Window collisions are a leading cause of fatality in birds in built-up areas, a tragic statistic that is rising considerably with the rapid growth of cities and the number of residential properties being constructed.
But just why do birds fly into windows, and is there anything that can be done to avoid such hazardous situations? Join us as we look at some of the reasons why birds might not be aware of a pane of glass in their flight path until it is too late.
A 2014 study reported that up to 1 billion birds die each year following collisions with windows. A leading cause of these fatalities is when birds in flight fail to realize that the enticing environment ahead of them is in fact simply the outside world reflected in a pane of glass.
Being unable to see glass or discern between a reflection of outdoor foliage or a potential ‘habitat’ visible indoors, behind a pane of glass, can prove to be hugely disadvantageous, particularly for urban-dwelling birds. Migratory birds are also at risk from severe injury or death from night-time window collisions, being drawn off course by bright lights illuminating the darkness.
Birds commonly fail to mistake reflections for the real world
Birds cannot grasp the concept of a window pane forming an invisible barrier between the end of their natural environment and the inside world. Indoor plants and foliage may also confuse birds, causing them to fly into glass when they are attempting to reach an enticing foraging spot.
Territorial birds may also catch sight of their own reflection in a well-polished window and boldly challenge what they perceive to be an intruder on their patch by flying into a glass plane to drive its rival away. This behavior has been particularly observed in Northern cardinals and American robins, and is especially common during breeding season.
Certain simple actions can be taken to limit the chances of glass collisions. However, in the ever-changing landscape of the modern world, it is sadly inevitable that large numbers of birds will continue to fly into windows and buildings each year.
Read on to learn more about what can be done to make windows in your home as bird-friendly as possible.
Territorial birds such as Eurasian Blue Tits often can be seen trying to fight off their reflection
Fortunately there are some simple steps you can take to minimize the chances of a bird flying into the windows or your home or place of work.
Tips for making your windows bird friendly include adding decal stickers to a window pane, to indicate that there is a solid surface ahead. Drawing patterns, such as gridlines, on the outside of a window pane with a bar of soap will have the same effect.
Birds tend to avoid surfaces with horizontal or vertical stripes. You’d simply need to ensure that the gaps between the gridlines is small enough for a bird not to attempt to fly through.
Backyards with bird feeders report a higher incidence of window collisions, which may just naturally correspond to a higher concentration of visiting birds. However, it makes sense to place feeders and bird baths as far from windows as possible.
Fitting exterior shutters is another option; this will effectively eliminate the amount of potentially hazardous glass surface that a bird might fly into. Alternatively, window awnings reduce the amount of glare on a window, and can potentially save birds’ lives by not reflecting tempting garden greenery.
A glass wall with anti-collision stickers to prevent bird strikes
Because many skyscrapers are illuminated at night and have a large surface area of glossy windows, they might be considered a more significant threat to birds. But in fact, statistics show that more window collisions take place during the day, and high-rise buildings with more than 11 floors account for only 0.1 percent of all collisions in the US.
Most buildings involved in bird collisions are either residential homes (44 percent) or low-rise blocks (55 percent) and almost half occur at home windows; low-rise buildings account for almost all of the rest.
Birds can suffer catastrophic injuries if they fly into a window, and research shows that even those that do not die instantly will sustain serious and irreversible trauma to their brain and other internal organs, which will typically end in fatality.
A bird’s chance of surviving a collision with a window depends on a number of factors, including the size and species of a bird, whether the building is a high or low rise, and the speed of the bird on impact. According to data, 64.5 percent of window collisions involving birds have a fatal outcome.
Sadly, many birds sustain serious injuries flying into windows, so even if they are initially stunned and fly off when they appear to have recovered.
In many cases, the likelihood of fatality is high, with trauma from the impact causing irreversible damage to a bird’s brain and other internal organs.
A sad picture of a great tit fatality after striking a window
Because birds, except for nocturnal species, are generally less active after dark, night-time window collisions are far rarer than those during bright daylight hours, but that’s not to say that they do not ever happen.
Certain bird species, including thrushes and warblers, do migrate at night, and are at risk of colliding with unlit buildings as well as with brightly lit ones. Unpredictable weather can also throw birds off course when flying over cities, where the city skyline can pose a serious risk under cover of darkness.
Overcast or foggy skies reduce visibility at higher altitudes, meaning birds fly at a lower level and there is greater danger of flying into various manmade structures.
A bird flying at a window
Even humans are unable to detect the presence of a transparent piece of glass. Freak accidents can occur when people misjudge whether a window or door frame is empty or filled with glass and end up bumping into an invisible barrier.
We are conditioned to look for visual clues, such as frames, handles, so thankfully these incidents are not common and rarely life-threatening.
Birds are also unable to see glass, but do not develop the same level of awareness as humans about window frames or catches, glass patio doors, and mirrored surfaces.
If they do survive a collision with a particular window, then there is a chance that they will become aware that that specific spot poses a threat, but this will not deter them from flying into other pieces of glass elsewhere.
A young blue tit fledgling looking at reflection in the glass
From observing bird behavior in front of glass or mirrored surfaces, it appears likely that they do not actually recognize themselves, but instead may see the reflected bird as a threat to their territory.
During breeding season, territorial birds are regularly seen tapping on windows in attempt to drive off the “intruder” who has dared to persistently encroach on their home turf, without realizing that it is in fact simply their own reflection and it is not possible to drive it away.
Many superstitions exist that involve birds, and birds flying into windows is no exception.
Some people believe that when a bird collides with a pane of glass it is a symbol of impending doom, or an indication of money worries. For others, it is a sign that change (either good or bad) is on the horizon, and the bird is simply a messenger.
Science explains these collisions as a simple miscalculation on the bird’s part as to where the natural environment begins and ends.
Do you have a question about this topic that we haven't answered? Submit it below, and one of our experts will answer as soon as they can.
Get the latest BirdFacts delivered straight to your inbox