Category Archives: Vocalizations

The definitive guide for distinguishing American crows & common ravens

For two birds that are surprisingly far apart on the family tree, American crows (Corvus brachyrhynchos) and common ravens (Corvus corax) can be awfully hard to distinguish, especially if you rarely see both together.  But with the right tools and a little practice you can most certainly develop the skill.  Fortunately, there are many different types of clues you can use to tell one from the other, so feel free to use the links to skip around to what interests you.

Physical Differences

Although crows and ravens are superficially quite similar, there are variety of features that can be used to tell one from the other. Overall size can be a good place to start.  This especially helpful if you live in an area where they overlap, but even if you don’t, I find that people who are used to seeing crows take notice when they see a raven in person because it feels ~aggressively~ large.  That’s because ravens, by mass, are about twice the size of an American crow.

IMG_3600

A common raven specimen (top) with an American crow specimen (bottom). On average, ravens are about twice as big as crows, but individually there are certainly large crows and diminutive ravens.

This size difference becomes most obvious is when you look at their face.  Raven’s are much more adapted for consuming carrion than crows are (crows cannot break through the skin of a squirrel) and their bills give the distinct impression that they could, in fact, pluck your eyes from your face with little effort. So if your sense of things is that you’re looking at a bill with a bird attached, then you’re probably looking at a raven, not a crow.

IMG_3603

With practice, judging the proportion of crows’ and ravens’ features, like bill size, becomes easier.

Crow vs. raven measuremntsWith practice, judging relative size becomes easier and more reliable, but for a beginner it may not be useful because it’s so subjective.  Instead, it’s easier to look at the field marks (birder speak for distinctive features) which provide more objective clues.

When looking at perched birds, the most helpful attribute is to look at the throat.  Ravens have elongated throat feathers called hackles, which they can articulate for a variety of behavioral displays.  Crows meanwhile have smooth, almost hair like throat feathers typical of other songbirds.

Crow v raven

Even when the feathers are relaxed, the textural differences between the two species throat feathers are apparent. Note that in this photo, the crown feathers of the crow are erect, while the raven’s is not.  The difference in crown shape should not therefor be judged in this comparison.

DSC_0079

When vocalizing or displaying the raven’s hackles become especially obvious.

In addition to the hackles, ravens can also articulate some of their other facial feathers in way crows cannot.  During threat displays for example, ravens will fluff out both the throat hackles and their “ear” tufts.

868AA791-9936-4AD1-BEC7-F7952F0B254F

For birds in flight, however, it’s often difficult—if not impossible—to clearly see the throat feathers.  Fortunately, the tail offers a reliable field mark in this case.  Whereas crows have a more squared or rounded tail (depending on how much they’ve fanned the feathers) a raven’s tail will have a distinct wedge shape. Additionally, although they are a bit more subtle, there are also some differences in the primary wing feathers.  While both birds have 10 primary feathers, in flight, ravens will look like they have four main “finger” feathers while crows will appear to have five. Ravens also have more slender, pointed primaries relative to crows.

crow vs raven

Vocal differences

With a little practice American crows and common ravens can easily be distinguished by their calls.  The call of a raven can be best described as a deep, hollow croak.  Crows on the other hand, caw.  Of course, they can both make at dozens of other sounds including rattles, knocks, coos, clicks, and imitations. With practice even these can be recognized by species, but that level of detail is not necessary for most identification purposes.

Juvenile common raven yell (Recording by Antonio Xeira-Chippewa County, Michigan)
Common raven water sound (Recording by Niels Krabbe-Galley Bay, British Columbia)
American crow call (Recording by David Vander Pluym-King County, Wasington)
American crow juvenile begging call (Recording by Jonathon Jongsma Minneapolis, Minnesota)
American crow rattle (Recording by Thomas Magarian-Portland, Oregon)
American crow wow call (Recording by Loma Pendergraft King County, Washington)
American crow scolding (Recording by Kaeli Swift-King County Washington)

Geographic/habitat differences

While both American crows and common ravens have wide distributions across North America, there are some key differences in where you are likely to find them.  The most notable difference is that ravens are absent throughout most of the midwest and the southeast.  Crows on the other hand, occupy most American states with the exception of the southwestern part of the country.  The below maps from Cornell’s All About Birds website offer more specific breakdowns (hover over the images to see the caption). Note that the reason the American crow’s west coast range appears to dry up from the Puget Sound north is not due to a lack of crows, but rather because the crow species that occupies the upper half of the North American west coast is not the American crow, but the northwestern crow (Corvus caurinus).  The continued distinction between these two “species” is likely coming to a close, however.  For more on our current understanding of the differences (or lack thereof) between those two species check here.

