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Bird–window collisions at houses have been identified as a significant source of mortality for North American birds, but which types of houses and windows are most problematic remains poorly understood. We assessed how neighborhood type, yard conditions, house attributes, and window type influenced collision rates. Data were collected from citizen scientists across Alberta, Canada, who surveyed their houses daily. In relation to the best-fitting model, the yard model explained 58.1% of the explained deviance, the neighborhood model 45.6%, and the house model 42.6%. The factors that had the largest effect for predicting collision risk included season and whether the house was in a rural or an urban area (rural areas in the fall had a 6.0× higher collision risk than urban areas in the winter), the height of vegetation in the front yard of the house (trees >2 stories high increased collision risk by 3.6× compared to houses with no trees), and the presence of a bird feeder (which increased collision risk by 1.7×). This suggests that multiple factors affect collision rates and that the suitability of a yard as bird habitat is likely a key driver. Given that few homeowners are likely to take an approach that reduces the number of birds in their yards, future focus needs to be given to bird-friendly urban design and developing the most effective window deterrents so that collisions can be reduced and birds enjoyed in urban environments.

Collisions with windows remain an important human-related threat to bird survival in urban landscapes. Accurately estimating the magnitude of avian mortality at windows is difficult and may be influenced by many sources of error, such as scavenging of carcasses. Failure to account for removal of carcasses by scavengers can bias estimates of window mortality. We tested the hypothesis that carcass survival depends on local habitat factors known to influence scavenger behavior. Scavenger activity on bird carcasses was documented at 20 buildings in an urban landscape in northwestern Illinois for 1 week during each season of a year. Known-fate models were used to relate carcass survival to local habitat composition and to evaluate temporal variation in survival. We also documented species of scavengers and the timing of scavenging using motion-triggered cameras. Daily carcass survival was greater in winter than during spring, summer, and fall. Survival was related negatively to canopy cover (trees and shrubs within a 50-m buffer) and window area, and positively to pavement cover. Using an exponential model of survival time, estimated mean time of survival of carcasses (t ± SE) was 82.9 ± 11.7 d for winter and 11.8 ± 7.2 d for other seasons. Raccoons (Procyon lotor) scavenged more carcasses than other species. Our results suggest that (1) carcass survival times may be short at locations with preferred habitats of known scavengers and predictable sources of food, and (2) knowledge of scavenger distribution and activity can inform predictive models of persistence. In studies of bird-window collisions, the influence of scavenger bias can be minimized by maintaining short time intervals between carcass searches. Search intervals can be inferred by estimating the number of days that a carcass should persist at a site, which can be calculated using predicted daily survival probabilities of carcasses at study buildings. La colisión con ventanas sigue siendo una amenaza importante sobre la sobrevivencia de las aves la cual está relacionada con los humanos en un paisaje urbano. Una estimación precisa sobre la magnitud de la mortalidad de aves en las ventanas es difícil y puede estar afectada por muchas fuentes de error, como los buscadores de de cuerpos. La incapacidad de tener en cuenta la remoción de cuerpos por los buscadores de cadáveres puede sesgar los estimativos de la mortalidad por ventanas. Pusimos a prueba la hipótesis que la permanencia de los cadáveres depende de factores conocidos en habitas locales que afectan el comportamiento de los buscadores de cuerpos. La actividad de los buscadores de cuerpos sobre los cadáveres de aves fue documentada en 20 edificios en un paisaje urbano al noreste de Illinois durante una semana en cada estación durante un año. Modelos deterministicos fueron usados para relacionar la permanencia de los cadáveres con la composición local del hábitat y evaluar la variación temporal en la permanencia. También documentamos las especies de los buscadores de cadáveres y cuando ocurrió el evento usando cámaras con sensores de movimiento. La permanencia diaria fue mayor en el invierno que durante la primavera, verano y otoño. La permanencia estuvo negativamente relacionada con la cobertura de dosel (árboles y arbustos dentro de un área de 50-m) y el área de las ventanas, y positivamente con la cobertura del pavimento. Mediante un modelo exponencial de supervivencia en el tiempo, estimamos el tiempo promedio de permanencia de los cadáveres (t ± SE) el cual fue 82.9 ± 11.7 días para el invierno y 11.8 ± 7.2 días para otras estaciones. Mapaches (Procyon lotor) buscaron mas cuerpos que otras especies. Nuestros resultados siguieren que (1) la permanencia de los cadáveres en el tiempo puede ser corta en lugares con hábitats conocidos y preferidos por los buscadores de cuerpos y con fuentes de alimentos predecibles y (2) conocimiento de la distribución de los buscadores de cadáveres y su actividad pueden proporcionar información para modelos predictivos de permanencia. En estudios de colisiones de aves con ventanas, el efecto de los sesgos de buscadores de cadáveres puede ser minimizado mediante el mantenimiento de intervalos cortos de tiempo entre las búsquedas de cadáveres. Los intervalos de búsquedas pueden inferirse estimando el número de días que un cadáver debería permanecer en un lugar, lo cual puede ser calculado usando probabilidades de supervivencia diaria predictiva de los cadáveres en edificios de estudio.

