Fatal bird-window collisions in an urban area of Costa Rica during the autumn migrations of 2018 and 2019

Window collisions are one of the greatest threats to birds in urban areas. However, few studies have systematically evaluated the extent and causes of bird-window collisions in Central America. In this study, our goal was to quantify fatal bird-window collisions during autumn migration across buildings with various configurations at the urban area occupied by the Universidad de Costa Rica campus. From 1 October to 27 November 2018 and 2019, we conducted three surveys per week at seven buildings with different façade structural features including the extent of windows, concrete, and aluminum sunshade louvers. We surveyed each building between 0800 and 1000 h (GMT-6) by walking around its periphery and searching for carcasses and compared the mean monthly number of them for each year. We recorded 60 mortality events of 23 species, the majority of which (n = 12) were migratory (e.g., Swainson’s Thrushes and Tennessee Warblers), although we also found carcasses of resident birds (n = 8; e.g., Red-billed Pigeons). Most carcasses were found at buildings with large window façade surfaces, and most carcasses were found during October, at the height of the migration season. Our results underscore the need to conduct longer term studies and extend them to other habitats, human-made structures, and buildings with different configurations to understand patterns of bird-window collisions across the Neotropics.