Category Archives: Science

Crows are watching your language, literally

That crows can recognize humans faces (and other physical attributes) has been a staple of our experiences with them for thousands of years.  It’s part of what has allowed them to take such a prominent place within our cultures, and it’s what keeps us refilling our pockets with peanuts or kibble, anxious for the chance to be recognized, to be seen by a wild animal. If, like me, you’ve been committed to such a relationship, you probably found yourself wondering about what it is they’re saying all the time. Although we still have more questions than answers, it’s not for lack of trying; in fact parsing crow “language” is still a hot topic in corvidology.  But for all our efforts to understand what crows are so often going on about, have you ever thought much about what they make of what we’re saying?

DSC_1974

Calling American crow

Ask any crow feeder about their ritual and there’s a good chance that it starts with more than just making themselves visible. To get “their” bird’s attention, about half of crow feeders start with some kind of auditory cue, like a whistle or gentle name calling.¹ Given that American crows (Corvus brachyrhynchos) can be individually distinguished by their calls, and many corvids—including the large-billed crows (Corvus macrorhynchos)—can recognize familiar conspecific* calls, this strategy seems far from superstitious.2,3 In fact, previous work has demonstrated that crows can discriminate human voices.

When presented with playback of their caretakers or unfamiliar speakers saying, “hey,”  hand-reared carrions crows (Corvus corone) showed significantly more responsiveness towards unfamiliar speakers.4 That their response is different is what suggests that they can discriminate, but it’s hard to not do a double take at the fact that the thing they seem more interested in is the person they don’t know.  Shouldn’t they be more interested in the folks that generally come bearing gifts? While we still don’t have a super satisfying answer to this question, it’s possible this comes from the fact that novel humans are less predictable, and therefore more threatening, than a familiar caretaker who can be safely ignored. Likewise, a new study out suggests that it’s not just individual people crows can hear the difference between, but entire languages.

In a newly released study conducted by Schalz and Izawa (2020), eight wild large-billed crows were captured in major cities around Japan and subsequently housed in aviaries at Keio University where they were cared for by fluent Japanese speakers.5  Given both their life histories and their time in the aviary, it’s safe to assume these birds had listened to a tremendous amount of Japanese throughout their lives. So, it stands to reason they might be able to actually recognize this language as familiar, but to date no one had looked at crows’ ability to discriminate between languages.  To test this question the researchers used playback to present recordings from multiple unfamiliar Dutch or Japanese speakers.  As with the carrion crow study, when these crows were presented with playback of a more familiar acoustic style—in this case a Japanese speaker—they didn’t show a strong reaction. Play them what was likely a completely unfamiliar language—Dutch—and the crows were rapt. Or at least they acted more vigilant and positioned themselves closer to the speaker. In other words, large-billed crows were able to discriminate between human languages without any prior training!

junlge crow

Large-billed crow (Corvus macrorhynchos) Photo: Anne Kurasawa

The next most obvious question is, well, why? What purpose would it serve to discriminate between different languages among unfamiliar speakers? One possibility is that it’s just an artifact of the auditory perceptual skills they need to successfully be a crow.  As I mentioned earlier, there’s a lot of information encoded in their calls, including individual identity, so being attentive to rhythmic classes may be important.  Another reason that’s worth pursuing, though, is that it may help tip them off to tourists, who may be more inclined to share or easier to take advantage of, than locals.  Fortunately the lead author on this study, Sabrina Schalz, will be starting her PhD on this topic in the coming fall. You can find her on twitter at @Sabrinaschalz, where she’s promised to keep us abreast of her future discoveries.

So the next time you’re hanging out in Japan, don’t forget to literally watch your language around the local crows. And to be safe, I wouldn’t divulge any secrets to them either.  They’re not called large-billed crows for nothing.

*conspecific=member of the same species

Literature cited
1. Marzluff JM, & Miller M. (2014). Crows and crow feeders: Observations on interspecific semiotics.  In: Witzany, G. ed., Biocommunication of Animals.  New York: Springer Science+Business Media Dordrecht. pp 191-211.

2. Mates EA, Tarter RR, Ha JC, Clark AB & McGowan KJ. (2015). Acoustic profiling in a complexly social species, the American crow: caws encode information on caller sex, identity and behavioural context, Bioacoustics, 24:1, 63-80, DOI: 10.1080/09524622.2014.933446

3. Kondo N, Izawa EI, & Watanabe S. (2010). Perceptual mechanism for vocal individual recognition in jungle crows (Corvus macrorhynchos): contact call signature and discrimination. Behaviour 147: 1051–1072.

4. Washer CAF, Szipka G, Boeckle M, and Wilkinson A. 2012. You sounds familiar: carrion crows differentiate between the calls of known and unknown heterospecifics. Anim Cogn 15: 1015-1019.

5. Schalz S. & Izawa E. (2020). Language Discrimination by Large-Billed Crows. In Ravignani, A., Barbieri, C., Martins, M., Flaherty, M., Jadoul, Y., Lattenkamp, E., Little, H., Mudd, K. & Verhoef, T. (Eds.): The Evolution of Language: Proceedings of the 13th International Conference (EvoLang13). doi:10.17617/2.3190925.

24 Comments

Filed under Crow behavior, Crows and humans, New Research, Science

A tale of two crows: northwestern vs. American

If you search nearly anywhere along the west coast from California to southern Alaska, you will find our most persistent avian neighbors: crows.  Cloaked in their Gothic outfits and uttering that all too familiar harsh caw, most people—even many experts—might not register that the neighbors in the north are not exactly like their counterparts in the south.  While it’s the American crows (Corvus brachyrhynchos) that have staked their claim to the contiguous states, it’s the northwestern crow (Corvus caurinus) that calls the coast home from British Columbia to southern Alaska. That is, at least as far as the field guides have been telling us since northwestern crows were first described scientifically in the mid 19th century.  Despite this early recognition that one of these things was not like the other, however, differentiating American crows from northwestern crows on the basis of phenotypic features like size, voice, and behavior has since proven to an almost impossible challenge; especially in places like Washington where the two ranges meet.  This has resulted in questionable hand waving by people like me about what those crows in Seattle really are.  I’ve always called them American crows without any qualifiers, but are they really? Might they be northwestern crows? Or something in between?  Fortunately, a new study by Slager et al. (2020) lays bare the reticulated evolutionary histories of the two crows of the Pacific Northwest.

