Rate-maximizing optimality models predict when oystercatchers exploit a cohort of the bivalve Scrobicularia plana over a 7-year time span

• Main Authors: Wanink, JH, Zwarts, L
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2001
• Subjects: foraging behaviour; Haematopus ostralegus; predicted grey mortality; prey depletion; random search model; DUTCH WADDEN SEA; KNOT CALIDRIS-CANUTUS; HAEMATOPUS-OSTRALEGUS; FUNCTIONAL-RESPONSE; MACOMA-BALTHICA; BURYING DEPTH; CERASTODERMA-EDULE; SEASONAL-VARIATION; MYTILUS-EDULIS; BODY-WEIGHT; Calidris canutus
• Online Access: https://hdl.handle.net/11370/b2e3da04-b221-460a-9fd8-9e2f455a4241; https://research.rug.nl/en/publications/b2e3da04-b221-460a-9fd8-9e2f455a4241

1. The timing of prey exploitation by oystercatcher Haematopus ostralegus L, was predicted from detailed knowledge of the characteristics of its prey, the clam Scrobicularia plana da Costa. 2, Growth, mortality and depth distribution of a single cohort of Scrobicularia were monitored on a tidal flat in the Dutch Wadden Sea during a period of 7 years. 3. A random search model predicted for every sampling date the encounter rate with buried clams providing oystercatchers vary the depth at which they probe their bill into the substrate. The time needed to handle encountered prey was estimated from experimentally determined relationships of handling time with clam size and handling time with burying depth. Encounter rate, handling time and body weight of the potential prey items were used in an optimal prey choice model to predict the average intake rate of an oystercatcher as a function of probing depth. 4, The predicted intake rate reached a profitable level only during three restricted periods. During the first period, a relatively high intake rate could only be achieved by probing extremely deeply, and the mortality rate of the clams remained at a low level. During the other two periods, maximal intake rate was reached by probing only the upper few cm of the substrate, and this time there was a high mortality in the prey population. 5. Although the observed peaks in clam mortality coincided with the predicted exploitation periods, they could not be explained fully by the estimated predation pressure. 6. Prey switching was predicted and confirmed during several exploitation periods. 7. Oystercatcher densities during winter peaks in bird abundance showed a tight relationship with predicted maximum intake rates.