Rock Sandpipers roosting on one of the beaches on St. Paul Island Photo Stephan Lorenz
First-time visitors to St. Paul Island, Alaska are often astonished by the abundance of Rock Sandpipers. Unlike many other species of shorebirds, Rock Sandpipers do not migrate far south and the majority of birders have never seen one, unless they have been to Alaska or searched for the species along wave-battered, rocky shores in the northwest during the winter. Many birders visiting the Pribilofs hope to catch a glimpse of Rock Sandpipers and it usually takes about 30 seconds in the airport parking lot of St. Paul Island. One or two birds invariably forage along the edge of the gravel lot or land in the middle of the road nearby. During the short drive into town visitors ask about the flying shorebird, Rock Sandpiper, what is that one feeding along the margin of the pond, Rock Sandpiper, wait something landed on the roof, Rock Sandpiper, and several hundred shorebirds on the mudflats of Salt Lagoon and a careful scan reveals that they are all… well you guessed it, Rock Sandpipers. While some may actually tire of Rock Sandpipers after two or three days on St. Paul Island, I find them endlessly fascinating.
Rock Sandpipers are fairly uncommon throughout most of their range, but incredibly abundant on St. Paul Island where several thousand pairs nest Photo Stephan Lorenz
Rock Sandpipers (Calidris ptilocnemis) are restricted to the Pacific Coast in North America and even during the winter usually don’t migrate beyond northern California with exceptional occurrences as far south as Los Angeles. Rock Sandpipers wintering in the northwest often associate with Black Turnstones and Surfbirds along rocky shorelines. The majority remain in southeast Alaska and British Columbia during the nonbreeding season and some Rock Sandpipers are year-round residents on Aleutian Islands. This species winters farther north than any other North American shorebird. Rock Sandpipers migrate north and west in spring to nest on the arctic tundra of western Alaska, the Alaska Peninsula, the Aleutians, and the Bering Sea islands.
A Rock Sandpiper surveys its territory on St. Paul Island Photo Stephan Lorenz
Even seasoned birders often have not seen too many Rock Sandpipers, since they winter in low numbers in the Lower 48 States and nest in farflung places. The species is fairly uncommon within its breeding range on mainland Alaska, but very common to abundant on the Aleutian Islands and Bering Sea islands. One of the best places to see Rock Sandpipers up close and personal is the aforementioned St. Paul Island, the largest island in the Pribilofs. Here birds gather by the hundreds and breed in every corner of the island. During a single day it is not uncommon to record several hundred birds.
Rock Sandpipers forage in a wide variety of habitats on St. Paul Island and this individual rests along a section of rocky shoreline Photo Stephan Lorenz
The species is easily recognized and compared to other sandpipers is fairly stocky with short, stout legs. The legs vary in color from yellowish to greenish yellow. The bill is of medium length with a slight downward curve towards the tip. The species is well adapted for foraging in a variety of habitats, including rugged, rocky terrain. Like most shorebirds, Rock Sandpipers feed on insects, mollusks, marine worms, and some vegetation. In breeding plumage Rock Sandpipers have a diffuse black belly patch and upper parts that vary from bright rusty to darker brown. The species is variable with three distinct subspecies found in Alaska alone and a fourth restricted to Russia. Even within a single subspecies birds can range from bright or dark. Watching Rock Sandpipers during the breeding season on St. Paul Island, I often have a very difficult time finding one that looks like another and this high variability makes subspecies determination sometimes difficult.
This is a very rusty-colored Rock Sandpiper from St. Paul Island where the nominate ptilocnemis subspecies breeds Photo Stephan Lorenz
This is the same subspecies as the bird above and was also photographed on St. Paul Island, the coloration of the head can be especially variable, ranging from rusty brown to almost completely white Photo Stephan Lorenz
Rock Sandpipers nest on the ground and incubate 4 speckled, greenish eggs. The nest cup, composed of grasses and moss, is usually tucked under some vegetation. Adult Rock Sandpipers will engage in vigorous distraction displays to lure away potential predators. Before nesting commences, males fly above their territories, often hovering, while giving their frog-like, descending calls. The birds also regularly raise one or two wings to display.
