Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system
We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans' attack rates, foraging costs and giving-up densities (GUDs) in natural and experimental food patches that d...
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ftunivwagenin:oai:library.wur.nl:wurpubs/372884 2024-02-04T09:59:58+01:00 Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system Nolet, B.A. Fuld, V.N. van Rijswijk, M.E.C. 2006 application/pdf https://research.wur.nl/en/publications/foraging-costs-and-accessibility-as-determinants-of-giving-up-den https://doi.org/10.1111/j.0030-1299.2006.13463.x en eng https://edepot.wur.nl/22184 https://research.wur.nl/en/publications/foraging-costs-and-accessibility-as-determinants-of-giving-up-den doi:10.1111/j.0030-1299.2006.13463.x info:eu-repo/semantics/restrictedAccess Wageningen University & Research Oikos 112 (2006) 2 ISSN: 0030-1299 aythya-fuligula bewicks swans competition european starlings food patch assessment predation wadden sea wading birds white sea info:eu-repo/semantics/article Article/Letter to editor info:eu-repo/semantics/publishedVersion 2006 ftunivwagenin https://doi.org/10.1111/j.0030-1299.2006.13463.x 2024-01-10T23:25:20Z We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans' attack rates, foraging costs and giving-up densities (GUDs) in natural and experimental food patches that differed in water depth. Unlike most studies that attribute habitat-specific differences in GUDs to predation risk, food quality or foraging substrate, we quantified the relative importance of energetic costs and accessibility. Accessibility is defined as the extent to which the animal's morphology restricts its harvest of all food items within a food patch. Patch use behaviours were measured at shallow (ca 0.4 m) and deep (ca 0.6 m) water depths on sandy sediments. In a laboratory foraging experiment, when harvesting food patches, the swan's attack rate (m3 s¿1) did not differ between depths. In deep water the energetic costs of surfacing, feeding and trampling were 1.13 to 1.21 times higher than in shallow water with a tendency to spend relatively more time trampling, the most expensive activity. Taking time allocation as measured in the field into account, foraging in deep water was 1.26 times as expensive as in shallow water. In the lake the GUD in shallow water was on average 12.9 g m¿2. If differences in energetic costs were the only factor determining differences in GUDs, then the deep water GUD should be 14.2 g m¿2. Instead, the mean GUD in deep water was 20.2 g m¿2, and therefore energetic costs explain just 18% of the difference in GUDs. At deep sites, 24% of tuber biomass was estimated to be out of reach, and we calculated a maximum accessible foraging depth of 0.86 m. This is close to the published 0.84 m based on body measurements. A laboratory experiment with food offered at a depth of 0.89 m confirmed that it was just out of reach. The agreement between calculated and observed maximum accessible foraging depths suggests that accessibility largely explains the remaining difference in GUDs with depth, and it ... Article in Journal/Newspaper Cygnus columbianus White Sea Wageningen UR (University & Research Centre): Digital Library White Sea Oikos 112 2 353 362 |
institution |
Open Polar |
collection |
Wageningen UR (University & Research Centre): Digital Library |
op_collection_id |
ftunivwagenin |
language |
English |
topic |
aythya-fuligula bewicks swans competition european starlings food patch assessment predation wadden sea wading birds white sea |
spellingShingle |
aythya-fuligula bewicks swans competition european starlings food patch assessment predation wadden sea wading birds white sea Nolet, B.A. Fuld, V.N. van Rijswijk, M.E.C. Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
topic_facet |
aythya-fuligula bewicks swans competition european starlings food patch assessment predation wadden sea wading birds white sea |
description |
We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans' attack rates, foraging costs and giving-up densities (GUDs) in natural and experimental food patches that differed in water depth. Unlike most studies that attribute habitat-specific differences in GUDs to predation risk, food quality or foraging substrate, we quantified the relative importance of energetic costs and accessibility. Accessibility is defined as the extent to which the animal's morphology restricts its harvest of all food items within a food patch. Patch use behaviours were measured at shallow (ca 0.4 m) and deep (ca 0.6 m) water depths on sandy sediments. In a laboratory foraging experiment, when harvesting food patches, the swan's attack rate (m3 s¿1) did not differ between depths. In deep water the energetic costs of surfacing, feeding and trampling were 1.13 to 1.21 times higher than in shallow water with a tendency to spend relatively more time trampling, the most expensive activity. Taking time allocation as measured in the field into account, foraging in deep water was 1.26 times as expensive as in shallow water. In the lake the GUD in shallow water was on average 12.9 g m¿2. If differences in energetic costs were the only factor determining differences in GUDs, then the deep water GUD should be 14.2 g m¿2. Instead, the mean GUD in deep water was 20.2 g m¿2, and therefore energetic costs explain just 18% of the difference in GUDs. At deep sites, 24% of tuber biomass was estimated to be out of reach, and we calculated a maximum accessible foraging depth of 0.86 m. This is close to the published 0.84 m based on body measurements. A laboratory experiment with food offered at a depth of 0.89 m confirmed that it was just out of reach. The agreement between calculated and observed maximum accessible foraging depths suggests that accessibility largely explains the remaining difference in GUDs with depth, and it ... |
format |
Article in Journal/Newspaper |
author |
Nolet, B.A. Fuld, V.N. van Rijswijk, M.E.C. |
author_facet |
Nolet, B.A. Fuld, V.N. van Rijswijk, M.E.C. |
author_sort |
Nolet, B.A. |
title |
Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
title_short |
Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
title_full |
Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
title_fullStr |
Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
title_full_unstemmed |
Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
title_sort |
foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system |
publishDate |
2006 |
url |
https://research.wur.nl/en/publications/foraging-costs-and-accessibility-as-determinants-of-giving-up-den https://doi.org/10.1111/j.0030-1299.2006.13463.x |
geographic |
White Sea |
geographic_facet |
White Sea |
genre |
Cygnus columbianus White Sea |
genre_facet |
Cygnus columbianus White Sea |
op_source |
Oikos 112 (2006) 2 ISSN: 0030-1299 |
op_relation |
https://edepot.wur.nl/22184 https://research.wur.nl/en/publications/foraging-costs-and-accessibility-as-determinants-of-giving-up-den doi:10.1111/j.0030-1299.2006.13463.x |
op_rights |
info:eu-repo/semantics/restrictedAccess Wageningen University & Research |
op_doi |
https://doi.org/10.1111/j.0030-1299.2006.13463.x |
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Oikos |
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112 |
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2 |
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353 |
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362 |
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