Bird-window collisions and carcass removal in southern Finland: patterns and implications

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.

BackgroundTo reduce bird fatalities from millions of window collisions each year in North America, it is important to understand how design and landscape elements relate to collision risk. The current study extends prior research that found that buildings near ornamental pear trees (Prunus calleryana) and buildings with mirrored windows significantly increased odds of collisions among eight buildings on the University of Utah campus in winter. The previous study found bird-friendly glass was not related to collision risk, although only one fatality occurred at two buildings with ORNILUX® ultraviolet (UV) or fritted windows. We reasoned that extending data collection to include fall might provide a better test of efficacy. We tested the following three hypotheses: (1) Buildings with mirrored windows would experience more collisions, replicating the original study; (2) the addition of fall migration data would reveal fewer collisions at the buildings with bird-friendly windows; (3) the danger of pear tree proximity would be heightened in winter, when fruit is ripe enough to appeal to frugivores, especially the Cedar Waxwings (Bombycilla cedrorum) that frequent these trees.MethodsTrained observers monitored buildings three times per week in Fall (September 12 to October 27, 2019) and Winter (October 29, 2019 to January 24, 2020). Collisions were photographed and documented in the iNaturalist University of Utah Bird Window Collision Project.ResultsThere were 39 total collisions, from 0 to 14 per building.Using generalized estimating equations, buildings near pear trees had 3.33-fold increased odds, mirrored windows had 5.92-fold increased odds, and bird-friendly windows had an 84% lower odds (Odds ratio = 0.16) of bird window collisions when analyzed separately; all were statistically significant (p < 0.01). A test of all possible combinations of risk and protective factors revealed that the best fit model included pear trees (odds = 2.31) and mirrored windows (odds = 2.33). A separate analysis tested the pear tree by season interaction model; it yielded the deadliest combination, with 40-fold increased odds for buildings near pear trees in winter season.DiscussionThis research provides the first peer-reviewed evidence found for the efficacy of bird-friendly fritted windows and ORNILUX ® UV windows in buildings. In addition, it replicated a study that established the dangers of mirrored windows and fruiting pear trees near buildings. These risks were especially dangerous to Cedar Waxwings, who constituted 62.2% of the identifiable window collision victims. This research highlights how building risks depend on window design, landscape choices, species, and season. If replicated, analyses of risk factors can help identify buildings that require mitigation to make existing windows less deadly. Results also support the installation of bird-friendly glass in new or renovated buildings to reduce fatalities.

Bird–window collisions (BWCs) represent a source of mortality for both resident and migratory birds that researchers aim to quantify. Factors that limit carcass detection, including removal of carcasses by scavengers and inherent error in observer detection, can complicate these efforts. We combined 2 studies to examine what proportion of carcasses were scavenged and removed and how successful observers were at detecting bird decoys of multiple types. In fall 2019 and spring 2020, we deployed 40 bird carcasses at Radford University campus buildings and monitored visitation events with game cameras for up to 4 nights/5 days. Scavengers visited 31 of the carcasses and scavenged (disturbed but not removed) 14/31. Scavengers included Felis catus (Domestic Cat, n = 6 events), Mephitis mephitis (Striped Skunk, n = 3), and Procyon lotor (Raccoon, n = 3). All mammalian scavenging events were nocturnal. Cats visited carcasses without disturbing them (n = 22 events), whereas Raccoons (3/3 events) and Striped Skunks (3/4) scavenged carcasses on discovery. Mammals scavenged or removed 3 carcasses in the first night after deployment (e.g., in the first 14 h), suggesting that scavenging can cause daily surveyors to miss ∼7.5% of carcasses. Across spring and fall 2020, we deployed 60 decoys of 4 unique types (varying in color or shape), partially obscuring them under shrubs and along landscaped herbaceous vegetation. We found that observers detected 48% of the decoys on their first attempts (min–max: 8.7–100%). Decoy type did not affect observer detection. By our estimates, 2 observers per day could have collectively missed 27% of carcasses. Although BWC projects typically complete surveys once or twice daily, we suggest twice-daily surveys when monitoring BWC during migratory seasons and once-daily surveys at other times to minimize carcass loss due to scavenging.

