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Are ravens smarter than a___?

One of the most common audience queries that follow my public corvids presentation is, “Who’s smarter, a raven or a ___ ?” The blank can been filled in by any number of animals, but most people want to know either how various corvids scale against each other, or how corvids like ravens compare against other animals known for their intelligence, such as primates, dolphins, or elephants. Inevitably, people are somewhat disappointed by my answer. As I’ve written about previously, trying to rank animals in this way is a precarious exercise. As an animal behaviorist, I of course think exploring the cognitive abilities of animals is fascinating and worth doing, but ranking them in the absence of any kind of consideration of why different animals display some cognitive skills and not others makes intelligence seem like some kind of evolutionary race. Instead, like all things, the possession of higher order cognition is simply a byproduct of what happened to work in the reproductive favor of a particular species, and should not be interpreted as a reflection of value. Even if we weren’t concerned about the ethical implications of these comparisons, the second issue with them is that they’re not very meaningful because different species have been presented with different tests which makes cross-species comparisons a bit apple and orange-y.

But while we should guard ourselves against the temptation to make intelligence a linear scale by which all life can be measured, we can acknowledge that a study by Pike et al. 2020 has made some incredible progression in solving that second issue.1 With their new testing paradigm, suddenly our apples and oranges are not so hard to compare after all. So let’s explore what’s interesting about the cognitive abilities of ravens and what exactly this study has shown us about what they have in common with some of our closest primate relatives.

Before diving into the details, we should take a moment to understand how animal behaviorists define intelligence* and how we are attempting to understand why corvids, primates, parrots, etc. have a mastery of higher-order cognitive skills that other animals do not appear to possess. In my field, the definition of intelligence is often described as the ability to flexibly solve problems using cognition rather than instinct or trial and error learning. Within that definition, “flexibility” and “cognition” are the keys because they strain out the behaviors that require things like insight, foresight, empathy, causal reasoning, etc. from those that are guided by simple, immovable mechanisms that can be carried out with little thought. Consider, for example, a bridge. Both humans and ants can build them; but whereas ants build them only in specific contexts and by the collective power of hundreds or thousands of individuals executing a simple task, humans can build them in a great many contexts because we understand and can manipulate complex properties of the physical world. The fact that both animals can accomplish bridge-building with such vast difference in our cognition warrants an interesting question: “Why did advanced cognitive abilities evolve in the first place?”

Although many explanation exist, the two I want to spend time on are the social intelligence hypothesis and the ecological intelligence hypothesis. The ecological intelligence hypothesis asserts that it is the harshness or complexity of the environment that drives advancing cognition (ex: the availability of novel foods that requires some problem solving to eat), while the social intelligence hypothesis suggests that it’s the demands of long lasting and complex social lives that most contributes to the intelligence of some species. While both ideas have supporting evidence, of most interest to the proponents of the social intelligence hypothesis is that social complexity (ex: the maintenance of long-term bonds that may include absences) is shown to correlate with relative brain size (specifically the neocortex) in mammals and birds. Of course, size isn’t everything, but those species still share other non-sized based brain features such as high neuronal connectivity, density and modularity. That birds such as corvids and parrots share these features with some mammals is especially striking given that birds and mammals diverged some 300 million years ago, and the resulting evolutionary differences in our brain architecture are evident.

When it comes to actually testing cognition, there are two main umbrellas of inquiry: social cognition and physical cognition. Social cognition refers to things like the ability to follow another individual’s gaze, learn a task from someone else, and interpret intentions. Physical cognition refers to things like object permanence (that objects continue to exist even though they can’t be seen), relative numbers, properties of tools, etc. Among corvids, New Caledonian crows have demonstrated remarkable physical cognition (they can infer an object’s weight by how it behaves in the wind!2), but because they’re not especially social corvids3, they have not demonstrated remarkable social cognition. Common ravens on the other hand, have social cognitive and potentially even physical skills that we believe rival that of primates. But because we’ve only tested corvids using a single cognitive paradigm at a time, we’ve been limited in our comparisons. Which is what makes the study by Pike et al. so unique. Theirs is the first to retool the Primate Cognitive Test Battery (which is the collective name for a suite of different cognitive tests that are routinely given to test primate intelligence) to assess the abilities of common ravens among nine physical and six social skills.

The nine physical skills were designed to test the eight study subjects’ understanding across three main themes: space, quantities and causality. Among the space tests the researchers were interested in evaluating how well ravens can understand object permanence and follow a moving object that is concealed (picture the classic shell game, but without the grift). For the quantities tests, the researchers presented ravens with things like a large and small pile of food to see which they would choose. Finally, for causality tests, they did things like let the ravens see them place a peanut in a cup, and then shake that cup vs. an empty one before allowing the bird to make a selection of which cup they wanted. Among the social skills, the researchers tested social learning, communication and theory of mind (the ability to think about the mental states of yourself and others). Each of these 6 total tests evaluated things like the being able to follow gaze, learn by instruction, and interpret intentions. Of course, all these tests were far more detailed and controlled than I am presenting them here; if you’d like a more detailed breakdown, you can read my personal, unedited, notes on the paper here.

