The importance of rice fields for glossy ibis (Plegadis falcinellus): Management recommendations derived from an individual-based model

Abstract

Artificial wetlands provide alternative habitats for waterbirds. The Doñana rice fields (SW Spain) are extensively used as a foraging site by the glossy ibis (Plegadis falcinellus). The aim of this study was to develop an individual-based model to predict the possible effects of glossy ibis’ population growth, reductions in the rice cultivated area, and changes on the phenology of the management processes of the paddies on the mortality rate of the glossy ibis population. We test the hypothesis that the glossy ibis breeding population of Doñana can obtain its energy requirements during the non-breeding season by feeding on rice fields alone. Our results show that the glossy ibis population growth is not currently lim- ited by rice field availability. However, a reduction of 80% would cause mortality rate increases above the observed mortality (5.9% per year), with values around 10% per year for populations between 50,000 and 100,000 birds. A reduction of 90% of the rice field area would cause mortality rate increase above the observed value for populations greater than 20,000 birds, reaching 60% per year with a population of 100,000 birds. Cultivated area in Doñana suffers temporary reduction on its area during drought periods. Taking into account the fact that the glossy ibis population for 2011 may exceed 22,900 birds, large scale changes in the area of rice fields due to habitat transformations and/or drought periods may have impor- tant effects on the viability of the glossy ibis population in Doñana.