Category Archives: New Research

October 20, 2021 · 9:54 pm

How smoke affects wildlife

It’s September 8th, 2020 when I step out my front door in Eastern Washington into a landscape that looks like the aftermath of a Martian dust storm. The video I am recording captures my bizarre, sepia-colored surroundings as I try to put words to the experience of having your world an entirely different color than it was the day before. Like any inconsequential casualty in a disaster movie, my usual sense of self-preservation has been abandoned in favor of standing in harm’s way, mouth agape with my phone outstretched to the sky. After a minute, I realize my error and head back inside where I, and millions of other people on the West Coast spent the next several weeks hiding from air that can kill you.

That year, wildfires would go on to burn a total of 10.2 million acres on the west coast, cause $19.8 billion dollars in damage and directly kill at least 37 people. Over the last 30 years, fire severity and duration have increased and it’s impossible not to notice. Decades of wrongheaded fire management coupled with increasingly hotter, drier summers have meant that the 2-3% of wildfire starts we fail to suppress burn under the very worst conditions, pumping the air full of the kind of fine particulates that are irritating at best and deadly at worst. Unsurprisingly, the public health community has been swift to respond, with hundreds of studies examining the outcomes of smoke inhalation on humans. But while I and many other people were able to escape indoors during the worst of it, crows were unanimously stuck in a sepia haze…breathing. One has to ask; how do they cope? How does any wild animal cope?

Among those wondering was Olivia Sanderfoot, an imminent PhD graduate from the University of Washington. While there, she spent the majority of her time asking different questions about how smoke impacts wildlife, especially birds. In pursing her own research, Dr. Sanderfoot made a striking realization: despite the fact that nearly every birder, biologist and person were all wondering about how animals deals with smoke, there were only a few research studies. So with the help of her graduate lab, including myself, she resolved to collect and synthesize what papers were available into a comprehensive review. Published just this week, I am eager to share what we found.

As of the time our article was accepted, there have been only 41 English language studies examining the impacts of smoke on wildlife. Of those, less than half (44%) examined in situ (free ranging) animals dealing with real smoke events. Most were controlled studies where animals were intentionally exposed to smoke to learn about its impacts on their health or behavior. We found that from insects to sugar gliders a variety of different animals had been studied, but only 7 papers focused on birds (and sadly none on crows). Birds are of particular interest not only because, crows, but also because birds have a more efficient respiratory system than any other vertebrate. While this usually offers many advantages, it also quite literally makes them the canary in the coal mine—their high sensitivity to air quality acting as an important bioindicator in addition to the obvious consequences to welfare and conservation.

Although we had hoped to find clear answers to exactly how wildfire smoke impacts animal health, we only found 10 papers that addressed health outcomes specifically, and only 4 that ultimately looked at survival. Still, there are many more papers examining this question either in domestic animals, or animals models that are used as proxies for humans. When taken together with those findings, it’s clear that smoke isn’t good for animals, resulting in anything from carbon monoxide poisoning, to respiratory tissue damage, higher blood acid levels, stunted growth, compromised immune systems, and even death. Beyond direct health effects, exposure to smoke can may also reduce reproductive success. For example, researchers monitored the red-knobbed hornbill, a sort of toucan-like bird native to Indonesia, suggested that smoke might have contributed to a decline in the bird’s nesting success.

Smoke can induce behavioral responses among animals as well. Animals may become confused, agitated, vocal, lethargic, or quiet. For example, Bornean orangutans rest more during and after smoke events, Bornean white-bearded gibbons sing less, and sugar gliders extend the duration of torpor. Meanwhile pinecone lizards flick their tongues more, Psammodromus lizards start running, and many species of bats rouse from their torpor. Some birds are harder to detect like bald eagles, bushtits, killdeer, osprey and marsh wrens, while cedar waxwings, western tanagers, red breasted nuthatches, and yellow warblers actually become easier to detect as particulate matter (smoke) increases.

When taken together, it’s clear that wild animals are sensitive to smoke, and that smoke can have dramatic impacts on their health and behavior. But perhaps the most important finding of our review is that the predictability of these consequences for any future wildfire event remains almost completely out of reach. Because the thing about smoke is that it’s not all created equal. Smoke can have vastly different consequences to health depending on what’s burning (just think of the carcinogenic difference between cannabis and cigarette smoke), not to mention the impact that concentration and duration of exposure can have. And unfortunately, most existing studies haven’t undertaken the kinds of robust studies of air quality that are needed for this kind of future predictive power. Still, knowing this, and having a framework of existing knowledge and methodology, means that future studies are poised to finally start building the foundation we need for sophisticated, predictive modeling.

Until then, we can expect that smoke events like the kind we experienced in 2020 will continue to haunt our changing planet, and while some humans can safely nest alongside their air purifiers, many more, and all our wildlife, are at the mercy of an airscape they cannot retreat from. For now, this is our reality but it need not get inhospitably worse. Just has humans are capable of bullheaded, catastrophic damage, we are also capable of a profound capacity to change, improve and heal. It’s time to take bold, industry/system level steps towards changing our climate future, if only we can find the will to do so.