Given their complex social lives and the abundance of data on raven social intelligence, the researchers expected to find that their subjects would perform better among the social tests relative to the physical ones, but that’s not what they found. To their surprise, the ravens actually performed similarly in both cognitive realms. This suggests that ravens possess a general intelligence and that the two realms may be linked enough in the brain that you can’t really disassociate one from the other. Still, across the 15 specific tests, ravens did better at some than others. For example, given their lifestyle as scavengers, it’s perhaps not surprising that among physical tests they performed the best at qualitative skills like assessing what pile of food was the biggest. Impressively, ravens were able to match adult-level success at many of these executive-order tasks starting at only 4 months old, which is younger than we typically see in parrots and even many primates. As for direct comparisons to primates, while ravens did significantly worse at spatial tests, they performed similarly to primates in quantitative and theory of mind tests, and only slightly worse in causal reasoning and communication. All in all, it seems ravens pretty closely match the performance of great apes across both social and physical cognition tests.

That said, there are some caveats to consider. First, these tests were administered by people, so there’s just no getting around the possibility of unintended influence. For example, previous studies have shown that ravens begin following the gaze of their flock mates around eight weeks old, by only start to follow the human gaze after fifteen weeks. So it’s possible that the birds’ responses to people among some of the social tests were more muted because they weren’t actually interacting with a fellow bird. Alternatively, they may have performed more poorly at some tasks because they viewed the experimenter as a competitor rather than as a neutral observer. There was also quite a bit of individual variation, and only a small number of birds were tested, so the researchers hesitate to make sweeping claims that the performance of these eight birds are representative. And when it comes to comparing ravens and primates, we’re back to our bridge dilemma because of course behavioral ability does not imply that the same complex cognitive mechanisms are at work.

Still, while these considerations are important, there’s no getting around that these birds demonstrated an incredible performance in both social and physical cognition tests. Put another way, an animal that diverged from mammals 300 million years ago, whose cortical architecture is significantly different, can play the shell game and scheme on their rivals just about as well as our closest relatives. So while I’ll continue to exercise restraint in answering, “Are ravens smarter than a ____ ?,” I have no doubt that these animals are as complex and enchanting as so many of us suspect them to be.


*To understand the topic at hand a discussion of cognitive intelligence and its definition is necessary, but it’s also worth learning about and unpacking why our judgement and language around intelligence as applied to people is increasingly considered harmful. Here are some resources to do that:


Literature cited:

  1. S Pike, MJ Sima, CR Blum, E Herrmann and R Mundry. 2020. Ravens parallel great apes in in physical and social cognitive skills. Scientific Reports 10, 20617
  2. SA Jelbert, R Miller, M Schiestl, M Boeckle, LG Cheke, RD Gray, AH Taylor and NS Clayton. 2019. New Caledonian crows infer the weight of objects from observing their movements in a breeze. Proc. R. Soc. B 286: 20182332
  3. Holzhaider JC., Sibley MD, Taylor AH, Singh PJ, Gray RD, and Hunt GR. 2011. The social structure of New Caledonian crows. Animal Behaviour 81: 83-9


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Do you see what I see: subjective consciousness in crows

Watching a crow eagerly eye me for a peanut, I can’t help but wonder what it’s thinking about. Is it thinking the same thing as its flock mate, or is it having its own experience? Is it aware of me? Of itself? The conscious experience is such a fundamental part of humanity, it’s nearly impossible for most of us to envision life without it. And by extension, its hard for us to imagine that animals don’t experience consciousness too. But the fact remains that scientifically investigating consciousness, especially in non-human animals, has been slow and contentious. Among birds, this research has been all the more elusive. Which is why a study looking at subjective consciousness in carrion crows by Nieder et al. (2020)1 made an enormous splash this past fall, and resulted in a lot of misleading headlines. So why has consciousness been so difficult to study and how did this team attempt to do it?