With respect to habitat, both birds are considered generalists, with ravens erring more towards what one might describe as an “extreme generalist”. Ravens can be found along the coast, grasslands, mountains (even high altitude mountains), forests, deserts, Arctic ice floes, and human settlements including agricultural areas, small rural towns, urban cities (particularly in California) and near campgrounds, roads, highways and transfer stations. Crows meanwhile are more firm in their requirement of a combo of open feeding areas, scattered trees, and forest edges.  They generally avoid continuous forest, preferring to remain close to human settlements including rural and agricultural areas, cities, suburbs, transfer stations, and golf courses.  In cases where roads or rivers provide access, however, they can be found at high elevation campgrounds.

Behavioral differences

There are books that could be (and have been) written on this subject alone, so we will limit ourselves to what is likely to be most essential for identification purposes.

Migration
While common ravens are residents wherever they are found, American crows are what’s called a “partially migratory species” because some populations migrate while others do not.  Most notably, the northern populations of crows that occupy central Canada during the summer breeding season, travel south to the interior United States once the snow-pack precludes typical feeding behaviors

Breeding
Although trios of ravens are not uncommon, and there have been observations of young from previous years remaining at the nest, ravens are not considered cooperative breeders. Crows are considered cooperative breeders across their entire range (though specific rates vary across populations and not much is known about migratory populations).  If helpers are present they typically have between 1-3. So if a nest is very busy with more than two birds contributing to nest construction, feeding nestlings, or nest defense, it’s more than likely a crow’s nest, not a raven’s.

IMG_5408 2

Common raven eggs left | American crow eggs right

Diet
Although both species consume a host of invertebrates, crows consume a larger proportion of inverts and garbage relative to ravens.  Mammals, especially from carrion, meanwhile make up the largest proportion of a raven’s diet across surveyed populations.  Access to refuse and population location, however, can dramatically shift the dietary preferences of both these omnivores.

Flight
Because ravens consume a lot more carrion, which is unpredictable in its availability and location, they spend a great deal more soaring than crows do.  So if you see a black bird cruising the sky for more than a few seconds, it’s most likely a raven.  Ravens are also unique from crows in that they barrel roll to advertise their territory.  So if you see a  barrel rolling bird, there’s a better chance it’s a raven.

Interactions
In places where they do overlap, interactions between the two are often antagonistic, with crows acting as the primary aggressors in conflicts.  Ravens will depredate crow nests if given the chance.

DSC_0675 (2)

A raven defends itself from a crow by rolling upside down.  Someday I’ll get a better photograph…

Genetic differences

Throughout most of our history, we have used external cues like appearance, voice and behavior, to sort one kind of animal from another.  Now that we have access to a plethora of genetic tools, however, we can ask a new level of the question “what’s the difference between an American crow and a common raven.”

To put it simply, American crows (Corvus brachyrhynchos) and common ravens (Corvus corax) are different species in the same genus, just like lions (Panthera leo) and tigers (Panthera tigris).  Species and genus refer to different levels of the taxonomic tree, where species represents the smallest whole unit we classify organisms.  The issue of species can get complicated quickly, however, so I’ll direct you here if you want to learn what a mess it really is.  Most important thing to appreciate now, is that if you want a quick, back of the envelope way to evaluate if two animals are closely related, look at the first part of their latin binomial (scientific) name.  If they share that part then they’re in the same genus (ex: crows and ravens belong to the genus Corvus).  If they don’t (ex: American crow is Corvus brachyrhynchos and the Steller’s jay is Cyanocitta stelleri) then they are more distantly related. 

