Interference Among Oystercatchers, Haematopus ostralegus, Feeding on Mussels, Mytilus edulis, on the Exe Estuary

• Published in: The Journal of animal ecology 1984-01, Vol.53 (1), p.217-231
• Main Authors: Ens, B. J., Goss-Custard, J. D.
• Format: Article
• Language: English
• Subjects: Animal ethology; Aves; Biological and medical sciences; Biomass; Birds; Brackish; Carrion; Correlation coefficients; Crows; Density; Estuaries; Food supply; Foraging; Fundamental and applied biological sciences. Psychology; Haematopus ostralegus; Marine; Mussels; Mytilus edulis; Psychology. Psychoanalysis. Psychiatry; Vertebrata
• ISSN: 0021-8790; 1365-2656
• DOI: 10.2307/4353

(1) Oystercatchers Haematopus ostralegus eating mussels Mytilus edulis on the Exe Estuary were aggressive and often stole mussels from each other. A stable and linear dominance hierarchy existed amongst ten birds studied in detail. The intake rates (biomass consumed per 10 min foraging) of six out of eight birds on which adequate data were obtained, decreased with increasing densities of oystercatchers. However, this did not happen in the two top-dominant individuals, which therefore did not seem to suffer from interference. (2) Interference in the subdominants was due to increased intraspecific kleptoparasitism, to decreased capture rates probably caused by avoidance, and, perhaps, to increased time spent in aggression. Subdominants avoided high densities of conspecifics, but they did not stop feeding when high densities occurred. (3) It is possible to account for our data in terms of the increased opportunities for dominants to steal food from subdominants at high bird densities. Competition for small-scale feeding sites may have been important too. It is suggested that the dispersion of oystercatchers over the mussel bed can be described by a modification of the `ideal despotic distribution' proposed by Fretwell (1972).