Almost seven million birds are killed each year when they fly into communication towers that broadcast TV and radio and make cell phone conversations possible. Worse, the towers often kill birds that are already rare. So says a study in the journal Biological Conservation. [Travis Longcore et al., Avian mortality at communication towers in the United States and Canada: which species, how many, and where?]

For example, tower impacts kill more than 2,000 yellow rails per year. That's roughly 9 percent of the total population. Ninety-seven percent of all birds killed are songbirds, especially warblers. The red-eyed vireo suffers some of the biggest losses, some 581,000 deaths annually, though that represents less than 1 percent of its population.

The Southeast and Midwest lead the country in tower-bird collisions. That's because these regions have the largest concentrations of the tallest towers, up to 900 feet high. While all of the more than 80,000 communication towers in North America cause problems, the roughly 1,000 tallest towers cause 70 percent of the bird deaths, luring birds to their doom with red warning lights that are always on.

A partial solution is relatively simple: replacing the always-on red lights with blinking ones could cut the deaths by as much as 70 percent. Otherwise, Twitter could have a monopoly on tweets.

—David Biello

[The above text is a transcript of this podcast.]

[Editor's note: A previous version of this podcast implied that cellphone communications towers were the major culprit. The upper sections of the highest towers are in fact primarily for broadcast communications.]