Within the Corvus genus, however, there is still a ton of evolutionary space available.  In fact, to find the closest shared relative of common ravens and American crows you’d need to go back approximately 7 millions years.  Although they are more visually distinct and don’t overlap geographically, American crows are more closely related to the collard crows of China, or the carrion crows of Europe, than they are to common ravens.

Crow phylogeny

Image from Jønsson et al. 2012

Laws and protections

US laws
In the United States, both American crows and common ravens are protected under the Migratory Bird Treaty Act.  This means that, like with nearly all native birds species, you cannot kill, possess, sell, purchase, barter, transport, or export these birds, or their parts, eggs, and nests, except under the terms of a valid Federal permit. It is this law that prohibits the average person from keeping these birds as pets, and requires that rescued crows be turned over to a licensed professional.  The MBTA also prohibits the civilian hunting of ravens under any circumstance.  Under 50 CFR 20.133, however states are granted an exception for crows, wherein with some restrictions, states can designate regulated hunting seasons.

In addition, under 50 CFR 21.43 of the Migratory Bird Treaty Act, you can also kill crows without a license and outside of the regulated hunting season if they are in the act of depredating crops, endangered species, or causing a variety of other destructive issues.  You can obtain the specifics of the Depredation Order here.  Such lethal control must be reported to Fish and Wildlife to remain within the law. No such depredation exceptions exist for ravens. 

Canadian laws
In contrast to the US, no corvids receive federal protections in Canada.  Crows and ravens may receive provincial protections, however.

Concluding thoughts

Before we pack it up, I want to leave you with one last useful piece of information.  This whole article was dedicated to the question of how American crows are different from common ravens.  Hopefully, you’re walking a way with a solid understanding that these animals are in fact different morphologically, behaviorally, and genetically. Asking if American crows are different from common ravens is a different question, though, than asking if “crows” are different than “ravens”.  Because while that first answer is a hard, “yes,” there is no one thing that initially classifies a bird as either a type of raven or a type of crow.  Generally ravens are bigger and have those elongated throat feathers, but there are plenty of crow named birds that could have been named raven and vice versa. So proceed cautiously and consider the specific types of birds the question’s author is referring to before offering specific answers.

If you want to continue to hone your skills I invite you to play #CrowOrNo with me every week on twitter, Instragram and facebook, all at the @corvidresearch handle.  While it’s not to quite this level of detail, I promise it will help advance your ID skills and introduce to to more of the world’s fantastic corvids. For a head start, keep this charming and informative guide illustrated by Rosemary Mosco of Bird and Moon comics handy!

raven vs crow

 

Reference literature
Jønsson K.A., Fabre P.H., and Irestedt, M. (2012).  Brains, tools innovations and biogeography in crows and ravens.  BCM Evolutionary Biology 12
https://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-12-72

Freeman B.G. and Miller, E.T. (2018).  Why do crows attack ravens? The roles of predation threat, resource competition, and social behavior.  The Auk 135: 857-867

Verbeek, N. A. and C. Caffrey (2020). American Crow (Corvus brachyrhynchos), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.

Boarman, W. I. and B. Heinrich (2020). Common Raven (Corvus corax), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.

31 Comments

Filed under Birding, Corvid diversity, Crow behavior, Crow curiosities, Raven behavior, Ravens, Taxonomy, Vocalizations, Wildlife

Crow Vocalizations Part II: Q&A

In Part I of this series I overviewed a new study from my colleague, Loma Pendergraft, about why crows call after discovering food.  For Part II, Loma answered follower-supplied questions on all things crow communication.  The topics we cover include:

Crow-human communication
Crow-other animal communication
Crow-crow communication
Crow sounds
The study of crow communication

I hope you find these answers helpful, or at least illuminating into all that is left to be discovered. Please feel free to leave any additional questions in the comments!

DSC_1944

Crow-human communication

Many people describe situations where they feel they have experienced “conversations” with crows, meaning a back and forth exchange of sounds. Do you think crows notice when we vocalize at them and attempt to vocalize back?
If a person and a crow regularly interact (usually because the person reliably feeds the crows), then it’s fairly common for ritualistic behavior to develop, especially if the behavior is rewarded with food. I don’t know if crows see our vocalizations as an attempt at communication, but they might see it as step one in a series of steps that ends with them being fed- they are vocalizing back to the person because the last time they tried, the person fed them afterwards.

