Editor’s note: The following column was originally published in the New Hampshire Union Leader on Feb. 6, 2010.
A LARGE FLOCK of crows was inquired of by a Manchester reader who wrote, in part: “I work at Public Service of New Hampshire, right below the Amoskeag Dam on Commercial Street. Across from our facility is an uninhabited island.
“Soon as fall starts turning to winter the crows arrive and spend their nights on that island. Hundreds and hundreds arrive at nightfall. It reminds us all of a scene out of the movie, ‘The Birds,’ especially when they get spooked. The falcons are also here, which makes it very interesting.
“This past week my husband and I were driving north from Manchester to Concord, and it appeared that at the same time at night, there were all these crows flying down to Manchester, following the river from the Concord area.
“My questions are: what causes this phenomenon and why do they seek this island and stay together during the night in such large quantities? Can you provide me with any other information on this matter?”
I would suggest the answer as to why this flock of crows decided to use the island was because it is uninhabited.
But the other crow flocks inquired of by our Manchester readers in past years have been close to where people were living. For example: Some time ago the good Sisters of the Monastery of the Precious Blood wrote of a great flock of crows that gathered in the trees of their campus each evening. The crows let themselves be known by their raucous cawing, squawks and mutterings as well as their crowding and jostling one another while they shifted about for a comfortable position to spend the night in the trees. Apparently the Sisters did not mind their nocturnal visitors in spite of their cacophony. They did wonder, however, as to why the crows selected their campus.
Several species of birds are noted for their tendency to flock. This is specifically true with respect to crows, blackbirds and starlings. During the winter months large numbers of crows band together and pretty much stay together until the breeding season begins. In late afternoon, these large gatherings of crows select a site to spend the night. Such places of assemblage are known as ‘roosts.’ With few exceptions, the crows that roost in any area in winter are birds that have migrated from somewhere else, usually to the north.
Generally speaking, crow roosts can be comprised of thousands of birds, but most of these large roosts are in more isolated areas. On this subject, Edward Howe Forbush, in his “Birds of Massachusetts and Other New England States,” had this to say: “In October before the frosts of autumn begin to form thin skims of ice around the shores of lakes in the northern woods, the crows, which have been drifting down from the highlands, form into great migrating flocks, not in any regular formation though occasionally columns or ring-shaped flocks are seen. More often the birds fly southward in irregular masses, usually in daylight, as they rarely move about at night. These great flocks continue to pour southward in November, leaving behind in New England only a remnant of the vast summer crow population.
“At night these crows assemble, sometimes from a distance of 40 miles around, to a common roosting place. In New England, white pine groves are favorites for crow roosts. Farther south, deciduous trees may be chosen.”
There are several reasons why birds travel in a flock. To answer that question, I turned to Robert Burton’s book, “Bird Behavior.” Burton wrote: “Some birds that spend the night in a communal roost disperse at dawn, but others stay in a flock during the day. Communal roosting can give the birds a measure of protection from predators and it also can help them to find or catch food. A further advantage is that it allows more time to devote to feeding. Flocking provides an early warning system as a predator approaches. The typical reaction from a bird of prey is for the flock to gather in a tight formation and circle or fly erratically, rather than to attempt to escape by speed. The only chance a hawk has to get a meal is to single out a straggler.”
Stacey Cole, Nature Talks columnist for more than 50 years, passed away in 2014. If readers have a favorite column written by Stacey that they would like to see reprinted, please drop a note to Jen Lord at firstname.lastname@example.org.