Experts have estimated that, of all birds migrating through eastern North America, approximately 70% pass through at least one major metropolitan area per migration event. During this time, birds face a number of dangers, one of the least understood of which is collision with anthropogenic structures. Conservationists and bird-lovers alike have frequently called attention to the avian mortality caused when the birds fly into buildings and communication towers. Indeed, there are several long-term datasets that document the many deaths caused by collision--as many as 25 million total mortalities from towers, and 1 billion mortalities from windows, cumulatively representing nearly a quarter of all breeding land birds in North America.
(Black-throated blue warbler (Dendroica caerulescens), identified as one of the birds most likely to fly into buildings and towers.)
http://www.science20.com/anthrophysis/avian_populations_are_not_impacted_collision_anthropogenic_structures-82708 Continued
