Grazing pressure and the interaction dynamics of the endemic Cyprus Warbler Sylvia melanothorax and its recently colonising congener the Sardinian Warbler S. melanocephala

Abstract

SummaryThe recent classification of the endemic Cyprus Warbler to a Species of European Conservation Concern by BirdLife International has renewed interest in its interaction with the Sardinian Warbler, a widespread Sylvia that was first confirmed as breeding in Cyprus in the 1990s and has since expanded in numbers and range. In areas where the Sardinian Warbler has become established, there has been a reduction in the abundance of the Cyprus Warbler, leading some researchers to suggest the recently arrived species is outcompeting its endemic congener. However, clear evidence of competition between the two species has not been found, and more recent research has suggested the closely related warbler species show preferences for subtly different scrub habitats, which might be influenced by the extent of grazing. We carried out line transect surveys during the breeding season at 48 scrub and open woodland sites across Cyprus in 2012, 2014 and 2016, recording Cyprus Warblers and Sardinian Warblers in order to estimate their densities. In addition, we recorded vegetation characteristics and estimated grazing pressure at these 48 sites. Our analysis showed that the Sardinian Warbler continues to increase in abundance over time and its higher abundances were associated with lower Cyprus Warbler abundances. Sardinian Warbler however was negatively associated with all but very low grazing pressure, whereas the Cyprus Warbler was more tolerant of grazing. Our findings suggest continued grazing of scrub sites is important for the maintenance of suitable habitat for the endemic warbler, which will help improve its conservation status.