An American crow, a relative of the carrion crow

First, let’s take a look at what we mean by consciousness. As it turns out, descriptions of consciousness get technical in a hurry, and they don’t all agree, which I suppose makes sense considering the philosophical and scientific challenge of asking, “how does an ethereal mind interact with the physical world?”2 It’s a tough question and one that can land you in an Inception-like hall of mirrors without careful consideration. So it’s critical to parse just what kind of consciousness a study is attempting to measure before making any effort to interpret their results. For the team behind this study, the focus was to determine if crows possess “subjective consciousness,” or the subjective experience of physical stimuli; in other words, the ability to have individually-specific experiences of external properties (AKA “qualia”). For example, you and I might look at a stop sign and quickly agree that it’s mostly red, but our respective experience of that redness could be quite different. A computer, on the other hand, probably does not experience qualia when detecting that an object is red, though whether or not this will soon be possible is a matter of great interest in AI circles. In addition, the study’s authors include in their definition the ability to access and report the experience of that subjective experience. For those with a background in psychology, you’ll recognize these two components as what Ned Block calls phenomenal and access consciousness.

At this point it’s helpful to step back and appreciate how much of the organismal world operates without any conceivable form of subjective consciousness. There are many a successful species that most definitely move through life by simply responding to various stimuli, without ever needing to take stock of their perceptions of those stimuli. Plants for example, react to noxious stimuli, but that doesn’t mean they have a subjective experience of pain. Even much of our own world operates without subjective experiences. Breathing for instance, happens probably 19,995 times a day without you noticing it. Highway hypnosis is another prime example. How is it that you can arrive safely at a destination you realize you don’t fully remember driving to? Because while you may not have had a subjective experience of the entirety of the drive, you were still accurately responding to the stimulus of the wheel in your hand, the pedal under your foot, and the various stimuli that presented themselves on the road.

But while it’s easy for most of us to accept that caterpillars and jellyfish probably move through life in this Simon-says kind of way, it becomes substantially more difficult to imagine that animals who look or act more like us don’t possess some from of consciousness. In fact, there are many ethologists who argue that they do, with varying levels of support.3 But the fact remains that it is difficult to demonstrate this because we cannot ask animals about their experiences and perceptions. We might, however, be able to leapfrog the inconvenience of working with nonverbal subjects by going directly to control center itself: the brain.

Among primates, including humans, the brain neurons that are responsible for representing what an individual perceives (i.e subjective experiences) are in the neocortex, which is part of the mammalian pallium.4,5 Until relatively recently, replicating such studies in birds was ignored, because bird brains are unique from mammalian brains in some key ways. As a result of these differences, we used to believe that birds had no equivalent to the mammalian neocortex, and were therefore incapable of flexible, complex thought. Now we understand that the circuits of the avian pallium are functionally organized in a similar way to the mammalian pallium, and furthermore that the avian pallium contains a staggering density of neurons.6,7 This is especially true among the corvids and parrots, which like non-human primates, can have as many as 1-2 billion neurons in their pallia.8 Given this organizational similarity, we’ve been able to show that birds do in fact have an analog to the mammalian prefrontal cortex, the part of our brain the allows us to process thoughts, feelings, and decisions. The question now is whether this avian analog, called the nidopallium caudolateral, also houses neurons that allow for subjective consciousness.

If any part of that was lost on you, we can summarize it as follows: the reason you and I can experience the exact same stimulus (the color green, the prick of a needle, the sound of C-sharp) differently, is because we experience subjective consciousness. Philosophical/religious discussions aside, the experience of consciousness is regulated by the brain, and we believe we’ve identified the brain areas and neurons that control this in humans and some primates. The goal of this study was to look to the analogous area of the bird brain where these neurons are housed in the primate brain, and see if they could demonstrate a neuronal basis for subjective consciousness in birds.

In theory that sounds simple enough (lol), but how exactly did they use neuronal activity to identify the experience of subjective consciousness? The fundamental “trick” of this study is that they exploited a stimulus that can give rise to two different percepts. Think of the classic optical illusion of the rabbit-duck. Whereas what you see first is a rabbit looking to the right, I see a duck looking to the left, and this difference is evidenced by the respective activity in our brains. This study used that same concept only instead of optical illusions, they used light.

The classic optical illusion of the rabbit-duck

By implanting electrodes in two carrion crows’ brains and training them to report if they saw a light, the researchers could investigate their subjective experiences by reducing the intensity of the light to near perceptual threshold levels and asking the crows to indicate whether they had seen it. Importantly this training wasn’t as simple as, “peck if you saw a light.” Instead, after the light was presented, there was a pause, after which the bird was shown either the color red or blue. Depending on whether the bird thought it saw the light or not, which color it was then shown informed how it was supposed to indicate its perception to the researchers. If the light had been detected, seeing the blue color meant it would only get a treat if it stayed still, whereas red meant it needed to move. If that light hadn’t been detected, then seeing blue meant it needed to move, while red indicated that the bird should stay still. Without this step of making the birds wait to find out what motor response indicated their answer (and earn them a treat) the study would only have revealed the neurons associated with preparing the correct motor response. Instead, they were able to look at the neuronal activity related to the immediate impact of the stimulus, and then to the activity related to processing this information into a perception.