IMG_5392

By examining differences in both nuclear DNA from 62 specimens and mitochondrial ND2 markers from 259 specimens collected across North America, the team was able to evaluate when these two likely initiated speciation, the process of becoming distinct species from a shared ancestor. What they found is that American and northwestern crows likely split some 440,000 years ago when late Pleistocene glaciers really made mess of things by geographically separating formally intact populations.  Isolated in their respective pockets of livable habitat (called glacial refugia) the formally united species did what all organisms do in the face of new selective pressure: they changed, and from one species emerged two.  Well, kind of.

Eventually of course, the Pleistocene ice ages came to a close and the glaciers that had divided their ancestors receded away.  Although their time apart made a lasting impression on their genome, it did not appear to make a lasting impression on their taste in sexual partners.  The team found extensive genomic admixture (the presence of DNA in an individual that originated from a separate population or species), suggesting pretty pervasive hybridization between the two species.  In fact, along their shared 900 km range from coastal Washington to British Columbia they found not one “pure” individual.  For just how long American and northwestern crows have been hybridizing remains unknown, but the evidence suggests that it’s been happening since well before colonial landscape changes.

These revelations beg two important and contradictory questions.  The first is the answer to just what the hell crows in Seattle are.  The answer appears to be option C: a hybridized mix of American and northwestern crow, but with slightly more all-American genes.  That seems to be true throughout the Washington coast.  Once you hit Oregon though, you’re getting almost all ancestral American crow.  The opposite pattern is true moving from British Columbia north: what starts as hybrids with a stronger northwestern crow bias, are “pure” northwestern crows once you hit Juneau.

SLager

Figure shows the extent of hybridization between American crows (red) and Northwestern crows (blue) along the PNW coast. Image from Slager et al. (2020).

The second question, however, is whether those distinctions are really of any biological value. After all, what appears to have happened is that while these two “species” may have gotten started on a path to different destinies, a changing climate brought them back together before any firm reproductive isolating mechanisms (i.e. physical features, behaviors, or physiology that prevent different species from breeding with one another) could take hold. While that kind of genetic evidence is already pretty damning, the phenotypic evidence that they might be different has likewise eroded.  When closely examined, the features that appeared to be diagnostic in the 19th century like the northwestern crow’s smaller size and intertidal habitat use, and a difference in vocalizations, seem to simply be reflections of local adaptions and individual differences present in both species. So, while the guidebooks might still call them different things, the fact that neither the crows themselves nor the ornithologists can really tell them apart warrants serious consideration of whether northwestern crows should be officially absorbed into the American crow.

As it happens, the authority on such things, the American Ornithological Society’s North and Middle America Classification Committee, is currently examining that very proposal as apart of the 2020 Proposal Set C.  Expect an official ruling soon.  While I don’t know for sure what they will decide, the evidence out of this current study does not bode well for the continued recognition of Corvus caurinus as a speciesSo if you want to see a northwestern crow, my advice is to do it sooner rather than later.

Literature cited

Slager DL, Epperly KL, Ha RR, Rohwer S, Wood C, Van Hemert C, and Klicka J. 2020. Cryptic and extensive hybridization between ancient lineages of American crows. Molecular Ecology doi: 10.1111/mec.15377

 

 

5 Comments

Filed under Corvid diversity, Crow life history, Diversity, New Research, Science, Taxonomy

What are crows thinking when they see death?

Full disclosure: I am not actually going to be able to tell you the answer to this question.  But I am going to get you closer than we have ever been before.  At least by my standards.  So now the question is where to begin…

Let’s begin by acknowledging that death means something to crows in a way that it doesn’t seem to mean something to most other animals, at least as far as we’ve recognized. What I mean by this is that crows don’t ignore their dead, they don’t reflexively flee from their dead, and they don’t just go about carrying out undertaking behaviors without a second thought (or a first thought).  They really see their dead and they respond in a variety of ways.  In my previous research, I found that generally, they respond to unfamiliar dead crows by alarm calling, followed by recruitment of other crows to the area to form a raucous group called a mob.  Then they disperse after about 15-30min.

DSC_1088

I’ve found that they do other things as well, like touching the bodies, though this really only happens in the spring.  When they touch them they might gently nudge, peck or even copulate with the crows, though that latter one is exceedingly rare.

Other people have seen more curious things though. Upon listening to my garbled explanation of my studies, my dental hygienist removed her hand from my mouth and proceed to explain, with detectable urgency, that she knew about these funerals.  That when she was a little girl living on her family’s farm her father shot a crow.  Instead of leaving, the others brought sticks and dropped them on their dead flockmate. She’d never forgotten it.

What these stories tell me is that how crows respond to death is complex, and we are still far from fully understanding all their behaviors.  And one of the hardest parts of this is that we can’t ask crows what they are doing.  Why did you leave a stick that one time?  Why did you rip up the body that other time?  Why did you call for 30min minutes until your voice choked out, while your neighbors a quarter mile away looked later at the same body and then left in silence to return to the dumpster?

This barrier means that we stand a high chance of either under or over-interpreting their behaviors around death; for example, being unable to accept that we might experience the grief of death uniquely, or being unable to accept that we, in fact, do not.  This is the challenge in studying how another organism responds to death, and it’s one I grapple with constantly.

