Use of an abandoned gravel-pit in inland Spain as a stopover site for the Aquatic Warbler Acrocephalus paludicola

Abstract

Stopover sites are of vital importance for migrating birds, especially long-distance migrant species. This study describes a wetland in NW Spain, as a particular habitat used by the Aquatic Warbler, one of the most threatened passeriformes in Europe, during postnuptial migration. It is a recently abandoned gravel-pit with an artificial water regime, a large area of standing water and a mosaic of vegetation predominated by a rush-meadow of Juncus effusus and a cattail community of Typha domingensis, a priori very favourable conditions for the Aquatic Warbler. The Acrola index value for this locality is very high, and together with some of the results including mean stopover period, fattening rate, interannual site fidelity and calculated potential flight distances, indicates that the mosaic of plant communities offers good conditions as a refuelling site for the Aquatic Warbler. Nevertheless, in only 3 years a process of homogenization has been observed in the vegetation, where rush-meadow cover has decreased noticeably and cattail and willow cover have increased. This process caused a decrease in the Acrola index throughout 2008–2010, as well as a significant decrease in the importance of this wetland with regard to others in Spain. Significant differences were found in body condition between the two age groups: adults are heavier and obtain more body fat, which provides them with greater potential flight autonomy. Although gravel pits can act as alternative wetlands, rapid changes in plant communities succession requires more active management than in the case of natural wetlands.