One afternoon, a few crows land in the trees around your street. A few days later, there are dozens, cawing at dusk before flying off together. It can look a little ominous. Cornell’s crow expert explains what is really going on, and it’s more interesting than scary.
In short
- Crows gather in large groups mainly in fall and winter.
- These winter roosts can range from fewer than 100 birds to over a million.
- Scientists have several explanations, from safety to sharing food information.
- Crows live in extended family groups and can recognize individual people.
A fall and winter ritual
The gatherings have a name: roosts. According to Kevin McGowan of the Cornell Lab of Ornithology, they are mainly a fall and winter phenomenon. Their numbers “peak in winter” and then decline near the start of the breeding season, usually in March. During nesting, breeding crows sleep on their own territories, then join the roosts afterward.
The size can be staggering. Roosts range from under 100 birds to over a million, and “roosts of tens of thousands are common,” McGowan writes. One roost in Fort Cobb, Oklahoma, was estimated at over two million birds. About 25,000 crows roosted near Auburn, New York, in the winter of 1932-33.
The noisy hour before dark
That loud scene at the end of the day has a logic. Crows gather in congregation areas about an hour or two before full dark, where they call, chase and fight. At dusk, the main group moves on to the final roost. McGowan has even seen flocks from several of these areas merge at one staging spot before heading to the roost together. The final roost may be a tight group in one woodlot or spread across many trees. Roosts can also move: the Auburn roost was once about 3 miles south of town before it shifted downtown.
So why do they do it?
Honestly, scientists aren’t completely sure: the reasons are “still largely a matter of conjecture,” the Cornell FAQ admits. But several ideas stand out. Crows may simply be choosing the best place to sleep, even if others share it. There is safety in numbers, since crows fear large owls. A roost may help birds share food information, with hungry crows following well-fed ones the next morning. And many roosts sit near a reliable food source, such as a landfill, for an early meal.
Not a gang, a family
McGowan also asks people to see a group of crows differently. Crows “live in large extended family groups,” he writes, and they can recognize individual people, something he suspects chickadees cannot. Some even follow people’s cars, and some recognize McGowan far from their home territories. Smaller backyard birds have their own winter struggles, like the chickadees that fight the cold every year.
The limit
The exact reasons for winter roosts are still debated, and they may differ from one place to another. A roost near your home is usually seasonal: it tends to shrink as the breeding season approaches. Like many animals, crows simply adapt to the cold season, just as rodents do when they look for a warm place to spend the winter. And there’s no sign in the Cornell FAQ that a gathering of crows means anything bad for the people living nearby.
That’s the story.