Should people give a signature sound when feeding “their” crows?
It certainly wouldn’t hurt. Crows are smart animals and they’ll quickly learn to associate “their” person’s call with imminent food. This would let the person call the crows to them over long distances.

Do crows try and get the attention of their human feeders with sounds? Might these sounds be just for them (like a specific name or greeting)?
Yes, crows will certainly try to use sounds to get their feeder’s attention. I have a family of crows that come to my office window, and they’ve learned that if they give a rattle call, I’ll feed them (this is actually because I’m often too focused on my computer to notice them unless they call). As to the personalized greeting, that’s possible, but I don’t know for certain.

Can you tell if you are in a crow’s good graces by the sounds it makes?
I don’t know about good graces, but you can certainly tell if you’re in a crow’s bad graces by the sounds they make. If a crow starts scolding you, you know it considers you a threat.

Can crows describe specific people to other crows?
Not directly through vocalizations (e.g. “the dangerous human has black hair and a red shirt”), but they can do so indirectly. If a crow sees a dangerous person, they communicate the presence of danger via vocalizations (“danger here”). When other crows arrive, they watch what the calling crow does to identify which person is dangerous (the screaming bird is divebombing the black-haired human with the red shirt; I better remember him).

Crow-other animal communication

Do crows eavesdrop on other birds to learn new information?
Yes. Crows will respond to the alarm calls of other birds to learn about a predator’s location.

Can crows communicate with other corvids?
Crows will respond to the alarm calls of other corvids (for example, it’s quite common in Seattle for a Steller’s jay to find a sleeping owl, alarm call, and subsequently attract a mob of crows).

Any evidence they listen to mammals? Like would they respond to a squirrel alarm call and vice versa?
I am not aware of any studies that examined whether crows respond to the alarm calls of mammals. I would argue that crows can probably identify certain species of mammalian predators (such as cats, raccoons, squirrels, etc) by listening to their vocalizations, but again, I’m not aware of any studies that examined this.

Crow-crow communication

Do individual crows have specific sounds (like names) for each other?
I don’t know, but there are some interesting anecdotal stories that might shed light on this. Pet ravens who’ve learned to mimic human speech will yell their own name when searching for their owner. This suggests that while the human assigns the name to the bird, the raven assigns the name to the pair bond between them.

Do crow dialects vary by region? If so, on what kind of spatial scale do we define region? Would crows from different regions react appropriately to calls from outside their region?
American crows west of the cascade mountains sound different (their calls are harsher and lower pitched) than the American crows throughout the rest of the country, probably due to ancestral hybridization with Northwestern crows. I don’t know if American crows have dialects in the sense that “traditional” songbirds (such as song sparrows) have dialects. While visiting Oklahoma, I tried playing back alarm calls that I’d recorded in Seattle- the Oklahoma crows reacted the same as Seattle crows (I didn’t have the opportunity to try other call types).

How much variation is there in how individual crows sound? Is it distinct enough to be identifying?
There is a LOT of variation in crow vocalizations, which made interpreting my results very difficult. However, there is evidence that this variation is distinct enough to allow for individual identification. 1

Crow sounds

How many difference sounds can a crow make?
More than most people think. The loud caws make up the bulk of their vocalizations, but they will also utter rattles, growls, coos, and other odd sounds. They are also decent mimics, and can learn to imitate the vocalizations of other animals (including people).

Is there a library that describes the different calls and what they mean?
You can find a large repository of crow recordings at the Macaulay Library, but I am not aware of any libraries that attempt to explain what the calls mean (mostly because we DON’T know what most crow calls mean).

What do the number of caws in a sequence mean?
We don’t know. They are probably important, but only as one component among many different elements.

How much do we know about crow syntax?
Next to nothing, unfortunately. We do know that structured calling has layered repetition in that caws are repeated several times in a series, and series are repeated over the course of several minutes. Here’s one of the more comprehensive studies that cover this topic: Parr, C. (1997). Social behavior and long-distance communication in Eastern American Crows. Ph. D. dissertation, University of Michigan, Ann Arbor, MI

Can you distinguish males and females from their calls?
I can’t, but there is evidence that the crows can distinguish between male and female calls.2

Do they learn their core sounds from a vocal tutor (as do other songbirds) or is it innate?
I don’t know, nor am I aware of any studies that have examined this.