Seabird populations are declining rapidly due to numerous anthropogenic threats, including habitat destruction, invasive species, longline fisheries bycatch, and plastic ingestion. However, few studies have investigated seabird collisions with anthropogenic structures, and those studies have primarily focused on a particular taxon or location. Little research has addressed seabird collisions with buildings and similar structures despite bird-building collisions being a major source of mortality for other groups of birds in coastal and inland areas. We conducted an analysis of seabird collisions using band recovery data spanning from 1930 to 2023 from the North American Bird Banding Program, focusing on records categorized as: “caught due to striking: stationary object other than wires or towers.” Our objective was to describe taxonomic and spatiotemporal patterns emerging from these collision records, information that can be used to identify research needs and make recommendations for monitoring seabird collisions. There were 407 records of 39 seabird species representing 13 families that were categorized as striking buildings or similar structures. Species in Laridae (gulls and terns) and Pelecanidae (pelicans) represented 80% of records; Diomedeidae (albatrosses) was the only other family representing more than 5% of records. Band recoveries of collision victims were concentrated in the eastern United States, southern Canada, and urban areas on the West Coast of the U.S. and Canada. Over half of records (n = 228) were from ocean coastlines, with fewer from inland (n = 146) and offshore locations (n = 30). Most records (∼90%) had no information about the type of structure with which the bird collided, but observer remarks indicate that seabirds collided with buildings, offshore oil platforms, docks/piers, and even boats. Elucidating and mitigating impacts of collisions with structures on seabird populations requires increased collision monitoring at coastal and offshore structures, which are highly underrepresented in this dataset and are likely a significant threat to seabirds. There is also a need for formal mechanisms for reporting seabird fatalities that account for sampling and detection-related biases and that allow observers to report specific structure types. Las poblaciones de aves marinas están disminuyendo rápidamente debido a numerosas amenazas antropogénicas, como la destrucción del hábitat, las especies invasoras, la captura acompañante en la pesca con palangre y la ingestión de plásticos. Sin embargo, pocos estudios han investigado las colisiones de aves marinas con estructuras antropogénicas, y esos estudios se han centrado principalmente en un taxón o lugar en particular. Pocos estudios han abordado las colisiones de aves marinas con edificios y estructuras similares, a pesar de que las colisiones entre aves y edificios son una importante fuente de mortalidad para otros grupos de aves en zonas costeras y continentales. Llevamos a cabo un análisis de las colisiones de aves marinas utilizando datos de recuperación de anillos desde 1930 hasta 2023 del North American Bird Banding Program, centrándonos en los registros categorizados como: “capturado debido a golpear: objeto estacionario que no sean cables o torres.” Nuestro objetivo fue describir los patrones taxonómicos y espaciotemporales que emergen de estos registros de colisiones, información que puede ser utilizada para identificar las necesidades de investigación y hacer recomendaciones para el monitoreo de las colisiones de aves marinas. Se registraron 407 colisiones con edificios o estructuras similares de 39 especies de aves marinas pertenecientes a 13 familias. Las especies de Laridae (gaviotas y gaviotines) y Pelecanidae (pelícanos) representaron el 80% de los registros; Diomedeidae (albatros) fue la única otra familia que representó más del 5% de los registros. Las recuperaciones de bandas de víctimas de colisiones se concentraron en el este de Estados Unidos, el sur de Canadá y las zonas urbanas de la costa oeste de Estados Unidos y Canadá. Más de la mitad de los registros (n = 228) procedían de costas oceánicas, y un número menor de lugares del interior (n = 146) y de alta mar (n = 30). La mayoría de los registros (∼90%) no contenían información sobre el tipo de estructura con la que colisionó el ave, pero los comentarios de los observadores indican que las aves marinas colisionaron con edificios, plataformas petrolíferas en alta mar, muelles e incluso embarcaciones. Para dilucidar y mitigar el impacto de las colisiones con estructuras sobre las poblaciones de aves marinas es necesario aumentar el seguimiento de las colisiones con estructuras costeras y estructuras de alta mar, que están muy poco representadas en este conjunto de datos y probablemente constituyen una amenaza importante para las aves marinas. También se necesitan mecanismos formales para informar sobre las muertes de aves marinas que tengan en cuenta los sesgos relacionados con el muestreo y la detección y que permitan a los observadores informar sobre tipos específicos de estructuras. PALABRAS CLAVE mortalidad de aves; collisiones de aves con ventanas; Bird Banding Laboratory; collisiones con edificios; monitoreo de la mortalidad; choques entre aves y ventanas

