It’s also a straightforward reference to the fact that birds congregate with others of their own species. So, when I’m asked, as I have been recently, about the considerable numbers of crows that people have seen roosting in the village of Malone, I’m inclined to simply answer, ‘birds of a feather…’
Roosting is a period of inactivity for birds; a time of rest and/or sleeping. Almost all birds gather to roost; some in much larger groups than others. During the breeding season, birds are likely to roost individually or in small groups. But in winter, as food and shelter from the cold and predators become harder to find, spending their nights at larger, communal roosting sites lessens their vulnerability.
We often take pleasure in seeing chickadees, finches, or juncos congregating at our winter feeders. These birds are here all year round, but because they remain dispersed across the countryside throughout the breeding season and are not dependent upon our feeders for their survival, we’re far less aware of their presence and of their overall populations.
It’s no different with crows. Their presence, especially in and around populated areas, becomes more apparent as the communal roosting season begins, usually in late fall. It isn’t until the winter really sets in, however, that they gather together to endure the frigid nights in groups of anywhere from several hundred to several thousand birds; assemblages so large that we can’t help but take notice.
In urban areas, roosts of tens of thousands of crows are not uncommon. For example, a roost that has, at times, numbered 70 thousand crows has been documented in the town of Auburn, NY. Roosts of hundreds of thousands of crows have been documented in several Midwestern cities and one roost, at a site in Fort Cobb, Oklahoma, was estimated at two million! Rural roosts in excess of 100,000 crows have been documented in North America since the early 1800s.
No one is absolutely certain as to why crows gather like this, but there are probably a number of reasons. First is the simple fact that there’s safety in numbers. Cornell University ornithologist, Dr. Kevin J. McGowan, has called this the “wagon train analogy,” asserting that “crows are most afraid of large owls, and sleeping with a bunch of other crows could afford some protection for an individual crow.”
McGowan has observed that, “Crows will congregate in some area away from the final roosting site, usually an hour or two before complete darkness. Here the crows spend a lot of time calling, chasing, and fighting. At dark, the main body of the group will move toward the final roosting spot. Sometimes this final movement is relatively quiet, but usually it’s still quite noisy.” He adds that “The final roost can be a cohesive group in a single woodlot, or it can be rather diffusely spread out over a wide area of suitable trees.”
Food may be a big factor as well. According to Dr. McGowan, it may be that “roosts congregate around a large, non-defendable, reliable food source so, first thing and last thing in the day, food is available. It need not be the best food, but it is something to eat.”
Another of Dr. McGowan’s theories is that gathering allows individual, inexperienced birds that have not been very successful at locating forage, to “watch for other individuals coming in to the roost that look fat and happy; that obviously found some rich source of food. Then the hungry individual can… follow them out first thing in the morning to the good food source.”
It’s fairly easy to see how the village of Malone, which is surrounded by miles of extremely productive cropland, would give these birds, um, something to crow about. They’re able to readily leave their collective roosting site during the day to forage in nearby fields, along roads and in yards, returning in the evening to spend the night in the relative warmth and safety of the ‘wagon train.’
In spring, these large roosts will begin to break up as mated pairs (crows mate for life) return to their home terrain. Unmated birds may continue to use the roost for several more weeks.
Because crows are especially susceptible to West Nile Virus (WNV) infection, some people have expressed fears that crows may transmit the disease to people and pets. In fact, WNV is spread by the bite of an infected mosquito. There’s no evidence of the disease being spread directly from birds to humans.
Photo of American Crow by Kevin McGowan.