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Unravelling the migration and moult strategies of a long-distance migrant using stable isotopes: Red Knot Calidris canutus movements in the Americas

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For long-distance migrants, such as many of the shorebirds, understanding the demographic implications of behavioural strategies adopted by individuals is key to understanding how environmental change will affect populations. Stable isotopes have been used in the terrestrial environment to infer migratory strategies of birds but rarely in marine or estuarine systems. Here, we show that the stable isotope ratios of carbon and nitrogen in flight feathers can be used to identify at least three discrete wintering areas of the Red Knot Calidris canutus on the eastern seaboard of the Americas, ranging from southeastern USA to Patagonia and Tierra del Fuego. In spring, birds migrate northwards via Delaware Bay, in the northeastern USA, the last stopping point before arrival in Arctic breeding areas, where they fatten up on eggs of spawning Horseshoe Crabs Limulus polyphemus. The isotope ratios of feather samples taken from birds caught in the Bay during May 2003 were compared with feathers obtained from known wintering areas in Florida (USA), Bahia Lomas (Chile) and Rio Grande (Argentina). In May 2003, 30% of birds passing through the Bay had Florida-type ‘signatures’, 58% were Bahia Lomas-type, 6% were Rio Grande-type and 7% were unclassified. Some of the southern wintering birds had started moulting flight feathers in northern areas, suspended this, and then finished their moult in the wintering areas, whereas others flew straight to the wintering areas before commencing moult. This study shows that stable isotopes can be used to infer migratory strategies of coastal-feeding shorebirds and provides the basis for identifying the moult strategy and wintering areas of birds passing through Delaware Bay. Coupled with banding and marking birds as individuals, stable isotopes provide a powerful tool for estimating population-specific demographic parameters and, in this case, further our understanding of the migration systems of the declining Nearctic populations of Red Knot.
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Document Type: Research Article

Affiliations: 1: Centre for Biodiversity and Conservation Biology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 1C6, Canada and, Department of Zoology, University of Toronto, Queen's Park, Ontario, Canada 2: University of Newcastle, School of Biology, King George VI Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK 3: British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK 4: Delaware Coastal Programs, Division of Soil and Water Conservation, DNREC, 89 Kings Highway, Dover, DE 19901, USA 5: Fundación Inalafquen, Pedro Morón 385 (8520) San Antonio Oeste, Río Negro, Argentina 6: NERC Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK 7: Endangered and Nongame Species Program, New Jersey Division of Fish and Wildlife, PO Box 400, Trenton, NJ 08625, USA

Publication date: 01 October 2005

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