The Boston Globe joined us for the MRWC Crow Patrol Walk & Talk last night. The reporter and photographer were fascinated with the Crows and spent time talking with many of the attendees!

Caws for celebration: In evening ritual, thousands of crows gather along the Merrimack

By Grace Gilson Globe Correspondent,Updated January 18, 2022, 5:43 p.m.

For decades, Lawrence has hosted a significant winter crow roost, bringing in estimates of at least 20,000 crows every year. ERIN CLARK/GLOBE STAFF

Evening commuters along Interstate 495 who gaze skyward might catch an astonishing sight: thousands of crows in flight, making their way in the direction of Lawrence.

The birds are a part of a huge nightly migration that ends at the Merrimack River. There, they will descend upon the treetops and roofs in chaotic, swirling patterns and let out a symphony of caws before quieting down about an hour after sunset. The phenomenon attracts birders and the curious.

Craig Gibson, a bird and conservation photographer and a chaplain at Lawrence General Hospital, has been cataloging the movement of the crows since 2017. He also started a blog called Winter Crow Roost.

This concentrated winter roost has been occurring for decades, according to Gibson, and is a common behavior among crows this time of year. It is unknown why they are drawn specifically to the Merrimack, but Gibson says they flock for safety from predators, to exchange information on foraging, and prepare for the mating season.

He regularly coordinates with local groups to bring people to the site where the crows roost so they can experience the phenomenon.

“What you see visually is mesmerizing, what you hear is this wild vocalization of all different varieties of calls from the birds, they’re swirling in flight, they’re settling in the trees, they’re making all these crazy noises,” Gibson said by phone Tuesday. “You’re carried away to this incredible experience that sets your heart on fire.”

According to data collected by Gibson, the crows that flock to the Merrimack River can number 13,000. Most are American Crows and pack into an area of just a quarter of a mile during their nightly roost.

Gibson works with a variety of conservation and environmental groups, including the Merrimack River Watershed Council, the Merrimack Valley Bird Club, and Mass Audubon to spread awareness about the nightly event and rally the community around nature.

“If you’re familiar with the movie ‘The Birds,’ it’s just like that,” said John Macone, an education and policy specialist for MRWC, which works to make Methuen and Lawrence more climate-resilient. Macone said he first saw the birds during his commute down 495.

Macone and MRWC worked with Gibson to help put on “The Crow Show,” which began Jan. 11 with a webinar on the crows for about 120 people and also featured an in-person event Tuesday evening.

Gibson hopes that growing out The Winter Crow Roost and partnering with more schools will allow his work to become a citizen-science project and hopefully show people what Lawrence has to offer.

“This is a city that is on the move and filled with hope for brighter days ahead, and my interest is to add to that a greater awareness about spectacular things that are happening in the natural world,” he said.