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Collisions with glass windows of buildings, transport shelters, noise barriers and fences are a major source of bird mortality. Public awareness of bird-window collisions has increased in recent years, thanks to investigations into dead birds under windows. However, because collision events are difficult to observe directly, there are still significant gaps in understanding how and why birds fly into windows, and what happens to the birds afterwards.
New research published in the journal PeerJ provides a first insight into what happens in the moments before a bird collides or avoids a window impact, by analyzing motion-triggered audio and video recordings in a residential environment equipped with bird feeders birds. The paper offers new insight into a very important conservation topic and provides empirical data that is currently lacking but necessary to inform estimates of bird mortality impacts at the population level as well as to design effective bird mortality technologies. collision prevention.
Researchers from Western University and Purdue University compared the characteristics of bird flights leading to collisions to those of flights leading to near misses. They recorded and analyzed 29 collisions and nine near-misses. Bird flight speed and approach angle both predicted collision outcomes, with faster flights at approach angles closer to perpendicular being more dangerous to birds. These data reveal previously undocumented variations in the birds’ pre-collision behavior.
The frequency and severity of collisions underestimated
Of the 29 collisions recorded during the study, only a small proportion resulted in immediate death and were detected by building occupants. Most collisions were followed by the bird flying away without leaving a trace. It is believed that some of these birds may suffer injuries and later die away from the window. This finding has implications for estimating the impacts of bird-window collisions at the population level and suggests that the magnitude of collisions may be largely underestimated by traditional survey methods.
“Collisions between birds and windows occur all over the world throughout the year, but the frequency and severity of collisions appear to be underestimated by the public, particularly in residential environments,” writes Brendon Samuels, the first author. “One reason is that collisions occur suddenly and are difficult to observe directly. When the birds then fly away, it is unclear what ultimately happens to them. Our findings highlight how common collisions can be in residential environments, particularly where bird attractions like bird feeders are located.
Research on bird-window collisions has primarily focused on quantifying the incidence of fatal window-to-window collisions in large structures, but residential buildings are the most numerous types of structures with windows and therefore represent the most great cumulative threat to birds. New housing development is a priority in many parts of the world as demand for large windows and glass railings continues to grow. Meanwhile, backyard bird feeding has grown in popularity over the course of the pandemic, attracting more birds to high-risk environments.
New buildings can be designed based on practices that limit the risk of collisions between birds and windows. Likewise, windows in existing buildings, such as those in homes, can be renovated using simple materials to add visual markers to the exterior of the glass. An important direction for future research is to characterize how birds orient their eyes to detect and avoid window collisions, so that collision deterrents can be optimally designed to match birds’ vision. This study documented birds approaching windows from varying angles. The authors recommend that the design and testing of crash prevention technologies take this into account.
The authors developed recommendations for actions to reduce bird mortality caused by window collisions and fill current knowledge gaps by providing scientists, practitioners, and policymakers with priorities that will help inform future research and monitoring studies.
Recommendations
Estimates of bird-window collision mortality that are based on data collected from building surveys and other observational monitoring dependent on carcass detection must consider that these methods will miss most events. collisions that occur, but may not leave any trace. The total number of collisions that occur in a given building or across a continent may be significantly underestimated.
Additional studies characterizing how flight characteristics affect the force experienced by a bird during a collision will provide better estimates of the negative effects on birds capable of flight after a collision.
Although this study did not examine the effectiveness of bird collision deterrents, the risk of collision on existing and new structures can be reduced through the application of “bird friendly” materials such as frit glass, window film or other visual markers.
This study found that bird collisions occurred almost as frequently with smaller transom windows as with large glass doors below. This contradicts previous research findings that collisions are positively correlated with window area. Further research is needed to examine how features of residential building facades, such as window area, influence crash risk. Windows of all sizes should be targeted to mitigate collision risk using deterrent technologies and evidence-based building design practices as outlined in bird-friendly standards and guidelines.
Because bird flight speed before impact predicts the lethality of window collisions, researchers recommend that bird attractants (feeders or baths) be placed near windows (within 1.5 feet or 0 .5 m) in order to reduce the space available where birds can gain speed.
Thanks to PeerJ for providing this news.
More information: Brendon Samuels et al, Opening the black box of bird-window collisions: passive video recordings in a residential yard, PeerJ (2022). DOI: 10.7717/peerj.14604
