Cost-benefit analysis of mollusc-eating in a shorebird II:Optimizing gizzard size in the face of seasonal demands

Aiming to interpret functionally the large variation in gizzard masses of red knots Calidris canutus, we experimentally studied how the digestive processing rate is influenced by the size of the gizzard. During their non-breeding season, red knots feed on hard-shelled molluscs, which they ingest who...

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Bibliographic Details
Published in:Journal of Experimental Biology
Main Authors: van Gils, J A, Piersma, T, Dekinga, A, Dietz, M W
Format: Article in Journal/Newspaper
Language:English
Published: 2003
Subjects:
gizzard
digestive constraint
intake rate
red knot
Calidris canutus
ultrasonography
optimization
phenotypic flexibility
BASAL METABOLIC-RATE
KNOTS CALIDRIS-CANUTUS
WADDEN SEA
ORGAN SIZE
RED KNOTS
TERRESTRIAL LOCOMOTION
HAEMATOPUS-OSTRALEGUS
FUNCTIONAL-RESPONSE
CERASTODERMA-EDULE
Red Knot
Online Access:https://hdl.handle.net/11370/2d679d3a-7078-4015-89ac-950438389121
https://research.rug.nl/en/publications/2d679d3a-7078-4015-89ac-950438389121
https://doi.org/10.1242/jeb.00546
https://pure.rug.nl/ws/files/6675927/2003JExpBiolvGils.pdf
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Summary:Aiming to interpret functionally the large variation in gizzard masses of red knots Calidris canutus, we experimentally studied how the digestive processing rate is influenced by the size of the gizzard. During their non-breeding season, red knots feed on hard-shelled molluscs, which they ingest whole and crush in their gizzard. In three experiments with captive birds we tested predictions of the hypothesis that gizzard size, via the rate of shell crushing and processing, constrains intake rate in red knots (against the alternative idea that external handling times constrain intake rate). Gizzard size within individual birds was manipulated by varying the hardness of the diet on offer, and was confirmed by ultrasonography. The results upheld the 'shell-crushing hypothesis' and rejected the 'handling time hypothesis'. Intake rates on with-shell prey increased with gizzard size, and decreased with shell mass per prey. Intake rates on soft (without shell) prey were higher than on with-shell prey and were unaffected by gizzard size. Offering prey that were heavily shelled relative to their flesh mass led to energy intake rates that were marginally sufficient to balance the daily energy budget within the time that is naturally available in a tidal system. We predicted the optimal gizzard sizes that are required to either (1) balance energy income with energy expenditure, or (2) to maximise net daily energy intake. The gizzard mass of free-living red knots in the Wadden Sea is such that it maximises daily net energy intake in spring when fuelling for migration, while it balances energy budget throughout the remainder of the year.

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