Do crows ever talk to themselves? Meaning, make sounds not intended for the ears of other crows?
Young crows will “babble” quietly to themselves. I have recorded captive crows uttering very quiet notes in the absence of any immediate neighbors, but as there were other crows in view, you can’t say with certainty that they were talking to themselves.

People described one particular sound in a variety of ways. Some called it clicking, other knocking, some described as the sound Predator makes. I suspect you’ll know it as the rattle call. By any name you wish you describe it, what does it mean?
Most scientists describe it as the “rattle call” (for those who haven’t heard it, it really does sound like the rattling growl of the predator from the 1987 movie). Unfortunately, we don’t know what it means. There is evidence that only female crows utter this sound.3

What do the soft “wow/hoo/wah” calls mean?
We don’t know. It has been described in several scientific papers, but those authors don’t know what it means either.

Have you ever heard them give a call you would describe as a single “beep” sound? Do you know what it means?
Unfortunately, I have not heard them utter this sound. Crows are decent mimics- perhaps what you heard was a crow mimicking something else?

Do you know what the “Gah” sound means?
Unfortunately, no.

Do you now what it means when they puff up and bow and make this kind of “rah RAH” sound?
It sounds like you are describing a vocalization that I labeled “medium call” in my paper (the puffed-up bowing display is commonly done with this call). I believe it is a territorial call- when I played it back to listening crows, they became agitated and responded with their own calls and dominance displays.

Do crows have predator-specific calls like chickadees or prairie dogs?
We don’t think they have species-specific calls the way that prairie dogs do, but there is evidence that they call louder and faster around more dangerous predators (such as hawks) in a similar manner to chickadees giving more “dee” notes to denote relative danger.4

Can crows mimic human voices? Would a wild crow ever learn to mimic human voices, or only captive ones?
Crows are capable of mimicking human voice, but I would only expect captive crows to do this. Hand-reared captive crows usually see themselves as people and bond with their owner the way they normally would a mate. Wild crows wouldn’t have the same exposure or motivation.

Do wild crows ever mimic non-human sounds (other birds, car alarms, etc.). If so, why?
They are capable of mimicking other sounds. I don’t know their motivation for doing so, but I would guess that there’s a social aspect to it (play behavior or impressing prospective/current mate).

The study of crow communication

Very bright people have poured energy and resources into studying crow communication with little return on investment. Why is this so difficult to study?
Crow vocalizations are difficult to study because there’s so many variables to consider. Individual caws can have a wide variation in duration, pitch, and inflection, and they can be uttered in a structured series (which itself can have variation in cadence and rhythm) or as unstructured calls. The context also matters- the same call might mean different things if uttered on/off territory or in the presence/absence of a mate, whereas different calls might mean the same thing depending on whether it’s uttered by a male/female or large/small bird.

I believe that you would need the following before you can “crack the code” on crow vocalizations: a large population of marked crows (caller’s ID, sex, age, and social status), constant tracking of which bird is calling (to account for individual call variation), the caller’s location (on/off territory, is it flying, on ground, or perched), info on what’s happening near the caller (mate nearby/away, food present, rival present), and a sound analysis program sophisticated enough to extract complex info from individual calls (such as pitch contour, pitch wobble, power envelope, and inflection duration) and the overall bout of calls (such as the time between calls within and between series or the cadence among series).

Is there evidence of identifiable morphemes?
None that I’m aware of. There was a study conducted 40 years ago that focused on a topic similar to morphemes- they examined which qualities of an assembly call were the most important for conveying the message to listening crows.5

From an animal communication perspective, can you explain the differences between “call and response” and “turn taking”?
I’m not very familiar with the differences between these terms, but it’s my understanding that “turn taking” animals aren’t focused on communicating with each other- they are simply waiting for the other to stop calling before they give their own call (there’s less noise and better transmission if two signals don’t overlap). In contrast, animals engaged in “call and response” are directly communicating with the other- one animal listens to another’s signal and formulates its response accordingly.

