Purple Martin Bridge Roost

At Manns Harbor on North Carolina’s Outer Banks, the William B. Umstead Memorial Bridge hosts a remarkable purple martin roost where as many as 100,000 birds gather nightly from July through August, with the roost active from mid-June to mid-September, a phenomenon documented since at least 1980. Purple martins in the East, east of the Rocky Mountains, depend entirely on people to provide nesting structures, and they are social colony nesters that prefer to live near human dwellings where predators are fewer. After nesting, some travel up to 150 miles from their breeding colonies to this pre-migratory staging area, arriving at sunset to sleep under the bridge and departing at sunrise to feed and build fat reserves for their annual migration to Brazil. The area’s abundant insects, supported by agricultural fields, national wildlife refuges, and wetlands, help sustain this large population, and the birds roost over water along the bridge’s western end on support structures, I-beam girders, and cables where predators are fewer. Each spring, birds return from Brazil and usually go back to the same colony to nest again. Purple martins are the largest swallow species, measuring 7-8 inches from beak to tail, adult males do not gain their purple plumage until two years of age, females and young are grayish, and they feed only on aerial insects caught in flight. Traffic on the bridge kills thousands of martins each year, almost all newly fledged young, and also endangers motorists when birds fly into and around vehicles.

Manns Harbor, North Carolina · United States