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Diet of Calidris maritima (Purple Sandpiper) during the Winter in Nova Scotia, Canada
Mark L. Mallory, Mark F. Elderkin, Nora C. Spencer, Taylor A. Betsch, Amy C. Russell, and Pamela L. Mills

Northeastern Naturalist, Volume 23, Issue 2 (2016): 205–210

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Northeastern Naturalist Vol. 23, No. 2 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 205 2016 NORTHEASTERN NATURALIST 23(2):205–210 Diet of Calidris maritima (Purple Sandpiper) during the Winter in Nova Scotia, Canada Mark L. Mallory1,*, Mark F. Elderkin2, Nora C. Spencer1, Taylor A. Betsch1, Amy C. Russell1, and Pamela L. Mills2 Abstract - Calidris maritima (Purple Sandpiper) is a shorebird found along northern coasts of Europe and eastern North America during the winter. While its winter diet is well known in Europe, the only North American study examining diet included 5 individuals and suggested a narrow diet focused on Littorina spp. (periwinkles). We examined the diet of Purple Sandpipers wintering at several sites in Nova Scotia, Canada, during 2013, and found that the birds consumed a broad variety of items, though principally marine invertebrates, dominated by periwinkles and Mytilus edulis (Blue Mussel), but also many arthropods. Our study confirms the importance of mollusks in the diet of this species and also indicates that Purple Sandpipers in North America have a similar winter diet to those studied in Europe. Introduction Calidris maritima (Brünnich) (Purple Sandpiper) is a medium-sized shorebird that breeds across most of the Arctic and winters in coastal northern Europe, Iceland, Greenland, and locations along northeastern North America from Newfoundland south through Virginia (Payne and Pierce 2002). It is the northernmost wintering shorebird (Summers et al. 1998). Unlike many other shorebirds, it is notable for using rocky intertidal habitats during the winter, including offshore islets (Summers et al. 2002). At these sites, foraging Purple Sandpipers are often associated with various seaweeds (e.g., Mastocarpus sp. [false Irish moss], Laminaria sp., [kelp], Fucus sp. [bladderwrack]; Summers et al. 2002). There have been suggestions that the Purple Sandpiper population has been declining at least in some areas, but the birds are notoriously difficult to see and count, and population estimates are reported with very large confidence intervals (e.g., Mittelhauser et al. 2014). Nonetheless, oiling of birds, disturbance at roosting and feeding sites, and harvest of Ascophyllum nodosum L. (Rockweed) are all currently considered threats to wintering Purple Sandpipers or their feeding sites in eastern North America (Payne and Pierce 2002, Smith and Bleakney 1969). The diet of Purple Sandpipers has been well studied during the breeding season, notably from Greenland, Iceland, and Svalbard, Norway (Bengtson and Fjellberg 1975, Cramp and Simmons 1983, Salomonsen 1950). During this stage of the annual cycle, the birds feed principally on insects (dipterans, hemipterans, and hymenopterans) as well as collembolans and spiders, but also may consume 1Biology Department, Acadia University, 15 University Drive, Wolfville, NS, B4P 2R6, Canada. 2Department of Natural Resources, 136 Exhibition Street, Kentville, NS, B4N 4E5, Canada. *Corresponding author - Manuscript editor: Greg Robertson Northeastern Naturalist 206 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 Vol. 23, No. 2 gastropods, annelid worms, and plant matter, depending on the location (reviewed in Payne and Pierce 2002). Similarly, the diet in the winter has been studied in Europe (Feare 1966, Summers et al. 1990), where observations show that Purple Sandpipers shift their diet to one dominated by marine gastropods and bivalves, as well as crustaceans, annelid worms, and occasionally insects and plant material (Dierschke 1993, Petersen 1973, Strann and Summers 1990). In contrast to these studies, there is a marked paucity of information on the winter diet of Purple Sandpipers in North America, with data coming from a single study of only 5 birds (Smith and Bleakney 1969). As part of a project to examine aspects of the phylogeography of Purple Sandpipers wintering in coastal Nova Scotia (Leblanc 2015), we were interested in gathering better information on their diet. In particular, we wanted to determine if Purple Sandpipers specialized on any prey item in this region, as suggested by Smith and Bleakney (1969), or whether they typically had a more catholic diet irrespective of study site (as suggested by the studies above). We also sought to compare the diet of Purple Sandpipers in Nova Scotia to the known diet of this species wintering in various locations in Europe. Field-site Description We collected 25 Purple Sandpipers in March 2013 at 5 locations around coastal Nova Scotia: Bon Portage and Duck islands (43°28'N, 65°45'W), Grey Island (43°36'N, 65°18'W), Little Hope Island (43°48.5'N, 64°47'W), Bowens Ledge (44°52'N, 62°9'W), and Flat Ledge, Tor Bay (45°13'N, 61°13'W). These sites were coastal but included rock ledges that were exposed for portions of the day depending on the tidal cycle, as well as wind, fetch, and sea condition (i.e., key wintering habitat of Purple Sandpipers; Payne and Pierce 2002, Summers et al. 2002). We conducted our sampling in a restricted window of