Crow curiosities: do crows migrate?

That birds travel seasonally is perhaps one of the most familiar facts about the natural world. Whether it’s the arrival of technicolor spring migrants, or the din of waterfowl above our heads in the fall, it takes no formal training to recognize that something novel and beautiful has suddenly erupted into our lives. Their ephemeral presence offers an opportunity to ground ourselves in time and place and reflect on the shape of our lives since our last meeting. Or, if you don’t want to get that deep with it, there’s always Looney Tunes or any number of other children’s cartoons to remind us that some birds come and go with the seasons.

At the same time, for most of us living in the continental United States, that crows will be nearby to accompany us throughout our year is something we take for granted. Their predictability on our telephone poles and near our garbage cans is one of those quiet details not everyones thinks of often, but whose consistency surely calms us as so many other things feel unsteady. But at the intersection of these truths is an interesting question: if migration seems such an essential part of bird life, why don’t crows do it? Or do they?

Of the world’s ~ten thousand birds species, only 18% actually undertake annual long distance migrations.1 But there are other types of migration including short distance migration, altitudinal migration (short migrations from shorter to higher altitudes) and partial migration. Partial migration is when only certain individuals within a population migrate, while others are sedentary, and it’s this one that applies to crows. Because while crows in temperate Seattle may be quite comfortable year round, those that call higher latitudes “home”, say central Canada, would have a tougher time making it through the winter unscathed. So much like a wealthy aging relative, they snowbird it to more welcoming climates for the winter.

Until the last decade or so that’s really all we knew about about crow migration. Some did it, some didn’t, and that was that. But given the value of better understanding this behavior, as well as the technological advances that make it possible, western science has finally turned its eye to inspecting these patterns more closely. Because there are so many questions one could ask about this phenomenon. Why do some crows migrate and others do not? Do the same crows migrate each year or can they opt out? Do they return to the same place? How far do they fly? How do they survive the journey? How do they sleep?

In some cases the answers to these questions are surprisingly nuanced. For instance, birds living in the Central and Southern Canadian provinces will nearly always migrate hundreds of miles south into the US, which makes sense because Canadian winters can be especially harsh. But studies have shown that other crows make even shorter migrations, only about 350 miles between contiguous US states with similar climates.2 What motivates these shorter-distance trips remains to be seen. Likewise, whether migrating is a discretional activity is still in question. From a climate change perspective, that individual birds might be able to choose whether or not to migrate each year would have important implications in their ability to adjust to changing conditions. But in the studies conducted so far there’s been no evidence that crows pick and choose each year, rather it seems that you’re either a migratory individual or not, albeit this is based on low sample sizes.3 As a result, migrating crows show extremely high site fidelity; returning to the same breeding and winter sites each year.

As far as distances go, there’s huge variability there as well. In a study that looked at crows from both sides of the country, the average distance traveled by east coast crows was 287 miles, while west coast crows traveled an average of 366 miles.3 The longest migration on record is 1740 miles.4 One thing that’s for certain is that migration is a daytime affair. While most birds migrate at night, crows are among the minority that stick to business hours for their travels. The most compelling explanation for strategy is the “fly-and-forage” hypothesis. Look, even for the arguably most efficient fliers in the animal kingdom, flying is hard work and crows need a lot of calories to sustain flight speeds up to 37mph covering as much as 186 miles in a single day.2 To accomplish this, crows will make up to several pit stops during a marathon flight session, allowing them to refuel and prepare for the next leg. Importantly, although crows migrate both in groups and alone, when stopped they almost always make sure to dine with others. Traveling in the daytime probably helps facilitate finding other crows, and by extension, the local feeding grounds.

When it comes to sleeping, crows leave the fancy mid-flight naps to the swifts and the frigatebirds, opting instead to sleep at night in communal groups. In fact crows will sometimes abruptly change direction just to follow local birds to the nearest roosting grounds. In other cases though, crows have been know to travel routes that allow for stops at the same roosts year after year, underscoring why roost locations should be considered key pieces of habitat.2

So as it stands, crow migration can be summarized the same way as most other parts of their lives: we know some stuff, not everything, we’re probably wrong about a few things, and our best bet is to accept our role as eager pupil and celebrate the gifts of knowledge as they are granted to us.

