Rest in peace, little pigeon!

It was a typical Tuesday afternoon when an ominous loud thud from the windows interrupted our professor’s passionate lecture. A feather was left stuck on the glass panel, with suspicious blood stains dotting the glass. I spun around and saw faces of horror and trauma – they had all, unfortunately, witnessed the full speed collision of an unsuspecting bird into the window.

Victim of the bird-building collision, a male Pink Neck Green Pigeon
Photo by Lim Chun Wei

A few weeks ago, in the same room, we learnt that bird-building collision (also known as window strike) is not a rare occurrence in cities. In the United States alone, an estimated 97.6 to 975.6 million birds die each year from window strikes (Klem, 1990). The worldwide death toll is estimated to be in the billions (Klem, 2008)! Singapore, however, does not have a comprehensive study on this issue. To change things up, the Bird Group embarked on a five-year study of migratory bird collisions in Singapore. Their preliminary data documented a total of 47 window strike between September 2014 and April 2015, with 20 in the central business district (Low, 2015).

Reasons for window strikes

So why do birds crash into windows? Can’t they see the glass? Well surprisingly (or not), windows are invisible to them (Klem, 1989). Birds usually cannot differentiate between reflections and real vegetation. They collide into window panes when flying through vegetation in urban areas, either by trying to reach the reflected greenery or attempting to fly through the corridors to vegetation on the other side (Klem, 2006). In some cases, a territorial bird sees its own reflection as a rival and launches repeated attacks on the window pane (Klem, 2006). Lastly, some migratory birds use celestial patterns to find their way at night. Artificial lights from buildings confuse them, thus attracting these birds to their doom (Low, 2015). On an unrelated note, Singapore actually tops the list as one of the world’s worst light polluted country (Falchi et al., 2016).

Perhaps our lights are a bit too bright?
Photo by Rodney Topor
(Image from:

Contrary to popular belief, most victims of window strikes die not from a broken neck, but instead, due to intracranial haemorrhage. A head on collision ruptures the blood-brain barrier, leading to sub-dural bleeding and brain damage (Klem, 1990a). The most observable external injury is usually a broken beak. And not all birds die from the collision. Some may be stunned or unconscious but then fly off once they recover. Others may merely be startled and fly off immediately (Klem, 1990a).

Ways to prevent window strikes

Over the past few years, many have poured in efforts in search for ways to prevent possible bird-building collision. Here are some of the commonly used methods to counter the window strike problem:

  1. Use of Window Patterns

A relatively simple way to counter window strikes would be to put patterns on the glass, so that the birds can see the windows. In the video below, Christine Sheppard, Collisions Program Manager for the American Bird Conservancy, has being working with her research team to find the most effective window patterns to prevent window collisions.

(Source: YouTube)

Their experimental results show that most birds avoid flying through a horizontal spacing of less than 2 inches (~5cm) or vertical spacing of less than 4 inches (~10cm). Therefore, decal patterns placed uniformly on the window pane or tape strips can be placed to prevent window strikes. UV stickers that are invisible to our eyes but visible to the birds can also be used to maintain the aesthetic of a “clear” glass (Cornell Lab, 2009). In any case, patterns must be on the outside of the window (facing the birds) for it to be effective.

  1. External window accessories

Do you have problems with birds hitting your windows but don’t want to change your window glass or tediously apply decals? Window screens could be your answer! Small-mesh netting or window screening can be placed outside a window, at least 3 inches away from the glass. If the netting is taut enough, birds can bounce off before colliding with the actual glass. External shutters or sun shade can also be used to block the reflection of the glass, making the window entirely opaque when it is not in use (Cornell Lab, 2009).

Bird screen used on window
(Image from:

  1. Switching off unused lights at night

(Source: YouTube)

For tall commercial buildings, like in the Central Business District, you should consider turning off the lights at night. I understand that a lit up building may create a pretty night-time skyline, but this video above may persuade you otherwise. It discusses reasons why birds might prefer to fly at night and how they are attracted to light sources in buildings (Soh, 2014). One campaign to switch off lights in Chicago resulted in an 80% drop in mortality due to bird-building collisions show how effective this strategy can be. Aside from saving birds’ lives, you get to save on electricity too. So it’s a win-win situation for you!

  1. Relocating bird feeders

For bird lovers who have bird feeders at home, you may want to reconsider their placements. If you would like to place the bird feeder nearer to your home, you should keep it within 0.9m from your window (Cornell Lab, 2009). Anything beyond that, the speed they gathered when taking flight from the feeder to the window can result in a fatal impact. For those who are uncomfortable with a bird feeder so near to home, you can alternatively, place your feeder at least 9m away from your windows (Cornell Lab, 2009). This would then ensure that birds will not associate them as possible habitats when they fly off from the feeder. Don’t let your love for birds be the cause of their death!

Final thoughts

Ever run into glass doors because you were not looking? You may have ended up with a bruised nose but to birds, glass can be fatal. Birds are not just simply pretty to look at, they also play important ecological roles. Birds are great seed dispersers and pollinators. So when the bird populations decline, reproduction rates of many plants also decrease too (Tabur & Ayyaz, 2010). Recognising the importance of birds, cities like Toronto, Chicago and New York City have put in place policies and guidelines to mitigate the bird-building collisions problem. Perhaps it’s about time for Building and Construction Authority (BCA) to look into updating its building regulations too?



Cornell Lab. (2009). Why Birds Hit Windows—And How You Can Help Prevent It. Retrieved from

Falchi, F., Cinzano, P., Duriscoe, D., Kyba, C. C., Elvidge, C. D., Baugh, K., & Furgoni, R. (2016). The new world atlas of artificial night sky brightness. Science advances2(6), e1600377.

Klem, D. Jr. (1990). Collisions between birds and windows: mortality and prevention. Journal of Field Ornithology 61:120–128.

Klem, D. Jr. (1990a). Bird Injuries, Cause of Death, and Recuperation from Collisions with Windows. Journal of Field Ornithology 61 (1): 115-19

Klem, D. Jr. (2008). Avian mortality at windows: the second largest human source of bird mortality on Earth. Tundra to tropics: connecting birds, habitats and people.

Klem, D. Jr. (2006). Glass: a deadly conservation issue for birds. Bird Observer34(2), 73-81.

Low, A. (2015). Migratory Bird Collisions in Singapore. Singapore Bird Group. Retrieved from

Loh, J. (2014). Lights Out Effort Reduces Deadly Bird-Building Collisions. VOA News. Retrieved from

Tabur, M. A., & Ayvaz, Y. (2010). Ecological importance of birds.