Assessing the influence of raptors on grape-eating birds in a Mediterranean vineyard

Several bird species may cause serious damage to grape production. The ability of raptors as biological control agents of grape-eating birds is poorly understood and under-used. We installed artificial nests and perches to encourage the presence and activity of raptors in vineyards located in central Spain and explored their effectiveness to reduce damage to grapes. We characterized the raptor community by field surveys and assessment of natural breeding sites, evaluated the abundance of grape-eating birds, and sampled damage to grape production for three consecutive years. Raptor community in the study area was diverse (13 species). Breeding of ornitophagous species such as Booted eagle Hieraaetus pennatusand Northern goshawk Accipiter gentilis was confirmed in the forest patches. We identified 10 grape-eating bird species, with Spotless starling (Sturnus unicolor) being the most abundant. Distance from the edges between vineyards and natural and semi-natural woody vegetation affected damage to grapes, with more damage close to the edges. The installed elements did not significantly reduce damage to grapes. Woody vegetation in and around the vineyards may reduce the success of the installed elements by providing shelter to grape-eating birds and suitable sites for raptor breeding and perching. Other variables such as vine orientation, land-cover, and distance to raptor nests did not affect damage to grapes. To promote the conservation of raptors and their regulating services in this Mediterranean agroforestry system, more research is needed to find methods to increase the presence of raptors in vineyards and to manage the woody shelters used by grape-eating birds around crops.