Bird-window Collisions Research Articles

Shadow-boxing: Major gaps to knock out in bird–window interaction research

Abstract Bird–window collisions are a leading source of bird mortality worldwide, estimated to kill as many as 1 billion birds annually in the U.S. alone. Though researchers have examined the factors contributing to general bird–window collisions, shadow-boxing, a nonfatal but potentially ecologically significant bird–window interaction, has primarily been excluded from the conversation. Shadow-boxing occurs when birds attack their reflection in human-made surfaces believing the reflection to be another individual intruding on their territory. Current bird–window interaction research often does not consider the unique drivers, impacts, and mitigation strategies associated with shadow-boxing. In this paper, we identify 5 major knowledge gaps: (1) building and environmental characteristics that lead to shadow-boxing; (2) the impacts on individual birds, (3) populations, and (4) people; and (5) the effectiveness of existing mitigation strategies for shadow-boxing. For each knowledge gap, we list research questions that will further our understanding of the scale and significance of shadow-boxing.

Evidence, consequences, and angle of strike of bird–window collisions

Evidence, consequences, and angle of strike of bird–window collisions

Navigating a path: Advocacy strategies of a migratory bird NGO

To achieve their goals, non-governmental organizations (NGOs) frequently interact with public and private stakeholders. Interactions can be generally characterized as falling within a continuum of collaborative to confrontational approaches, with each approach having advantages and disadvantages. A more collaborative approach may lead to opportunities to share data and access funding; however an NGO may risk its goals becoming compromised. Similarly, a more confrontational approach can draw attention to NGO causes and effect change, but may limit opportunities for partnership. This paper considers how a NGO concerned with preventing bird-window collisions has balanced between collaboration and confrontation with municipal government and commercial properties. While this NGO’s strategy has been largely collaborative, its experience also demonstrates that confrontational approaches, while less frequent and indirect, also have a role in attaining objectives.

Citizen science to address the global issue of bird–window collisions

Bird–window collisions (BWCs) are a major threat to avian populations, annually causing up to one billion bird deaths in the US alone and untold numbers of fatalities worldwide. Until recently, there has been limited institutional and governmental recognition of this issue and few coordinated, national‐level efforts to address it. To fill this need, citizen‐science campaigns have stepped in to generate scientific information about BWCs, raise public awareness, and advocate for policy and actions to reduce collisions. We review the BWC issue and showcase how citizen‐science programs in multiple countries have achieved these outcomes. Additional citizen‐driven successes in addressing BWCs are possible if key constraints are overcome, including funding limitations and challenges of proactively engaging stakeholders who can reduce BWCs at scale. Addressing this global conservation issue will also require building upon the recent increase in attention to BWCs by government agencies, nongovernmental organizations, commercial entities, and professional scientists.

Another emerging threat to birds: avian mortality estimates from roadside transparent noise barrier collisions in South Korea

Summary Birds in flight are prone to collide with various transparent or reflective structures. While bird–window collision has been recognised as a critical conservation issue, collision with other transparent structures has been less understood. Noise barriers made of transparent materials are considered critical hazards for birds; however, little is known about the bird mortality they cause. We conducted the first nationwide-scale estimates of bird-collision mortality caused by transparent noise barriers (TNBs) along roads in the Republic of Korea. The total length of existing roadside transparent noise barriers was estimated at 1,416 km nationwide (as of 2018), and it had been increasing exponentially. Based on carcass surveys at 25 sites, daily mortality at the observed barriers was 0.335 ± 1.132 birds/km on average, and no difference in observed mortality was detected between both sides of a single barrier and between road types (i.e. local roads and motorways). Finally, we estimated that approximately 186,000 birds (95% confidence interval: 162,465–204,812 birds) are killed annually by collisions with roadside TNBs. As privately installed barriers were not considered in this study, the actual mortality is likely be higher than our estimates. Thus, collision with TNBs could become an emerging threat to avian conservation, especially in developing and urbanising regions around the world. As such structures are not formally recognised as conservation issues of importance, more systematic surveys aided by citizen science, both for the status of TNBs and bird-collision mortality, are needed in addition to management and mitigation policies.

Seasonal variation in drivers of bird-window collisions on the west coast of British Columbia, Canada

Seasonal variation in drivers of bird-window collisions on the west coast of British Columbia, Canada

Field-testing effectiveness of window markers in reducing bird-window collisions.

