It was mid-winter, early evening, and as dark as the sky could get given the street lights of the city neighborhood. Over ten hours after leaving the Twin Cities, I finally pull the car into the cramped parking lot behind my college-age daughter’s apartment building in Ann Arbor, MI. I open the car door to an unexpected din and look up to see a flock of crows in the branches of a tree above the car. When my daughter, Noelle, comes out to meet me, I say, “Wow, look at all the crows in this tree!” She gives me one of those looks kids reserve for their parents, that translates to something like, ‘you poor, dear, clueless thing.’
“Um, Mom? Look around.”
The trees to either side are also full of crows, and the trees next to them. As far as we can see, the treetops are a mass of shifting birds and flapping wings. Judging from the sound, they surround us on all sides, extending far out of sight beyond the rooftops. The ground and parked cars are covered in their whitewash. Not a place to dawdle.
The birds keep up their excited ruckus all through the night: all manner of calls that we can hear through the closed windows and thin walls of the apartment. It’s thrilling, marvelous, a little unnerving. “How long has this been going on?” I ask Noelle the next morning. “For awhile,” she shrugs. “You get used to it.” Clearly, the only choice is to choose your mindset.
This seasonal convergence of crows in Ann Arbor, I later learn, is a longstanding tradition in the city. Once back home in Minnesota (after cleaning the car windows with an unfortunate gas station squeegie enough to see a smeary Chicago) I get in touch with Washtenaw County Audubon, and am astounded to learn of its magnitude.
“In recent years, counts have been in the 10,000-12,000 range,” says Jacco Gelderloos, “but they have historically been much higher, more like 15,000-20,000.”
Gelderloos has participated as a volunteer in the annual Audubon Christmas Bird Count in Ann Arbor for more than 20 years, 15 of which he has also served as compiler of results for the city’s inclusion in National Audubon’s hemisphere-wide totals. In the past few years, he’s been designated the counter of the crow roost.
Each year on the 3rd Saturday of December, volunteers fan out across this Michigan city, recording all birds of all species they observe in their assigned zones. The search area is a circle with a 7.5-mile radius centered on the Foster Road Bridge. Volunteers are typically assigned one of 8 areas within this circle for the day-long count.
Records of the Ann Arbor Christmas Bird Count (CBC) date back to 1940. But it wasn’t until the mid-90s that its organizers decided to take a different approach with the crows to get a better handle on the numbers in the huge winter flocks that were becoming a regular occurrence in the city. From that point on, each year, they have had a designated person who—at some point on the afternoon of the count—tries to figure out where the crows are gathering for the night and find a vantage point to count them as they fly in.
It’s not like finding a needle in a haystack, but there are distinct challenges.
First, it helps to know a bit about the phenomenon of such winter gatherings. As Dr. Kevin McGowan of the Cornell Lab of Ornithology writes: “Crows have been congregating in large roosts (communal sleeping groups) in the fall and winter for as long as there have been crows. Crow roosts can range from small scattered roosts of under one hundred individuals to the spectacularly large roosts of hundreds of thousands, even more than a million crows. Before heading to roost, crows will congregate in some area away from the final roosting site, usually an hour or two before complete darkness. Here the crows spend a lot of time calling, chasing, and fighting. Right at dark the main body of the group will move toward the final roosting spot. Sometimes this final movement is relatively quiet, but usually it is still quite noisy. I have seen crows coming together from several separate congregation areas, heading to one final staging area where they all coalesce, then everyone heads to the final roost. The final roost can be a cohesive group in a single woodlot, or it can be rather diffusely spread out over quite a wide area of suitable trees.”
In Ann Arbor, according to Jacco Gelderloos, there tends to be one primary location of the roost each winter, but the location changes from year to year and has also been known to move around from week to week in a given year. (Coincidentally, four of the most favored roosting sites have all been within a mile—as the crow flies—of my daughter’s apartment: one being the Forest Hill Cemetery, ¾ mile away, and one being her immediate neighborhood. “So, she was really in the thick of it,” he notes.)
For purposes of the count, it’s not enough to know where they will likely settle for the night, but rather where they will gather before dark, in the so-called pre-roost aggregations, which may be a succession of staging areas nearby. After scattering to feed during the day in nearby agricultural fields and elsewhere in the city, the crows regroup in late afternoon. “The trick is to be there as they arrive, to count them against the sky as they fly in,” says Gelderloos. “It’s nearly impossible to count them once they’re in the trees, where they’re constantly shifting from branch to branch and tree to tree.”
A little advance sleuthing helps. “In the days and weeks before the count, I’ll post on local birding sites or WhatsApp message boards, asking if people have an idea where the roost might be at that time. That gives me a place to start. Then, on the day of the count, I’ll go out in the afternoon and watch for streams of crows to see where they’re headed. This year, they started to gather in one place near Central Campus, but then they took off toward downtown. So, it was back in the car, follow the crows. Then they changed course and returned to the previous staging area, where I was able to find a good vantage point to do the count. Shortly after, as it was nearly too dark to see, I noticed they had moved on again.”
