Wings allow birds to avoid massive road mortality that culls the urban herd of mammals and herps. . . . The full magnitude of roadkill is difficult to estimate, but collisions with large animals are certainly on the rise. In a 2008 report to Congress, the Western Transportation Institute noted that in 2004, one in twenty reported vehicle collisions in the United States—some three hundred thousand—involved wildlife, most likely deer. These collisions annually kill two hundred Americans and injure twenty-six thousand, at an estimated cost of more than $8 billion. The cost to wildlife is also extreme. In the United States, between half a million and one million deer are killed each year, and twenty-one species of vertebrates are federally endangered in part because of road mortality; only three are birds. The Humane Society of the United States estimates that more than three hundred million vertebrates die annually in vehicle collisions. Worldwide, the annual death toll is staggering . . . .John M. Marzluff, Welcome to Subirdia: Sharing Our Neighborhoods with Wrens, Robins, Woodpeckers, and Other Wildlife (New Haven: Yale Univ. Press, 2014), pp. 170-71.