Predicting seasonal and annual fluctuations in the local exploitation of different prey by Oystercatchers Haematopus ostralegus :A ten-year study in the Wadden Sea

• Main Authors: Zwarts, L., Wanink, J.H., Ens, B.J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1996
• Subjects: Oystercatcher; Haematopus ostralegus; Wadden Sea; optimal diet model; food exploitation; food intake rate; prey switching; BIVALVE MACOMA-BALTHICA; MUSSEL MYTILUS-EDULIS; KNOT CALIDRIS-CANUTUS; NEREIS-DIVERSICOLOR; EXE ESTUARY; SCROBICULARIA-PLANA; BURYING DEPTH; TIDAL FLATS; BODY-WEIGHT; WADERS; Calidris canutus
• Online Access: https://hdl.handle.net/11370/3fd95694-c5a2-4d0f-8955-b760fae50ee7; https://research.rug.nl/en/publications/3fd95694-c5a2-4d0f-8955-b760fae50ee7; https://pure.rug.nl/ws/files/144261931/a84_401_440.pdf

We predict the intake rate and prey choice of Oystercatchers feeding along the Frisian coast, Dutch Wadden Sea, combining the optimal prey choice model (Charnov 1976) with detailed measurements of the widely fluctuating food supply. Assuming that the birds maximize their intake rate, the birds should never eat Mussels Mytilus edulis during 10 years of observa- tions, Mya arenaria during two short periods, Macoma blathica and Scrobicularia plana during most summers and Cockles Cerastoderma edule in most winters. Observations on feeding Oystercatchers confirmed the predictions. Due to the seasonal variation in burying depth of Scrobicularia and Macoma, these prey were in winter, if not inaccessible, hardly worthwhile exploiting because of the increase of handing time and searching time with burying depth. Hence, the seasonal variation in intake rate was very large in these deep-living prey compared to surface prey, such as Cockles and Mussels. Consequently, Oystercatchers usually switch from surface to deep-living prey in spring and back to surface prey in autumn in order to maximize their intake rate. Oystercatchers will never achieve a high intake rate when they feed on small prey, even when these prey would occur in extremely high densities. The reason for this is that the yield of small prey during handling is even less than the intake rate during feeding of 1 mg ash-free dry weight (AFDW) s(-1) which Oystercatchers need to meet their energy demands juring the limited feeding periods in the tidal habitat. Since Oystercatchers eat only large bivalves, they might be vulnerable because cohorts of prey may disappear completely before they can be harvested. Despite the very large annual variation in the biomass of the different prey species in the Wadden Sea, the total food supply harvestable by Oystercatchers is large enough for them to stay ir, the area, unless ice covers the tidal flats. However, Oystercatchers cannot survive in the Wadden Sea when their diet is restricted to one or two prey species. They need ...