opportunity at each location; thus, there may be some bias in our sampling, given that some marine invertebrates (notably mollusks) partition intertidal habitats (e.g., Feare 1966, MacDonald 1969) and are only available for portions of the tidal cycle (which may not match the time when we sampled). Furthermore, we did not assess whether Purple Sandpipers were actively foraging prior to collection; our priority was to obtain birds for a genetic study (Leblanc 2015), so the dietary examination was an opportunistic project added on to the primary research. We collected the birds with a 20-gauge shotgun using steel shot, and froze the carcasses at -20 °C within 12 h. We did not immediately pour ethanol into their digestive systems, so some soft-bodied prey could have been digested during this 12-h period. Methods We weighed and froze the Purple Sandpiper carcasses in the field, and transported them to Acadia University, Wolfville, NS. We thawed, reweighed, and removed the proventriculus and gizzard from all samples. We opened and rinsed these parts of the digestive tract, collected all materials therein, and placed the collected food Northeastern Naturalist Vol. 23, No. 2 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 207 items in vials filled with 95% ethanol. These materials consisted primarily of hard parts of ingested prey—columella, paired hinges, and complete or incomplete shells of molluscs, head cases of insects, and other identifiable materials of invertebrates or plants (Table 1). We examined the dietary materials under a dissecting microscope and identified them to the lowest taxonomic level possible using voucher specimens stored at Acadia University for reference and a key to local inshore and mudflat flora and fauna of the Bay of Fundy (Bromley and Bleakney 1985). In an effort to generate conservative, minimum estimates, and to the extent possible, we reassembled hard parts to count how many individuals had been consumed. Results All Purple Sandpipers appeared healthy; the birds had a mean mass of 71.5 g ± 1.4 SE (range = 59.3–92.0). We found 1020 items in the proventriculi and gizzards of the 25 Purple Sandpipers, 653 (64%) of which were organic material and 367 (36%) were grit; no pieces of plastic debris were observed. We found grit in 24 of 25 birds. Nearly all of the organic material was animal prey; traces of marine algae (Corallina officinalis L. [Common Coral Weed]) were found in 4 birds from Little Table 1. Items found in the digestive tract of 25 Purple Sandpipers collected around Nova Scotia, Canada, in winter 2013. Five sandpipers were collected at each sampling location. BP = Bon Portage and Duck islands, GI = Grey Island, LHI = Little Hope Island, BL = Bowens Ledge, and FL = Flat Ledge. We have included whether the dietary taxon was present (P) in birds sampled, and then have pooled data across sites (overall %) to describe the general winter diet of Purple Sandpipers in Nova Scotia. Percent occurrence refers to the percentage of birds that had eaten at least 1 of the items, whereas percent frequency refers to the percentage of each type of prey out of all organic items identified (plant + animal material). Sampling Location Overall % Dietary item BP GI LHI BL FL Occurrence Frequency Mollusca 100 82 Unknown mollusk P P P P P 84 18 Bivalves 84 26 Mytilus edulis P P P P P 72 16 Unknown bivalve P P P P P 40 8 Gastropods 100 40 Littorina littorea P P P P P 56 5 Littorina saxatilis P P P P 32 6 Littorina obtusata P P P P 40 3 Margarites helicinus P 4 1 Lacuna vincta (Montagu) P P P 20 1 Nucella lapillus P P P P 28 4 Unknown gastropod P P P P 80 22 Arthropoda 28 14 Brachyura P P 16 3 Gammaridae P P P 16 1 Chironomidae larvae P P 16 10 Corallina officinalis P P 16 1 Unknown organic material P P P 20 3 Northeastern Naturalist 208 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 Vol. 23, No. 2 Hope Island and comprised <1% of the total items. The Purple Sandpipers had 27 ± 3.2 SE (range = 3–64) food items in their digestive tracts, which represented a mean taxonomic richness (number of different identifiable taxa) of 4.8 ± 0.4 (range = 2–9). All birds had remains of mollusks and undigested parts of at least 1 gastropod (principally Littorina spp. [periwinkles]), and most had remains of at least 1 bivalve (principally Mytilus edulis L. [Blue Mussel]) as well as other, unknown bivalve remains (Table 1). Approximately 1 in 4 Purple Sandpipers had arthropod remains, which consisted of crabs, amphipods or insect larvae (chironomids); these items were all in birds collected near Grey Island. Discussion We anticipated that a new analysis of Purple Sandpipers’ winter diet in Nova Scotia might suggest that they have a more catholic consumption of prey items than indicated in previous work (Smith and Bleakney 1969). Certainly during the breeding season, the diet of Purple Sandpipers varies markedly by the habitat the birds occupy (Bengston and Fjellberg 1975); principal prey varies from insects to mollusks depending on the sampling location. Feare’s (1966) observations of Purple Sandpipers wintering in the UK suggested that they consumed almost entirely gastropods—Littorina littorea L. (Common Periwinkle), L. saxatilis (Olivi) (Rough Periwinkle), Nucella lapillus L. (Dog Whelk), and a few other periwinkles—and Blue Mussels. However, that study was based principally on observed fecal