What they found is that like primates, crows exhibit a two-stage process, where neuronal activity during Stage I mostly reflects the intensity of the physical stimulus, followed by a second spike in activity that reflected their perception. The patterns of activity in Stage II were so consistent, that the researchers could predict whether the crows would say they saw the light or not by looking at this activity alone. Most importantly, while the responses of the two birds were the same if the light intensity was bright and unambiguous, when shown faint lights, the two birds responded differently. Meaning that despite being shown the exact same stimulus, the two birds had different subjective experiences of whether they had seen it or not. There were also instances of false positives, where the birds indicated that they had seen a light that wasn’t really there. In these cases their brains behaved during Stage II just as they did when they had actually seen a bright light. This is important because it further demonstrates that the brain activity the researchers were measuring correlated with the crows’ subjective experience, rather than as a result of the intensity of the stimulus itself.

What this shows us is that carrion crows have the neurological substrates that support subjective consciousness, and it indeed appears that they have individual experiences of stimuli. It does not show us, despite many articles to the contrary, that they are “self-aware” or engage in metacognition (the ability to “ponder the contents of their own minds“). Still, these findings makes crows pretty unique among animals, putting them in a category shared only by primates. Furthermore, it underlines that despite the differences between mammalian and avian brains, the two are are remarkably functionally analogous, at least with respect to some species. In fact some have gone as far as to say that this and other studies indicate that the continued assertion that birds do not have a cerebral cortex is outdated and wrong.8 Moving to the 30,000ft view, the findings of this study invite numerous questions about what such shared abilities say about the evolution of consciousness across species. Did it evolve independently multiple times or has is been present since before the evolutionary split between birds and mammals some 320 million years ago? Either way, if I was a betting person, I would wager that the list of animals in possession of subjective consciousness will only continue to grow as we find new ways of exploring these once out of reach questions.

~Many thanks to Dr. Andreas Nieder for helping me parse the methods and findings of this fascinating and complex paper.

Literature cited

  1. Nieder A, Wagener L, and Rinnert P. 2020. A neural correlate of sensory consciousness in a corvid bird. Science 369: 1626-1629
  2. Glatterfelder JB. 2019. Subjective consciousness: What am I? In: Information—Consciousness—Reality. The Frontiers Collection. Springer, Cham.
  3. Boyl M, Seth AK, Wilke M, Ingmundson P, Baars B, Laureys S, Edelman DB, Tsuchiya N. 2013. Consciousness in humans and non-human animals: recent advances and future directions. Frontiers in Psychology 4:
  4. Dehaene S. and Changeux JP. 2011. Experimental and theoretical approaches to conscious processing. Neuron 70: 200-227
  5. de Lafuente V. and Romo R. 2005. Neuronal correlates of subjective sensory experience. Nature Neuroscience 8: 1698-1703
  6. Shanahan M, Bingman VP, Shimizu T, Wild M, and Güntürkün O. 2013. Large-scale network organization in the avian forebrain: a connectivity matrix and theoretical analysis. Font Comput Neurosci 7: doi: 10.3389/fncom.2013.00089
  7. Olkowicz S, Kocurek M, Lučan RK, Porteš M, Fitch WT, Herculano-Houzel S. and Němec P. 2016. Birds have primate-like numbers of neurons in the forebrain. PNAS 113: 7255-7260
  8. Herculano-Houzel S. 2020. Birds do have a brain cortex-and think. Science 369: 1567-1568


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CR sticker shop is live

Whether you want to finically support the blog, or simply get more corvids in your life, my etsy shop is the perfect way to do either. With corvid themed stickers and magnets designed by artists like Madison Erin Mayfield and Laurel Mundy there’s a corvid for everyone on your list. Orders will ship over the weekend, and my hope is that even with Covid mailing delays, all orders will arrive well in time for gift giving season. I hope you check it out!

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Crow curiosities: can crows see UV?

Recently, a marvelous set of blue crow photos from Carl Bergstrom had the internet’s corvid fans doing a collective double take. In addressing what could be responsible for such spectacularly odd images, many people’s first instinct was to wonder if these photos might be revealing the hidden ultra-violet lives of crows. After all, as a group, passerines (aka songbirds, of which crows are part of) are well known for their abilities to express themselves and see beyond the visual spectrum available to people. But while, “can crows see in UV? Is their perception of the feathers adorning their flock mates different from our own?,” feel like simple enough questions, a google search after their answers results in an almost unprecedented silence from the otherwise vast body of crow knowledge that exists beyond your search bar. Sure, you can find the occasional popular science article that talks about the visual systems of birds and maybe includes a photo of a crow, but these articles never provide citations and most speak simply in generalizations about passerines, not about crows specifically. The reason for this knowledge gap is that while the visual systems of birds is generally well studied, there are over 10,000 species of birds and not all of them can be the darling of every field of research. So while crows take a disproportionate share of our scientific attention, relative to many other species, not much has actually been done on their visual systems; what does exist is spread out and sometimes hard to find. But this is a question that comes up time and time again so let’s take a moment to harness what has been done, and offer the best possible answers to these questions that science currently has to offer.