There might, however, be one secret weapon into deeper parts of how crows respond to their dead that we can reach without needing a Dr. Doolittle-esque translator:  their brains.  While all animals only have a certain number of ways they can outwardly express themselves, how the brain responds to stimuli can tell you a great deal more about what an animal might be thinking.  Which brings us to my newest paper.1

Now before I go on, I’m going to say up front that I suspect this current study might not sit well with some of my readers. Until now all of my studies have used wild crows and did not require the handling of birds or any kind of direct manipulation.  Spying on the brains of animals, however, is not so hands-off.  It almost always requires surgery. And it’s almost always lethal. I say almost, because sometimes we can actually learn quite a lot without opening up an animal.  Without slicing up its brain. Without keeping it captive forever.  This is one of those times.

Most people are familiar in some capacity with functional neuroimaging, especially fMRI. It’s a way to look at how the brain responds to different stimuli without needing surgery or euthanasia. fMRI works by tracking blood flow while an awake subject encounters a stimulus.  It’s how we have uncovered that psychopaths don’t experience empathy when picturing others in pain, or that some dogs value praise from their owners more than food.2,3 Using fMRI in a non-human animal requires a great deal of training, however because fMRIs are big weird noisy machines that would be objectively terrifying for the uninitiated. Which means that they would never work with a wild crow.  So instead, our team used a different kind of non-invasive imaging technique to spy on the minds of crows: FDG-PET.

Unlike fMRI which tracks real-time blood flow, FDG-PET tracks metabolic activity and most importantly it can do so retroactively.  The FDG in FDG-PET, stands for fluorodeoxyglucose, which is a modified glucose molecule with a radioactive tracer attached to it. It’s the same stuff we give humans when we’re going to PET image them for, say, a tumor.  The modified part is that unlike most glucose, this stuff doesn’t break down, it gets stuck wherever the body used it up.  The tracer on the other hand, does wash out. Still, for a brief window of time-about 20 minutes after injection-we can stimulate an awake animal in a variety of way, visually, acoustically, etc., and the brain will use up the glucose (FDG) in order to process that information. The animal can then be anesthetized and placed into a PET machine where, via a mechanism involving photons and gamma rays that was far too complex for me to bother retaining beyond my graduate exams, the machine can detect the tracer.  The imaging process takes about 20min, after which the bird wakes up, none the wiser for the invasion of privacy.

Crow scanner
An anesthetized crow in our specially fitted PET scanner at the UW Medical Center. The wingtips are bound during the scanning process to keep the feathers tidy and out of harm’s way. Photo by Andy Reynolds for Audubon.

After a lot of image processing and analysis, we can then infer how active a particular area of the brain was while experiencing one stimulus relative to a control.  So while there are some advantages to an fMRI approach, FDG-PET is the only mechanism that allows us to see how a crow’s brain was responding while it was awake and unconstrained 20min ago, instead of while it is strapped down in a big scary scanner.  At the conclusion of the study, each subject is banded and released.  Although our study used only a modest 7 subjects (which is a normal sample size in the imaging world) it brings me great pride to report that, not only did all of our subjects survive, but all left our care with better or equivalent body condition than they came in with.  Some of them have even been resighted successfully breeding in a subsequent season. Again, when it comes to spying on animal brains, this is the exception, not the rule.

Release
My former advisor and coauthor of the current study, John Marzluff, releasing one of the subjects at the conclusion of the study. Photo by Andy Reynolds for Audubon.

So now that some of the technical details are out of the way let’s get down to brass tacks and talk about what we actually learned from all this.  Our lab has previously used this method to understand what neural circuits process different faces, like familiar friendly or dangerous faces, as well as how crows perceive different kinds of threats.  But on the heels of my fieldwork looking at their responses to dead crows,  we wanted to know more about what was going on in their brains.  So we had a two stimulus paradigm: a visual one where we compared brain activity between when crows saw a dead, unfamiliar crow, and a dead, unfamiliar, song sparrow (the control), and an auditory one, where we played them recordings of wild, unfamiliar crows reacting to dead crows, and unfamiliar crows begging (the control).

To aid with our analysis we selected 5 particular brain areas a priori, which means before the study, to examine for brain activity.  These sites included the hippocampus and striatum, which are responsible for fear and spatial learning, the septum and amgydala, which aid with social behaviors, conspecific recognition and affect, and the NCL or nidopallium caudolaterale, which is responsible for executive decision making like our prefrontal cortex.

Among the visual paradigm, what we found was that between the threatening (dead crow) and control groups (dead song sparrow and responses from three birds in a previous study that saw only an empty room) there weren’t a ton of differences in relative brain activity.  Crows that saw a dead crow didn’t show more activity in the regions associated with affect, social behaviors or fear learning.  Instead, what we found is that, like when they see a familiar threat like a hawk, it’s their executive center that shows the most difference.4  At first this was a surprise, but given the number of ways they can respond to their dead, and possibly because they didn’t know this bird, it makes sense that they might be wondering exactly what they should do in that moment.  In case you are tempted to think that might be what’s going anytime they’re in this strange situation, know that a previous study using the same approach found very different neurological responses to when they see familiar threats, new threats, and friendly people.4  So there’s no reason to suspect that the protocol alone is what was responsible for NCL activity.

With respect to the auditory tests, we detected even fewer differences.  The most notable finding was that both kinds of calls, alarm and begging, stimulated NCL activity relative to the birds that saw only an empty room.  I can’t pretend to know exactly what this means.  But it does bode well for my idea that crow communication is quite complex and context dependent, therefore requiring a great deal of brain power to decipher and interpret.  But I speculate.

So, as I said, while this study in no way provided definitive answers to, “What are crows thinking when they see death?,” it’s gotten us as close as we have ever come and given us some good ideas for what might be going on.  But as with all science, the first study is the one warranting most skepticism.  I have no doubt we will continue to learn much more in future and I can’t wait to see where this study fits into the vast field of knowledge that awaits us.

If you would like to read this study in its entirety (which is full of extra details, analysis, and explanation) check out this link, which will remain active until April 15th, 2020.  After that, shoot me an email if you want the PDF, I am more than happy to pass it along.  If you would like to read the popular science article from the Audubon where many of these photos were sourced, but that came out before this study was released, follow this link.