The online version contains supplementary material available at 10.1007/s11252-022-01304-w.

Opening the black box of bird-window collisions: passive video recordings in a residential backyard.

Collisions with windows on buildings are a major source of bird mortality. The current understanding of daytime collisions is limited by a lack of empirical data on how collisions occur in the real world because most data are collected by recording evidence of mortality rather than pre-collision behaviour. Based on published literature suggesting a causal relationship between bird collision risk and the appearance of reflections on glass, the fact that reflections vary in appearance depending on viewing angle, and general principles of object collision kinematics, we hypothesized that the risk and lethality of window collisions may be related to the angle and velocity of birds' flight. We deployed a home security camera system to passively record interactions between common North American bird species and residential windows in a backyard setting over spring, summer and fall seasons over 2 years. We captured 38 events including 29 collisions and nine near-misses in which birds approached the glass but avoided impact. Only two of the collisions resulted in immediate fatality, while 23 birds flew away immediately following impact. Birds approached the glass at variable flight speeds and from a wide range of angles, suggesting that the dynamic appearance of reflections on glass at different times of day may play a causal role in collision risk. Birds that approached the window at higher velocity were more likely to be immediately killed or stunned. Most collisions were not detected by the building occupants and, given that most birds flew away immediately, carcass surveys would only document a small fraction of window collisions. We discuss the implications of characterizing pre-collision behaviour for designing effective collision prevention methods.

LEED Certified Buildings and Bird-Friendly Window Design

Green buildings (i.e., LEED certified buildings) emphasize access to daylight and views for occupants’ wellbeing, comfort, and productivity. Window glazing allows access to daylight and views but is often detrimental to birds. Annually, up to a billion bird in the United States die due to window collisions. A comprehensive literature review and data analysis of LEED and methods of deterring collisions was conducted to determine solutions to limit bird deaths at LEED certified buildings. Deterrence factors of building design, outdoor surroundings, and occupant behavior were evaluated, due to their collective impact on bird-window collisions. To best prevent collisions and adhere to LEED, window glazing with visual markers and sound deterrents should be used. Certain façades should be avoided and building lights should be turned off during migration season. Additionally, vegetation near buildings is encouraged in LEED certification, but increases the frequency of bird-window collisions. These findings suggest that LEED, particularly the credit “Daylight and Quality Views,” is not completely aligned with current bird-safe design practices. While certain window glazing is acceptable for both LEED and bird-safe design, the two are not mutually exclusive. Due to this, it is recommended that window glazing that aligns with LEED and is bird-safe, is made clear within the LEED “Daylighting and Quality Views” credit description. LEED and bird-safe design practices also have contradictory views on vegetation near buildings. There should also be further research into if vegetation near buildings would still increase bird-window collisions if deterrent factors, such as bird-safe windows, were utilized.

Bird–building collisions increase with weather conditions that favor nocturnal migration and with inclement and changing weather

AbstractCollisions 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.

Bird protection treatments reduce bird-window collision risk at low-rise buildings within a Pacific coastal protected area.

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.

Stakeholder perceptions of bird-window collisions.

Bird-window collisions are a major source of human-caused avian mortality for which many mitigation and prevention options are available. However, because very little research has characterized human perspectives related to this issue, there is limited understanding about the most effective ways to engage the public in collision reduction efforts. To address this research need, we: (1) evaluated how two stakeholder groups, homeowners and conservation practitioners, prioritize potential benefits and obstacles related to bird-window collision management, (2) compared priorities between these groups, and (3) evaluated potential conflicts and collective strength of opinions within groups. We addressed these objectives by merging the strengths, weaknesses, opportunities, and threats (SWOT) and analytic hierarchy process (AHP) survey approaches. Specifically, survey respondents made pairwise comparisons between strengths and weaknesses (respectively, direct outcomes and barriers related to management, such as fewer collisions and increased costs) and opportunities and threats (indirect outcomes and barriers, such as increased bird populations and fewer resources for other building-related expenses). Both homeowners and conservation practitioners ranked strengths and opportunities higher than weaknesses and threats, indicating they have an overall positive perception toward reducing bird-window collisions. However, key obstacles that were identified included costs of management and a lack of policy and guidelines to require or guide management. These results suggest that substantial advances can be made to reduce bird-window collisions because both homeowners and conservation practitioners had positive views, suggesting their receptivity toward collision management measures. However, because of more neutral views and conflicting responses within the homeowner group, results also highlight the importance of targeting homeowners with education materials that provide information about bird-window collisions and solutions that reduce them. Because bird-window collisions are a human-caused phenomenon, such information about human perspectives and priorities will be crucial to addressing this threat and thus benefitting bird populations.

