Winter ecology of Rock Sandpipers

Rock Sandpipers are a species unique to the north Pacific, with breeding populations found in near-shore habitats ringing the Bering Sea (Gill et al. 2002). Likely numbering fewer than 100,000 individuals and with at least 4 recognized subspecies, this robin-sized shorebird displays physiological feats of wonder by virtue of its being the farthest-north wintering shorebird in the Pacific region. As fall approaches and most of its congeners move far south to warmer climes, Rock Sandpipers move relatively short distances. In fact, the subspecies breeding in the Aleutian archipelago is non-migratory, inhabiting the same wind-swept stretches of coastline all year long.

Perhaps the most enigmatic subspecies is the nominate race, the ‘Pribilof Sandpiper’ Calidris ptilocnemis ptilocnemis, restricted in its breeding to three isolated islands in the Bering Sea (Figure 1). During the non-breeding season, this subspecies is distributed along rocky shores and expansive mudflats along the Alaska Peninsula and Cook Inlet. Observers first noted these birds within the last 10 years wintering along the frozen, seemingly inhospitable coasts of upper Cook Inlet. Annual winter surveys now record the presence of many thousands of these hardy birds, and a large proportion of this subspecies’ population apparently makes a living all winter long in this region. Freezing temperatures, severe storms, extensive ice coverage, and brief periods of daylight characterizes upper Cook Inlet in the winter.

Figure 1. Breeding range of the 'Pribilof Sandpiper' in Alaska - inset box on the left.

Rock Sandpipers in Cook Inlet in February

Upper Cook Inlet is the site of the largest human population center in Alaska, as well as extensive off-shore oil and gas production. Additionally, use of the lower Susitna River drainage’s rich coal and timber reserves has been proposed for the region. Thus, this subspecies faces numerous potential anthropogenic threats, and a better understanding of winter ecology of this subspecies would greatly aid conservation efforts and help mitigate potential harmful impacts to this subspecies. Specifically, this study will determine:

1. The timing and movement of birds to and from upper Cook Inlet
2. The size of the breeding population of the C. p. ptilocnemis subspecies
3. The proportion of this subpopulation using upper Cook Inlet sites during the non-breeding season
4. Biotic (body condition, food abundance, predator abundance) and abiotic (temperature, ice and snow cover) factors that affect Rock Sandpiper usage of upper Cook Inlet sites during the non-breeding season

To address these questions, we will collect information on the body condition, daily energy expenditure, time budget, and foraging techniques employed by these birds at these sites. Between-site comparisons will quantify the relative importance of food abundance, predator abundance, and local site conditions, and how these factors influence body condition and small-scale movements. Upper Cook Inlet has long been recognized as a key resource to migrating and breeding shorebirds (Gill and Tibbitts 1999), but only recently has the surprising value of this region been recognized for Alaska’s shorebirds during the winter. A better understanding of this unusual shorebird’s winter ecology will greatly inform conservation efforts about this species and enhance the public’s appreciation of this unique Alaskan natural resource.