Literature cited
1. Swift KN, MarzlufF JM, Tempteton CN, Shimizu T, and Cross DJ. (2020). Brain activity underlying American crow processing of encounters with dead conspecifics. Behavioural Brain Research 385: https://doi.org/10.1016/j.bbr.2020.11254

2. Decety J, Chen C, Harenski C, Kiehl K. (2013). An fMRI study of affective perspective taking in individuals with psychopathy: imagining another in pain does not evoke empathy. Frontiers in Human Neuroscience: https://doi.org/10.3389/fnhum.2013.00489


3. Cook PF, Prichard A, Spivak M, Berns G. (2016). Awake canine fMRI predicts dogs’ preference for praise vs. food. Social Cognitive and Affective Neuroscience 11: 1853-1862


4. Cross DJ, Marzluff JM, Palmquist I, Minoshima S, Shimizu T, Miyaoke R. (2013). Distinct neural circuits underlie assessment of a diversity of natural dangers by American crows, Proc R SocB 280: 1–8

19 Comments

Filed under Being a scientist, Cognition, Crow behavior, Death, Graduate Research, New Research, Science

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

The bird of many names

Camp robber. Whiskeyjack. Canada jay. Gray jay.  I know of no other bird that goes by as many names as the Canada jay.  In fact, it has so many names it’s possible for two people to be swapping stories and not even realize they are discussing the same animal. Why this sweet-faced bird possesses a number of aliases better befitting an agent of espionage is, in part, the result of a rather fascinating bit of birding history replete with controversy, colonialism, chaos, and a contest of national importance.

DSC_0164

Before we get to the jays though, I want to put in your mind the image of the Ouroboros. If you’ve never seen it before, the Ouroboros is a symbol from Egyptian iconography that depicts a snake or a dragon eating its own tail. The image is meant to imply infinity; the idea that where you end is also where you begin, on and on, forever. Because, as you’ll see, it’s impossible to tell this story without eating our own tails at many different points along the way. So let’s start with the name that’s both the beginning and potentially the end of this story: Canada jay.

ouroboros-snake-eating-its-own-tail-eternity-or-vector-12076546

On May 23rd, 2018 the American Ornithological Society announced that Perisoreus canadensis, the bird formerly known as the gray jay, would be officially recognized as the Canada jay.  Although this change felt disruptive to some, for the folks spearheading the campaign, including foremost Canada jay expert Dan Strickland, this was the righting of a historical wrong more than a half-century in the making.

According to Strickland’s research, which he details in a facinating article called “How the Canada Jay Lost its Name and Why it Matters,” one of the earliest scientific references to this bird was in an 1831 zoology book called Fauna boreali-Americana where they name it as a Canada jay. Even James Audubon used the name Canada jay when he described it in the 1840s. From here the story of the jay’s name gets hairier, with lots of different dates, acronyms, and taxonomic nuance, but I want to try and take you through it because it tells you so much about why things ended up as they did.

During the early 1800’s the process of discovering* and naming birds was something of a wild west operation. It wasn’t until 1883 that an official body, the American Ornithologist’s Union, AOU, (now called the American Ornithology Society, AOS), was formed to take leadership and help legitimize the field of ornithology in North America. Part of this goal was to act as the official body for taxonomic and nomenclature decisions. In keeping with this goal, AOS publishes a checklist of North American birds every decade or so. So who is on that list, and what they call it, means a great deal. For the first two publications (1886 and 1895) our bird was called the Canada jay, but then after 1895 all more or less goes to hell.

At the root of this naming disaster was a failure to provide a clear and rigorous English naming system at both the full and subspecies level. Instead, the system (if you could call it that) was that birds with only one species (monotypic species) were given a binomial Latin name and an English common name, but birds with subspecies (polytypic species) like our bird, may or may not be given an English common name or a Latin binomial name. Instead, their subspecies were given Latin trinomial names and English common names. What this meant is that if you saw a Canada-jay like bird, unless you knew which subspecies it was, the best your guide could tell is that it was merely a Perisoreus jay. This also meant that the name “Canada jay” effectively got downgraded to describing a single subspecies: Perisoreus canadensis canadensis. An effort to name yet another Perisoreus subspecies, Perisoreus obscurus griseus, appears to be when the name “gray jay” first comes into play.

I doubt anyone would question why failing to provide common names to full species would cause confusion, but matters were made worse because there was no system in the nomenclature behind the common names for the subspecies. This lead to problems like not being able to identify from the English name alone if you were talking about a species or a subspecies, and having subspecies from different respective species sharing the same root name. For example “clapper rail” could refer to subspecies of either Rallus obsoletus or Rallus longirostris.

In the late 1930s, people grew increasingly frustrated with this system and started to put pressure on AOS to develop a more logical naming scheme. At the forefront of this effort was a recommendation by Alden Miller to adopt a system where full species would be given English common names and binomial Latin names, and subspecies would only be provided a trinomial latin name. For example, Perisoreus canadensis would be given the English common name of Canada jay, and its Alaskan range subspecies would be known only as Perisoreus canadensis fumifrons.

Although this scheme was well supported, during the 1940 vote, it was inexplicably voted down. Instead, in 1947 the committee welcomed a new system where both the full species and the subspecies were given common names but, in an attempt for clarity, required that the subspecies’ common name was both rooted in the full species’ common name and geographically relevant. It’s this decision that officially killed the “Canada jay” because the committee likely felt it would be too geographically awkward to have subspecies names like the “Alaskan Canada jay” or the “Oregon Canada jay” and so instead, they opted for gray jay as the official full-species name.

By 1954, however, this system grew too taxing and the committee essentially adopted Miller’s 1930’s suggestion: only full species get official common names and subspecies are named and identified by their trinomial Latin name. For some reason, though they did not revert back to the original* name of Canada jay as their rules suggested they should, and instead they curiously retained the name gray jay. This may have been the last of it if not for a ~political~ controversy that would rock the nation of Canada a half-century later.