Bird-window collisions are one of the main causes of avian mortality worldwide, with estimations reaching up to almost one billion of dead individuals annually due to this cause in Canada and the USA alone. Although this is a growing conservation problem, most of the studies come from North America, evidencing the lack of knowledge and concern in countries with high biodiversity and growing population development. Our objectives were: (1) to estimate the current situation of bird-window collisions in Argentina, a country with around 10% of the world’s avian biodiversity, and, (2) to identify drivers of bird-window collisions at a national and local scale, focusing on a city surrounded by a protected area. We used a citizen science project called “Bird-Window Collisions in Argentina” that consisted of an online survey that collected data on collision metrics and risk factors. We found that more than half of participants reported at least one collision during the last year, suggesting this issue is common and widespread. In addition, our data show that the number of windows and the presence of vegetation reflected in windows are factors that strongly influence the risk of collision at national scale. On the other hand, the environment surrounding buildings affects the rate of bird-window collisions at local scale, being greater in buildings surrounded by tall vegetation than in buildings surrounded by a greater proportion of urbanization (human-made structures). We call for attention on a topic that has been poorly evaluated in South America. We also encourage future scientific studies to evaluate additional risk factors and mitigation strategies accordingly, to provide a better understanding of bird-window collisions particularly in a highly biodiverse region as South America.

Collisions with glass windows are a significant source of avian mortality, with over one billion birds affected annually in North America alone. However, studies on this subject in Latin America are still scarce, which is worrying for conservation, given that the region has the highest bird diversity in the world. To address this gap, here we investigated bird-window collisions on a university campus in Brazil, assessing which factors are associated with non-random patterns. Collision monitoring was conducted every 2-3 days from November 2022 to November 2023 in Sorocaba, Brazil, through the detection of evidence such as carcasses, injured birds, feather piles, traces of impact (i.e., feathers, body contours, or blood) and third-party information. To identify biological traits and environmental factors that may be potentially related to higher collision frequencies, we obtained biological characteristics of the species involved, as well as the buildings and their surroundings. We used generalized linear mixed models to evaluate the relationships of the biological and environmental variables on the collision frequency. Our results revealed a positive correlation between glass area and collision frequency, underscoring the critical need for preventive measures. This study contributes to advancing the understanding of the issues related to bird-window collisions within Neotropics and calls for public policies and architectural interventions to mitigate these events, promoting the coexistence between urban development and bird conservation.

Urban development from an avian perspective: causes of hooded crow ( Corvus corone cornix) urbanisation in two Finnish cities

An automatic bird sound recognition system is a useful tool for collecting data of different bird species for ecological analysis. Together with autonomous recording units (ARUs), such a system provides a possibility to collect bird observations on a scale that no human observer could ever match. During the last decades, progress has been made in the field of automatic bird sound recognition, but recognizing bird species from untargeted soundscape recordings remains a challenge. In this article, we demonstrate the workflow for building a global identification model and adjusting it to perform well on the data of autonomous recorders from a specific region. We show how data augmentation and a combination of global and local data can be used to train a convolutional neural network to classify vocalizations of 101 bird species. We construct a model and train it with a global data set to obtain a base model. The base model is then fine‐tuned with local data from Southern Finland in order to adapt it to the sound environment of a specific location and tested with two data sets: one originating from the same Southern Finnish region and another originating from a different region in German Alps. Our results suggest that fine‐tuning with local data significantly improves the network performance. Classification accuracy was improved for test recordings from the same area as the local training data (Southern Finland) but not for recordings from a different region (German Alps). Data augmentation enables training with a limited number of training data and even with few local data samples significant improvement over the base model can be achieved. Our model outperforms the current state‐of‐the‐art tool for automatic bird sound classification. Using local data to adjust the recognition model for the target domain leads to improvement over general non‐tailored solutions. The process introduced in this article can be applied to build a fine‐tuned bird sound classification model for a specific environment.