Before we get to the heart of our questions though, let’s take a beat to review the more technical aspects of vision, and why our visual experience of the world is different from our dogs’ or possibly crows’. Vertebrate eyes work fundamentally via the same 5 step process: Step 1) light enters eye through pupil, Step 2) the cornea bends the light that passes through the pupil, Step 3) the light then passes through the lens which focuses it on the retina, Step 4) rods and cones of retina detect light and color and, Step 5) cells in retina convert this into impulses which go to brain. But while the general process is conserved across most species, the details of each of these steps can vary in life altering ways. Crucial to this discussion is that fourth step that involves the rods (which are motion sensitive light detectors) and the cones (which are contrast sensitive color detectors). Depending on the classes of cones a species possess, an animal can be either dichromatic (most mammals), trichromatic (primates and marsupials), or tetrachromatic (birds and reptiles), which translates to different levels of color vision. 1 While we are able to detect red, green and blue light, most birds have a fourth cone that allows them to more acutely detect short wavelength colors near the ultraviolet range. The ability to simply detect UV isn’t enough though (in fact humans are sensitive to UV light), you must also have the ability to transmit that part of the spectrum. While our eyes filter it out, rendering it invisible to us, birds have special oil droplets in their cones that allow for the passage of UV light, while limiting its damage.2 Among birds, that 4th cone (called the short-wave sensitive 1 or SWS1) can be further divided into two variants: the violent-sensitive variant (VS birds) or the ultra-violet sensitive (UVS birds) variant. Without getting any more technical, suffice it to say that UVS birds have a much keener visual experience of the UV spectrum, relative to VS birds, though both can detect UV light.3

The function of this “enhanced” vision is many fold.4 For one, it allows for greater contrast of the environment, rendering what may look to our eyes as a flat wall of green vegetation, as a much more dynamic plane, enhancing a bird’s ability to fly through dense foliage. Like insects, UV sensitivity is also important among many types of nectarivorous (nectar drinking) and frugivorous (fruit-eating) birds. Many fruits, for example, are coated in a UV-reflecting waxy substance that helps advertise their availability to would be seed dispersing birds. And finally, descriptive UV patterns in feathers opens an entire world of visual signaling that is otherwise completely hidden from us. Given the ways we might image crows would benefit from exploiting any one of these possibilities, it makes sense that they would possess the kind of rich UV experience that many other birds are known for.

Which brings us, finally, to the rub. While it’s true that most passerines are what we call UVS birds, corvids, like flycatchers and most raptors, are VS birds, meaning their visual system is biased toward the violet-spectrum and they are not considered especially sensitive to UV light.3,5 The low UV-detection abilities of corvids and many raptors, appears to offer a lifeline to smaller passerines, which exploit these visual differences in their plumage, allowing them to remain conspicuous to potential mates, while staying inconspicuous to their potential predators.6 Given this finding, we would expect crows not to, for example, show a great deal of UV detail in their feathers, and the research seems to bear this out. A study of large-billed crows found them to be so weakly iridescent, that the authors proposed their violet-blues hues may simply be an artifact of chance, and play no functional role.7 Likewise, unlike many other passerines, crows don’t seem to communicate aspects of their identify via secret codes in their feathers. A 2007 study, for example, confirmed that American crows, fish crows, and Chihuahuan ravens are sexually monochromatic from an avian visual perspective, meaning there’s no UV signaling of “male” or “female” hidden from us in their feathers.8 These birds were among only 14, of the 166 North American passerines sampled, for which this was true.

Despite these findings though, the role of UV in the lives of crows and other corvids hasn’t been rendered completely immaterial. When presented against high contrast backdrops (green foliage), fish crows are more adept at picking out UV reflecting berries than matte black Vaccinum berries. On the other hand, when both are presented in front of a backdrop that offers no contrasting advantage to the UV reflecting fruit (sandy backdrops) they pick out both berries equally.9 And while the UV spectrum may not be super useful to crows for coding information, that doesn’t mean the feathers of corvids don’t carry any weight. Common magpies, for example, convey all sorts of information from sex to age to territory status in their iridescent tail feathers.10 Taken together, these findings seems to suggest that there is a lot more to unpack with respect to the role of UV in the lives of corvids than, well, meets the eye, and species-specific studies may be necessary to fully parse the potential nuance.

