
A murder of crows fill the sky in Lewiston. Photo by Doug Hitchcox
I know it is January because everyone keeps talking about murders . . . of crows! (And because the new season of The Traitors has started but I’ll save that for a different column.) A “murder” is a colloquial name for a collective group of crows. We could just call it a flock — a fine word for a group of birds — but a murder is a “term of venery” as it is only used to refer to crows. In the winter we get many reports of large congregations of crows, typically in the evenings, and since these massive groups often cause such (unwarranted) alarm, I wanted to devote this column to the “whats and whys” of crow roosts.
One of the most underappreciated aspects of bird behavior is what they do and where they go in the evenings, especially where they sleep. I will admit that a few years ago I went to a presentation on “bird sleep” and I can tell you that it was about birds and that everyone was asleep by the end, so perhaps it isn’t the most exciting of topics. That said, most birds seem to have this funny way of disappearing in the evening. They are really just good at finding a safe place to sleep where they are protected from the elements and from predators. This is especially true for those that are sleeping singly, or in small groups, so unless you are out with a thermal scope, you probably aren’t going to find them. However, some birds take a different approach and will roost in large numbers, like our American crows, and we also see resting congregations of shorebirds, especially during spring and fall migrations, and waterfowl like ducks and geese.
Some of the roosts in Maine include thousands of crows: the Greater Portland roost, which use to be seen regularly staging around Back Cove then roosting in Deering Oaks, has moved to the trees closer to the Maine Mall, and typically hosts around 4,000 birds; the Lewiston roost, typically seen near the Public Works department, can swell to 12,000 birds. These numbers are only seen in the winter when birds are not breeding, and therefore are less territorial, and we see a combination of local birds and migrants joining in numbers. Other large roosts in Maine are in Brewer, Waterville and Augusta, which makes sense as these populated areas are going to have fewer predators and easy access to food, especially when agricultural fields or dumps are nearby.
Safety is apparently a major factor in forming roosts, as you are much less likely to be picked off by an owl if you have thousands of others keeping a lookout, and statistically you are less likely to be chosen if there are thousands of other options. Some studies also show that warmth plays a role in roosting. I find it fascinating to think about the heat given off by thousands of crows in trees. We’ve probably all seen the shots from nature documentaries of emperor penguins huddled together for warmth, and while the winter Lewiston breeze hardly compares to the Antarctic freeze, these birds apparently have a similar style of taking turns warming in the center of the groups and cycling through.
There has also been evidence of information sharing in roosts between corvids, specifically ravens, so I suspect it is a matter of time (specifically, a grad student with time) before we have more proof of communication in roosts but we do often see them departing together to good feeding areas in the morning.
Since I mentioned ravens, I wanted to add a few recommendations for telling these two species apart. Common ravens are larger than American crows, and are more likely to be found in rural, undeveloped, forested areas. The voices are usually diagnostic, with ravens typically making deep “croaks” while crows have the classic “caw.” It is definitely worth acknowledging that all the corvids (the family that includes ravens, crows and jays) have huge vocal repertoires and can make some unbelievably cool noises (water drops from ravens, trust me and Google it) and even mimicry. Behavioral differences can be seen in flight as crows tend to have more direct flight with constant wing beats (to me, it looks like they are rowing a boat), while ravens will often glide and fly a bit more effortlessly with wings often drooped (though this all depends on what they’re doing, where they’re going, and how windy it is). And one fun fact I’ll leave you with comes from their binomals: they are both in the genus Corvus, which means “raven” but the specific epithet for American crow is brachyrhynchus, which is “short bill.” So a better name for American crow, or at least a direct translation, would be the short-billed raven, and bill length can be a helpful way to tell them apart!
I’ll end with the encouragement to go look for a crow roost. It is one of the largest congregations of birds we still get to see. Seeing these groups makes me reflect on the fact that only a little over 100 years ago we had “cloud darkening” flocks of passenger pigeons that would be seen in the millions across the country, and now they are extinct. We have a couple of months left this season to see crows forming roosts in the evening. The way they move, and the sounds they make, are really mesmerizing to watch.
Have you got a nature or wildlife question of your own? It doesn’t have to be about birds! Email questions to ask@maineaudubon.org and visit www.maineaudubon.org to learn more about birding, native plants, and programs and events focusing on Maine wildlife and habitat. Doug and other naturalists lead free bird walks on Thursday mornings starting at 8 am, at Maine Audubon’s Gilsland Farm Audubon Sanctuary in Falmouth.
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