Bird-building collision risk: An assessment of the collision risk of birds with buildings by phylogeny and behavior using two citizen-science datasets

Abstract

Bird collisions with buildings are the second largest anthropogenic source of direct mortality for birds (365–988 million birds killed annually in the United States). Recent research suggests that this mortality occurs disproportionately across species. However, previous work had relied on regional and annual measures of relative species abundance. Our research identifies which species experience higher or lower collision rates than expected from local abundances using two sets of citizen science data: Minnesota Project BirdSafe and the Mississippi River Twin Cities Important Bird Area Landbird Monitoring Program. Our analysis used a measure of relative species abundance that spatially overlaps the area monitored for building collisions and was measured weekly, allowing for a temporally and spatially more specific analysis than most previous analyses. Abundance and collision data were used to model phylogenetic and behavioral traits associated with increased collision risk. Behavioral traits included diurnal/nocturnal migration timing, length of migration, and foraging strategies. Our analysis shows that birds that predominately migrate during the day have a decreased risk of building collisions despite peak collision numbers occurring during early morning; this result suggests that more nuanced behavioral or physiological differences between diurnal and nocturnal migrants could contribute to bird-building collision risk. Additionally, for many species, local abundance is the predominant determining factor for collision risk. However, for ~20% of species studied, the family, genus, and/or species of a bird may affect the collision risk.

Flight morphology and visual obstruction predict collision risk in birds

“…If species traits contribute to collision risk, we expect vulnerability estimates to be both repeatable across different studies, and also more similar among closely-related species, as found in a previous study of a single metropolitan region [11].…”

“…We compiled estimates of species collision vulnerability from four previous studies that surveyed bird collision fatalities in North America, and that focused primarily on large buildings during spring and fall migration seasons [1,3,10,11] (see Table S1 for details of each study). Two of the studies were conducted at a continent-wide scale, while the other two focused on single metropolitan areas; all four studies differed substantially in monitoring protocol and coverage.…”

“…Additionally, several recent studies have established habitat-related correlates of collision mortality, such as building size and type, glass surface area, light pollution, surrounding land cover, and regional urbanization [6][7][8][9][10]. Behavioural correlates of collisions have also been identified, including nocturnal migration behavior [5,11], insectivory [10,12] and the use of social flight calls [3]. Knowledge of the sensory and biomechanical causes of building collisions is needed to devise effective strategies to prevent these fatalities.…”

“…In the absence of direct observations of collisions, an alternative way to evaluate causes is to consider the physiological traits of species that are most at risk. Not all bird species are equally vulnerable to building collisions; certain species like the white-throated sparrow, blackthroated blue warbler, and ruby-throated hummingbird have been found to collide more frequently than expected, given their abundance at the spatial scale over which collisions are counted [1,5,10,11]. Shared traits among these vulnerable species can be a clue to common causes of collisions, and can allow risk to be predicted in other populations that have not been studied [3].…”

“…Here, we evaluate whether traits related to sensory guidance and flight performance predict the vulnerability of bird species to collisions. As a first step, we analyzed the concordance among published species vulnerability estimates from four previous studies of North American birds [1,3,10,11]. These four studies are based on >106,000 bird fatalities across 62 geographic locations, and focus primarily on large buildings, with substantial variation among studies in terms of landscape type, building type, survey methods, analytical methods, the spatial scale of the analysis, and site-specific environmental features, such as vegetation and artificial light (see Table S1 for details).…”