2016_national_bird

In 2015 the Royal Canadian Geographical Society sought to declare a national bird of Canada, a spot that remained egregiously vacant, by hosting a massive public vote to choose among 40 potential candidates. As the popular vote neared an end, five front runners had emerged: the gray jay, the Canada goose, the common loon, the black-capped chickadee and the snowy owl. Ultimately, the common loon would go on to win the popular vote by a 10% margin. Once voting closed, however, the RCGS convened a panel of experts to debate which bird they thought was most worthy. To the shock and upset of the voters, in 2016 RCGS ultimately chose the gray jay, a bird many voters complained did not have the connotation of national pride that the loon did. In the end, though, none of it-the year and a half long competition, the 50,000 votes, the ensuing controversy-mattered because the actual Canadian government had no interest in naming a national bird.

Still, the public’s perception that the jay was not a strong enough symbol did not sit well with Canadian jay scientists like Strickland and Ryan Norris who knew of the jay’s more patriotic heritage. Determined to understand and ultimately reverse the 1954 ruling, Strickland set out to show AOS that the decision to retain the name “gray jay” was not in keeping with their own rules. And, as you already know, in 2018 he succeeded; the bird formerly known as the gray jay (which was formerly known as the Canada jay) is now officially reknown as the Canada jay. The Ouroboros has finally caught its tail. Well, for many people it has.  I want to enter yet one more heir into this contest, the one that I believe holds the most legitimacy to the throne: the whiskeyjack.

Unlike the name might suggest, whiskeyjack isn’t derived from campfire tales about these gregarious birds robbing campers of their whiskey.  It’s an English name derived from the indigenous Cree (and other Algonquian family languages) name for the bird, Wisakedjak. In Cree culture (and some other First Nations peoples of the subarctic region) Wisakedjak is a sacred figure who is known as a trickster and in some cases for being among the creators of the world.  It’s a befitting name for this clever little corvid and the merits of its legacy are without question.  In fact “whisker-jack” can even be found in the English literature as early as 1740, nearly one hundred years before the name Canada jay would first be used. I’m not alone in my support either, even during the 1947 debate, L.L. Snyder notes that “‘Whiskeyjack’ is used universally in the north (& will continue to be).”

Throughout this article, you may have noticed the occasional * following words like “original” or “discovered” and that’s because those words are only relevant when thinking about natural history in post-colonial terms. But the truth is that most wildlife were already known, already named, already studied by the various peoples that called this continent home before their lands were taken from them, and their traditional knowledge erased in favor of a Western approach. So if our goal is to honor the heritage of this bird, I can think of no name more appropriate than the “whiskeyjack jay.” That is the return to the beginning that this magnificent bird deserves.

***

 

7 Comments

Filed under Birding, Canada jays, Science, Wildlife

2018 research round up

As 2018 draws to a close, I want to dedicate a post to five of the most interesting and important publications about our favorite family of birds that came out this year. For the sake of a brevity, the reported studies are largely condensed with some tests/results omitted and little attention to normally key experimental elements like controls, statistical analyses, etc. Please click on the study title to be directed to the full publication.

DSC_0506

1. Townsed AK, Frett B, McGarvey A, and Taff CC. (2018). Where do winter crows go? Characterizing partial migration of American Crows with satellite telemetry, stable isotopes, and molecular markers.  The Auk 135: 964-974

Background: Depending on where you live, the answer to, “Do crows migrate?,” can be quite different.  For example, most Seattle residents would probably say no, since large numbers of crows can be seen here year round, while someone in say, a southern Canadian province, may notice a sharp decline in the number of crows during the winter.  That’s because crows are what’s know as “partial migrant species” meaning that within a population, some individuals may be migratory and others resident with more migratory strategies biasing in areas with harsh winters.  Despite the role of partial migration in how scientists currently explain the evolution of complete migration, little is known about the phenomenon.  Even elemental questions such as: is this behavior fixed or flexible within individuals, is it environmentally influenced, and how might species use it to adapt to changing conditions remain under-explored.

Methods: The study looked at two populations of overwintering crows: one in Ithaca, New York and a second in Davis, California.  They used a combination of intrinsic (meaning originating in the body) and extrinsic (meaning originating outside the body) markers to track the movement and origin of their 18 tagged subjects over 2-4 years.  The intrinsic makers included molecular and stable isotope data, and the extrinsic marker was a satellite tracking device that was attached to the bird via a light backpack.  I won’t go into the details of the molecular and stable isotope data, but suffice it to say that stable isotopes were used to identify the place of origin via the unique properties of the local food and water that embed into an individual’s tissue and the molecular data was used to sex individuals and establish relatedness.

Key findings: Of the 18 tagged crows across both east and west coast populations, they found that almost 78% were migratory.  This was a shock to me, TBH.  I had no idea just how many crow were making these annual trips.  The distance these birds traveled varied widely, with some going as “little” as 280 km (173 miles) and others as much as 1095 km (680 miles). Among resident birds, they found that individuals never ventured further than 25 km (15.5 miles) from the center of their breeding site.  For both resident and migratory individuals they found that birds were very loyal to their breeding sites; returning to the same territory year after year.  Given this finding, it should not be surprising to learn that individuals did not vary from year to year in whether they were migratory or not.  Together these results offer clues to how crows may respond to climate and urbanization induced changes in temperature to their local environments.

DSC_0582

2.  von Bayern AMP, Danel S, Auersperg AMI, Mioduszewska B, and Kacelnik A. (2018). Compound tool construction by New Caledonian crows. Nature Scientific Reports 8

Background: For decades people considered the use of tools to be a uniquely human feature.  Now we know that all sorts of animals, ranging from fish to monkeys, use tools and a handful of animals even create tools.  Among the small number of animals that create tools, we have only seen wild individuals modifying a single object.  For example, stripping a twig of small leaves or branches in order to probe small holes for insects.  Whether any wild animal is capable of making compound tools, those made by combining seperate non-functional parts, is unknown.  Even in captivity, this behavior only has limited observation in the great apes.  Understanding what animals are capable of this complex task and how they achieve it, might give us insight into the evolution of our own exective functions.