Wildlife collisions with human-built structures are a major source of direct anthropogenic mortality. Understanding and mitigating the impact of anthropogenic collisions on wildlife populations require unbiased mortality estimates. However, counts of collision fatalities are underestimated due to several bias sources, including scavenger removal of carcasses between fatality surveys and imperfect detection of carcasses present during surveys. These biases remain particularly understudied for bird–window collisions, the largest source of avian collision mortality. In Stillwater, Oklahoma, USA, we used bird carcasses collected during window collision monitoring to experimentally assess factors influencing scavenging and observer detection, and we employed trail cameras to characterize the scavenger community and timing of scavenging. We recorded nine scavenger species, but the domestic cat and Virginia opossum were responsible for 73% of known-species scavenging events. The most frequent scavenger species were primarily nocturnal, and 68% of scavenging events occurred at night. Scavenger species best predicted time to first scavenging event, season best predicted carcass persistence time, and both season and carcass size predicted whether any carcass remains persisted after scavenging. Our results also suggest that observer detection was influenced by substrate, with greater detection of carcasses on artificial substrates. Our findings related to scavenging timing have important implications for the unbiased estimation of collision mortality because the timing of peak scavenging relative to timing of peak mortality can substantially influence accuracy of adjusted mortality estimates. Further, the differences in correlates for time to first scavenging and time to carcass removal (i.e., persistence time) illustrate the importance of explicitly measuring these often-independent events that are frequently conflated in the anthropogenic mortality literature.

Bird-window collisions are a significant and growing threat to birds, but the issue is still understudied in many geographical areas and stages of the avian annual life cycle. The mountainous topography and numerous distinct biogeoclimatic zones along the Pacific coast of Canada and the United States may result in regional and seasonal differences in collision mortality and species vulnerability to collisions. We surveyed daily for evidence of bird-window collisions over six 21-day periods in fall, early winter, and late winter between 2019 and 2022 at a university campus in southwestern British Columbia, Canada, and assessed individual species’ vulnerability to collisions by examining whether species-specific collision rates were disproportionate to their local abundance. We accounted for poor detectability of some species in fall, by integrating point count data from our study site with mist net capture data from a nearby banding station to improve abundance estimates. Collision mortality peaked in fall, but early winter collision mortality was significantly higher than in the later winter months, potentially due to movements of altitudinal migrants into our low-elevation study area in early winter. We estimated that an average of 885–1,342 (median = 1,095) birds are killed at 51 buildings campus-wide each year between September 15 and February 10, the peak fall migration wintering period. Forest birds, particularly species that switch to highly frugivorous diets in fall and winter, were most vulnerable to collisions across the seasons studied. Non-breeding season mortality due to collisions may be substantial for these species, particularly when considering cumulative mortality across the entire non-breeding period. The potential role of collision mortality in species declines should be further explored by assessing collision frequency and species vulnerability across life cycle stages in other geographical locations, and through improved data on migratory connectivity and linkages between declining breeding populations and non-breeding season mortality.

In North America, up to one billion birds are estimated to die annually due to collisions with glass. The transparent and reflective properties of glass present the illusion of a clear flight passage or continuous habitat. Approaches to reducing collision risk involve installing visual cues on glass that enable birds to perceive glass as a solid hazard at a sufficient distance to avoid it. We monitored for bird-window collisions between 2013 and 2018 to measure response to bird protection window treatments at two low-rise buildings at the Alaksen National Wildlife Area in Delta, British Columbia, Canada. After 2 years of collision monitoring in an untreated state, we retrofitted one building with Feather Friendly circular adhesive markers applied in a grid pattern across all windows, enabling a field-based assessment of the relative reduction in collisions in the 2 years of monitoring following treatment. An adjacent building that had been constructed with a bird protective UV-treated glass called ORNILUX Mikado, was monitored throughout the two study periods. Carcass persistence trials were conducted to evaluate the likelihood that carcasses were missed due to carcass removal between scheduled searches. After accounting for differences in area of glass between the two buildings, year, and observer effects, our best-fit model for explaining collision risk included the building's treatment group, when compared to models that included building and season only. We found that the Feather Friendly markers reduced collision risk at the retrofitted building by 95%. Collision incidence was also lower at the two monitored façades of the building with ORNILUX glass compared to the building with untreated glass. Although more research is needed on the effectiveness of bird-protection products across a range of conditions, our results highlight the benefit of these products for reducing avian mortality due to collisions with glass.

