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Habitat switching by Bewick's swans: maximization of average long-term energy gain?

  1. B. A. Nolet1,*,
  2. R. M. Bevan2,
  3. M. Klaassen1,
  4. O. Langevoord1,
  5. Y. G. J. T. Van Der Heijden1,3

Article first published online: 1 NOV 2002

DOI: 10.1046/j.1365-2656.2002.00662.x

Issue

Journal of Animal Ecology

Journal of Animal Ecology

Volume 71, Issue 6, pages 979–993, November 2002

Additional Information

How to Cite

Nolet, B. A., Bevan, R. M., Klaassen, M., Langevoord, O. and Van Der Heijden, Y. G. J. T. (2002), Habitat switching by Bewick's swans: maximization of average long-term energy gain?. Journal of Animal Ecology, 71: 979–993. doi: 10.1046/j.1365-2656.2002.00662.x

Author Information

  1. 1

    Department of Plant–Animal Interactions, Centre for Limnology, Netherlands Institute of Ecology, Royal Netherlands Academy of Arts and Sciences (NIOO-KNAW), PO Box 1299, 3600 BG Maarssen, the Netherlands;

  2. 2

    Department of Agricultural and Environmental Science, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK; and

  3. 3

    Department of Ecology, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, the Netherlands

* B.A. Nolet, Centre for Limnology, NIOO-KNAW, PO Box 1299, 3600 BG Maarssen, the Netherlands; Tel. + 31-294-239318; Fax: + 31-294-232224; E-mail: b.nolet@nioo.knaw.nl

Publication History

  1. Issue published online: 1 NOV 2002
  2. Article first published online: 1 NOV 2002
  3. Received 18 February 2002; accepted 20 June 2002

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Keywords:

  • Cygnus columbianus bewickii;
  • depletion;
  • habitat shift;
  • Potamogeton pectinatus;
  • time–energy budget

Summary

  • 1
    In a system where depletion drives a habitat shift, the hypothesis was tested that animals switch habitat as soon as the average daily net energy intake (or gain) drops below that attainable in the alternative habitat.
  • 2
    The study was performed in the Lauwersmeer area. Upon arrival during the autumn migration, Bewick's swans first feed on below-ground tubers of fennel pondweed on the lake, but subsequently switched to feeding on harvest remains in sugar beet fields.
  • 3
    The daily energy intake was estimated by multiplying the average time spent foraging per day with the instantaneous energy intake rate while foraging. In the case of pondweed feeding, the latter was estimated from the functional response and the depletion of tuber biomass. In the case of beet feeding, it was estimated from dropping production rate. Gross energy intake was converted to metabolizable energy intake using the assimilation as determined in digestion trials. The daily energy expenditure was estimated by the time–energy budget method. Energetic costs were determined using heart rate.
  • 4
    The daily gain of pondweed feeding at the median date of the habitat switch (i.e. when 50% of the swans had switched) was compared with that of beet feeding. The daily gain of beet feeding was calculated for two strategies depending on the night activity on the lake: additional pondweed feeding (mixed feeding) or sleeping (pure beet feeding).
  • 5
    The majority of the swans switched when the daily gain they could achieve by staying on the pondweed bed fell just below the average daily gain of pure beet feeders. However, mixed feeders would attain an average daily gain considerably above that of pondweed feeders. A sensitivity analysis showed that this result was robust.
  • 6
    We therefore reject the hypothesis that the habitat switch by swans can be explained by simple long-term energy rate maximization. State-dependency, predation risk, and protein requirements are put forward as explanations for the delay in habitat switch.
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