Methods: This study used eight wild caught captive New Caledonian crows.  Like many experiments involving novel objects, this one occurred over multiple different phases.  In phase I the birds were provided a long stick and a baited test box where food was within reach when using the stick, but not without it.  In phase II the birds were presented with the same baited test box, except that instead of a single long stick, they were given a hollow cylinder and a second, thinner cylinder that needed to be combined in order to generate a tool long enough to reach the food.  In phase III, the birds were given the same problem, only now with novel combinable items.  In phase IV, the researchers tested whether the birds were combining elements because they understood that they needed to, or if because they derived some other benefit from the process.  To do this, they presented birds with a bait box that had two tracks: one where the food was within reach of a single element and one where it required a compound element. In the final phase, birds were presented a bait box that required the combination of more than two elements.

New cali

Image from von Bayern et al. 2018

Key findings: All birds passed the initial tool use phase handily.  Given that New Caledonian crows frequently use single element tools in the wild, this was not at all surprising. In the second phase, half of the subjects (four) were able to combine the two elements after no more than two failed attempts. These subjects were then able to transfer this knowledge when presented novel combinable objects. When given a bait box with food presented on the close and far tracks, birds most often only made compound tools when it was necessary, suggesting that they don’t do it just for fun.  In the final phase, only one bird succeeded in making a tool that required more than two elements.  These findings demonstrate that New Caledonian crows are not only on par with what’s know about compound tool use in the great apes, but actually exceed them.

Unfortunately what this study does not explicitly answer is whether the birds were able to create the needed tools as a result of mental mapping (i.e imagining the correct tool and how it might be assembled) or by happy accident.  Without this knowledge, what their ability to make compound tools suggests about the evolution of things like insight remains mysterious.  Given all the other remarkable ways New Caledonian crows show innovation when it comes to tool use, however, both myself and the authors of this study are hedging that it’s indeed cognition behind these behaviors rather than more simple mechanisms.

3. Boeckle M, Szipl G, and Bugnyar T. (2018). Raven food calls indicate sender’s age and sex. Frontiers in Zoology 15

Background:  One of the most frequent inquiries that come my way are requests to decipher various crow calls.  Given all we know about crows, this doesn’t seem like such an impossible request, but the reality is that crow communications remains one of the most impenetrable black boxes of crow behavior.  I’ll save more on this for a future post dedicated to an upcoming publication by my colleague Loma Pendergraft, who spent his MS learning this fact the hard way.  But suffice it to say that any progress on this front in the various Corvus species is groundbreaking news.  We do, however, know more about raven calls. For example long “haa” calls are thought to recruit other individuals to sources of food.  What was unknown at the start of this study was whether these calls encoded any class-specific information about the caller, such as their age or sex. Calls that impart class-level information about the caller have been previously demonstrated in some marmots and monkeys.

Methods: The researchers recorded hundreds of “haa” calls from wild ravens which had previously been color banded and whose age and sex were known.  Using acoustic software they analyzed the vocalizations for patterns in call elements like frequency and inflection rate.

Key findings: As the study’s title suggests, ravens appear to encode information about their age and sex in “haa” food calls.  For animals like ravens that live in “fission-fussion” social systems, meaning flexible social groups where individuals regularly reencounter familiar individuals, but also encounter unfamiliar ones, class-level information helps individuals quickly assess important aspects of a caller’s identity.  Such information may be key to helping individuals decide if they want to join a feeding event or not.  This decision is particularly important because aggression at feeding events can cause mortal injury, so grouping with a bad crowd can come at a high price.

DSC_0240

4. Kroner A, and Ha R. (2018). An update of the breeding population status of the critically endangered Mariana Crow (Corvus kubaryi) on Rota, Northern Mariana Islands 2013–2014. Bird Conservation International 28: 416-422 

Background: The Mariana crow or Aga is a native species to the islands of Guam and Rota.  After the introduction of the brown tree snake to Guam in the 1940’s, Guam’s entire population of Aga were wiped out leaving only those found on Rota to continue the species.  In 1982, the population hovered around 1,300 individuals but things were clearly in decline. In 1984 the Aga was officially listed as endangered and today is considered critically endangered by the IUCN.  Unlike on Guam, there is no clear reason why the Aga continues to decline on Rota, though habitat loss, persecution by humans, natural disasters and introduced predators like cats likely all work together.

Methods: During 2013-2014 researchers counted breeding pairs by surveying all known island territories.  During these counts (which took 845 hours of labor and traversed 1,485 hectares!) the researchers also documented any unpaired or subadult birds. Since the entire island could not be surveyed, to ultimately estimate the population size the researchers used models that accounted for missed detections.

Key findings: Spoiler alert: They are A BUMMER.  In all that searching only 46 breeding pairs were detected.  Accounting for unpaired birds and detection failures, the researchers estimate that the current population of Aga hovers around 178 individuals.  Obviously that number alone is a gut punch but it’s especially true when you consider that that’s a 10-23% decline since 2007 and a 46-53% decline since 1998.  Researchers estimate that at least 75 pairs are needed to maintain a viable population of Aga.  Without intensive predator management and community level advocacy for these birds, their future is sadly looking grimmer and grimmer.

5. Walker LE, Marzluff JM, Metz MC, Wirsing AJ, Moskal ML, Stahler DR, and Smith DW. (2018). Population responses of common ravens to reintroduced wolves. Ecology and Evolution 8: 11158-11168

Background: One of the most persistent myths about common ravens is that they have a symbiotic relationship with grey wolves; intentionally showing them carcasses they find and then sharing in the bounty together.  But while the case is actually that ravens are unwelcome dinner guests at the wolves’ table, there’s no question that the two species have profound effects on one another. The reintroduction of wolves to Yellowstone in 1995 therefore offers a valuable way to study how the presence of wolves affects the spatial distribution and feeding behaviors of park ravens.

