Author: Cara Giaimo / Source: Atlas Obscura
Earlier this week, the weather radars that focus on the William B. Umstead bridge in North Carolina’s Outer Banks began to look a little strange. Each day at dawn, a huge cloud of activity swelled out of the bridge and then dissipated into the surrounding body of water, the Croatan Sound.
At dusk, another cloud would appear, swooping in from the sound and back towards the bridge again.The bridge is not creating its own small thunderstorms. Instead, the Doppler radar is picking up on a huge group of temporary residents: about 100,000 purple martins. In the summertime, large gatherings of martins can be found all over the South, from an abandoned mall in Texas to a parking garage in Oklahoma. But this flock’s particular choice of habitat has changed how their human neighbors use—and think about—local infrastructure.
Purple martins are North America’s largest swallows. The males are known for their chipper calls and their glossy plum-colored feathers. They split their time between North and South America, spending winters near the equator and summers in the southern United States.
Purple martins who travel down the west coast of the U.S. tend to roost on their own, generally in abandoned woodpecker holes. But east coast ones depend almost entirely on human help. “The summer residence of this agreeable bird is universally among the habitations of man,” the ornithologist Alexander Wilson wrote in 1808, adding that he had seen them nesting in pigeon-houses and in cornices, as well as in hollowed-out gourds hung on trees by members of the Choctaw and Chickasaw tribes.
Purple martins who fly through North Carolina these days have plenty of roosting options: Many fans still put out houses and gourds for them, and stand guard against competing species, like starlings and house sparrows. But about 40 years ago, a whole lot of birds decided to switch to co-op housing. They started…
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