THE WINTER FEEDING ECOLOGY OF AVOCETS RECURVIROSTRA-AVOSETTA ON INTERTIDAL AREAS .2. DIET AND FEEDING MECHANISMS

The diet and feeding methods of Avocets Recurvirostra avosetta using t he most common feeding strategy (Normal Feeding Strategy) on emerged i ntertidal areas in the Tagus estuary, Portugal, were studied during tw o winters. Avocets using the Normal Feeding Strategy fed non-selective ly in the top 20 mm of sediment, ingesting prey bigger than a minimum threshold dimension of around 1.5 mm. Some mud was also ingested whils t feeding. Prey were captured by the mechanical action of the bill, an d the estimated number of items captured per sweep was quite high (mea n = 10.9 worms). Most of the biomass ingested by Avocets consisted of oligochaetes, spionid worms, Capitella capitata and small ragworms Ner eis diversicolor. The estimated intake rate of Avocets suggested that the energy ingested during daylight hours did not represent a signific ant percentage of the daily requirements. Thus, feeding on emerged int ertidal areas is probably a secondary component of their daily gross f ood intake, unless night feeding yields higher intake rates due to inc reased prey availability.