Methods: This study was a collaborative effort between avian and spatial ecologists at the University of Washington and Yellowstone wolf biologists.  Using data from 2009-2017 on wolf abundance and prey kills, and raven surveys taken both within the interior of the park and at anthropogenic food sources in surrounding areas (ex: the Gardner town dump), the researchers were able to model raven abundance during both the study period and before the reintroduction of wolves.  I won’t go into the details of how these models are created, but suffice it to say that their purpose is to take the data you give them and find what predictors best explain your observed outcomes.  For example if, say, you have a bunch of data about where ravens were located at different times, and have data on different possible predictors, say, wolf abundance, weather, carcass abundance, carcass biomass, and distance to anthropogenic food, etc., the right model could help you identify that carcass biomass is the best predictor of raven abundance.

Key findings: Previous studies have demonstrated that wolves make more kills during severe winters with higher snowpack, because prey have a more difficult time evading them.  As a result, the researchers hypothesized that ravens would depend more heavily on wolf kills during severe winters,  but this is not what they found.  Instead, Yellowstone ravens seem to lean more on consistent, anthropogenic food sources during tough winters, but lean more on wolf provided carrion during more mild winters.  Still, the presence of wolves has increased and stabilized the number of ravens in the park, because they provide a second year-round source of food, in contrast to human hunter provided kills which are seasonally limited.  These findings are yet another demonstration of the value of top carnivores in stabilizing food webs and providing food for a cascade of creatures.

DSC_0085

6. And as a bonus let’s not forget the most important 2018 study of them all, “Occurrence and variability of tactile interactions between wild American crows and dead conspecifics,” which you can read all about here. 😉

leslie

 

 

7 Comments

Filed under Conservation, Crow behavior, crow intelligence, New Research, Raven behavior, Ravens, Science

You need to know more about jay spit

Look, I’m a reasonable person.  I know what you’re thinking.

“Literally never has it occurred to me I might know too little about jay spit.”

But here’s the thing: it’s actually super interesting and you really can’t understand Canada jays without knowing about their saliva.  It would be like trying to understand the internet without cat videos-you just can’t do it.  So trust me when I tell you this is the information you didn’t know you needed.

DSC_0164

In the early 1960’s Walter Brock was examining Canada jay corpses when he discovered that they have massive salivary glands on par with the ones found in woodpeckers.1 Such generously sized glands are found in no other songbird.  Furthermore, like the woodpeckers, it’s not just that Canada jays make a lot of saliva, but they make a lot of sticky saliva.  At the time this discovery was made, it was already known that the enlarged glands of woodpeckers served to allow for a foraging tactic called “tongue probing” where, like anteaters, the birds use their long sticky tongues to extract food from narrow crevices.  Although Canada jays don’t have especially long tongues, the ability to tongue probe seemed the most parsimonious explanation for this strange adaptation, and Brock suggested that this strategy may actually be the key to the jays’ winter survival.  A study a few years later examining their foraging behavior revealed that they don’t feed in this manner, however.  They feed more or less the same way the other corvids do.2  It seems instead, that it’s what they do with the food after that’s different.

DSC_0440

Rather than using their copious amounts of weird, sticky spit for acquiring food, it’s used for depositing it.  If you watch a jay closely after it’s got a bit of food you’ll notice it seems to have missed Emily Post’s memo about chewing with your mouth closed. Over the course of a few seconds you’ll see the food peek out from the bill as the bird moves it around inside its mouth.

DSC_0366

This jay picked up this bit of food about 60sec before this photo was taken.  Now it’s working it around with its tongue, coating it in sticky saliva.

Once sufficiently spit coated, the bird will deposit the food blob (called a bolus) onto the foliage or trunk of a tree.  No matter the material or angle, once the spit dries the food is safely secured come hell or high-water.  Because these caches are pretty small there’s little fear that many will be found.  More importantly, by stashing food high in the trees instead of burying them into the ground like many other cache-dependent corvids do, Canada jays can thrive in areas that receive much heavier snowfall, allowing them the title of the most northern residing jay in North America.

Here’s where it all really comes together though.  If you’ve seen me write about Canada jays before you’ll have noticed that it’s almost inevitable that I’ll use the phrase “Cute little faces” at some point to describe them.  But have you ever wondered why? Why do they have such cute little faces?  While jays do feed more or less in the same way as other corvids the one exception is that they don’t hammer at objects.  If you’re ever given a crow or a Steller’s an unshelled peanut you’ll know exactly the motion I mean. Without the need the hammer objects, or dig holes for burying food, Canada jays don’t need the heavy bills their cousins do.2  Instead they have the blunt little bill that helps give them their characteristic baby-faced look.  So not only is their spit responsible for their ability to tough it out in some of the harshest winter environments this continent offers, but it also means they get to look super cute while doing it.

So like I said, you don’t really know Canada jays until you know a thing or two about their spit.

DSC_1042

Literature cited

  1.  Brock WJ. (1961). Salivary glands in the gray jay (Perisoreus). The Auk 78: 355-365
  2. Dow DD. (1965). The role of saliva i food storage by the gray jay.  The Auk 82: 139-154

16 Comments

Filed under Birding, Canada jays, Corvid trivia, Diet, Field work, Jay behavior, Science

Putting the “crow” in necrophilia

It’s early April 2015, and John Marzluff and I are standing with a film crew attempting to capture some footage of a crow funeral to compliment a story they are working on about Gabi Mann.  I’ve already set the dead crow on the ground, it’s placed just out from a cherry tree resplendent in springtime blossoms.  After only a few moments of waiting, the first crow arrives and alights on the tree, its head cocking around to get a better look at the lifeless black feathers beneath it.  I hold my breath for the first alarm call, ready for the explosion of sound and the swarm of birds that will follow it.  But it doesn’t come.  Instead, the bird descends to the ground and approaches the dead body.  My brow knits together in surprise but, ah well, I think, the shots of it getting so close and then alarm calling will make good footage.   The audience will have no questions about what it is responding to.  To my continued surprise, however, the silence persists; only now the crow has drooped its wings, erected its tail, and is approaching in full strut. No, no, this can’t be, I think.  But then it happens.  A quick hop, and the live crow mounts our dead one, thrashing in that unmistakable manner.  “Is it giving it CPR?” someone asks earnestly.  Still in disbelief, John and I exchange glances before shaking our heads and leaving the word “copulation” to hang awkwardly in the air.  After a few seconds another bird arrives to the cherry tree and explodes in alarm calls, sending our first bird into its own fit of alarm, followed by a more typical mobbing scene.  The details of what I’ve just witnessed as still washing over me when I hear John lean over to me…”You need to start your field season tomorrow.”

