Migratory Bird Mortality: Cats, Windows, and Human Infrastructure

Billions of birds die each year from collisions with windows, predation by cats, and other human-caused mortality sources. These are among the largest and most preventable sources of wild bird welfare harm, with practical solutions available to everyone.

Key Facts

Window strikes kill an estimated 600 million birds annually in the US alone, and up to 1 billion globally — one of the largest sources of anthropogenic bird mortality alongside cat predation
Birds cannot perceive glass as a barrier; they fly toward reflections of sky or vegetation, or attempt to fly through transparent windows, striking at full flight speed
Strikes cause a spectrum of outcomes: immediate death from neck or brain injury, delayed death from internal haemorrhage or concussion, or survival with injuries that reduce subsequent survival probability
Domestic and feral cats kill an estimated 1.3-4 billion birds annually in the US (American Bird Conservancy estimates), making cat predation the largest source of anthropogenic bird mortality
Birds that appear to recover after a window strike often die within 24-72 hours from internal injuries; apparent recovery followed by death in apparently "stunned" birds is common
Communication towers, power lines, and onshore wind turbines are additional significant mortality sources, though smaller in aggregate than windows and cats
Simple, cost-effective solutions exist for window strikes: external netting, window film with UV patterns (visible to birds but transparent to humans), tape strips, and external screens all reduce strikes by 75-90%
Light pollution from buildings during migration season is a significant threat; nocturnal migrants use stars for navigation and are disoriented by lit buildings, leading to fatal collision events

Welfare Considerations

Window strikes and cat predation cause suffering that is both individual (the pain, fear, and death of each individual bird) and population-level (the cumulative removal of billions of birds from already-declining populations). A bird striking a window at speed experiences acute trauma — many die instantly from internal injuries, but a significant proportion survive injured for hours or days, experiencing pain and distress before dying from haemorrhage, predation while compromised, or delayed brain injury. Cat predation involves the additional welfare dimension of a prolonged hunt-and-catch sequence during which birds experience fear and physical injury before death. The welfare case for addressing both window strikes and outdoor cat predation is compelling: both cause substantial and unnecessary suffering, and both have practical solutions. The challenge is primarily cultural — persuading cat owners to keep cats indoors (where cats themselves also have better health outcomes) and persuading householders and building managers to implement window treatments requires sustained public education and building code reform.

What You Can Do

Apply bird-safe window treatments to windows where strikes are occurring — external netting, UV-reflective film, tape strips at 5cm intervals, or commercial products like Feather Friendly or CollidEscape
Keep domestic cats indoors or provide outdoor access only through enclosed "catios" — this protects both birds and cats (who have dramatically longer lives when kept indoors)
Turn off non-essential building lighting during peak migration nights (particularly in spring and autumn) — or participate in "Lights Out" programmes operating in many major cities
If you find a window-strike bird, place it in a ventilated cardboard box in a quiet, dark place for 1-2 hours — if it does not recover, contact a wildlife rehabilitator rather than releasing a compromised bird
Advocate for bird-safe building standards in your community — several cities now require bird-friendly glazing in new commercial construction
Support American Bird Conservancy, FLAP Canada, or equivalent national organisations working on bird-friendly buildings and collision prevention