Thousands of crows have returned to their traditional roost in Fredericton after weeks of being on the move.

For the last week, the murder of crows has been roosting back in its usual spot in a wooded area on the University of New Brunswick campus.

The large flock of birds, estimated to be made up of well over a thousand individual crows, had been moving its wintering population throughout the city's downtown, wintering over night on a brightly lit parking garage and other downtown rooftops.

The murder of crows that gather annually in Fredericton is estimated to be in the thousands. (Shane Fowler/CBC) "They could be in search of some place safer," said Joseph Nocera, an ornithologist at the University of New Brunswick, when CBC News first questioned the move in December 2016. "It makes you think that something must have changed in their original roost site that made them seek another."

Nocera had listed a number of factors that could have been responsible for the large flock's move away from the roost they had been using for years.

Crows have roosted in the stretch of woods that divide the University of New Brunswick campus and the St. Thomas University campus for more than a decade. (Shane Fowler/CBC ) A change of lighting had been suggested by Nocera, as well as the possible introduction of a predator. Great horned owls often predate on crows.

Large populations of crows gather annually during winter months in order to protect against the elements, and predator threats. According to Nocera, research indicates that a large population is also a strategy that offers crows the best chance at foraging for food and surviving the winter.