“It’s kind of surreal; fortunately, they come in in an orderly fashion, streaming in from the same direction. I like to choose a particular tree or some prominent landmark on the horizon and count them as they pass it. It’s like taking a snapshot; there’s a hundred, there’s another hundred; then, as most have arrived and their numbers start to drop off, there’s fifty, another fifty. You don’t use binoculars, which would just limit your field of vision. It’s really a sight to behold.”
He shares a spreadsheet that tells the tale of Ann Arbor’s winter gatherings of crows. In the years 2003—2008, the total for the one-day CBC exceeded 20,000 four times, reaching a high of 29,000 in 2004. Much lower counts in many years since then are believed attributable to the West Nile Virus, which hit crows and jays especially hard. This year’s total of 13,300 is heading in the right direction.
An accountant by trade, Gelderloos is careful to acknowledge that these are not exact population numbers for any of the bird species present in the area on the day of the count. There are variables that factor into the result, such as the quality of the vantage point for the the crows. The number of people counting in a given area is also a factor; participants in Ann Arbor’s count have doubled in the past few years. National Audubon has a formula to adjust for this that takes into account the number of people counting and the number of hours they count. “That said,” says Gelderloos, “we have been pretty diligent about tracking these crow populations over the years, and the numbers from the Christmas Bird Count are definitely revealing trends.”
These winter multitudes are thought to be a mix of more local, resident crows and regional migrants that seasonally exit the northern-most parts of the crows’ range in Canada. Why they would gather in these large, communal sleeping groups outside of the nesting season, or why they would regularly choose Ann Arbor, is in the realm of conjecture. Bird experts suggest a host of reasons: the likelihood that having more sentries offers greater protection from great horned owls (their primary predator); the city lights, which give them a better chance of seeing a predator coming; the “heat bubble” that keeps urban areas 5-10 degrees warmer than outlying areas; the chance to share in food discovered by others; the specific qualities of the roost locations themselves, such as the presence of large oak and hickory trees, or plentiful acorns.
Whatever the reasons, these aggregations of birds from multiple families and multiple territories are of particular interest to researchers trying to understand crow social behavior.
Cynthia Parr got to know Ann Arbors crows better than most when she made them the subject of her 1997 PhD dissertation, in the process becoming the subject, herself, of numerous suspicious activity reports to local police as she climbed trees and observed their activities in neighborhoods, parks and cemeteries. Her paper, “Social Behavior and Long-distance Vocal Communication in Eastern American Crows,” focused mostly on the breeding season, but she also observed the flocks in their pre-dark staging areas from November through February when, she notes, “they emitted all the vocalizations I know them to make.”
According to Parr, the crows’ social system involves long-term social relationships among kin and territorial neighbors, as well as transient associations among winter flock members. Part of her work involved looking for clues in their vocalizations into how human language evolved. “Calls may be more relevant to this subject than bird songs for several reasons,” says Parr. Unlike songs, she notes, calls are used by both sexes and both genders throughout the year. “Because mating competition has not shaped calls to be ritualized, long-distance signals like song, they more closely resemble in acoustic features and usage the elements of language. … Calls are used between individuals who share interests, while songs are usually transmitted between competitors or potential mates: individuals with different interests. Hence calls should contain more honest information than songs.”
We think of songs as the more complicated, message-laden form of bird communication. But Cornell’s “All About Birds” notes that crows have at least 20 types of calls. Researchers like McGowan have unwrapped the humble “caw” of children’s books to find encoded information on the sex and even the identity of the caller, and differences in qualities like pitch, duration, cadence, and timbre in different contexts, whether recruiting food or mobbing predators.
It’s hard to know what all was being communicated among the multi-family, multi-territory, likely multi-national crows creating the steady ruckus throughout my night in Ann Arbor, but I trust that it was not random noise-making. I like to think that it was honest. In her paper, Parr concludes that Eastern American crows possess “an unusual social organization marked by both fluidity and stability, by cooperation as well as competition.” It sounds like there are things that humans could stand to learn from crows beyond the evolution of our own language.
It won’t be long, now, before the wintering flock disperses and the resident crows begin nest building. No doubt the birders of the Washtenaw Audubon Society continue to scan the landscape and listen for birds, as is their habit, whether or not there is counting to be done. Once you start watching birds, you can’t help but have their interests at heart.
Jacco Gelderloos hopes that the increase in volunteers participating in the Christmas Bird Count in the years since the pandemic began is here to stay. “Birds in general could use our help. They have so many challenges that face them on a regular basis just under natural circumstances. We as humans make their lives harder in so many respects, whether it’s habitat destruction, climate change, letting our cats outdoors, light pollution. You don’t need to donate a million dollars or buy a nature preserve. There are lots of small things we can do that add up to bigger things. Support a local conservation group. Buy bird-friendly coffee. Try to make their lives a little easier. We owe it to them, for the joy they give us.”
With thanks to Jacco, Rob French, and the Washtenaw Audubon Society Learn more about the Christmas Bird Count and other birding opportunities in Michigan from the Michigan Audubon Society. Find out how to participate in the annual count where you live and access count results from the National Audubon Society.
Minneapolis-based photographer Karen Kraco is a devoted observer of crows and “enjoys capturing just about anything the wondrous world presents.” Find more of her amazing images at Kraco Creative.