Bird-window collisions: a critical review

Bird-window collisions are a principal source of mortality for free flying wild birds the world over. This report is an update on this important conservation issue for birds and people. Geographical documentation of bird-window collisions is growing and includes wherever birds and sheet glass and plastic coexist in the human-built environment worldwide. Collision injuries, cause of death, and rehabilitation efforts of strike victims are increasing globally. The fundamentals of cause, species affected, and environmental conditions in which bird-window collisions occur are described. Alternative solutions and the means to evaluate them include tunnel testing, field experiments, and field studies at actual buildings. The number of individuals attracted to the vicinity of windows by lights, vegetation, or feeders pose no lethal collision threats if existing and new windows are treated to transform them into barriers that birds will see and avoid. Treating windows with uniform patterns following the 2 × 4 or 2 × 2 rules provide effective bird-window collision deterrents at exiting retrofit or remodeling and new construction sites. A list of continuing legal and research needs and avian conservation advocacy and education by several principal constituencies, especially among natural and social-psychological scientists, and citizen-scientists is stated and encouraged.