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Foraging conditions ‘at the end of the world’ in the context of long-distance migration and population declines in red knots

Authors

  • GRACIELA ESCUDERO,

    1. Área de Biología y Manejo de Recursos Acuáticos, Centro Nacional Patagónico, Puerto Madryn, Argentina
    2. Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
    3. Department of Conservation Biology, Estación Biológica de Doñana – CSIC, Sevilla, Spain (Email: gescudero@cenpat.edu.ar or gra_aves2@yahoo.com)
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  • JUAN G. NAVEDO,

    1. Conservation Biology Research Group, Universidad de Extremadura, Badajoz, Spain
    2. Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Mazatlán, Sinaloa, México
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  • THEUNIS PIERSMA,

    1. Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen
    2. Department of Marine Ecology, Royal Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands
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  • PETRA DE GOEIJ,

    1. Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen
    2. Department of Marine Ecology, Royal Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands
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  • PIM EDELAAR

    1. Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
    2. Department of Conservation Biology, Estación Biológica de Doñana – CSIC, Sevilla, Spain (Email: gescudero@cenpat.edu.ar or gra_aves2@yahoo.com)
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Abstract

The long-distance migrant red knot (Calidris canutus ssp. rufa– Scolopacidae) alternates between the northern and southern ends of the New World, one of the longest yearly migrations of any bird and paradoxically overflying apparently suitable habitat at lower latitudes. This subspecies is sharply declining, with a major mortality event following 2000, attributed to commercial overharvesting of food resources at its Delaware Bay (USA) stop-over site. A full understanding of this peculiar migrant requires an assessment of the foraging conditions at its southern hemisphere wintering sites. Here, for a major wintering site in Argentinean Tierra del Fuego (Río Grande), we describe and compare food abundance, diet and intake rates during January–February in 1995, 2000 and 2008. The two main prey types were the burrowing clam Darina solenoides and three species of epibenthic mussels Mytilidae. In the year 2000, food availability and intake rate were higher than those recorded at other sites used by knots anywhere else in the world, contributing to the explanation of why red knots carry out this impressive migration. Intake rate in 2008 on the two main prey types was dramatically reduced as a result of birds eating smaller prey and strongly increased human disturbance; the same year we also found a high prevalence of a digenean parasite in Darina. We suggest that during the strongly enhanced winter mortality in 2000, knots did not yet face ecological problems in their southernmost wintering area, consistent with the previous evidence that problems at northern stop-overs negatively affected their numbers. However, in 2008 the ecological conditions at Río Grande were such that they would have facilitated a further decline, emphasizing the importance of a hemispheric approach to research and management.

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