Breeding adult The breeding plumage is acquired in the spring (March-May), usually during spring migration, and is retained until fall (September-October); thus, spring migrants and very early fall migrants can be observed in this plumage in B.C. The feathers of the back and scapulars of breeding-plumaged birds are black with variable (usually relatively broad) reddish to cinnamon-rufous or rufous-buff feather edges, giving the upperparts a mottled appearance. The rump and uppertail coverts are dark blackish-grey. The short-pointed tail is grey with black central feathers. The upperwing coverts are primarily grey or brownish-grey, with blackish-grey primary coverts. The flight feathers are also blackish-grey with a bold white stripe extending across the bases of the secondaries and inner primaries (primaries also with extensive whitish shafts). The underparts are usually largely whitish, with variable dark blackish-brown mottling on the upper breast forming an irregular dark patch; the belly, flanks, and undertail coverts are variably (usually finely) streaked with dusky-grey. The underwing coverts are largely white except for blackish-grey spotting along the front edge of the wing; the underside of the flight feathers is dark grey with a white stripe along the base of the secondaries and primaries. The crown, nape, hindneck, and sides of the neck are cinnamon-rufous or buffy with fine black streaks (heaviest on the crown), with a grey tinge to the hindneck. The relatively broad whitish supercilium contrasts with the dusky-brown lores and dark spot on the rear portion of the ear coverts; the remainder of the ear coverts are buffy and finely streaked with black. The remainder of the head and throat are whitish, often with fine dusky streaks (heaviest in C.p.couesi and relatively sparse in C.p.tschuktschorum). The iris is dark, the slender bill is blackish (often with a small area of yellow at the base), and the legs and feet are dull greenish-olive.
Non-breeding adult This plumage is held between ~October and ~March/April, and most individuals observed in B.C. are in this plumage. The back, scapulars, and upperwing coverts are dark slate-grey, often with a slight purplish or bluish tone, with darker feather centres on the back and scapulars. The pattern of the rump, uppertail coverts, tail, and flight feathers is similar to that of the breeding-plumaged adult. The head and neck are wholly dark slate-grey, often with some fine pale or blackish streaking on the foreneck, extending onto the whitish underparts as bold, dense, dark grey spotting that is heaviest on the breast, sides, and flanks. The crown and lores are usually slightly darker than the rest of the head, and there is typically a paler grey area in front of (and sometimes around) the eye. Bare part colouration is generally similar to the breeding adult, but the bill has a brighter and more extensive yellowish or greenish-yellow base and the legs and feet are brighter yellowish.
First-winter immature Birds in this plumage occur from ~October through ~March of the first year. This plumage is very similar to the non-breeding adult, but the rufous or reddish feather edges on the scapulars of juvenal plumage are retained, as are the flight feathers and wing coverts (which often appear worn relative to the rest of the plumage).
Juvenile This plumage is held until July or August of the first year and is lost before fall migration; thus, it is extremely unlikely that birds in this plumage will be observed in B.C. This plumage is somewhat reminiscent of the breeding plumage (extensive rusty upperparts, etc.), but lacks the irregular dark patch on the upper breast, has fine grey streaking on the head, neck, and breast, has a buffy wash across the breast, has extensive rufous and buffy edges on the feathers of the upperwing coverts, and has narrow pale edges on the scapular feathers that form a pale ‘V’ or ‘braces’ on the upperparts.
Measurements Total Length: 22-23 cm Mass: 59-106 g
The identification of winter-plumaged Rock Sandpiper is relatively straightforward in B.C., especially when the narrow habitat preferences of the species are taken into account. It is most similar to winter-plumaged Dunlin, which is similar in size, but is overall darker slate-grey (rather than paler brownish-grey in Dunlin) with bold dark grey spots on the white underparts (underparts of Dunlin mostly clean white). Furthermore, it is stockier than the Dunlin, with relatively shorter legs, shorter bill, and bulkier body. The plumage pattern is also similar to the non-breeding plumage of the Surfbird, but that species is considerably larger than the Rock Sandpiper, with a short, straight, relatively thick bill and bold white rump and tail pattern.