Worldwide, billions of birds die annually due to window collisions. Nevertheless, few accounts document bird-window collisions in the Neotropics. In this study, we document species that collided with windows in Monteverde, Costa Rica, and describe their ecological and conservation status. We gathered information from different sources, including data from museum records and accounts by Monteverde residents who participated as “citizen scientists” between May 2014 and December 2017. We conducted carcass searches between March 2015 and February 2016. We classified window-strike species by migratory, forest dependence, trophic guild, weight, abundance, conservation, and endemism status. We registered 103 species striking windows in Monteverde, which includes 98 of 267 species known to occur in three life zones in Monteverde and five not registered in the area. Window strike casualties’ frequencies differed by species, trophic guild and migratory status. Most window victims were residents, small, insectivorous, considered common or fairly common, with declining population trends. The families with the most species represented were Parulidae (14 spp.), Trochilidae (13 spp.), Turdidae (10 spp.), and Tyrannidae (9 spp.). Most species were passerines (Order Passeriformes) (71 spp.). No hawks or vultures were found colliding with buildings. The three species most commonly killed by windows were frugivores: Swainson’s Thrush (Catharus ustulatus), Northern Emerald-Toucanet (Aulacorhynchus prasinus), and Black-faced Solitaire (Myadestes melanops). Among window-kills were five species whose status on the IUCN Red List are Near Threatened and one Vulnerable, including the Resplendent Quetzal (Pharomachrus mocinno) and the Three-wattled Bellbird (Procnias tricarunculatus). Six species are listed as in danger of extinction and four are listed as species with reduced populations by the National System of Conservation Areas for Costa Rica (SINAC). 12 endemic species are strike casualties. The premontane wet forest is the life zone where more species were found (n=64 spp.), followed by the premontane moist forest (n = 49 spp.) and the lower montane wet forest (n = 31 spp.). These findings demonstrate the urgent need for conservation measures to mitigate bird mortality due to window collisions. Promoting use of methods to protect birds from windows should be an important goal for this IBA and the rest of Costa Rica. We also recommend collecting data in order to increase understanding about bird window collisions.

Collisions with building windows are a top bird mortality source, but few studies have evaluated how bird–window collisions are influenced by weather. By monitoring collisions daily at 21 buildings in Minneapolis, Minnesota, over 4 migration seasons, we show that weather influences numbers of window collisions of nocturnal migrants in spring and fall, indicating that collisions may be forecastable based on weather conditions. Collisions increased with weather favoring migration, such as consecutive nights of south wind in spring and even short periods of north wind in fall. We also found evidence that spring and fall collisions increase with weather changes that impede migration, such as changes from fair conditions and tailwinds early in the night to headwinds near sunrise. Our study suggests complex weather effects never before considered in the context of bird collisions, including possible time lag effects of conditions 2–3 nights before collisions occur, effects of multi-day sequences of conditions, and interactions between conditions at different times of night. More research is needed to determine if the accuracy of weather-based collision prediction systems improves by integrating such nuances and to clarify mechanisms through which these complex effects operate, such as influences of weather on migration intensity and collision avoidance behavior. Weather-based forecasts may allow refinement of collision mitigation approaches (e.g., reducing building lighting on certain nights or using temporary glass coverings or treatments). However, because challenges remain to communicating such temporally targeted actions and implementing them in a timely manner, other bird-friendly practices (e.g., season-long lighting reduction and permanent glass treatments) should continue to be prioritized.

Expansion of urbanization and infrastructure associated with human activities has numerous impacts on wildlife including causing wildlife-structure collisions. Collisions with building windows represent a top bird mortality source, but a lack of research into timing of these collisions hampers efforts to predict them and mitigate effects on avian populations. In Stillwater, Oklahoma, USA, we investigated patterns of bird-window collisions at multiple temporal scales, from within-day to monthly and seasonal variation. We found that collisions peaked during overnight and early morning hours, a pattern that was consistent across seasons. Further, temporal variation in fatal collisions was explained by an interaction between season and avian residency status. This interaction illustrated the expected pattern that more migrant individuals than residents collided in fall, but we also documented unexpected patterns. For example, the highest monthly total of collisions occurred in spring migration during May. We also found similarly high numbers of resident and migrant collisions in spring, and a roughly similar amount of migrant mortality in spring and fall migration. These findings, which provide unprecedented quantitative information regarding temporal variation in bird-window collisions, have important implications for understanding mechanisms by which birds collide and improving timing of measures to reduce this major bird mortality source.