Read the whole paper here: https://iopscience.iop.org/article/10.1088/1748-9326/ac30f6/pdf

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Filed under Birding, Climate change, Conservation, Corvid health, New Research, Wildlife

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June 21, 2020 · 11:11 pm

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?

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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.

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

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April 13, 2020 · 8:47 pm

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.

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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 species.  So 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

 

 

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

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March 17, 2020 · 5:26 pm

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.

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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

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

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August 26, 2019 · 8:43 am

Dumpster diving is giving crows higher cholesterol—but does it matter?

Whether it’s from actively watching crows, or simply just existing in a city, we’ve all seen it: the overflowing garbage bin with fat-stained wrappers littered at its base, and the crows snapping up each bit of leftover junk like spilled money.  Cheetos, cheeseburgers, fries, nuggets, chips, or pizza, they will devour basically anything fatty and salty with absolute glee.  This behavior is so canonically crow that it’s stapled into our contemporary imagery of these birds.  Take this 12ft statue called “Crow with Fries” by artist Peter Reiquam.

cikSOsc

Photo c/o salishsea

I’d wager that most people don’t think about this behavior beyond simply finding it amusing or annoying, but I suspect that if you describe yourself as crow lover, naturalist, or bird watcher, you’ve been struck with the same thought as me: “This stuff is called junk food for a reason—it’s bad for you.  What’s it doing to these birds?”

Given that anthropogenic foods can account for as much as 65% of an urban crow’s diet, it seems essential to understand what a diet derived from regularly feasting at McDonalds might do to an animal with 0.7% the body mass of a typical human.1  Unfortunately, we could do little more than shrug and speculate as to its effects.  The data for a more informed understanding just didn’t exist.  That is, until today.

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A new study published in The Condor by Dr. Andrea Townsend et al. examines the relationship between urbanization, junk food, and the body conditions of crows.2  To conduct this study, her team blood sampled 140 wild crow nestlings along an urban to rural gradient.  They found that plasma blood cholesterol levels increased in correlation with the amount of impervious surface, which is a typical way we measure urbanization.  This finding suggests that crows in the city have more access to high cholesterol foods and they make haste in gobbling it up.

Correlation is not causation, however, so to confirm this, they ran an additional supplementation study where they provided 10 rural crow parents with 3 McDonalds cheeseburgers 5-6 days a week, and then looked at how their nestling’s blood cholesterol levels compared with unsupplemented nestlings from the same area. They found that eating cheeseburgers most days of the week had a demonstrable effect on the subject’s cholesterol levels.  While this finding may not be raising any eyebrows, the actual logistics of carrying out a study that required buying hundreds of cheeseburgers each week, and sometimes in one order, certainly did.  In one of their more memorable attempts, Hannah Staab called to place an order for 125 pickle-less cheeseburgers, a request to which McD’s staff replied, “Sure, we’ll get right on that.”  When she arrived several hours later to pick them up, however, they hadn’t made any, having been convinced that the call was a prank.  The peculiarities of urban fieldwork never falter.

prank

So far, these findings tell us little more than what most people could have probably intuited, but they were crucial to laying the foundation for the real clogged heart of this study: Whether any of this is actually a bad thing.  In the final piece, they examined the body condition, and 2-3 year survival of the 140 nestlings sampled along the urban to rural gradient.  They found that cholesterol levels had no detectable effect on survival and were actually correlated with higher indices of body condition (meaning mass adjusted for size), a feature that is sometimes tied to higher reproductive success and survival. In other words, there might actually be a scenario where regularly pigging out on McDonalds doesn’t kill you and is maybe kinda helpful?

Needless to say, this caught everyone off guard, including Dr. Townsend, who told me, “I was surprised that we didn’t detect any negative health effects. I was thinking—based on the human literature—that high-cholesterol birds would have lower survival rates, but we didn’t see any effect of cholesterol on survival.”

So what gives? Is the universe really just this unfair?  While we can’t rule out that the answer is simply, “Yes,” the authors speculated that it’s possible a longer study would bear out health consequences that take more than a few years to accrue. There’s also something to be said for the fact that body condition has complex and not always agreed upon relationship with fitness and survival.3 While some studies show pudgy birds have more resources to produce more offspring and keep on ticking, others find inconsistent support. Alternatively, crows may just not live long enough to see their lifestyle catch up to them.  Future long-term studies will be necessary to fully understand whether crows have truly found a loophole in the junk-food problem. For now however, I’m happy to wish my favorite dumpster divers well, though I’ll hold off placing my own orders.

