Thousands of purple birds swarm Outer Banks bridge. NC lowers speed limit to protect them

Thousands of visitors cross the William B. Umstead Memorial Bridge—known locally as Old Manns Harbor Bridge—on their way to Roanoke Island and the Outer Banks every year.

But from mid-July through August, thousands of avian tourists visit the bridge, too.

Each year, thousands of shiny songbirds—purple martins—choose to roost under the bridge, creating a potential hazard for both birds and people.

The NCDOT has established a special 20 mph speed limit zone and set up flashing lights at the bridge to protect the more than 100,000 birds that roost under its west end, especially since the birds tend to commute at the same time people do—in the morning and evening. The bridge speed limit is normally 55 mph.

"LOW FLYING BIRDS. SPEED LIMIT 20 WHEN FLASHING. DUSK AND DAWN," the DOT signs before the bridge read.

The William B. Umstead Memorial Bridge carries the two-lane U.S. Highway 64 over the Croatan Sound between Manns Harbor and Roanoke Island in Dare County.

Drivers who want to avoid the birds can instead travel across using the Virginia Dare Memorial Bridge.

The martins annually migrate to Brazil, and make a pit stop in North Carolina during the summer. The birds roost under the bridge at night and depart at dawn to feed, according to DOT.

The birds return to their roost at sunset.

Visitors can safely view the flock of birds at Dare County's multi-purpose pier at the end of the bridge, according to DOT.

The flock of birds is so large during its peak that it can be spotted on Doppler radar, according to DOT.

Purple martins are the largest species of North American swallow. They are "one of America's most-well-loved songbirds for their chattering song, aerial acrobatics, insect-eating habits and their tolerance for humans," according to the Purple Martin Conservation Association.

The nearly three-mile Umsteaed bridge was built in 1955-56. It was the largest state bridge project of the 1950s, according to DOT.

The bridge was one of several links between mainland North Carolina and its Outer Banks planned to make the area a tourist destination, according to the N.C. Department of Transportation.

The DOT has partnered with the Coastal Carolina Purple Martin Society since 2007 in an effort to educate the public about the flock of migratory birds and to protect the birds and drivers.

The lowered speed limit is in effect at sunrise and sunset while the birds are traveling to and from their roost under the bridge.

"The lower speed limit is monitored by law enforcement and allows both motorists and birds safe passage across the sound," according to DOT. "Since the lights and speed limits were installed, the Coastal Carolina Purple Martin Society has seen a dramatic decline in bird deaths around the ."

PURPLE MARTIN FACTS FROM THE PMCA:

- Average size: 7.5 inches long, 15-16 inch wingspan and about 2 ounces.

- Color: Adult males have dark plumage (black, blue, purple), with dark purple feathers on their head, throat and belly. Adult females are lighter in color, more gray brown and white, but also have purple feathers on their head and back.

- Habitat: East of the Rockies, purple martins nest almost entirely in homes provided by people, such as bird houses. Native Americans, particularly Choctaw and Chickasaw, have made homes for the for centuries.

- Diet: Martins are primarily aerial insectivores, which means they eat insects while flying. Contrary to popular belief, martin's don't eat many mosquitoes, since they feed higher in the sky and during the day.

- Nest: Built of pine straw, twigs and mud and lined with green leaves.

- Eggs: Martins average about 4 to 6 eggs per clutch, which incubate for about 16 days.

- Migration: Thousands of migrate annually from Pennsylvania to Brazil—a trip which takes about 4 to 6 weeks and covers 5,000 miles each way—stopping in the Carolinas along the way.

For more information, go to purplemartinroost.com.


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Citation: Thousands of purple birds swarm Outer Banks bridge. NC lowers speed limit to protect them (2018, July 26) retrieved 17 June 2019 from https://phys.org/news/2018-07-thousands-purple-birds-swarm-outer.html
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