Solar power plants and bird populations in the agricultural landscape

Abstract

Solar power is rapidly increasing in Sweden, with many solar parks constructed on agricultural land. At the same time, farmland bird species are suffering a steep long-term population decline. The effects of solar parks on local bird populations are not well known. Previous studies from Europe and other continents are suggesting opposing results. To estimate the effects of solar parks on bird populations in the agricultural landscape, a bird survey was conducted in Western Sweden during the breeding season of 2025. In total, 200 line transects were carried out, surveying 10 solar parks and 10 adjacent reference areas (agricultural fields), during two periods, to account for seasonal variability due to early and late migrants. Detection probability was shown to differ greatly between solar parks and reference areas, with lower detection probability in the solar parks. The effects of solar parks on population density and species diversity were examined using generalized linear mixed models (GLMM), while controlling random effects as well as testing for other potential explanatory variables. Solar parks were shown to increase population density, but not species diversity, compared to adjacent agricultural fields. Additionally, population density was shown to be positively influenced by low vegetation cover and higher wind. Species diversity increased with the later period and increased size of the area. The average density of threatened birds was not shown to differ between area types. Certain species or species groups seemingly preferred reference areas as they were not observed in the solar parks. An edge effect was found inside the solar parks, with higher diversity in the outer edges compared to the interior parts of the parks. The results suggest solar parks contain more individuals but potentially fewer species than surrounding agricultural fields. Further species specific studies are desirable, to avoid additional pressure on threatened bird populations.