Literature cited

  1. Marzluff JM, McGowen KJ, Roarke D. and Knight RL. 2001. Causes and consequences of expanding American crow populations in Avian ecology and conservation in an urbanizing world (J.M. Marzluff, R. Bowmanm and R Donelly, eds).  Kluwer academic Press, norwell, Ma.
  2. Townsend AK, Staab HA, and Barker CM. 2019. Urbanization and elevated cholesterol in American Crows. The Condor page 1-20
  3. Milenkaya O, Catlin DH, Legge S, and Walters JR. 2015. Body Condition Indices Predict Reproductive Success but Not Survival in a Sedentary, Tropical Bird. Plos One https://doi.org/10.1371/journal.pone.0136582

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March 14, 2019 · 3:38 pm

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?

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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.

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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.

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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 

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December 31, 2018 · 9:18 pm

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.

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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.

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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.

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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.

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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.

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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

 

 

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July 16, 2018 · 3:55 pm

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.

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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.

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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.

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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.

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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.

***

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

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March 17, 2016 · 1:48 am

Why the crow smiles

There’s hardly a corvid species that doesn’t strike me as beautiful but there’s only one that’s always struck me as particularly gleeful.  Looking at the New Caledonian crow it’s evident there’s something different about the shape and proportions of its bill. It’s a bit shorter and more blunt, and it lacks the obvious downward curve of a typical crow bill, with lower mandible actually curving slightly up. Put together, these features appear to give it the perpetual grin that trademarks this species.  I’ve joked that this must be because they’re always feeling very pleased with themselves for being so smart, and thanks to new research, I’ve come to learn my joke had it backwards.

A New Caledonian crow’s bill appears in sharp contrast to a typical American crow. Photo: “Science Meets Adventure”

By using tomography scans, Hiroshi Matsui and his team were able to compare the shape and structure of the NC crow’s bill with that of its close relatives. Their conclusion, which they report in the March issue of Scientific Reports, is that this shape makes the handling and manufacturing of tools easier. Looking at photos of the birds in action, it feels intuitive that the more exaggerated curve of a raven or American crow bill would have a hard time achieving the dexterity that NC crows need to use their stick and hook tools.

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Given this new research it’s time to amend my joke. It’s not that NC crows grin because they’re smart, they’re smart because they grin.

Literature cited

  1.  Matsui, H., Hunt, G., Oberhofer, K., Ogihara, N., McGowen, K., Mithraratne, K., Yamasaki, T., Grey, R., and Izawa, E. 2016.  Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows.  Scientific Reports 6. doi:10.1038/srep22776

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Filed under Crow behavior, crow intelligence, Crow life history, New Research

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March 2, 2016 · 7:19 am

I spy with my raven eye…

…someone trying to steal my lunch.  Turns out, humans are not the only ones wary of peeping Toms; new research shows raven can imagine being spied on by a competitor.

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***

The other day my friend and I were having a very merry time at the thrift store when, without cause or provocation, this women decides to up and ruin our trip.  Well really, she simply spotted the same gorgeous caste iron dutch oven that my friend wanted and reached it first, but the consequence was the same (it was a tragically beautiful dutch oven). This dynamic-my friend having her own intentions (to obtain and own that dutch oven for herself) and recognizing that this other women had her own intentions (to obtain and own that dutch oven for herself) is something so second nature to being human we rarely give it any thought.  But the ability to attribute mental states to those around us is an incredibly profound and complex cognitive task.  Understanding if this ability, called Theory of Mind, exists in other animals has been among our top interest as ethologists.

Like other corvids, ravens cache food and, as a consequence, run the risk of their caches being stolen by others.  It has long been known that if ravens can see that they are being watched, they behave differently when it comes to caching than if they are alone.  This is interesting, but doesn’t necessarily speak to whether they posses theory of mind because of the confounding effect of “gaze cues”.   Basically, the correlation between head cues and competitor behavior make skeptics doubtful about non-human animals having the ability to know what others might be seeing.  So raven master Thomas Bugnyar and his colleagues Reber & Bruckner recently published an elegant study to address just this issue.

By training captive ravens to look through a peephole, and then allowing them to cache food with the peephole opened or closed, the researchers were able to show that ravens behaved as if they were being watched when they could hear ravens and the hole was open, but not when they could hear ravens but the peephole was closed.  What this suggests is that ravens are capable of remembering their own experience of looking through a peephole to see into another room, and can imagine that another bird might be doing the same thing even if they cannot see this bird.

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Experimental set up.  Bugnyar et al. 2016.  Nature Communications

Theory of mind and imagination (which are not mutually exclusive) are the cornerstones of what makes for a powerful cognitive toolkit and have long been thought to be uniquely human.  As we continue to build on the body of work showing non-human primates, corvids and some other animals posses some of the same skills we do, many will be challenged to redefine what it means to be human.  Personally, framing the question that way doesn’t interest me.  To me the more interesting question is not how are humans different from ravens, but how are we the same and why? What is it about being human and being raven that make possessing imagination important?  Fortunately there is still loads more research to be done, and when it comes to teasing out this question I can only imagine the possibilities.

Literature cited:

Bugnyar, T., Reber, S.A., and Buckner, C.  (2016) Ravens attribute visual access to unseen competitors.  Nature Communications 7.  doi:10.1038/ncomms10506

 

 

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