Man-made structures kill billions of birds annually
According David Bird from the Montreal Gazette over a billion of North American songbirds won't make their way southward for locations promising more productive food resources and more favourable climates. Among the impediments are buildings and towers. While they do not represent an absolute barrier to songbird migration, they definitely increase the mortality risk to birds migrating in either direction.
On a continent-wide basis, estimates for total collision mortality for communication towers have ranged from roughly 1 million to 50 million birds annually, while similar estimates for collisions with windows have ranged from 3.5 million to 5 billion birds annually.
If one uses the most frequently cited estimates of 25 million mortalities from tower collisions and one billion from window collisions, the combined mortality would represent 21 per cent of the estimated breeding population of 4.9 billion North American landbirds.
According to the ornithology scientists Todd Arnold and Robert Zink there is a Top 5 of "super-colliders" - bird species most likely to strike buildings: the swamp sparrow, the fox sparrow, brown creeper, Nelson's sparrow, and the warbler, the black-throated blue warbler (25 to 57 times more likely to collide with a building than expected by chance). On the other hand there’s also a Top 5 for “superavoiders”: tree swallow, northern mockingbird, blue-gray gnatcatcher, cliff swallow, and horned lark (105 to 208 times less likely to hit a building than expected by chance).
For towers, the Top 5 “super-colliders” were four warbler species (including the black-throated blue!) and a sparrow, while the American robin, common grackle and black-capped chickadee joined the cliff swallow and horned lark as the Top 5 “superavoiders”.
Source: Montreal Gazette