What is "towerkill"

Towerkill is a phenomenon in which large numbers of birds are killed by antenna towers. The U.S. Fish and Wildlife Service estimates that between 5 and 50 million birds are killed in the U.S. each year by tower kill. Window crashes, by comparison, kill between 100 and 900 million birds a year, and are still by far the largest human-related cause of wild bird death. The effect on overall bird populations by towerkill may be small, but the phenomenon is of considerable concern to ornithologists because many endangered bird species are being killed, and because so many birds are killed in such a small area of land. In at least one instance, several thousand birds were killed at a single tower in one night. Additionally, the unnatural lights on communication towers disrupt bird migration patterns in ways that are still not fully understood. At least 231 species have been affected, with neotropical migrants making up a large proportion of all species killed.