In the mean time, while the errant photo of a blue crow may be eye catching, it’s probably not revealing an otherwise visually hidden secret, like that time a ghost showed up in the background of your vacation photo. Instead, blue crows are probably just an artifact of the photographer’s white balance gone awry in the golden hues of a fine day.

Literature cited

  1. Bowmaker JK. 1998. Evolution of colour vision in vertebrates. Eye 12, 541–547
  2. Lind O, Mitkus M, Olsson P, Kelber A. 2014 Ultraviolet vision in birds: the importance of transparent eye media. Proc. R. Soc. B 281: 20132209.
  3. Ödeen A, Håstad O & Alström P. 2011. Evolution of ultraviolet vision in the largest avian radiation – the passerines. BMC Evol Biol 11: 313.
  4. Withgott J. 2000. Taking a Bird’s-Eye View…in the UV: Recent studies reveal a surprising new picture of how birds see the world. BioScience 50: 854–859.
  5. Brecht KF, Nieder A. 2020. Parting self from others: Individual and self-recognition in birds. Neuroscience & Biobehavioral Reviews 116: 99-108.
  6. Håstad O, Victorsson J, Ödeen A. 2005. Differences in color vision make passerines less conspicuous in the eyes of their predators. Proceedings of the National Academy of Sciences 102: 6391-6394.
  7. Lee E, Miyazaki J, Yoshioka S, Lee H, Sugita S. 2012. The weak iridescent feather color in the Jungle Crow Corvus macrorhynchos. Ornithol Sci 11: 59–64.
  8. Muir DE. 2007. Avian Visual Perspective on Plumage Coloration Confirms Rarity of Sexually Monochromatic North American Passerines. The Auk 124: 155–161.
  9. Schaefer HM, Levey DJ, Schaefer V, and Avery ML. 2006. The role of chromatic and achromatic signals for fruit detection in birds. Behavioral Ecology 17: 784-789
  10. Nam HY, Lee S, Lee J, Choi C, and Choe JC. 2016. Multiple Structural Colors of the Plumage Reflect Age, Sex, and Territory Ownership in the Eurasian Magpie Pica pica. Acta Ornithologica 5: 83-92.


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Crows removing ticks: helpfulness, opportunism, or something else?

Guest post by Thom van Dooren

If you’ve spent much time at all watching YouTube videos of corvids, you’ve likely come across some of the numerous examples of them engaging in the seemingly helpful act of removing ticks and other ectoparasites from all kinds of other animals. The lucky ‘client’ might be a rhino, a sambar deer, or a cow.  Admittedly, it isn’t always entirely clear that these crows are being exclusively helpful, engaging in what biologists call symbiotic cleaning. In at least some of these cases, there seems to be a reasonable chance that they’re (also) playing, pestering, or even getting ready to take a bite out of an unsuspecting animal. 

In a few cases though, the results of their cleaning work speak for themselves. One recent set of camera trap videos circulating at the moment on social media shows a group of corvids, probably Torresian Crows (Corvus orru), removing ticks from several, somewhat reluctant, wallabies. The ticks have been around for a while, as evidence by their size, and cover large parts of many of the animals’ ears and necks. As the wallabies arrive at a watering station that has been set up for them in the dry summer of southern Queensland, the crows move in. They carefully sidle up to the wallabies while they’re drinking, and then, in one swift movement, a beak flashes out and returns with a tasty, protein-rich, tick.

While these videos fascinate, delight, and frequently disgust, YouTube viewers, these behaviors are not uncommon in the animal kingdom. Symbiotic cleaning, across species lines, is a particularly common practice for fish, crustaceans, and birds. The animals who receive these cleaning treatments are mostly larger fish and herbivores. In the case of corvids, studies have documented the symbiotic cleaning of deerwild boars, camels1, and a handful of other species.

Perhaps my favorite example—sadly, one without footage—is another Australian case involving the same species, the Torresian Crow. At the top of the Northern Territory, on the Cobourg Peninsula, these crows have struck up an unlikely relationship with banteng (Bos javanicus), a species of feral cattle that was introduced to Australia in 1849. Over the last couple of decades, scientists have observed crows landing on the backs of resting banteng. The banteng will then roll onto its side and lift its upper legs—which is not a comfortable or easy posture for a banteng—so that the crow can access the area under the legs and belly. Moving into this space, crows have then been observed removing ectoparasites, likely ticks, from these exposed areas. 

While this kind of cleaning is not in itself exceptional, the degree of attunement between the cleaner and the client in this case is fascinating. In many cases, as with the wallabies, the clients seem not to agree to the treatment at all. In other cases, as in a beautiful set of photos of a house crow cleaning a cow in India, we can see some degree of ‘posing’ and positioning to facilitate access. But in the case of the banteng and the crow, a whole procedure seems to have been worked out and agreed to. Torresian crows aren’t known to have similar relationships with any other mammals, and banteng around the world aren’t known to deliberately expose themselves for grooming by any other bird. Yet this is happening here. We will never know which crafty individuals struck up this mutualism, how those first awkward interactions took place, how a proposal was made, and how an agreement was reached that such vulnerability was worth the risk. But we do know that this behavior is spreading as more and more banteng and crows around the region get in on the action.

