Rock Sandpiper: A hardy sandpiper lingering late

Shorebirds are renowned for epic, long-distance migrations, some flying from arctic breeding areas to the southern hemisphere to escape winter cold and find abundant food.

But not so, the hardy rock sandpiper.

These squat, short-legged sandpipers are short to mid-distance migrants that winter further north than other shorebirds. They are usually the last shorebird I see in the fall, when a few hang on into October to feed along rock jetties in the Nome area.

Recently, I’ve enjoyed watching a small flock of rock sandpipers flit along Nome’s breakwater, clinging to slick, algae covered rocks, picking off small invertebrates as waves break and splash around them.

Rock sandpipers are a Beringian species that breed on Bering Sea islands and on the Seward Peninsula, which is the northern extent of their North American breeding range.

They breed in the alpine tundra habitat of coastal mountains, often within 10 miles of the coast. In the Bering Strait region, the species is widespread but uncommon across the southern uplands on the western half of the Seward Peninsula, and most common at the western tip of the peninsula.

Typically rock sandpipers arrive during the last half of May when their breeding areas may still be snow-covered. Then, they sometimes are seen in flocks feeding along the coast until their nesting areas thaw.

Males arrive on the breeding ground first to set up territories. They often reclaim their previous territory, and sometimes reunite with their previous mate. Males circle high over their territories on fluttering wings while singing rhythmic trills that carry far over the open tundra. These displays are used to defend their boundaries and attract a mate.

Intruding males and other similarly sized shorebirds are hastily chased away.

Once a pair bond is formed, the male performs a “scraping” display. He leads his mate around the territory to possible nest sites, crouching and turning as if preparing a nest cup. With drooping wings, he leans forward and “points” to each site with his bill while calling. When his mate is satisfied, she shows her approval by walking to that nest site.

Usually, nests are in dry tundra amidst wetter ground where insects are abundant. The nest is a deep cup made mostly by the male, lined with lichens and dried willow leaves, some of which are added by the female.

Egg laying typically begins in the first half of June. The male guards his mate attentively through egg-laying, deterring any intruding males with displays, ground and air chases or combat, if necessary.

Four eggs are usually laid, and a 23-day incubation period begins when the last egg is laid. The parental roles of rock sandpipers vary. Usually both parents incubate, but occasionally one of the parents does it all, and that could be either the male or the female.

The downy, open-eyed chicks are able to leave the nest within six hours of hatch but need frequent brooding through their first week to maintain body temperature, especially if the weather is cold or wet.

The parents lead their brood to wet, insect-rich areas where the mobile youngsters feed themselves by pecking insects off of vegetation or the ground or by snatching flying insects from air.

Usually both parents care for the chicks for up to eight or nine days, but if the female is depleted after egg production, she may leave earlier. Then, the male alone guides and protects the brood until they fledge in about three weeks.

On their tundra breeding ground, rock sandpipers peck and probe in wet areas for worms, spiders and adult and larval insects, especially beetles. Sometimes they chase flying insects, capturing them in the air. Those breeding near the coast may also fly to coastal mud and sand bars to forage for aquatic invertebrates in small flocks while nesting.

Except during the short breeding season, rock sandpipers live along the coast and feed in wave-splashed intertidal areas on aquatic invertebrates. They pick small prey off of rocks with tweezer-like bills and sometimes hammer into barnacles or mussels.

They also probe into sand and mud in search of small clams or worms. Sensors on the bill allow them to forage by touch for unseen prey. Like many other shorebird species, rock sandpipers are attracted to beached carcasses of marine animals to feed on fly larvae.

After fledging, juveniles move to intertidal habitat on the coast where they flock with other rock sandpipers and shorebirds. By late July and early August fledged young are noticeable on Seward Peninsula shorelines, but many adults and juveniles soon depart for food-rich premigratory staging areas on the Yukon-Kuskokwim Delta. There they join huge, mixed flocks of molting shorebirds that are feeding in preparation for migration.

Rock sandpipers breeding on the Seward Peninsula winter along the coast from southcentral Alaska to northern California. In winter they are not territorial and often flock with surfbirds, sanderlings and black turnstones. Each species has a bill of a different shape and length for foraging on different prey, at different depths, thus avoiding competition.

Rock sandpipers wintering along icy coastlines in southern Alaska face cold temperatures and extreme weather. The species has specialized adaptations to cope with northern winter conditions that other shorebird species lack.

Rock sandpipers develop heavier winter plumage for better insulation. They carry more fat during winter, presumably for fuel if food is scarce. Their breast muscles, which the birds use to generate heat by shivering, increase is size. And unlike most other sandpipers,­ feathers extend further down the legs to cover most of the tibia.

Rock sandpipers are listed as a “species of least concern,” but their numbers are believed to be declining. Their small breeding range and coastal habitat, likely to be affected by climate change, are reasons for concern about this hardy, northern sandpiper.

Click here to hear the call and song of a rock sandpiper on a Nome area breeding ground during a flight display.