Breeding-plumaged Rock Sandpipers are also similar to breeding plumage Dunlin, but the dark patch on the underparts is on the breast (black patch on underparts of Dunlin is more extensive and is on the belly and lower breast). Furthermore, the upperparts are darker and less extensively rufous in breeding-plumaged Rock Sandpiper, and the head and underparts are more densely and heavily mottled and speckled with black, brown, and dark grey.
Although the song usually accompanies courtship displays on the arctic breeding grounds, some late spring migrants on the Queen Charlotte Islands have been documented giving these songs prior to arrival on the breeding grounds. The song is a complex trill consisting of repeated low, growling, two-syllable phrases separated by short pauses: per-deeerr….per-deeerr….per-deerrr or rita…rita…rita…rita. The call note is an abrupt, low, grating or squeaking chrreet or cheerrt. Feeding birds sometimes give a variety of soft, scratchy notes.
This species is a non-breeding winter visitor to B.C.
The Rock Sandpiper forages almost exclusively within the splash zone along rocky shorelines; it infrequently forages in more sheltered locales. It commonly associates with other shorebirds of similar rocky habitats, particularly Surfbirds, Black Turnstones, and Dunlin, and is generally the least numerous of these species in any given area. Foraging birds usually occur singly or, more often, in small groups of up to 10 individuals, although occasional flocks of dozens or even hundreds of birds are also recorded (especially along the northern coast of the province). Although it is commonly found in mixed-species flocks, foraging groups of Rock Sandpipers often feed in areas away from those used by other members of the flock. It forages primarily on algae and a wide variety of aquatic invertebrates such as barnacles, amphipods, small crabs, marine snails, bivalves, and intertidal insects (especially larval flies). Foraging birds glean and pick prey from the surface and crevices of rocks along the immediate shoreline, often dodging crashing waves while they search for prey.
Source: Paulson (1993); Gill et al. (2002)
True to its name, the Rock Sandpiper is closely associated with rocky marine shores and is rarely found outside of this habitat. Most foraging and roosting occurs on rocky offshore islets, reefs, jetties, breakwaters, and rocky headlands, although some birds are found on log booms, wharves, and rocky or cobble beaches. It is usually rare on softer substrates such as mudflats, sandy beaches, and estuarine habitats, although it is somewhat more frequent in these habitats on the Queen Charlotte Islands during spring migration.
Source: Campbell et al. (1990b); Paulson (1993); Gill et al. (2002); Paulson (2005)
The Rock Sandpiper breeds in coastal areas of western Alaska and throughout the Aleutian Islands, as well as locally in extreme northeastern Russia. It winters along the coast of the northeast Pacific from the Aleutian Islands and south-coastal Alaska south to northern California, although it is generally rare south of British Columbia.
Winter Uncommon and local along the entire coast of British Columbia, including Vancouver Island and the Queen Charlotte Islands, although it is fairly common along some remote coastlines of northern B.C. (particularly the Queen Charlotte Islands). It is generally very rare or absent from areas of high freshwater influence, such as at the heads of major inlets or at the mouths of major rivers, and is most common along the northern and central mainland coast, on the Queen Charlotte Islands, and on western and northern Vancouver Island.
Migration and Vagrancy Generally a rare to uncommon spring and fall migrant along the coast, although it is locally fairly common in some areas of the north coast (e.g., Queen Charlotte Islands). Fall migrants begin to appear in northern portions of the B.C. coast as early as August (occasionally even in late July) and numbers build through September. It does not appear in southern areas of the coast, however, until mid- to late October (very rarely as early as late August) and is one of the latest migrant shorebirds to appear in this region. Peak movements on the north coast are in September and October, while peak fall movements on the south coast are in November and early December. Wintering individuals are augmented by northward-bound spring migrants in early spring (March), with peak movements occurring in April and early May (earlier in the south); the latest individuals have generally left the province by late May.
