Photo by cuatrok77, Wikimedia Commons
(Click on the link to listen to an audio version of this blog …. Winter crows
Around 3:30 on a cloudy, late November afternoon, I was looking out my back window and saw crows gathering in the bare branches of my neighbor’s tall cottonwood tree. I counted twenty-three crows in the branches at first. They came in a large, single group and took up perches well separated from each other. Their black bodies were in crisp silhouette against the bright blue sky. I could see them bobbing vigorously up and down as they cawed. I could hear their cawing, too, even though the windows were all closed up.
In a minute or two after the first twenty-three settled into the cottonwood, three or four more crows arrived and picked out unoccupied branches. Then three or four more arrived, and then three or four more. The agitation of the growing perched flock increased with each arriving trio or quartet. Finally, the energy in the flock hit a critical mass and the birds exploded out of the tree and flew off to the south with smaller groups settling on the bare branches of other neighborhood trees (mostly the taller maples and locusts). When the cottonwood was emptied of crows, a new cluster of birds arrived. Soon there was a new dozen or two perched on its branches, and then a new small group arrived, and then another, and then another, and then suddenly the whole flock burst away again setting off a chain reaction of similar explosive flights from clusters of birds in the surrounding trees.
Photo by D. Sillman
Winter crows!! The hundreds of crows I was watching here in Greeley are just a small fraction of the crow winter-roost flocks that have been seen in other parts of the country. Winter flocks of tens of thousands of crows up to several million crows have been reported from all across the country! The estimated 31 million American crows in North America can form some extremely large aggregations!
Lancaster, PA, for example, had 20,000 overwintering crows in its Park City Mall a few years ago, and a number of other towns in Pennsylvania have faced the loud (and messy) problem of large flocks of winter, roosting, “urban” crows! The warmth and lights of the city environment and the protection it brings from great horned owls and other crow predators are thought to be some of the factors that are selecting for these urban-centered crows
Bothell crows. Photo by UW News, Flickr
In Bothell, Washington just north and east of Seattle, 16,000 crows regularly gather in a winter flock on the campus of the University of Washington-Bothell. This winter roosting started in 2009 possibly because the campus’ trees had grown sufficiently tall to provide protective night roosts for the crows and also because a restored wetland on campus helped to make the area safe and secure for the birds and also generated a potential habitat for food.
Back in late November, I went for a bike ride over to nearby Sanborn Park here in Greeley and saw several hundred Canada geese dozing as they floated about on the park’s lake and a similar number of America crows poking and pecking at the broad grass expanses around the lake. There was also a flock of migrating ringed-bill sea gulls on the edge of the lake resting up for their coming push down to the Gulf Coast. The park was full of birds!
During the breeding season crows disperse into small family groups, but in the winter they migrate often hundreds of miles to form their huge, roosting flocks. Possibly they do this for protection from predators, possibly for warmth, possibly for increased social interactions as part of their mate selection process. There are also suggestions that the crows in the winter roost exchange information about the distant habits they have come from or have seen in their journey to the roost. The intelligence of the American crow and their ability to communicate information through their flocks and over years and even decades of time is not something to underestimate!
Back in 2016, the American crow was featured on the cover of an issue of Audubon magazine (the bird equivalent, I am sure, of a musician being on the cover of Rolling Stone!). The articles in this issue focused on a number of scientific studies that evaluated the intelligence and individual and communal memories of crows.
Winter crows at Sanborn Park, Greeley. Photo by D. Sillman
John Marzluff at the University of Washington in Seattle, for example, went out in the 1990’s and caught and banded (and then released) a cohort of crows. Marzluff and his banding team wore “caveman” masks while they were netting and banding the crows. Subsequently, Marzluff and his team returned to the crow banding area and were ignored unless they wore their caveman masks (even Dick Cheney masks did not elicit a violent crow response!). Not only did the crows that had been directly captured and handled by the “caveman” scientists remember and react to the caveman masks, but also their fellow flock members quickly learned the caveman face and joined in on the mobbing and commotion. Marluff’s team regularly returns to this crow territory and, although it has been over twenty years since the initial trapping event and the originally trapped crows are now undoubtedly all dead and gone, the flock still responds in what the article labels a “crow-pocalyspe” whenever the caveman masked researchers return.
These studies (along with some remarkable brain activity analyses using PET scanners and radioactive isotopes) not only show the individual crow to be extremely intelligent (Mazluff calls them “flying monkeys!”) but also highly connected within its flock to a communication and information system that has to be defined as a culture!
Communication between individuals in the foraging groups and within the larger flocks is a very important aspect of crow biology. The remarkable and extensively documented intelligence of crows (their ability to solve food-gathering problems, to learn to mimic human vocalizations, to employ a variety of complex strategies to gather food etc.) is thought to be a direct extension of their evolutionary success as a social, highly efficiently communicating species. Crows, by the way, have longer rearing and nurturing periods than other bird species. These “learning periods” are even longer than those observed in many mammalian species. These nurturing periods can last up to a year and a half and enable the parental generation to communicate extensive amounts of very functional survival information (hunting and foraging strategies and techniques, habitat selection preferences, etc.) to their offspring.
Photo by D. Sillman
I remember watching a small, foraging group of crows a few years ago back at my old home in Pennsylvania. The group consisted of several adults and one, very obvious fledgling. The fledgling stood out because of his dazed and confused behavior. The other crows actively foraged around my yard and field and were quite purposeful in their activities. The fledge wandered about, often following one of the adults, poking its beak into randomly encountered tufts of grass or piles of debris. A passing car or truck out on the road would instantly scatter the small flock of crows and send them off on short, quick flights up into the surrounding trees. The fledge, though, would remain motionless after the car or truck had passed and would just stare at the unusual source of noise until it finally noticed that it was alone! Only then would it fly off to find the adult on which it was imprinted.
This fledge’s very non-adaptive behavior continued for several weeks. Then, quite suddenly, all of the crows in the foraging group began to behave like adults! My assumption was that the fledge finally “got it” and started to behave like an adult crow, but an equally compelling hypothesis might be that the fledge was taken by a predator or died in some accident. Fledgling birds of all species have a very poor survival rate because of the steepness and severity of their survival learning curves!
Photo by D. Sillman
A study published a few years ago in The Auk looked at individual crows in large winter flocks in upstate New York and in California. These crows were fitted with satellite transmitters, and their flight patterns for the next few seasons were observed. These researchers found that 73% of the western crows and 86% of the eastern crows migrated on average of 500 km (300 miles) between their summer breeding grounds and their winter roosts. Also, these crows were extremely consistent in their selection of their breeding sites but extremely flexible in the selection of their winter roost locations. The authors’ of this paper felt that this winter roost selection flexibility was an important trait for the crows and that it gave the species sufficient flexibility to rapidly adapt to their changing habitats and environment.
The crows are loud and not at all kind to other birds, but I do love to have them around!