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.

Millions of birds die every year from collisions with glass panes worldwide. These estimates are still scarce in the tropics, and more studies are needed to evaluate the effectiveness of preventive measures. We compared the efficacy of two methods to prevent bird-window collisions: birds of prey vs. circular decals (BPD and CD, respectively), contrasted to glass panes without any intervention. We estimated bird-window collisions in four buildings, two twin buildings with CD treatment proportionally interspersed with no decals glass panes, and two BPD-treated buildings with proportionally control area without any device. We recorded 14 collisions from nine species, mostly Columbina talpacoti (4) and Tangara sayaca (3). The highest number of collisions was against glass windows with no intervention (9; 64%), followed by those with BPD (5; 36%). No accidents were recorded against glass panes with CD. Our data may support that circular decals are more efficient than BPD to prevent bird-window collisions.

Bird-window collisions are the second leading cause of human-related avian mortality for songbirds in Canada. Our ability to accurately estimate the number of fatalities caused by window collisions is affected by several biases, including the removal of carcasses by scavengers prior to those carcasses being detected during surveys. We investigated the role of scavenger behavior in modifying perceived carcass removal rate while describing habitat-specific differences for the scavengers present in a relatively scavenger-depauperate island ecosystem. We used motion activated cameras to monitor the fate of hatchling chicken carcasses placed at building (under both windows and windowless walls) and forest (open and closed canopy) sites in western Newfoundland, Canada. We recorded the identity of scavengers, timing of events, and frequency of repeat scavenging at sites. Using 2 treatments, we also assessed how scavenging varied with 2 levels of carcass availability (daily versus every third day). Scavenger activities differed substantially between forest and building sites. Only common ravens (Corvus corax) removed carcasses at building sites, with 25 of 26 removals occurring under windows. Burying beetles (Nicrophorus spp.) dominated scavenging at forest sites (14 of 18 removals), completely removing carcasses from sight in under 24 hours. Availability had no effect on removal rate. These findings suggest that ravens look for carcasses near building windows, where bird-window collision fatalities create predictable food sources, but that this learning preceded the study. Such behavior resulted in highly heterogeneous scavenging rates at fine spatial scales indicating the need for careful consideration of carcass and camera placement when monitoring scavenger activity. Our observations of burying beetle activity indicate that future studies investigating bird collision mortality near forested habitats and with infrequent surveys, should consider local invertebrate community composition during survey design. The high incidence of invertebrate scavenging may compensate for the reduced vertebrate scavenger community of insular Newfoundland.

BackgroundIn 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.MethodsWe 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.Results and ConclusionsAfter 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.

Context Increasingly, ornithologists are being asked to identify major sources of avian mortality so as to identify conservation priorities. Aims Considerable evidence suggests that windows of office towers are a lethal hazard for migrating birds. The factors influencing the risk of bird–window collisions in residential settings are not understood as well. Methods Citizen scientists were requested to participate in an online survey that asked about characteristics concerning their homes and yards, general demographic information about participants, and whether they had observed evidence of bird–window collisions at their home. Key results We found that 39.0% of 1458 participants observed a bird–window collision in the previous year. The mean number of reported collisions was 1.7 ± 4.6 per residence per year, with 38% of collisions resulting in a mortality. Conclusions Collisions were not random, with the highest collision and mortality rates at rural residences, with bird feeders &amp;gt; rural residences without feeders &amp;gt; urban residences with feeders &amp;gt; urban residences without feeders &amp;gt; apartments. At urban houses, the age of neighbourhood was a significant predictor of collision rates, with newer neighbourhoods reporting fewer collisions than older neighbourhoods. Most people remembered collisions occurring in the summer months. Implications Our results are consistent with past research, suggesting that window collisions with residential homes are an important source of mortality for birds. However, we found large variation in the frequency of collisions at different types of residences. Proper stratification of residence type is crucial to getting accurate estimates of bird–window collisions when scaling local data into larger-scale mortality estimates.