Do crows sing (by the technical definition)?
This is a tricky question. Bird song is learned, more complex than calls, species specific, and serves the dual purpose of warning males away from the territory and attracting/courting females. We don’t know if crow caws are learned or innate, but they do fit the remaining criteria for song (although the various coos, rattles, and other soft notes mates utter to each other might be part of the courtship behavior). It might not sound like a traditional bird song, but structured crow caws seem to fit the technical definition for it.

Do crows meet the definition of having language?
Anytime a scientist describes an animal’s communication system as a language, it makes the linguists angry. Language has many definitions, but all acknowledge that it’s a complex form of communication with rules and syntax (for example, there’s a difference between “hat on head” vs “head on hat”) that’s limited to humans. While crows are certainly capable of communicating basic information among themselves, this communication does not meet the definition of having language.

***

Thanks again to everyone that sumitted questions for this post and to Loma for taking the time to respond.  To learn more about Lomas’ work or ask him more questions please check out his blog.

Literature cited

    1. Mates, E. A., Tarter, R. R., Ha, J. C., Clark, A. B., & McGowan, K. J. (2015). Acoustic profiling in a complexly social species, the American crow: caws encode information on caller sex, identity and behavioural context. Bioacoustics, 24: 63-80
    2. Yorzinski, J. L., Vehrencamp, S. L., McGowan, K. J., & Clark, A. B. (2006). The inflected alarm caw of the American crow: differences in acoustic structure among individuals and sexes. The Condor108 518–529
    3. Tarter, R. R. (2008). The Vocal Behavior of the American Crow, Corvus brachyrhynchos [master’s thesis]. The Ohio State University
    4. Yorzinski, J. L., & Vehrencamp, S. L. (2009). The Effect of Predator Type and Danger Level on the Mob Calls of the American Crow. The Condor, 111: 159–168
    5. Richards, D. B., & Thompson, N. S. (1978). Critical Properties of the Assembly Call of the Common American Crow. Behaviour 64: 184–203

18 Comments

Filed under Crow behavior, Crow curiosities, Vocalizations

Crow Vocalizations Part I: New Science

If there’s one general area of questioning that overshadows all others that I receive, it’s questions about vocalizations. One caw, five caws, quiet wows, and loud clicks. We can’t help but to ask what it all means, and wonder how we might better understand and connect with crows if only we knew. To the chagrin of virtually everyone that has asked me a vocalization question, however, the answer is almost always a very disappointing shrug of ignorance. So to help you better understand what we do know about crow vocalizations and why it pales in comparison to what we don’t know, I am dedicating two posts to this topic. The first one–this one–will cover a recent study authored by my colleague and former labmate, Loma Pendergraft. Part II will take the form of a vocalization Q&A. So sit back, grab a snack, and get ready to know more, or maybe less, about crow vocalizations than you ever thought you could.

***

Why are you yelling at the dinner table?

If you’ve ever fed a crow  you may have noticed that shortly after whatever tasty morsel you’ve offered hits the ground, the receiving crow will give a couple caws. If you’re anything like Loma Pendergraft, your next thought will be, “Why?” Are they inviting family members to the feast? Are they trying to scare off competitors? Do the number of caws mean anything?

DSC_1974

Unlike most crow feeders that have to settle for a disappointingly fruitless Google search for an answer, when Loma first asked this as a graduate student he was in a unique position to test it. After three years of labor, his findings have been published in a new paper entitled: Fussing over food: factors affecting the vocalizations American crows utter around food.1 As I can already feel your anticipation in finally finding out what all those food calls are about let me start with a spoiler; you are probably not going to learn what you had hoped to from this study. But you will learn something invaluable about crow communication and how we study it. So with that out of the way let’s start at the beginning.

Generally speaking, if an animal vocalizes at a food source, it must incur some benefit from that vocalization that outweighs the potential costs. Costs include things like getting your food stolen by a competitor or drawing the attention of predators. Conversely, the benefits may consist of things like being able to share resources with your mate or kin, claiming ownership, or attracting other individuals to help you secure a food source away from another bird.