Window strikes are among the most worrisome causes of bird mortality. Being responsible for billions of avian deaths, bird-window collisions have been widely studied in the US and Canada, with few studies from Europe, Asia, and Latin America. Thus, there is still a dearth of knowledge regarding this alarming phenomenon in regions where biodiversity and urbanization peek, such as Latin America. In this study, we assessed bird-window collisions in Xalapa, a small-to-medium-sized Neotropical city located in Southeast Mexico. We gathered data under two schemes: (1) a standardized survey procedure and (2) non-systematic records. Regarding the former, we evaluated the role of building and surrounding vegetation traits, as well as the location of focal buildings in driving bird-window collisions. Considering both schemes, we recorded bird-window collisions for 43 species. The most frequent striking groups were hummingbirds and thrushes, which had already been identified as vulnerable given some of their natural and life history traits. Regarding the standardized survey, we found no statistical differences in the number of collisions among seasons; yet, we did record a predominance of strikes from resident bird species over migrants among all studied seasons. Our results show a significant positive relationship between the amount of surrounding vegetation area of the studied buildings and bird-window collision frequency, while building non-glass material area showed a significant negative relationship. Based on our findings and the limitations of our study, we encourage future research to combine systematic and standard surveys throughout the year with citizen science, together with carcass removal assessments and bird density surveys in the immediate vicinity of focal buildings.

Birds that reside in urban settings face numerous human-related threats to survival, including mortality from bird-window collisions (BWCs). Our current understanding of this issue has largely been driven by data collected during spring and fall migration, and patterns of collision mortality during the summer breeding season remain relatively unexplored. We assessed BWCs during four breeding seasons (2009-2012) at a site in northwestern Illinois, USA, by comparing the abundance, richness, migratory class, and age of the species living around buildings to species mortally wounded by window collisions. We also systematically assessed the daily timing of BWCs throughout the breeding season. We documented BWCs in 4 of 25 (16%) species and 7 of 21 (33%) species in 2009 and 2010, respectively. The relationship between BWCs and abundance depended on age. For adults, BWCs were highest in the least abundant species, e.g., Red-eyed Vireo (Vireo olivaceus), and lowest in species with high abundance values, e.g., Chipping Sparrow (Spizella passerina). For juveniles, mortality was greatest for the most abundant species, and the American Robin (Turdus migratorius) accounted for 62% of all juvenile carcasses. Early in the breeding season, collision mortality was restricted to adults of Long-distance Migrants, whereas juveniles of all three migratory guilds (Long-distance and Short-distance Migrants and Permanent Residents) died at windows from late June through early August. Daily mortality for all species was highest between sunrise-1600 h and lowest from 1600 h-sunrise the next day. Generally, the species observed as carcasses matched birds considered a 'high risk' for BWCs, e.g., Ruby-throated Hummingbird (Archilochus colubris), and those considered 'low risk' were not observed as carcasses, e.g., Blue-gray Gnatcatcher (Polioptila caerulea). Our results suggest that the number of BWCs during the breeding season does not necessarily increase with abundance, but rather appears related to variation among species and age classes, which may have important implications on the population health of affected species. The mechanisms driving these differences are unknown, but may be related reproductive behavior, flight speed, distance movements, and dispersal patterns.

Bird collisions with windows are an important conservation concern. Efficient mitigation efforts should prioritize retrofitting sections of glass exhibiting the highest mortality of birds. Most collision studies, however, record location meta-data at a spatial scale too coarse (i.e., compass direction of facing façade) to be useful for large buildings with complex geometries. Through spatial analysis of three seasons of survey data at a large building at a university campus, we found that GPS data were able to identify collision hotspots while compass directions could not. To demonstrate the broad applicability and utility of this georeferencing approach, we identified collision hotspots at two additional urban areas in North America. The data for this latter exercise were collected via the citizen science database, iNaturalist, which we review for its potential to generate the georeferenced data necessary for directing building retrofits and mitigating a major source of anthropogenic bird mortality.

Bird-window collisions occur across North America and are estimated to kill hundreds of millions of birds annually. Previous studies show that collisions occur non-randomly and can be influenced by building characteristics, time-of-year, and species-specific physiology and behaviour. Much of the available research is based in northeastern North America, though different species and habitats in the West may be affected differently. We collected strike data from 2 buildings in Victoria, British Columbia, from June to October 2018. We found that window width was positively related to the probability of a strike occurring, whereas vegetation distance to window, window aspect, and the building at which it occurred did not predict strike probability. A substantial increase in strikes occurred in September and October, which coincides with peak migration on Vancouver Island, and suggests that migration influences collision risk to bird species.