Accidental in fall in the northwestern interior (Atlin).
Source: Campbell et al. (1990b); Paulson (1993)
Population and Conservation Status
Although it has always been relatively scarce in B.C., especially along the southern portions of the coast, there is recent evidence that wintering populations have decreased in some areas from southern B.C. to California. For example, the number of individuals detected on Victoria Christmas Bird Counts has dropped noticeably over the past several decades and it is no longer found regularly on that count; this was formerly the count that most reliably recorded this species in southern B.C. These declines have been mirrored in many places along the coasts of Washington, Oregon, and California, although in some other areas the numbers are stable or even increasing. It is currently unclear what the overall population trend for this species is. Because it does not breed in Canada, it is not recognized as a species of conservation concern by either COSEWIC (Committee on the Status of Endangered Wildlife in Canada) or the B.C. CDC (Conservation Data Centre).
Source: Paulson (1993); Gill et al. (2002)
This species is very closely related to the Purple Sandpiper (Calidris maritima) of the North Atlantic region, and many authors in the past have chosen to lump them into a single species. At the other extreme, several of the recognized subspecies of Rock Sandpiper have been separated as distinct species in the past. Currently, however, Rock and Purple Sandpipers are recognized as distinct species that are nonetheless very closely related and likely form a superspecies (although this is still debated). Rock and Purple Sandpipers are also closely related to Dunlin, a relationship that has recently been confirmed by assessing the genetics of this entire group.
Four subspecies of Rock Sandpiper are recognized throughout its relatively small range, rendering it one of the most polytypic of all species of Calidris. Three of these subspecies appear to range south into B.C. during the winter, although only two have been confirmed in the province (and only one is considered to occur with any regularity).
The three subspecies found in B.C. are as follows:
Calidris ptilocnemis ptilocnemis This subspecies breeds on the Pribilof Islands and other islands in the Bering Sea and winters along the southern coast of Alaska from the Alaska Peninsula to the Alexander Archipelago (mostly in Cook Inlet). It has been recorded as a vagrant in Washington (Ocean Shores), and in B.C. is known from a single photo-documented record on the Queen Charlotte Islands in May. It is larger than any other subspecies, and in winter plumage it is noticeably paler grey with virtually unmarked white undertail coverts and lower belly. Breeding-plumaged birds are brighter and more extensively rufous than other subspecies, with a paler head, more prominent dark spot on the ear coverts, and a largely unmarked white belly and undertail coverts.
Calidris ptilocnemis tschuktschorum (Portenko) This subspecies breeds along the Bering Sea coasts of Alaska (north of Bristol Bay) and eastern Siberia and winters from south-central Alaska south to California; it is the most common subspecies in B.C. Birds in non-breeding plumage are essentially indistinguishable from C.p.couesi, but birds in breeding plumage can often be distinguished from couesi by the brighter and more extensive reddish edges on the feathers of the upperparts, heavier and more well-defined dark patch on the upper breast, and a paler head and neck with more prominent dark dusky-brown patch on the ear coverts and whiter throat.
Calidris ptilocnemis couesi (Ridgway) This subspecies is largely resident throughout the Alaska Peninsula and Aleutian Islands, although occasional individuals apparently of this subspecies have been recorded south at least to Washington during the winter. It has not been fully documented in B.C., but its apparent presence farther south suggests an occurrence in the province. Non-breeding birds are essentially identical to C.p.tschuktschorum, but breeding-plumaged birds can be distinguished by the narrower and more cinnamon-rufous (vs. reddish) feather edges on the upperparts (the upperparts thus appearing darker), less extensive dark mottling on the upper breast creating a less well-defined dark patch, and heavier dark mottling on the head and neck with a less well-defined dark patch on the ear coverts.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
16/09/2019 3:09:11 PM]
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