A Bird's-Eye View: Novel Use of Drone Images to Quantify Differences in Altitudinal Reflections in Bird-window Collision Studies

Bird-window collisions (BWCs) constitute a significant source of mortality for both resident and migratory birds. Because windows reflect surrounding landscape components, such as vegetation or sky, birds do not always perceive glass as a barrier. Here we demonstrate a novel technique to classify and quantify reflections in windows on the Radford University campus in southwest Virginia, U.S.A. We deployed a consumer-grade Unmanned Aerial Vehicle, i.e., drone, to photograph 14 contiguous or near-contiguous window columns across five campus buildings in August 2020. For each study aspect, the drone (equipped with an RGB camera) captured images at ca. 5 m altitudinal increments from the ground floor to the roof of each building (three to six images/vertical column). We then manually classified each image in ImageJ to calculate approximate proportions of reflected: (1) vegetation, (2) sky, (3) and artificial structures or impervious surfaces, plus (4) nonreflective glass. We used a generalized linear model to determine how proportional reflections of vegetation, sky, buildings, and nonreflective glass varied across vertical increments. We found the proportion of sky significantly decreased with increasing photo heights, whereas proportion of nonreflective glass significantly increased with increasing heights. This supports previous findings that because birds are drawn to sky reflections, they may collide at relatively lower positions on buildings. Inconsistency in landscape design and building positioning on the campus precluded trends in vegetative or building reflections by height. Our pilot study demonstrates the applicability of a consumer-grade drone for investigating visual characteristics of reflections that influence BWCs from variable observation angles. We suggest the expanded use of drone images as a straightforward technique to measure changes in reflection characteristics from varying degrees of observation. They are a novel method in developing a BWC risk assessment as well as potential mitigation strategies in a suburban or campus environment with buildings of intermediate heights.

Do lighting conditions influence bird–window collisions?

Do lighting conditions influence bird–window collisions?

Using citizen science to identify environmental correlates of bird-window collisions in Poland

Bird collisions with windows are among the highest sources of human caused mortality to this group of animals. However, environmental correlates of spatial patterns in collision risk are poorly understood, thus making mitigation measures difficult to implement. We took advantage of Covid-19 lockdown in the spring of 2020, when people were obligated to stay mainly at home, and performed a memory-recall questionnaire survey concerning bird-window collisions in Poland. We received information on bird-window collisions with 1800 buildings across the whole country accompanied by characteristics of each building, its vicinity and resident's behavior (time spent home, window cleaning). We supplemented these data with landscape description and performed statistical models to estimate importance of 13 explanatory variables as predictors of number of bird-window collisions. Reported number of collisions increased with the share of forests and arable land within 2 km of the building, and with proximity to rivers. Number of collisions also increased when single trees were close to buildings. More collisions were reported for houses than for flats and for new buildings than for old ones. Reported number of collisions increased with window cleaning which might suggest that cleaning reduces glass visibility for birds. As bird-window collision risk is highly variable among buildings but can be reduced with several measures improving glass visibility for birds, we recommend to use predictive models to identify collision hotspots for applying these measures. New houses located near rivers, in forests or agricultural landscapes have highest collision risk, and trees near buildings, often planted to benefit birds, can additionally elevate collision rate, thus potentially creating ecological traps. In such collision hotspots, reduction of window cleaning frequency can be considered as a mitigation measure unless the visual markers improving glass visibility for birds are installed on the panels.

Bird-window collisions: Mitigation efficacy and risk factors across two years.