Typical wing display of a Rock Sandpiper Photo Stephan Lorenz
This crouched position is part of a distraction display to lure away potential predators Photo Stephan Lorenz
Rock Sandpiper chicks are precocial and quickly move around on their own, but still under the watchful eye of their parents, look at those massive feet Photo Stephan Lorenz
The chicks will quickly leave the nest and soon feed themselves. It is not uncommon for some of the less travelled roads on St. Paul Island to be busy with Rock Sandpiper chicks trying to get their bearings.
Rock Sandpiper roosting among kelp St. Paul Island Photo Stephan Lorenz
An agitated Rock Sandpiper calling during a territorial bout with a neighboring pair on St. Paul Island Photo Stephan Lorenz
The nominate subspecies (C. p. ptilocnemis) breeds only on the Pribilof Islands and St. Matthew and Hall Islands in the Bering Sea. This population migrates to the the Alaskan mainland for the winter with large concentrations in Cook Inlet. It is the largest and brightest subspecies and is abundant on St. Paul Island. This “Pribilof” subspecies is generally paler with less black below and has a broader white wing stripe and more white in the tail, especially noticeable in flight.
An average individual of C. p. ptilocnemis with paler chestnut above and less black below here feeding on kelp St. Paul Island Photo Stephan Lorenz
The bold, white wing stripe of the nominate subspecies is obvious in flight Photo Stephan Lorenz
Birds breeding on the Alaskan mainland, Alaska Peninsula, and islands of the northern Bering Sea belong to the C. p. tschuktschorum subspecies (say that ten times fast). This is also the subspecies that winters furthest south, reaching the Washington, Oregon, and California coasts. The different subspecies essentially leapfrog during their annual migrations. This subspecies is smaller and darker above with a more extensive blackish belly patch. Although I find the extent of the black underparts is extremely variable and not necessarily a good field mark for subspecies identification.
This Rock Sandpiper was photographed on St. Lawrence Island where tschuktschorum nests Photo Stephan Lorenz
Another individual from St. Lawrence Island Photo Stephan Lorenz
The subspecies C. p. couesi is somewhat intermediate in color and size and its breeding range is restricted to the Aleutian Islands where it can be common. For example, it can be easily observed on Adak Island. During migration all three subspecies can occur side by side and differences in size and color may be quite obvious.
A Rock Sandpiper from the Aleutians, specifically this one was photographed on Adak Island Photo Stephan Lorenz
Another individual from Adak Island showing some of the variation, especially early in the breeding season Photo Stephan Lorenz
During the winter months Rock Sandpipers molt into a plumage dominated by somber grays.
A Rock Sandpiper in winter plumage on St. Paul Island Photo Stephan Lorenz
Juvenile Rock Sandpiper lack the black coloration on the belly and have fine streaks on the breast. Also the upper parts look finely scaled with fresh feathers. The bill may appear a bit shorter and the legs a brighter yellow.
Juvenile Rock Sandpiper on St. Paul Island Photo Stephan Lorenz
Rock Sandpipers are the most abundant breeding shorebird in the Pribilof Islands. On St. Paul Island, the largest in the Pribilof group, the birds can be found on the roads, grassy tundra, rock promontories, top of hills, beaches, and even on roofs of buildings. Despite being so common, I never tire of observing them closely as they battle for foraging space on washed up kelp, bravely lure away an arctic fox from their concealed nest, or flutter high above the tundra displaying to a mate below. Thus, I think they deserve a few more photographs, so here we go…
Rock Sandpiper on exposed tundra Photo Stephan Lorenz
Rock Sandpiper feeding among kelp Photo Stephan Lorenz
Rock Sandpiper keeping a wary eye on the observer Photo Stephan Lorenz
Rock Sandpiper perched atop a wild celery flower Photo Stephan Lorenz
Rock Sandpipers wander through their territory searching for insects and this one took a momentary break to keep an eye on an arctic fox Photo Stephan Lorenz
Rock Sandpipers are fairly vociferous, calling regularly in flight and from the ground Photo Stephan Lorenz