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Did you know that in winter crows amass in large flocks by the thousands and tens of thousands? Here in Massachusetts, you can see such flocks throughout the state in certain roosting areas. There’s one in Lawrence, another in Athol, one in Springfield, one in Framingham, one in Worcester, even one on Martha’s Vineyard (where the crows have to fly over water to reach the roost each night).
According to Dana Duxbury-Fox of the Brookline Bird Club, estimates of the number of crows in Lawrence, for instance, vary from 14,000 to 24,000. That’s a lot of crows to swoop in each night to roost. And there’s not just one kind of crow. There are American crows, which we are probably used to, and about 600 of their smaller, southern cousins, the fish crow. Where do all these birds come from?
Because these birds are not banded, it is not known precisely where they come from. But Duxbury-Fox said a Utica study found that about one-fourth of the American crows are local year-round birds. The rest are migrants from Canada and northern New England who travel south in winter, searching for better weather and more food. Hawks watchers on Lake Erie observe thousands of American crows flying south out of Canada each year.
The crows in Lawrence begin arriving in late October. Why do they flock together in such large groups? Scientists think they do this for several reasons. During the summer crows stay in small family groups of two to eight birds. But in the winter, when food is scarcer, groups can communicate with each other about food locations. They can stay warmer by roosting close together in warm places. Young crows can find mates in these groups. And there is safety in numbers: Horned owls prey on crows at night, and a group of crows can keep watch better.
Since the 1960s, many crows have moved their winter roosting areas from rural sites to urban sites. It is not known for certain why this has occurred, but cities have some advantages:
- They are warmer than rural areas, as city buildings and roads absorb heat.
- Cities have more lights. Crows do not have good night vision, so they prefer roosting in areas where they can spot their enemies better.
- Cities are noisy. Crows have learned to prefer areas with background noise – the sound of traffic or running water. Some scientists think this noise makes it difficult for owls to hear and find crow prey.
- Finally, crows have learned to avoid hunters. People don’t hunt in cities, so crows feel safer.
Sort of like co-workers gathering for drinks after work on Friday, crows come together at the end of their foraging day, with groups arriving in staging areas an hour or two before dark and making a racket talking, playing and squabbling with each other. The crows stage in different places each evening; eventually, as it gets dark, the groups fly to the roosting area for the night.
There seems to be a hierarchy of roosting. The first crows to arrive take the outer edges of the trees. Later crows perch beneath these birds. The best spots are near the tops of trees, as the crows below get covered in bird droppings. The crows chatter for a bit, and then, like someone has flipped a switch, all is quiet. Crows wake up and begin vocalizing about 90 minutes before sunrise. As day breaks, the crows begin dispersing in all directions in search of food.
In Lawrence, the crows roost in a narrow line of trees along the Merrimack River that people do not frequent, so the crows are not harassed. In other places, crows are less welcome. Penn State University once had thousands of crows nesting in the center of campus. The school decided to act. Knowing crows prefer well-lit sites, they aimed floodlights on a stand of trees away from people and shooed the crows away from the populated area. It worked! The crows moved their roost to the well-lit trees, a location the crows remembered in the following years.
Crows fan out about 20 to 30 miles in all directions to forage. In some part of the country, winter crows congregate on landfills; much of Massachusetts’ waste is incinerated in trash-to-energy facilities and the landfills that do exist are covered at the end of each day with 6 inches of soil, Duxbury-Fox said.
So what do crows eat? A better question might be, what don’t they eat? Crows are clever omnivores and they may eat leftover corn in fields, carrion, parking lot french fries, small mammals, seeds and nuts, mollusks and fish in addition to their garbage from landfills or elsewhere. They are expert problem solvers, so it won’t take a crow long to figure out how to open a discarded food package. If something is edible, a crow will figure out how to get it.
One 1918 analysis of several hundred Massachusetts crow pellets (crows regurgitate undigestible bits just like owls) revealed remnants of fish, snakeskin, eggshells, mice, a mole, shrews, seeds and parts of 20 plants. A more recent 2017 analysis of Lawrence winter crow pellets found 95 percent of the pellets were composed of Oriental bittersweet berries. Other foods included seeds, corn, acorns, mice, a (road-killed?) rabbit, a songbird, a snail, a beetle, a McDonald’s ketchup package and plastic wrap.
People have been observing winter crows in our area for a long time. Ornithologist Arthur Cleveland Bent said in 1946,
Along the New England coast winter is one of the most interesting seasons for a study of crows. At this time they are more numerous than during summer … They may be seen leaving the roosts early in the morning, often before sunrise, in groups of two or three to a dozen or 20 … Sometimes their wanderings take them long distances, going hither and thither until a carcass or other food supply is located. At all times they are alert and suspicious, always proceeding toward food with caution, often alighting on convenient vantage points to carefully inspect the surroundings and to make sure no harm is in store for them.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
The far left and far right of the background on the feature image to this post (not seen above) was generated digitally and is not real. The rabbit was photographed and is real.
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