There are lots of lessons that might be taken from all these inter-species interactions. One that particularly interests me, visible in the comments below many of these YouTube videos, is the desire to cash this behavior out in simple, black and white terms. Either this cleaning is an example of a helpful altruist, or it is a nasty, opportunistic, crow taking advantage of another. Biologists, too, are not immune to these kinds of explanations—although which ones are preferred does shift over time, as things like ‘selfish genes’ go in and out of fashion. As Robert Poulin and Alexandra S. Grutter noted, writing in the mid 1990s: “Over the past few decades … the opinion of scientists regarding cleaning symbioses has changed, from selfless cooperation, to a mutually beneficial interaction, and finally to a one-sided exploitation.”

Of course, how these interactions are characterized depends a lot on whether we’re after the adaptive, evolutionary, explanation, or the psychological motivations of the individual involved. When it comes to clever corvids, there seems no reason to assume that all individuals engage in this behavior for the same proximate reasons. Some Torresian Crows might clean wallabies or banteng purely for the tasty snack. But can we hold open room for the possibility that others might, at least in part, be motivated also by the desire to help out, to remove a difficult parasite? As I’ve argued elsewhere, I want explanations that, at the very least, refuse to rule out in advance the possibility that corvids might be engaged in something like “targeted helping” across species lines. More than this, I think we need explanations that refuse one size fits all, black and white, options.

When it comes to the ethical behaviors of humans, many people have likewise often looked for either/or explanations, altruism or selfishness. But for hundreds of years at least some philosophers have been arguing for the need to destabilize these categories. When we look closely, our own actions are very rarely purely selfless or selfish, they are a complex, shifting, sea of grey. Perhaps it is time to recognize that similar, even if thoroughly distinctive, dynamics might be at work in the black and white worlds of corvids and other nonhuman animals?

Thom van Dooren is a philosopher and a corvid enthusiast. His most recent book is The Wake of Crows: Living and Dying in Shared Worlds (Columbia University Press, 2019). He is an associate professor and Australian Research Council Future Fellow at the University of Sydney and a Professor II at the University of Oslo.

You can read an excerpt of Kaeli’s review of The Wake of Crows for the journal Oryx here.

Literature cited
1Lewis, A. D. (1989). Notes on two ravens Corvus spp. in Kenya. Scopus13.2, 129–131. 


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Join me virtually tonight!

Tonight at 7:00pm PST, Timberland Regional Libraries is hosting an evening of crows and literature featuring myself and Hollow Kingdom author Kira Jane Buxton.  The night will start with a reading from Kira’s book, which features an irreverent crow navigating a zombie apocalypse in Seattle.  Afterwards Kira and I will host a game of crow and literary themed trivia, followed by a Q&A with myself.  It promises to be a family friendly event for crow lovers and book worms alike.  Registration is required but the event is free.  I hope to meet some of you there!

Register here 

Crow trivia


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The adorable guide to distinguishing American crows and common ravens

Recently, I published what I hope is one of the most comprehensive crow vs. ravens guides readily available on the web. But sometimes, you don’t want to pour through a bunch of text and details, you want just a quick reference, or a shorthand way of explaining to an inquiring newbie that crows and ravens are actually different.  To that aim, I am so excited to share that I teamed up with artist Rosemary Mosco of Bird and Moon comics to create a guide that is equal parts charming and informative.  Share it widely and spread the corvid love!

raven vs crow

Since initially sharing our comic Rosemary and I have been absolutely delighted at its reception, including the number of education programs asking to use it.  Among those is the Kituwah Preservation and Education Program, whose mission is to preserve and promote the Cherokee langue through engagement and service.  Cherokee is a beautiful, complex language that like all other indigenous American languages is endangered of dying out due to the cultural genocide that the US government inflicted on indigenous Americans during the late 19th and early 20th century.  I am incredibly honored to contribute to KPEP’s mission even in this small way.  Please feel free to share this image widely, just make sure to attribute the design to Rosemary Mosco, and the translation to the Kituwah Preservation and Education Program.

raven vs crow Cherokee


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Tickets for 3/3/20 talk in Portland

Hi all! From time to time I get messages on here from people lamenting that they missed the ticket sales for upcoming talks, so this time I am doing my due diligence and letting you be the first to know. For the third time (!) Portland’s Science on Tap is having me back to talk crows and this time it will be in my biggest venue yet, the Aladdin Theater.  Tickets are going on sale 12/13/19 at 10:00am (the link below will not be active until then).  I hope to see you, or someone who deserves a super sweet holiday gift, there!

