At sunrise and sunset, the speed limit on the William B. Umstead Bridge, locally known as the Old Manns Harbor Bridge, is dropping to 20 mph as more than 100,000 migrating purple martins gather there.

From mid-July through August, the west end of the bridge on Croatan Sound becomes home to the purple martins as they prepare for their annual migration to Brazil. The birds roost under the bridge at night, departing at dawn to feed and returning at sunset. The flock is so large during its peak it can be seen on radar.

Since 2007, The NC Department of Transportation has partnered with the Coastal Carolina Purple Martin Society to educate the public about the flock and protect both the birds and passing motorists. NCDOT activates flashing lights and a 20-mph speed limit at sunrise and sunset.

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

As an alternate, motorists can use the Virginia Dare Memorial Bridge. Those wishing to view the flock safely can do so at Dare County’s multi-purpose pier at the west end of the bridge.

Martins who have raised their young during the spring in colonies managed by humans come here from as far away as 150 miles. The Coastal Carolina Purple Martin Society will conduct educational experiences at the west end of the bridge and aboard the Crystal Dawn headboat. Bridge talks will take place at sunset Thursdays and Saturdays on July 26, July 28, Aug. 2 and Aug. 4. For more information, visit purplemartinroost.com, send e-mail to purplemartinroost@gmail.com or call 252-473-1493.

Sunset cruises aboard the Crystal Dawn are set for Thursdays and Saturdays on July 26, July 28, Aug. 2 and Aug. 4. Tickets are $30 per person. The tour leaves from Pirates Cove Marina between Nags Head and Manteo at 7 p.m. and returns at approximately 9:30 p.m. For tickets and more information, contact Crystal Dawn at 252-473-5577 or crystaldawnheadboat.com.