Diane R. writes
I have about 200 crows outside yesterday and today making a huge ruckus, flying every which way. This is unusual. Although we do have crows in the neighborhood, they don’t usually swarm like this. They are hollering at the tops of their lungs about something. What could this be about?
I couldn’t picture where 200 crows might be assembling in Cambridge or Somerville, so I followed up with Diane to uncover some additional information. These crows are amassing in the central part of Englewood, Colorado, a southern suburb of Denver, an urban area that still has some wildlife.
Diane further explains: At first I thought they were chasing off magpies, but it was more than that. And yesterday some gulls appeared circling the same area, but not landing, so I don’t think this had anything to do with a food source. I think they were gathering to go find a warm place to roost, maybe, because the temperature finally dropped below freezing a few days ago and we got our first dusting of snow.
Diane, I think you have hit the nail on the head. In winter, crows come together at the end of their foraging day. This behavior occurs throughout North America, including here in Massachusetts. Crows arrive in staging areas an hour or two before dark and make a racket chattering, playing, and squabbling with each other. The crows may stage in different places each evening; eventually, as it gets dark, the groups fly to the roosting area for the night. There, they continue making a ruckus until, like a light switched off, they all go silent at the same time. Sometimes these roosting flocks can reach thousands or even tens of thousands of birds.
Rooster mania
Why do crows flock together in 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: Great horned owls, for example, 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 why this has occurred, but cities have some advantages for crows:
- They are warmer than rural areas because city buildings and roads absorb heat.
- Cities have more lights. Crows do not have good night vision, so they like to roost in areas where they can spot their enemies better.
- Cities are noisy. Crows prefer areas with background noise, such as 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.
Crows started amassing in entire blocks of downtown Denver in 2022. Some of these crows live in the area year round. Others are migrants from Canada or higher elevations where it is difficult to find food in winter.
Counter-crow tactics
Crows have been a nuisance in Colorado for a long time. In fact, farmers used to complain about them damaging crops. Things got so bad that in March 1936, a group of Boulder VFW members took things into their own hands. According to the Rocky Mountain News, the veterans surrounded 50,000 roosting crows in a two-acre grove. As soon as it got dark, they attacked swiftly, blazing away with their shotguns as fast as they could. The men shot 800 crows that night. They cooked the crows in pot pies. One of the hunters described the taste, “The flavor is superior to that of all game birds with the exception of quail.” (And I thought “eating crow” was something to be avoided.)
It is not recorded whether or not the hunters succeeded in moving along these roosting crows. But crows can pass down memories for generations, so they may have avoided the area for a long while afterwards.
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.
Denver has taken a different tack: Crows in downtown Denver were noisy and leaving a mess behind. To scare the crows away, the city hired falconers with hawks trained to hunt at night. This method also worked. The crows moved to a roost about half a mile away.
Some places, like Sweden, have used crow intelligence and behavior to their advantage. In a city near Stockholm, researchers, in a pilot program, trained crows to pick up cigarette butts in exchange for peanuts (literally). Since cigarette butts make up 62 percent of the litter in this city, employing crow cleaners could save the city money. Research is ongoing, but if picking up toxic butts is not harmful to the crows, the operation might be rolled out city-wide.
During the day, crows fan out about 20 to 30 miles in all directions to forage. In some parts of the North America, winter crows congregate on landfills. So what do crows eat? A better question might be, what don’t crows eat? Crows are clever omnivores and they may eat leftover corn in fields, carrion, parking lot French fries, small mammals, seeds and nuts, in addition to garbage. 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.
Colorado crows, like Massachusetts crows, leave their winter roosting sites when the breeding season begins — sometime around March. Crows form life-long pair bonds, and young crows find their mates during their communal winter roosting.
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.
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