Buy Tickets




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A letter to my readers

Hello blog followers.  It’s been a long time.  Looking over my stats today, I was pretty horrified to see I’ve only published a whopping 4 times this year.  I don’t have a very good excuse.

2019 was certainly professionally busy, but not more so than in years past.  Probably the biggest reason for my absence is that I am sinking considerably more scicomm time on places like twitter and Instagram, and it doesn’t leave a lot of room for blog articles. Which is a shame, because that’s where some of my best science communication has happened.

I also think that because I’ve historically treated the blog as a place where I only publish researched, 800 word articles, I’ve been hesitant to just send out quick updates a la a more traditional blog.  But since at least some of you don’t follow me on the other platforms, you end up missing a lot of stuff.

Like, for example, did you know I published a short fiction story about crows (a very specific crow to be exact) on Audible this year?  I did! And I’m damn proud and excited.  And as followers of my writing, you all are probably among the most interested audience for that kind of material, and I didn’t even tell you.

So take this as a vow that 2020 will be better.  I already have a ton of ideas for new articles, at least some of which will come out before the end of the year.  Teaching an ornithology class has vastly improved my arsenal for communicating some pretty cool bird biology through the vehicle of corvids.  Oh right, did you know I am no longer a postdoc but a lectuter at the Unviersity of Washington?  Yeah, we need to catch up more.

Thanks for your patience and continued readership.




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Denali field notes: A hare of another color

Up until the last few weeks, spotting snowshoe hares before they darted out from the adjacent vegetation was something I considered myself fairly lucky to do.  After all, it’s literally a matter of life and death for them to remain as undetected as possible.  As September came to a close, however, I found myself spotting them more often and from further away than I had previously, and not just from weeks of practice.  Their concealment was being betrayed by the very mechanisms designed to keep them safe.


There aren’t a lot of animals that call Denali home all year long, but those that do need effective strategies for staying alive during the essentially 8 months long winter.  For Denali’s snowshoe hares, one of these strategies is to adapt in an entirely new winter outfit, something only 20 other animals in the northern hemisphere do.1 While in the summer they are a mottled reddish brown, starting around late September the hares grow in their nearly all white coats. The ears are typically the first to change, with the rest of the body following suit shortly thereafter.


This transformation is mediated by changes in the photoperiod that affect melanin production.  Although the full explanation is quite complex, the core mechanism is that the shorter day length increases the hormone melatonin, which suppress the melanin producing hormone prolactin.1


While this strategy is good one for long winters blanketed in snow, changes in snow regimes are making this transition more precarious.  Camouflage mismatch–which is generally considered when more than 60% of the coat is different from the surrounding environment–can result either from winter coats that have come in too early, before the snow arrives, or because the snow pack lingers inconsistently.  This year, the lower elevations of the park have yet to see so much as a flake of snow, though you wouldn’t know that by looking at the hares.  As I have already experienced, such mismatch makes hares considerably easier to detect, a big problem for basically everyone’s favorite winter meal.2


Although hares can adjust the timing of their molts to a small extent, it won’t be enough to keep them in sync with the more dramatic shifts climate change has in store for the future.  This is especially problematic because hares don’t seem to be very aware of their mismatch and attempt to compensate behaviorally by say, hiding behind vegetation or choosing resting spots that more closely match their color.3 Other animals, particularly birds, seem better at this.  Rock ptarmigan for example will actually dirty themselves to more closely match patchy snow.4


Given the immense selection pressure on these animals to match their environment and the high variation in the traits responsible for such color changes, it’s possible that hares will be able to keep pace with an already changing arctic landscape, but we don’t know for sure.  The alternative will be to add hares to the growing list of once common animals that now require invasive management strategies to stay afloat in the anthroproscene.


Literature cited

1. Zimova M, Hackländer K, Good JM, Melo-Ferreira J, Alves PC, Mills SL. (2018). Function and underlying mechanisms of seasonal colour moulting in mammals and birds: what keeps them changing in a warming world? Biol. Rev. 93: 1478 – 1498.1478 doi: 10.1111/brv.12405

2. Pedersen S, Odden M, Pedersen HC. (2017). Climate change induced molting mismatch? Mountain hare abundance reduced by duration of snow cover and predator abundance. Ecosphere 8: 01722

3. Zimova M, Mills SL, Lukacs PM, Mitchell MS. (2014). Snowshoe hares display limited phenotypic plasticity to mismatch in seasonal camouflage. Proc. R. Soc. B DOI:

4. Montgomerie R, Lyon B, Holder K. (2001) Dirty ptarmigan: behavioral modification of conspicuous male plumage, Behavioral Ecology 12: 429–438.


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