Spatial variation in tuber depletion by swans explained by differences in net intake rates

Nolet, Bart A., Langevoord, Oscar, Bevan, Richard M., Engelaar, Kirsten R., Klaassen, Marcel, Mulder, Roef J. W. and Van Dijk, S. 2001, Spatial variation in tuber depletion by swans explained by differences in net intake rates, Ecology, vol. 82, no. 6, pp. 1655-1667, doi: 10.1890/0012-9658(2001)082[1655:SVITDB]2.0.CO;2.

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Title Spatial variation in tuber depletion by swans explained by differences in net intake rates
Author(s) Nolet, Bart A.
Langevoord, Oscar
Bevan, Richard M.
Engelaar, Kirsten R.
Klaassen, MarcelORCID iD for Klaassen, Marcel
Mulder, Roef J. W.
Van Dijk, S.
Journal name Ecology
Volume number 82
Issue number 6
Start page 1655
End page 1667
Total pages 13
Publisher Wiley
Place of publication London, Eng.
Publication date 2001
ISSN 0012-9658
Keyword(s) Bewick's Swan
Cygnus columbianus bewickii
Energy expenditure
Fennel pondweed
Giving-up density
Lauwersmeer, The Netherlands
Optimal foraging
Patch use
Plant-herbivore interaction
Potamogeton pectinatus
Sago pondweed
Tundra Swan
Science & Technology
Life Sciences & Biomedicine
Environmental Sciences & Ecology
Summary We tested whether the spatial variation in resource depletion by Tundra Swans (Cygnus columbianus) foraging on belowground tubers of sago pondweed (Potamogeton pectinatus) was caused by differences in net energy intake rates. The variation in giving-up densities within the confines of one lake was nearly eightfold, the giving-up density being positively related to water depth and, to a lesser extent, the silt content of the sediment. The swans' preference (measured as cumulative foraging pressure) was negatively related to these variables. We adjusted a model developed for diving birds to predict changes in the time allocation of foraging swans with changes in power requirements and harvest rate. First, we compared the behavior of free-living swans foraging in shallow and deep water, where they feed by head-dipping and up-ending, respectively. Up-ending swans had 1.3-2.1 times longer feeding times than head-dipping swans. This was contrary to our expectation, since the model predicted a decrease in feeding time with an increase in feeding power. However, up-ending swans also had 1.9 times longer trampling times than headdipping swans. The model predicted a strong positive correlation between trampling time and feeding time, and the longer trampling times may thus have masked any effect of an increase in feeding power. Heart rate measurements showed that trampling was the most energetically costly part of foraging. However, because the feeding time and trampling time changed concurrently, the rate of energy expenditure was only slightly higher in deep water (1.03-1.06 times). This is a conservative estimate since it does not take into account that the feeding costs of up-ending are possibly higher than that of head-dipping. Second, we compared captive swans foraging on sandy and clayey sediments. We found that the harvest rate on clayey sediment was only 0.6 times that on sandy sediment and that the power requirements for foraging were 1.2-1.4 times greater. Our results are in qualitative agreement with the hypothesis that the large spatial variation in giving-up densities was caused by differences in net rates of energy intake. This potentially has important implications for the prey dynamics, because plant regrowth has been shown to be related to the same habitat factors (water depth and sediment type).
Language eng
DOI 10.1890/0012-9658(2001)082[1655:SVITDB]2.0.CO;2
Field of Research 060299 Ecology not elsewhere classified
Socio Economic Objective 970105 Expanding Knowledge in the Environmental Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2001, Wiley
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