Counting all crows in Ann Arbor
The American crow (Corvus brachyrhynchos) is plentiful in Ann Arbor in the winter, so plentiful that if you find yourself under the wrong tree at the wrong time you can hear nothing but its cawing and see nothing but black where there used to be a sky.
If this is your first season in Ann Arbor, it's time to think about crows, and to be prepared to not be surprised when you see them. Crows are smart and well adapted to living near humans, and humans are just getting used to dealing with them on their own terms.
How many crows are there?
Every year an annual Christmas Bird Count is done by the local Audubon Society. Volunteers go out and identify and count all of the birds that they can see, and report these numbers in to the national organization. Locally, bird counting has been going on for more than 60 years, so there is some long-term tracking of area bird populations.
Crows are somewhat challenging to count accurately. Because they congregate in large flocks, the ability to accurately measure how many of them there are in an area depends on area birders' knowledge of where they are likely to gather. Dea Armstrong, the City of Ann Arbor ornithologist with the Natural Area Preservation unit, noted that any individual year bird count should not be considered as an exact measure, but rather that population trends should be looked at over a number of years.
The table of data below is from the Audubon Society's Christmas Bird Count database for crows in the Ann Arbor area.
Common American Crow from Audobon's "Birds of America" Volume 4, 1842.
Add this to your list of Top 10 lists for the Ann Arbor area: in a good year, we'll have a nationally outstanding crow population. (Top that, Boulder or Madison.) The Middle River Fork Valley in Illinois is regularly at the top of the crow-counting charts, with bird counts running 10 times what the Ann Arbor area has in peak years.
Why do crows like it here?
Kevin McGowan of Cornell University Ornithology has an excellent Frequently Asked Questions about Crows in which he attempts to answer the broader question of why crows like urban areas. Crow populations near cities all over the country have been growing, so it's not just that crows like Ann Arbor. He notes by way of historical comparison:
A number of possible explanations exist for the relatively recent influx of roosting crows into urban areas. The birds are not making drastic shifts in behavior; crows have been gathering into winter roosts for as long as there have been crows. We know, for example, from work done in the 1930s by John Emlen at Cornell University that approximately 25,000 crows were gathering in a roost near Auburn, N.Y., in the winter of 1932-33, and that a large roost was present in 1911-12 (Emlen, J. T., Jr., 1938, Midwinter distribution of the American Crow in New York State, Ecology 19: 264-275). The big difference is that they were roosting 3 miles south of town then and are roosting smack in downtown Auburn today. Any increase in size of the roost would be imperceptible, compared to the change of locale.
McGowan suggests possible reasons for crows moving to the city instead of the outskirts of town. Cities are warmer than the surrounding countryside, which may be attractive in the winter. There are fewer owls in cities, and the ambient light lets crows see whatever owls there are, helping them avoid their main predator. Urban areas have big trees, protected from logging and preserved in parks, which are suitable for large crow flocks.
Where do they live?
Crows generally feed in the countryside during the day, and come back to town in the afternoon and evening to flock together. Crows gathering in the area in the evening won't have spent their day in western Michigan, notes Armstrong, but they could have been in farm fields throughout the county or in adjacent counties.
The area where crows flock varies from year to year. In the past, black clouds of crows have been seen over the Diag, the Arboretum, Forest Hills Cemetery, the golf courses near Michigan Stadium, and Pioneer Woods. In recent years, a flock has been seen between South State Street and the Ann Arbor Railroad tracks and near the Ann Arbor Airport.
Crows are regular in their habits, and the same crows will show up at the same place time after time.
How do I get rid of them?
Basically, you don't get rid of them. There are so many crows in the area in good years that any effort to scare crows away from one location will simply cause them to move somewhere else nearby.
The Internet Center for Wildlife Damage Management has a guide to crow control, aimed primarily at controlling agricultural damage. It suggests a variety of methods used to scare crows away from your crops, including methods to frighten crows away with loud noises. Some frightening methods used are simply loud explosions, as with propane-powered cannons; others are more subtle and involve playing back recorded crow distress calls.
The University of Michigan has successfully discouraged crows from spending their time on the Diag, much to the relief of students who were tired of the loud noises and the messy crow poop. A 1999 University News Service release describes the use of "what is essentially a flare gun" to disperse crows on campus. "They don't like to be harassed, and, if you do it enough, they'll pack up and go, for a while. Persistence is the key," said University of Michigan pest specialist Dale Hodgson at the time. I attempted to contact Hodgson for this story, but an email was not returned and the phone number listed at the University for him was not a working number.
The amazing intelligence of crows
Crows are remarkably intelligent creatures. This TED talk by Joshua Klein has a wonderful illustration of their inventiveness, culminating in his demonstration of a vending machine operated by crows.
Edward Vielmetti writes about town fauna for AnnArbor.com.