallow scrape, often with a lining of leaves. It is about 11 cm (4.3 in) across and 3 cm (1.2 in) deep. It may be built amongst vegetation or on bare stony or rocky ground. Several pairs may nest close together.[8]

A single clutch of two to five eggs is laid with four being most common. The eggs measure about 41 mm × 29 mm (1.6 in × 1.1 in) and weigh around 17.9 g (0.63 oz). They are smooth, slightly glossy and oval to pear-shaped. They are variable in colour but are commonly pale green-brown with dark brown markings, densest at the larger end. Incubation begins when the first egg is laid and lasts for about 22–24 days. The female is mainly responsible for incubating the eggs but the male may help towards the end.[8]

The young birds are precocial and are able to leave the nest soon after hatching. They are buff above with dark grey markings and are white below. They are able to feed themselves but are protected by the parents, particularly the male. They fledge after 19–21 days.[8]