SANDERLING (CALIDRIS ALBA) POPULATION STRUCTURE AND POLLUTANT EXPOSURE AT MAJOR WINTER AND MIGRATORY STOPOVER SITES INCLUDING CHAPLIN LAKE, SASKATCHEWAN

Sanderling (Calidris alba) are a long distance migratory shorebird species found across a large range of coastal winter sites throughout North, Central and South America. As with many of the long distance migrant shorebirds, Sanderling have experienced significant population declines during the past 30 years, possibly due to pollution and other anthropogenic threats at wintering and migratory stopover sites. Sanderlings annually fly from their winter grounds to Arctic nesting grounds in Canada, migrating in an elliptical pattern, with significant numbers using the Central flyway in spring. This study aims to identify the population structure and wintering origins of Sanderlings that migrate northward along the Central flyway and stop in large numbers at Chaplin Lake, Saskatchewan, Canada. Despite the lack of research, this site is recognized for its hemispheric importance for shorebirds, particularly Sanderling (WHRSN Category 1). It also aims to identify the extent shorebirds are exposed to dioxins and dioxin-like compounds (DLCs), at selected stopovers across their range in North and South America to ultimately link the migratory patterns and potential risks of exposure to these contaminants. Over 400 Sanderling were captured, measured and banded in Chaplin Lake, Saskatchewan on spring migration from 2012-2015. A total of 29 Sanderlings banded in Chaplin Lake were resighted, mostly during autumn migration following the elliptical migratory pathway along the east coast of North America, indicating band resightings alone were insufficient to determine wintering origin. A primary (P5) covert feather was sampled from 283 birds for stable isotope (δ15N, δ13C and δ2H) analysis to infer the population structure and possible differences in winter origin. Additionally, feathers from 73 Sanderlings from Padre Island, Texas were similarly analyzed because birds from Texas Gulf coast were hypothesized to use the same migratory pathway as the Chaplin Lake population. Through a combination of isotopes, 3 distinct clusters of Sanderling were identified within the Chaplin Lake population, suggesting birds at this stopover winter over a broad geographic area. Clusters 1, 2, and 3 represented 28, 50, and 22% of Chaplin Lake population, respectively. The probability of the Texas Sanderling samples belonging to one of the three previously determined clusters was also estimated. The percentage of Padre Island, Texas birds assigned to clusters 1, 2, and 3 was 19, 25, and 56% respectively, implying strong overlap between populations. Using a combination of feather isotopic values, body morphometrics, known distributions and previously reported isotope data suggested possible origins of cluster 1, 2, and 3 as southern South America (e.g. Chile or Argentina), northwestern South America (e.g. Peru), and the Gulf of Mexico (e.g. Texas), respectively. In order to assess the extent shorebirds are exposed to DLCs and conduct a preliminary hazard assessment, sediment samples were obtained from a set of wintering and stopover sites in North and South America to ultimately characterize potential toxicity risks. Sediment samples from migratory stopover or wintering sites in Canada, The United States, Colombia, Ecuador, Uruguay and Brazil were collected in partnership with local shorebird researchers. Following extraction, a novel application of the in vitro Luciferase bioassay method was used to assess the potency of the sediment extracts to activate the aryl hydrocarbon receptor (AhR) in the H4IIE-Luc cell line. Toxic induction of sediments ranged from 11.11 in Aracaju, Brazil to 20.43 pM 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent (TCDD-EQ) in Padre Island, Texas. Although 5 out of 8 sites showed TCDD-EQ values significantly above controls, all samples analyzed had concentrations of TCDD in sediment below published USEPA regulatory limits. Calculated TCDD exposure from the most contaminated site, Padre Island, was estimated to range from 0.0009 ng TCDD-EQ /day for a larger Willet (Catoptrophorus semipalmatus) to 0.0203 ng TCDD-EQ /day in a small Semipalmated sandpiper (Calidris pusilla), which is below published toxicity hazard thresholds for birds. However, these results should be interpreted with caution, since sediment ingestion was the only route of exposure considered, whereas contaminants in the invertebrate diet may be more important. The information collected about Sanderling migration ecology and connectivity has revealed new insight into the population structure and potential wintering origins at a key stopover site in the Central flyway. It is also an important step to determine the potential contaminant threats that shorebirds face during the annual cycle, specifically from DLCs caused by industrial pollution across their migratory range. This provides a basis to guide future work to determine the health and specific contaminant levels of this migratory shorebird population in the Central flyway which spends part of its annual cycle in diverse coastal areas of North, Central and South America.

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