Crow Roosts: A Murder Mystery

Come wintertime in New England, you may think you've stepped into a scene from Alfred Hitchcock's 1963 film "The Birds" with the number of black, winged creatures swarming the air. The birds you see are likely American Crows and Fish Crows, species of crows that traditionally roost communally in the winter. Just like humans, crows depend on each other to make it through the winter months. While the winter roosts are not well understood, an excerpt from a journal article from JSTOR, "Falsifiability and the Information Centre Hypothesis," describes the hypothesis that colonies and roosts are assemblies of birds utilized as information centers. For crows, the purpose of a roost is to exchange vital information that will aid each other in enduring the harsh weather and decreased food supply. Some birds, whether from age or familiarity of the area, may be better at finding food leading less experienced birds to follow them to feeding sites. Robert Burton writes in his book "Bird Behavior": "Communal roosting can give the birds a measure of protection from predators and it can also help them to find or catch food. . . Flocking provides an early warning system as a predator approaches." To protect themselves from a bird of prey, they will flock together in a tight formation and fly erratically to deter the predator. The only chance a predator has at catching its meal is to hope for a straggler amongst the bunch. Prior to congregating at a winter roost location, smaller groups of crows will flock from their daytime feeding areas to staging areas in the afternoon. At the staging areas, close to the roost location, the crows are noisy and feed, preen and scan their surroundings while awaiting the roost. The staging areas can change depending on the day, but the staging areas and roosts can occur in both rural and urban areas. Usually about an hour after sunset, the crows will flock to the roost. Roosts are often found in groups of trees near bodies of water and are used again and again so long as they are undisturbed areas. Springfield and Lawrence, Massachusetts are popular locations where impressive roosts have been seen. The Mass Audubon's website claims that Springfield hosts one of the largest roosts in Massachusetts with over 7,000 birds gathering together, but Lawrence now holds the title for largest roost. Roosts can vary in number from a few hundred birds to more than 500,000, occasionally reaching numbers upwards of 2,000,000 (wintercrowroost.com). Larger roosts are more likely in less populated areas, but there are many accounts of impressive groups in urban areas. The city of Lawrence, an ideal roost location due to its closeness to the Merrimack River, has long since been a popular place for roosts. As we progress through the winter months, we notice a change in the number of roosting birds. In Lawrence, the roost is around 2,500 in October, but come January and February (when more birds have migrated south from Canada and northern New England) there are an estimated 15 to 20,000 crows. Those in towns north of Lawrence and near the Merrimack River should keep their eyes out for migrating birds and nightly roosts as they match catch a glimpse of this evening ritual. This behavior has become a spectacle of sorts, especially in places like Lawrence that can expect a yearly roost. In instances where the roosts may be great in number and in a "poor location" there are known techniques to help disperse the crows to prevent safety concerns. While the posed health risks from birds can often be exaggerated, roost locations that are reused by flocks and frequented by humans are most likely to pose a health risk from the disease organisms growing amongst the droppings, feathers and debris. Strategies include making the area temporarily off limits, cleaning up after the birds in soiled areas or dispersing the crows by making the roost location undesirable. Harassment techniques, mostly using visual and audio scare tactics, can temporarily disrupt crows from frequenting their desired roost location. Eventually, crows come to realize that these scare tactics are not real, and they habituate to them, returning to the roost. More disruptive strategies involve altering the site altogether by pruning tree branches, lessening the available perches and exposing the tree to weather. Large-scale interventions such as this should not be undertaken without the guidance of the Department of Agriculture. Although roosts pose a bit of an annoyance to the public, radical alterations should not be made lightly. Any changes to the landscape will not only disrupt the crows, but other species of animals as well. Whatever their intent is, roosts are fundamental to the winter survival of crows; the show they provide is only a bonus.