Coping with the Cold: An Ecological Context for the Abundance and Distribution of Rock Sandpipers during Winter in Upper Cook Inlet, Alaska

Abstract

Shorebirds are conspicuous and abundant at high northern latitudes during spring and summer, but as seasonal conditions deteriorate, few remain during winter. To the best of our knowledge, Cook Inlet, Alaska (60.6˚ N, 151.6˚ W), is the world's coldest site that regularly supports wintering populations of shorebirds, and it is also the most northerly nonbreeding location for shorebirds in the Pacific Basin. During the winters of 1997 -2012, we conducted aerial surveys of upper Cook Inlet to document the spatial and temporal distribution and number of Rock Sandpipers (Calidris ptilocnemis) using the inlet. The average survey total was 8191 ± 6143 SD birds, and the average of each winter season's highest single-day count was 13 603 ± 4948 SD birds. We detected only Rock Sandpipers during our surveys, essentially all of which were individuals of the nominate subspecies (C. p. ptilocnemis). Survey totals in some winters closely matched the population estimate for this subspecies, demonstrating the region's importance as a nonbreeding resource to the subspecies. Birds were most often found at only a handful of sites in upper Cook Inlet, but shifted their distribution to more southerly locations in the inlet during periods of extreme cold. Two environmental factors allow Rock Sandpipers to inhabit Cook Inlet during winter: 1) an abundant bivalve (Macoma balthica) food source and 2) current and tidal dynamics that keep foraging substrates accessible during all but extreme periods of cold and ice accretion. C. p. ptilocnemis is a subspecies of high conservation concern for which annual winter surveys may serve as a relatively inexpensive population-monitoring tool that will also provide insight into adaptations that allow these birds to exploit high-latitude environments in winter.

Ways to be different: foraging adaptations that facilitate higher intake rates in a northerly-wintering shorebird compared to a low-latitude conspecific

“…Rock sandpipers are the shorebird species with the most northerly nonbreeding distribution in the Pacific Basin, common at locations along the eastern Pacific coast from 61°N (Ruthrauff et al, 2013b) to ∼40°N (Gabrielson and Lincoln, 1959;Paulson, 1993). There are four recognized subspecies of rock sandpiper (American Ornithologists' Union, 1957;Conover, 1944) and the extremes of the species' nonbreeding distribution are occupied by ptilocnemis to the north and tschuktschorum to the south (Gill et al, 2002).…”

“…Ptilocnemis is distributed primarily on mudflat habitats in upper Cook Inlet, Alaska (61°N, 151°W) during winter (Gill et al, 2002;Ruthrauff et al, 2013b). The average daily temperatue in upper Cook Inlet is ≤0°C for nearly half the year, making this the coldest site regularly used by shorebirds (Ruthrauff et al, 2013c).…”

Identical metabolic rate and thermal conductance in Rock Sandpiper(Calidris ptilocnemis)subspecies with contrasting nonbreeding life histories

“…Because of migratory propensity and prevailing environmental conditions, the nonbreeding distributions of C. p. ptilocnemis and C. p. tschuktschorum represent the life-history extremes for the species. Calidris p. ptilocnemis (hereafter ptilocnemis) spends the nonbreeding season primarily in upper Cook Inlet, Alaska (61°N, 151°W; Ruthrauff et al 2013), a site with expansive mudflats and abundant food resources. In the winter, the mean daily temperature in this region is <0°C for nearly 5 months from November to March; consequently, the upper intertidal zone in Cook Inlet accretes with thick sea ice, and critical mudflat habitats become less accessible as the winter progresses (Ruthrauff et al 2013).…”

“…Calidris p. ptilocnemis (hereafter ptilocnemis) spends the nonbreeding season primarily in upper Cook Inlet, Alaska (61°N, 151°W; Ruthrauff et al 2013), a site with expansive mudflats and abundant food resources. In the winter, the mean daily temperature in this region is <0°C for nearly 5 months from November to March; consequently, the upper intertidal zone in Cook Inlet accretes with thick sea ice, and critical mudflat habitats become less accessible as the winter progresses (Ruthrauff et al 2013). By contrast, C. p. tschuktschorum (hereafter tschuktschorum) is distributed along the eastern North Pacific coast from about 59° to 37°N in winter (Gill et al 2002).…”

Birds of Middleton Island, a Unique Landfall for Migrants in the Gulf of Alaska

“…casual in fall, when up to four birds observed in late oct 2016 (BWR, RaM, LhD), but our understanding of this taxon's status at Middleton may be incomplete, as systematic searches of large flocks of Rock sandpipers were rarely undertaken. notes: nominate ptilocnemis-larger and paler than the other subspecies, with bolder wing stripe-winters primarily in cook inlet (see Gill 1997, Gill and Tibbitts 1999, Ruthrauff et al 2013) and has been recorded in winter at Kodiak island (uaM specimens) and homer (a. J. Lang, in litt., 2009). Beyond alaska it has been recorded as far east and south as Washington (aversa 2001).…”