Quick Answers
Birds can be either dead or stunned when they collide with windows. Smaller birds are more likely to die instantly from the impact, while larger birds may just be temporarily stunned. It depends on the speed and angle at which the bird hits the window, as well as the size and fragility of the bird. If a bird is only stunned, it can often recover if given some time to rest in a safe place.
Birds frequently collide with windows on buildings, vehicles, and homes. In fact, window collisions are one of the leading causes of bird deaths worldwide. It is estimated that up to 1 billion birds die each year from striking windows in the United States alone (2). When a bird hits a window, there are two possible outcomes – the impact may kill the bird instantly, or it may just stun or knock out the bird temporarily. But how can you tell the difference between a dead bird versus one that is unconscious or stunned? There are several factors that determine whether a bird will survive a window collision.
What Causes Birds to Hit Windows?
Before examining the effects of window strikes, it is helpful to understand what causes birds to hit windows in the first place. There are a few key reasons why birds collide with glass (3):
- Reflections – Windows can reflect nearby trees, shrubs, or sky that birds may try to fly towards.
- Transparency – Birds do not see glass and may try to fly straight through what appears to be an open space.
- Light emission – Artificial lights from inside buildings can disorient birds at night.
Birds have very sharp vision for detecting movement, but they cannot easily distinguish glass from open air. Windows essentially create an invisible barrier that birds do not sense.
Factors That Determine Impact Severity
Several factors influence the severity and outcome when a bird hits a window (4):
Speed of Impact
Birds that are flying faster when they collide will experience more traumatic injuries. Low-impact collisions are less deadly.
Bird Size and Species
Small birds such as hummingbirds are much more vulnerable to being killed from a window strike compared to larger birds. Larger birds have thicker skulls and more body mass to absorb the impact.
Window Size
Larger glass expanses are linked to higher mortality rates, as birds reach greater speeds flying across longer distances. Smaller windows cause less damage.
Angle of Impact
Direct head-on collisions are more lethal compared to glancing blows or strikes with the body rather than head.
Glass Type
Some modern glass types with UV coatings or etching may help reduce collisions. Older glass tends to cause more deaths.
These factors work together to determine the amount of force and trauma that occurs when a bird hits a window. Under the right conditions, a strike can be gentle enough to just stun the bird without causing life-threatening injuries.
Signs a Bird is Dead from Window Strike
There are clear signs that indicate a bird was immediately killed from a collision with glass. Here are the characteristics of a bird that is dead (5):
- No visible breathing, completely still and unresponsive
- Eyes are closed
- Body is limp (no muscle tension)
- Legs are curled up underneath body
- No response to gentle stimulation
Birds killed instantly from window strikes will exhibit these unmistakable signs of death very soon after the impact. The body becomes stiff within an hour after dying (known as rigor mortis). If there is any question about whether the bird is dead or unconscious, it is best to monitor for at least an hour for any return of breathing, movement, or eye opening. Birds that remain motionless with closed eyes for over an hour can safely be declared deceased.
Physical Trauma from Lethal Collisions
Severe window collisions cause traumatic injuries that can kill birds rapidly (1):
- Skull fractures – The skull is shattered from the blunt force, damaging the brain.
- Neck trauma – The neck may snap from the collision’s whiplash effect.
- Internal hemorrhaging – Organs like the lungs and liver bruise and bleed profusely.
- Ruptured air sacs – Delicate respiratory structures in the body cavity burst.
These severe internal injuries typically result in immediate or very rapid death at the site of impact. There is no chance for recovery or treatment when such extensive damage occurs.
Signs a Bird is Stunned from Window Strike
In some instances, a bird can hit a window without sustaining critical injuries and will be temporarily stunned or knocked out for a period of time. Here are signs that a bird is still alive but unconscious after a window collision (6):
- Eyes are fully or partially closed
- Body is limp but some muscle tension remains
- Slow, irregular breathing
- Inability to lift head or move but occasional twitching of feet or wings
- No response to touch or stimulation
Birds in this stunned state will be unresponsive but may show some reflexive movements like toe clenching or beak opening. Recovery takes anywhere from a few minutes to a few hours depending on the impact severity. Birds that start to revive will lift their heads, open their eyes, attempt to shuffle away using their feet, and ultimately try to fly off.
Minor Injuries in Birds Stunned by Windows
While a stunned bird often recovers fully, some may sustain minor wounds from a window strike:
- Head trauma – Cuts, bruises or swelling around head and face.
- Eye injury – Pupil dilation or discharge from ocular trauma.