Literature cites
1. Sekercioglu C.H. 2010. Partial migration in tropical birds: The frontier of movement ecology. Journal of Animal Ecology: https://doi.org/10.1111/j.1365-2656.2010.01739.x

2. Ward M.P. and Raim A. 2011. The fly-and-social foraging hypothesis for diurnal migration: Why American crows migrate during the day. Behavioral Ecology and Sociobiology 65: 1411-1418

3. Townsend A.K., Frett B., McGarvey A. and Taff C.C. 2018. Where do winer crows go? Characterizing partial migration of American crows with satellite telemetry, stable isotopes, and molecular markers. The Auk 135: 964-974

4. Brewer D., Diamond A.W, Woodsworth E.J, Collins B.T.,, and Dunn E.H. 2000. Canadian Atlas of Bird Banding, vol 1: Doves, Cuckoos, and Hummingbirds through Passerines, 1921-1995. Canadian Wildlife Service, Ottawa, ON, Canada

11 Comments

Filed under Climate change, Crow behavior, Crow life history, Movement

11 responses to “Crow curiosities: do crows migrate?

  1. Thomas

    Ours tend to “migrate” from the font yard to the back yard. It mostly depends upon where they think they are most likely to receive a peanut for their efforts. 😉

  2. Barbara Kimm

    This is interesting but does not address my crow observation questions. Over 5 years I have lived in two places about 12 mi. apart. My observations are the same in both places over a few years. In the Spring two crows and I enter a mutual training regime. They ask me for food and I give it to them, once a day, if they ask. If they have babies they will bring them to me, show them the food, then the parents will disappear leaving the juveniles to feed for the season. I can identify them by individual behavior and sounds that they make ( one clucked like a chicken, another has made a clicking sound). They show up about Daylight Savings time here in the PNW, stay the season and disappear about the end of PDST. There are other crows in my area but they are not the ones who came to me. “Mine” will come back in the Spring but only once or twice. They will sit on my railing, ask for food as they did the year before, then disappear. I will be without crow friends for several weeks until a new pair comes in and we work again on training each other. It is NEVER the same pair, or juvenile threesome, each year. So, where do they go in the winter? Why do they come back in the Spring but don’t stay? It is a complete mystery to me!

    • Hi Barbara, that is a unique situation! Without eyes on the ground, I’d be just wildlife speculating so I won’t offer an explanation. But you have my agreement that that’s very curious!

  3. adexterc

    I now live in AZ. I have been here two years. At the start, I was really pleased with all the big black birds around. Ravens? Maybe. Recently, I have seen almost no crows or ravens. Zero. The summers are hotter and drier in just two years. Think they are they going North to high ground?
    I am glad to see new posts

  4. Mikal Deese

    Albuquerque, NM, has some Crows year around. Yet the summer population is about a tenth of the wintering crowds. It seems to me that they enjoy their winter vacation as much as New Yorkers like to head south for their. Raucous social groups disperse over the city during the day, and then stream up the Rio Grande to their traditional nighttime roosting grounds. Sleeping is preceded by the cocktail hour of gossiping and then settling for the night.

  5. Kass

    I’ve always found it really intriguing why a small portion of crows stay up here in Winnipeg, while most others leave. I’m sure it has to do with the available resources only supporting so much of a population, but it makes me wonder what factors influence some crows into staying or going. Does it run in the family, or does age become a factor?

    Either way, it’s still a delight to see them around, and offer a little food when they’re watching. Knowing that they’re getting a bit more familiar and comfortable with me on an individual level is rewarding in and of itself.

  6. Matt

    I like on a hill in Portland Oregon and right around dusk all the crows fly somewhere for the night. It is cool to watch because of all the crows in a large group. It seems like they have leaders that just hang out on trees and give directions. Then there are different little groups but they are all one big group. Is the a hierarchy of the crows? Do they have jobs or roles in their communities?

    • Hi Matt! The short answer is kinda sorta. There are definitely hierarchies within the broader community (some birds will always be the first to eat while others are forced to be the last) but as far as we know there aren’t specific jobs within the broad community. Within individual family units there are, however. Males, females, and helpers all have semi-specific roles during the breeding season. Great questions!

  7. Rosemary Sarka

    Thank you for this. I have been feeding and observing crows for about a year. I have what I think is a family. I have read one of the Marzluff books, but I still have many fundamental questions.

    Rosemary Sarka

  8. I really enjoyed reading this. Would have loved to study migration further. You said that some migrating crows will change direction to follow local birds for that communal resting spot at night. How do they identify that a bird (or flock/murder of birds) is local? I love that behavior aspect!

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