Feather isotope analysis discriminates age-classes of Western, Least, and Semipalmated sandpipers when plumage methods are unreliable |
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Authors: | Samantha E Franks David B Lank D Ryan Norris Brett K Sandercock Caz M Taylor T Kurt Kyser |
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Institution: | Centre for Wildlife Ecology, Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada;Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada;Division of Biology, Kansas State University, Manhattan, KS 66506-4901, USA;Queen's Facility for Isotope Research, Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON K7L 3N6, Canada |
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Abstract: | ABSTRACT Avian age‐class discrimination is typically based on the completeness of the first prebasic molt. In several calidrid sandpiper species, juvenal flight feathers grown on Arctic breeding grounds are retained through the first three migrations. Thereafter, flight feathers are grown annually at temperate migratory stopover sites during the fall or on the subtropical wintering grounds. Standard methods for distinguishing age classes of sandpipers rely on a combination of traits, including body plumage, coloration of protected inner median covert edges, and extent of flight feather wear. We tested the ability of stable hydrogen isotope ratios in flight feathers (δDf) to distinguish young birds in their first winter through second fall from older adults in three calidrid sandpiper species, Western (Calidris mauri), Least (C. minutilla), and Semipalmated (C. pusilla) sandpipers. We compared the apparent reliability of the isotope approach to that of plumage‐based aging. The large expected differences in δDf values of flight feathers grown at Arctic versus non‐Arctic latitudes enabled use of this technique to discriminate between age‐classes. We determined δDf values of known Arctic‐grown feathers from juveniles that grew their flight feathers on the breeding grounds. Flight feather δDf values of southward‐migrating adults showed bimodal distributions for all three species. Negative values overlapped with species‐specific juvenile values, identifying putative second fall birds with high‐latitude grown juvenal feathers retained from the previous year. The more positive values identified older adults who grew their feathers at mid‐ and low latitudes. Importantly, δDf analysis successfully identified first‐winter and second‐fall birds not detected by plumage‐based aging. Flight feather wear alone was a poor basis for age classification because scores overlapped extensively between putative second fall birds and older adults. Flight feather hydrogen isotope analysis enables more definitive assignment of age classes when standard plumage methods are unreliable. |
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Keywords: | age-class discrimination Calidris mauri Calidris minutilla Calidris pusilla deuterium hydrogen molt shorebird stable isotope analysis |
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