Bird–window collisions
However, due to differences within the taxon, built environments, time of year, and other effects, there is great variation in the nature and frequency of collisions.
Examples include differences in vision, degree of flocking, flight behaviors, and more specific life history traits, such as provisioning of young.
[6] The reason for these species' vulnerability is not well understood, but it is speculated that species-specific behaviors are a likely contributor, as other factors like flight altitude differ greatly between these groups.
[2] Species like Cedar Waxwings, which make up a disproportionately high amount of window collisions in the fall and winter, are thought to be susceptible due to their flocking behaviors.
[15] Building layout, orientation, and spacing within a city is another a contributing factor to bird-window collisions, as we often see topographical features within urban planning that channel or concentrate bird movements.
We may also see channeling effects at a fine scale, when architectural corridors guide bird flight paths into areas of increased collision risk.
[19] It is therefore speculated that these artificially illuminated areas conceal the visual navigation cues that these birds rely on, resulting in them becoming disoriented.
[8] This hypothesis has been well supported by several observations of birds being attracted to and disoriented by lights, particularly in conditions of poor-visibility, which makes them more susceptible to colliding with buildings.
[22] Conditions which reduce visibility, such as fog, rain, or snow, can disorient birds, especially those that migrate at night and rely on visual cues.
Low wind speeds can also result in poor lift for larger, soaring raptors, which can lead to collisions with skyscrapers.
[25] Some of the highest reports of bird fatalities from window collisions have occurred when migrating passerines began their journey in good weather conditions, but hit a cold front which forced them to lower altitudes.
The use of ultraviolet (UV) signals to make windows appear visible to birds, while once one of the most common means of combatting this issue, is no longer recommended by experts.
In December 2019, a bill passed mandating that the lowest 75 feet of new buildings, and structures above a green roof, must use materials such as patterned glass which are visible to flying birds.
