Bird of the Month - November 2002

Rock Sandpiper
Calidris ptilocnemis

by David Fix

The list of ‘life birds’ kept by birdwatchers living in the Redwood Region typically grows quite large before there is a checkmark alongside the name of Rock Sandpiper (Calidris ptilocnemis).  To see one of these winter shorebirds well requires a hike into their chosen habitat of surf-splashed rocky coastline.  Although one’s expedition in search of this species may entail nothing more adventuresome than a low-tide walk along a rocky shoreline in sturdy boots and warm clothing, still there is the feeling that a special place is being visited in pursuit of a special bird. 

This species is among the later-arriving migrants, usually appearing only in mid-October or in November.  It is uncommon this far south, and is seldom encountered away from the flocks of Surfbirds and Black Turnstones in which it seems to hide.  Rock Sandpipers are so scarce here, and are so cryptically patterned, that success in the search is far from guaranteed.  However, once one of these drab grayish ‘rockpipers’ is in view, it is often possible to enjoy a close-range study as it forages among its larger cousins, picking methodically at marine algae and invertebrates clinging to the slick rockscape from which the bird seems inseparable.

Along with the closely-related Purple Sandpiper (C. maritima) of the North Atlantic, the several distinctive races of Rock Sandpiper comprise a superspecies of medium-small sandpipers typical of subarctic and arctic tundra in summer and rocky shores in winter.  Rock Sandpipers nest in western Alaska.  In contrast with other tundra-nesting shorebirds, they typically do not migrate great distances.  Indeed, the bulk of the population of the nominate subspecies  C. p. ptilocnemis apparently overwinters in Alaska’s Upper Cook Inlet, feeding during the fleeting hours of low sunlight in scour-tracks created in the mudflats by room-sized icebergs that retreat with the ebbing tide!  This phenomenon was discovered only as recently as 1997 (Field Notes 51:786-787), suggesting that much remains to be learned about even the regular North American bird species.  Only a very small minority of the world population moves as far south as Washington, Oregon, and California.  This species has always been quite scarce in our area and is never numerous.  Christmas Bird Count data suggest a decline over the past several decades;  the cause is not understood.  

While Rock Sandpipers are in our area, groups of from 1-4 birds (exceptionally more) may be looked for at tidepools, on rocky promontories, and along jetties.  They have a marked tendency to ‘sub-flock’ in groups of Surfbirds, among which their rather similar plumage pattern, yellow legs, and foraging behavior cause them to be easily overlooked.  A rather long, slightly decurved bill and a simple flight pattern (white wing-stripe, dark back, whitish sides of tail) and smaller size distinguishes them from Surfbirds and both species of turnstone.  Field guides treat this species well, but fail to warn that other small shorebirds such as Dunlins, Least Sandpipers, Sanderlings, and Spotted Sandpipers sometimes feed with or near ‘rockpiper’ flocks on rocky shores, creating a pitfall for the over-eager birder.  Outer Point St. George, Trinidad harbor, and the north jetty of Humboldt Bay are traditional wintering sites.  Good luck--and remember to watch the waves!