BackgroundResearch on bird-window collision mitigation is needed to prevent up to a billion bird fatalities yearly in the U.S. At the University of Utah campus (Salt Lake City, Utah, USA), past research documented collisions, especially for Cedar Waxwings (Bombycilla cedrorum) drawn to fruiting ornamental pears in winter. Mirrored windows, which have a metallic coating that turns window exteriors into mirrors, had frequent collisions, which were mitigated when Feather Friendly®bird deterrent markers were applied. Bird-friendly windows–ORNILUX®ultraviolet (UV) and fritted windows–also reduced collisions when data were collected across fall and winter. Extending this prior research, we evaluated additional mitigation and tested the replicability of effects for pear trees, mirrored windows, and bird-friendly windows across two years.MethodsUsing published data from eight buildings monitored for collisions in year 1 (Fall and Winter, 2019–2020), we added another year of monitoring, Fall and Winter, 2020–2021. Between years, Feather Friendly®mitigation markers were added to collision-prone areas of two buildings, including both mirrored and transparent windows.ResultsThe two buildings that received new Feather Friendly®mitigation had significantly fewer collisions post-mitigation. Control areas also had nonsignificant decline in collisions. The interaction of area (mitigation vs. control) by time (year 1 vs. 2) was significant, based on generalized estimating equations (GEE). The total yearly collisions across all eight buildings declined from 39 to 23. A second GEE analysis of all 8 buildings showed that mirrored windows, pear trees, and bird-friendly windows were each significant when analyzed separately. The best-fit model showed more collisions for mirrored windows and fewer collisions for bird-friendly windows. We found pear tree proximity to be related to more collisions in winter than fall. In addition, pear trees showed reduced collisions from year 1 to 2, consistent with new mitigation for two of three buildings near pear trees.DiscussionFeather Friendly® markers can mitigate collisions with transparent windows, not only mirrored windows, compared to unmitigated areas over 2 years. Results also underscore the dangers of pear tree proximity and mirrored windows and the efficacy of bird-friendly windows. Thus, bird collisions can be prevented by window mitigation, permanent bird-friendly windows, and landscape designs that avoid creating ecological traps.

Cat and dog predation on birds: The importance of indirect predation after bird-window collisions

Predation of free-living birds by cats (Felis silvestris catus) and dogs (Canis lupus familiaris) is one of the main urbanization impacts on avifauna worldwide. In addition to direct predation, these pets capture birds after window collisions, an unexplored human cause of avian mortality. In this study we (1) estimated the number of cats and dogs in Argentina, (2) calculated the metrics of direct bird predation by cats and dogs, (3) analyzed factors that influence the probability of pets capturing birds, and (4) estimated annual bird mortality due to pet predation following bird-window collision events. To this end, we conducted an online survey to collect information on bird predation by cats and dogs in Argentina, both direct and indirect after bird-window collisions. We found that more than 68% of participants had at least one dog or cat, and of these, 45.3% reported having observed at least one case of bird predation by cats or dogs in their household. We estimated that the rough annual bird mortality rate due to predation following bird-window collisions could reach approximately 6 million birds in Argentina (range = 1–11 million birds). Our results show that direct bird predation by pets but also indirect predation after bird-window collisions represents a considerable source of avian mortality, which requires further attention in pursuit of solutions.

Biases in Bird-Window Collisions: A Focus on Scavengers and Detection Rates by Observers

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.

Multi-scale temporal variation in bird-window collisions in the central United States

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.

Ultraviolet-reflective film applied to windows reduces the likelihood of collisions for two species of songbird.

Perhaps a billion birds die annually from colliding with residential and commercial windows. Therefore, there is a societal need to develop technologies that reduce window collisions by birds. Many current window films that are applied to the external surface of windows have human-visible patterns that are not esthetically preferable. BirdShades have developed a short wavelength (ultraviolet) reflective film that appears as a slight tint to the human eye but should be highly visible to many bird species that see in this spectral range. We performed flight tunnel tests of whether the BirdShades external window film reduced the likelihood that two species of song bird (zebra finch, Taeniopygia guttata and brown-headed cowbird, Molothrus ater) collide with windows during daylight. We paid particular attention to simulate the lighting conditions that birds will experience while flying during the day. Our results indicate a 75–90% reduction in the likelihood of collision with BirdShades-treated compared with control windows, in forced choice trials. In more ecologically relevant comparison between trials where all windows were either treated or control windows, the estimated reduction in probability of collision was 30–50%. Further, both bird species slow their flight by approximately 25% when approaching windows treated with the BirdShades film, thereby reducing the force of collisions if they were to happen. Therefore, we conclude that the BirdShades external window film will be effective in reducing the risk of and damage caused to populations and property by birds’ collision with windows. As this ultraviolet-reflective film has no human-visible patterning to it, the product might be an esthetically more acceptable low cost solution to reducing bird-window collisions. Further, we call for testing of other mitigation technologies in lighting and ecological conditions that are more similar to what birds experience in real human-built environments and make suggestions for testing standards to assess collision-reducing technologies.