remains, which would bias observations towards those materials that passed through the gut relatively undigested. A more recent analysis of Purple Sandpiper winter diet in the UK from 8 different sampling locations found that the birds consumed >30 taxa (Summers et al. 1990). Gastropods still predominated in the winter diet, but in some locations, such as banks of cast seaweed at the high-water mark, Purple Sandpipers relied considerably on Coleopa flies, amphipods, or occasionally polychaete worms. Our sampling in Nova Scotia increased by at least 8 the number of species known to be eaten by Purple Sandpipers wintering in North America. The food items we documented include some of the organisms consumed by Purple Sandpipers in the winter in Europe (Cramp and Simmons 1983, Payne and Pierce 2002, Summers et al. 1990), including Blue Mussel, Common Periwinkle, Margarites helicinus (Phipps) (Pearly Top Shell), Lacuna sp. (sea snails), Gammarus sp. (a scud), Common Coral Weed, small crabs, and insects. Moreover, our data on ingested organisms per bird (5 species and 27 prey items) were similar to those from studies in the UK. Feare (1966) found 6 species but 10–20 individual items consumed per bird, while Summers et al. (1990) found ~7 species in birds at each sampling location and ~19 items per bird (calculated from tables and graphs in these papers). Smith and Bleakney (1969) found that Purple Sandpipers in Nova Scotia ate Rough Periwinkle and L. obtustata L. (Flat Periwinkle), but there was no evidence of Common Periwinkle in their 5 samples taken from the Bay of Fundy region. They suggested that Purple Sandpipers might avoid the thicker-shelled Common Periwinkle because it might be more difficult to crush in the gizzard. In contrast Northeastern Naturalist Vol. 23, No. 2 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 209 to their results, we found that Common Periwinkle was the most commonly consumed periwinkle; Summers et al. (1990) also found this species was often eaten at multiple locations in the UK. Smith and Bleakney (1969) had evidence that Purple Sandpipers at their sites were eating Semibalanus balanoides L. (Acorn Barnacle), but we found no remains of this species in our samples from 5 different locations in Nova Scotia, and Summers et al. (1990) found only a trace of this barnacle in Purple Sandpipers from 1 site in the UK. We speculate that Purple Sandpipers may eat barnacles during times of food stress. Consistent with recent findings on the diet of migrating Calidris pusilla L. (Semipalmated Sandpipers; Gerwing et al. 2016), we suspect that many shorebirds foraging in the winter rely on more components of coastal ecosystems than previously considered. Estimates of diet-item diversity are likely low because soft-bodied organisms tend to be under-represented in studies based on dissection of birds (e.g., Barrett et al. 2007), such that many traditional studies (including our work) probably missed some prey that were digested quickly. Modern genetic techniques (e.g., Gerwing et al. 2016) will continue to provide new insights into this aspect of diet composition. Furthermore, ours is only the second study in North America to examine the winter diet of Purple Sandpipers, and ours employed a larger sample size than Smith and Bleakney (1969), which may partly explain the increase in diversity of winter prey that we observed. Given the broad latitudinal wintering range of this species, it is likely that Purple Sandpipers show considerable regional variation in their winter diet in North America. We note that we found no plastic debris in the guts of any of these Purple Sandpipers. This pollutant is now ubiquitous in marine environments (Provencher et al. 2014) and has recently been found in some coastal-wintering waterfowl (English et al. 2015) in habitats similar to those used by Purple Sandpipers. We encourage any researchers conducting dissections to monitor plastic consumption by wildlife to track the spread of this environmental contaminant. Acknowledgments We thank the personnel who assisted with field collections and dissections, Natalie Leblanc and Don Stewart for project support, and 2 anonymous referees for insightful comments on the manuscript. Financial support was provided by the Nova Scotia Department of Natural Resources and the Canada Research Chairs (MLM). All collections were conducted under animal care (ACC 12JP01) and scientific permits (CWS SC278 4). Literature Cited Barrett, R.T., C.J. Camphuysen, T. Anker-Nilssen, J.W. Chardine, R.W. Furness, S. Garthe, O. Huppop, M.F. Leopold, W.A. Montevecchi, and R.R. Veit. 2007. Diet studies of seabirds: A review and recommendations. ICES Journal of Marine Science 64:1675–1691. Bengtson, S.A., and A. Fjellberg. 1975. Summer food of the Purple Sandpiper (Calidris maritima) in Spitsbergen. Astarte 8:1–6. Bromley, J.E.C., and J.S. Bleakney. 1985. Keys to the fauna and flora of the Minas Basin. National Research Council, Atlantic Research Laboratory, Wolfville, NS. NRCC 241119. NR16-11/1985E. 366 pp. Northeastern Naturalist 210 M.L. Mallory, M.F. Elderkin, N.C. Spencer, T.A. Betsch, A.C. Russell, and P.L. Mills 2016 Vol. 23, No. 2 Cramp, S., and K.E.L. Simmons. 1983. The birds of the Western Palearctic, Vol. 3: Waders to Gulls. Oxford University Press, Oxford, UK. 913 pp. Dierschke, V. 1993. 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