- Beak damage – Chipped or fractured upper or lower beak.
- Broken feathers – Missing or snapped feathers, especially on wings.
- Foot injury – Sprains, fractures, or limb misalignment.
These minor injuries may heal on their own over time or require veterinary treatment. Even birds that make a full recovery may suffer some permanent disability, like vision loss from damaged eyes.
Providing Care for a Stunned Bird
If you find a bird dazed or unconscious from an apparent window collision, here are important steps to help it recover (7):
- Gently place the bird in a cardboard box lined with a soft cloth. Keep in a warm, quiet, dark place.
- Do not try to give food or water, as injured birds may aspirate liquids.
- Monitor breathing and response every 15-20 minutes, without excessively disturbing the bird.
- Once the bird revives, release it outdoors near site of collision.
- If no improvement after 2 hours, take the bird to a wildlife rehabilitation center.
Extending this emergency care gives the stunned bird the best chance of regaining normal function. Even if the bird initially seems to recover, veterinary evaluation is recommended to check for any underlying injuries requiring treatment before release back to the wild.
Key Points for Caring for Stunned Birds
Some key points to remember when handling stunned birds:
- Do not offer food/water.
- Keep warming pad under box in cool weather.
- Open box outdoors when releasing bird.
- Take to rehab center if unable to fly after 2 hours.
- Wear gloves to avoid biting/scratching injuries.
With appropriate care, many stunned birds make a full recovery within a day and can be returned to the wild.
Preventing Bird Window Collisions
Given the high mortality rates from window strikes, the best way to protect birds is to prevent collisions. Here are some effective deterrents to apply on windows (8):
Screens and Netting
Install screens or netting over glass surfaces. This creates a visible barrier that birds avoid.
Decals and Tape
Apply strips or patches of tape/decals with patterns that birds can see and recognize as an obstruction.
UV Liquid
Use UV liquid window applications that reflect wavelengths visible to birds but transparent to humans.
Films and Glass Treatments
Special window films or glass etching/fritting techniques can make glass more visible to birds.
Shutters and Awnings
External shutters or awnings can deter daytime collisions. Close at night when reflections are most disorienting.
Lights Out Programs
Eliminate unnecessary interior lighting, especially in high-rise buildings, to avoid attracting birds at night.
Conclusion
Bird-window collisions result in hundreds of millions of bird deaths each year. Small birds often die immediately on impact. Larger birds like jays or mourning doves may survive the initial blow but require prompt care. By understanding the factors that contribute to strikes, recognizing signs of injury, and implementing deterrents, we can reduce this dangerous hazard to birds worldwide. With quick action and supportive care, even some hard collisions end with the bird flying safely away once again.
References
1. Klem, D. (2009). Avian mortality at windows: the second largest human source of bird mortality on earth. In Rich, C. and Longcore, T. (Eds.), Proceedings of the Fourth International Partners in Flight Conference, McAllen, TX. U.S. Forest Service General Technical Report. PSW-GTR-191 Albany, CA: Pacific Southwest Research Station, p. 244–251.
2. Loss, S.R., Will, T., Loss, S.S., and Marra, P.P. (2014). Bird-building collisions in the United States: Estimates of annual mortality and species vulnerability. The Condor, 116(1), 8-23.
3. Klem, D., Farmer, C.J., Delacretaz, N., Gelb Y., and Saenger, P.G. (2009). Architectural and Landscape Risk Factors Associated with Bird-Glass Collisions in an Urban Environment. The Wilson Journal of Ornithology, 121(1), 126-134.
4. Gelb, Y. and Delacretaz, N. (2009). Windows and vegetation: Primary factors in Manhattan bird collisions. Northeastern Naturalist, 16, 455–470.
5. Veltri, C.J. and Klem, D. Jr. (2005). Comparison of fatal bird injuries from collisions with towers and windows. Journal of Field Ornithology, 76(2), 127-133.
6. Bayne, E., Scobie, C., and Rawson-Clark, M. (2012). Factors influencing the annual risk of bird-window collisions at residential structures in Alberta, Canada. Wildlife Research, 39(7), 583-592.
7. Kummer J.A., Bayne E.M., and Machtans C.S. (2016). Use of citizen science to identify factors affecting bird-window collision risk at houses. The Condor: Ornithological Applications, 118, 624-639.
8. Ocampo-Peñuela N., Winton R.S., Wu C.J., Zambello E., Wittig T.W., and Cagle N.L. (2016). Patterns of bird-window collisions inform mitigation on a university campus. PeerJ, 4:e1652.