***

What crows do around dead crows is something I’ve dedicated much of my academic life to understanding.  In the course of my first study, my findings made for a nice clear narrative: crows alarm call and gather around dead crows as a way of learning about dangerous places and new predators.  Although there are other hypotheses we can’t rule out, certainly danger avoidance is at least partially driving this behavior.  An important detail of that original study though, is that because of the way it was designed, with a dangerous entity always near the dead crow, our live crows were never in a position to ever get very close to our dead stimulus. So the possibility that they do other things around dead crows, like touching them, couldn’t be explored.

DSC_1139

It’s been 3 years since that day in April and during that time it has taken every ounce of my power to remain tight lipped when journalists would ask “what’s the most interesting thing you’ve learned from your studies?” Because until we were able to scientifically vet the prevalence of this behavior, I wasn’t willing to say much about it for fear of making necrophilia mountains out of mole hills. But with our findings now officially available in the journal Philosophical Transactions B, I am delighted to finally share what has been the most curious secret of my PhD: crows sometimes touch, attack, and even copulate with dead crows.

DSC_1028

Although this statement is jarring in its own right, what really gives it power is that we know this not just from that first fateful day with the film crew, but through an experimental study testing the response of hundreds of birds over several years.  That’s important because it allows us to say not just what they’re doing but possibly why they’re doing it (and at least why they’re not doing it).  So how did we conduct this experiment?

First, I dove into the literature to try and see if there was any precedent for this kind of behavior in other animals.  Although there have been no systematic studies, repeated observations of animals touching, harming, even copulating with their dead occur in dolphins, elephants, whales, and many kinds of primates, among some other animals.  Based on this, we hypothesized that this behavior may arise from: attempts to eat it, attempts to learn from it, or a misuse of an adaptive response (like territoriality, care taking, mate guarding, etc.). To test these ideas I searched the neighborhoods of Seattle until I found a breeding adult pair and (while they weren’t looking) presented one of four stimulus options: An unfamiliar dead adult crow, an unfamiliar dead juvenile crow, a dead pigeon or a dead squirrel.  The latter two stimuli being key in helping us determine if the behavior was food motivated, whereas the nature and prevalence of the interactions themselves (common, uncommon, exploratory, aggressive, sexual) helped us address the other hypotheses.  In all, I tested 309 individual pairs of crows; or in other words, once again I freaked out a lot of Seattle residents wondering why there was a woman with a camera, binoculars, and some dead animals loitering in front of their house for long periods of time.

Our main findings are that crows touched the animals we would expect them to eat (pigeons and squirrels) more than the dead crows, and although crows sometimes make contact with dead crows, it’s not a characteristic way they respond.  Because this behavior is risky, this seems to back up previous studies in crows that suggest that they are primarily interested in dead crows as a way of self preservation and avoiding danger.

DSC_1142

A crow tentatively pokes at one of our dead crows

That said, in nearly a quarter of cases, crows did make some kind of contact with dead crows.  Like with mammals, we saw that these behavior could be exploratory, aggressive and in rare cases even sexual (about 4% of crow presentations resulted in attempted copulations), with the latter two behaviors being biased towards the beginning of the breeding season.  Importantly, the latter two categories of interactions were rarely expressed independently, and it was often a mixture of the first two; in rare cases, all three.  In the most dramatic examples, a crow would approach the dead crow while alarm calling, copulate with it, be joined in the sexual frenzy by its presumed mate, and then rip it into absolute shreds.  I must have gone through a dozen dead crows over the course of the study, with some specimens only lasting through a single trial. It was an issue that may have been insurmountable if not for the donations of dead crows by local rehab facilities and the hard work of my long time crow tech turned taxidermist, Joel Williams.

It’s hard to witness this behavior without wondering if maybe the crows somehow don’t recognize that it’s dead and are instead responding like they might to a living intruder or to a potential mate.  So we tested that idea too, by conducting a second experiment where we presented either a dead crow or a life-like crow mount.  The differences in their response was clear.  They dive bombed the “live” crows and less often formed mobs, just like we would expect them to do for an intruder.  They also attempted to mate with the “live” birds but in these cases it was never paired with alarm calling or aggression.  So the issue doesn’t seem to be that they think it’s alive.

The fact that this behavior was rare, and often a mix of contradictory behaviors like aggression and sex, seems to suggest that none of those hypotheses I outlined earlier are a good fit for this behavior.  Instead, what we think happens is that during the breeding season, some birds simply can’t mediate a stimulus (the dead crow) that triggers different behaviors, so instead they respond with all of them. This may be because the crow is less experienced, or more aggressive, or has some neurological issue with suppressing inappropriate responses.  Only more experiments will help us determine what makes this minority of birds unique, and whether expressing these seemingly dangerous behaviors are the mark of the bird that is more, or less reproductively successful in the long haul.

DSC_1088

So while there’s still much more left to be explore here, I can finally say that this is without a doubt some of the most interesting behavior in crows I’ve ever witnessed.  I hope you will check out the publication here, and seek out all the other amazing work being reported in this special thanatology (death science) themed issue.

***

57 Comments

Filed under Being a scientist, Breeding, Crow life history, Field work, Graduate Research, New Research, Science