DSC_0242

To try and determine what, if any, of these might motivate the calls that crows produce, Loma conducted three experiments. In the first, he attempted to look for patterns in their vocal behavior by categorizing and quantifying the calls given around food of varying amounts. For example, perhaps for an amount of food small enough as to be consumable by one crow they keep quiet, but for a significant amount they have a specific three-note “I found food” call to alert their mate. In Experiment 2, he ground-tested his ideas about how he was interpreting the calls from Experient 1 by doing playback. Essentially, he wanted to show that if he thought a three-note call was used to attract a mate, then by playing it back the mate should come in. Finally, in Experiment 3 he tested whether the different calls he had recorded had any effect on the listener’s ability to find the food.

To conduct these tests, Loma used wild crow pairs that he located all around Seattle. To prevent the birds from learning his face, he used a variety of sometimes hilarious disguises.  He fed each pair three different amounts of food over the course of three trials: 1 peanut, 5 peanuts or a bountiful 25 peanuts. To try and suss out both if there were any patterns in calls given around food and if calls varied with the amount of food, he recorded their behavior before and after feeding them, and then used vocal analysis software to detect patterns in call structure.

What he found was that, unlike the grand reveal we were all hoping for, few clear patterns emerged from the call data. When crows are around food, they give shorter calls than they did before, and their calls around only a single peanut are longer than when they are around a more substantial amount of food. But in all the other areas where you might expect some pattern to emerge; call rate, peak frequency, the number of syllables, etc., none did.

DSC_1996

Still, the fact that they give short calls around food is suggestive of something, so Loma attempted to determine in Experiment 2 if these short calls are used to either attract birds in or repel them away by playing back those short calls and watching for how the birds responded. The resulting response was more of a whimper than a bang. Or maybe I should say more of a short call than a bang. Because outside of matching the short calls with their own short calls, the crows hardly changed their behavior. Even in Experiment 3 where he looked for whether specific calls aided in the listener’s ability to locate the food, he came away still puzzled. Crows were only able to locate food in 38% of cases and were no better than when played the control chickadee calls.

A cynic may walk away from these findings feeling as if nothing has been gained; that we know little more about what crows are saying around food than we did before. While it’s true we may not have learned much about what they are saying, this study did reveal something important about what they are not saying. Because while Loma found few patterns once the food was down, he did discover that crows give longer calls in the absence of food and that those medium calls prompted territorial behavior when played back. The implication is that crows do not give territorial calls around food, perhaps to avoid risking its discovery by adversaries.

In addition, while it makes for a less compelling headlines, failing to support our hypotheses offers fundamental insights and lays the groundwork for future studies to keep pressing forward. In this case, Loma and his coauthor John Marzluff question whether the difficulty of detecting clear patterns in “x” vocalization leading to “y” behavior is because crows encode so much context-specific information in their calls. In fact, a previous study on American crows found that acoustic variation can indicate the caller’s sex and identity.2 Perhaps the reason we have so much difficulty in mapping out the world of crow communication is that, unlike a crow, we fail to detect all of the information they can ascertain and use to determine how to respond.

So, yes, in some ways we are no closer to Dr. Doolittling the crows than we were before. Instead, we are left with the more compelling reality that our inky friends likely posses an incredibly rich and complex vocal system. For me, this continued mystery only serves to endear them further. After all, do any of us love these birds because we find them straightforward and predictable? I doubt it.

***

Want to learn more about Loma’s research or this study in particular? Don’t forget to head over to his blog.  There you can drop him a line with more crow questions or to request his new paper in full.  He did so much more than I summarized here, it’s really worth a full read!

Literature cited

  1. Pendergraft LJ T and Marzluff JM. (2019). Fussing over food: factors affecting the vocalizations American crows utter around food. Animal Behaviour 150: 39-57
  2. Mates EA, Tarter RR, Ha JC, Clark AB, and McGowen KJ. (2014). Acoustic profiling in a complexly social species, the American crow: caws encode information on caller sex, identity and behavioural context. Bioacoustics 24 

14 Comments

Filed under Crow behavior, crow diet, Crows and humans, New Research, Science, Vocalizations