The First Hop: Use of Beaufort Sea Deltas by Hatch-Year Semipalmated Sandpipers
River deltas along Alaska’s Beaufort Sea coast are used by hatch-year semipalmated sandpipers (Calidris pusilla) after leaving their terrestrial natal sites, but the drivers of their use of these stopover sites on the first “hop” of fall migration are unknown. We quantified sandpiper temporal distribution and abundance as related to food resources at three river deltas during the beginning of their fall migration (post-breeding period) to compare the habitat quality among these deltas. We conducted population counts, sampled invertebrates, and captured birds to collect blood samples from individuals for triglyceride and stable isotope analyses to determine fattening rates and diet. Patterns of sandpiper and invertebrate abundance were complex and varied among deltas and within seasons. River deltas were used by sandpipers from late July to late August, and peak sandpiper counts ranged from 1000 to 4000 individuals, of which 98% were hatch-year semipalmated sandpipers. Isotopic signatures from blood plasma samples indicated that birds switched from a diet of upland tundra to delta invertebrate taxa as the migration season progressed, suggesting a dependence on delta invertebrates. Despite differences in diet among deltas, we found no differences in fattening rates of juvenile sandpipers as indicated by triglyceride levels. The number of sandpipers was positively associated with abundance of Amphipoda and Oligochaeta at the Jago and Okpilak-Hulahula deltas; an isotopic mixing model indicated that sandpipers consumed Amphipoda and Oligochaeta at Jago, mostly Chironomidae at Okpilak-Hulahula and Spionidae at Canning. Regardless of the difference in sandpiper diets at the Beaufort Sea deltas, their similar fattening rates throughout the season indicate that all of these stopover sites provide a critical food resource for hatch-year sandpipers beginning their first migration.
KeywordsCalidris pusilla Fall migration Stopover Alaska Invertebrates Stable isotope Triglyceride
Study collaboration and funding were provided in part by the US Department of the Interior, Bureau of Ocean and Energy Management, Environmental Studies Program under Cooperative Agreement Number M11AC00006. The National Fish and Wildlife Foundation, US Fish and Wildlife Service Arctic National Wildlife Refuge, Arctic Landscape Conservation Cooperative, US Geological Survey Alaska Cooperative Fish and Wildlife Research Unit, Institute of Arctic Biology, and Manomet Conservation Sciences provided additional funding and logistical support. Bureau of Ocean and Energy Management required approval of the final manuscript before submission or publication. We thank the many dedicated field technicians who helped collect samples. We had lab support from the Mark Wipfli aquatic invertebrate lab, Alaska Stable Isotope Facility, and the Alaska Sealife Center. We are also thankful to the Kaktovik Inupiat Corporation for letting us conduct research on their lands and the people of the village of Kaktovik for their help and friendship. We thank Dan Ruthrauff, Jim Lovvorn, Shiway Wang, and one anonymous reviewer for their thoughtful reviews of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. This study was performed under the auspices of University of Alaska, Fairbanks IACUC approval #148889.
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