Window and glass surface collisions kill hundreds of millions of birds annually in North America alone, making it one of the leading human-caused sources of bird mortality and one of the most preventable.
Window collisions cause acute welfare harm in two ways: the impact itself causes concussive injury, internal bleeding, and death, and survivors who are stunned and recover slowly on the ground are vulnerable to predation and exposure before regaining flight capacity. The enormous scale of this mortality source makes it a significant welfare concern numerically, and the availability of proven prevention measures makes most of this suffering preventable. Individual building owners, urban planners, and corporate facilities managers all have capacity to implement solutions. The welfare case for action is clear and the technical solutions are mature.