Tag Archives: crow calls

Crow Vocalizations Part II: Q&A

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

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

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

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Crow-human communication

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

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

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

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

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

Crow-other animal communication

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

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

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

Crow-crow communication

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

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

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

Crow sounds

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The study of crow communication

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

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

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

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

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

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

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

Literature cited

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

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Filed under Crow behavior, Crow curiosities, Vocalizations

Crow Vocalizations Part I: New Science

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

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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.

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

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

Crow curiosities: who is begging in April?

Right now, in early spring, you may have noticed a crow or two fluttering their wings and making the classic “waaah, waaahhh” sound that roughly translates to “feed me, feed me”!  Although it’s tempting to think these are young crows, it’s far too early in the breeding season for fledglings to be on the loose.  So who are these juvie doppelgangers? Adult female crows.

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Begging juveniles like this one won’t be roaming around the PNW until mid June and later.

During the nest building stage you may hear females making these sounds just while on the ground foraging with their mate or while perched near the nest like this female was.  Why do they do it?  It’s essentially a way to prime the pump and remind their mate that they’re going to need to be fed once they’re saddled to the nest and can’t forage as much for themselves.  Once they are actively incubating, they’ll continue to beg only now it’s really a demand for the food they need and can’t get for themselves without risking their eggs getting too cool.  Although males will take a turn on the nest, they do not have a formal brood patch and can’t do much more than temporarily keep the eggs insulated.

Although it’s tempting, hopefully now you won’t be fooled by this April trick!

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A male returns to the nest with a bill-load of peanuts for his hungry mate.

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Filed under Crow behavior, Crow curiosities

The many sounds of crow, including the jaws theme

I am constantly fascinated by the vocal repertoire of crows.  They produce over 20 calls, but I would venture a guess that for most people (I being one of them) the vast majority of those sounds are too subtle to distinguish between.  As I hear it, there are four majors “classes” of call that are easy to differentiate, even for a completely novice birder.  Those are: The classic ‘caw’, the harsh ‘scold’, the female courting ‘rattle/knock’ call, and the juvenile begging sound.  To make up the rest of the over 20 sounds, they use a combo of caws, clicks, coos, grunts and rattles.  While more has been decoded than I offer here, there is still much that remains a mystery.  Take for example their scold call.

Me getting yelled at by a Raven in Yellowstone that wanted a treat NOW!

Me, getting yelled at by a raven in Yellowstone that wanted a treat NOW!

Stimulus days featuring either our dead crow or our dead crow+the hawk consistently draw the largest number of birds.  In fact based on last year’s data, the dead crow+hawk stimulus draws the greatest numbers of birds by a large margin.  That’s not a huge surprise since hawks are a primary predator and responding very strongly to an obvious kill would provide a safety mechanism to the ‘neighborhood’.  Needless to say, with few exception once the first bird comes across this scene it alarm calls (scolds) and either very quickly or over a few minutes will draw a crowd of 10-30 birds.  It can certainly be more or less but somewhere in that range is most typical in my experience.  Now, none of this is particularly interesting.  What’s interesting is what happens the next day.  As a reminder, all our stimulus trials feature one of the known dangers paired with a person.  In the case of the dead crow+hawk this person is standing 2m away from the stuffed birds.  In half my trials I send this person out the next day and in the other half they get sent out a week later.  This is to test for any “guilty by association” inferences the birds are making about these people simply because they were near a known threat.  To my elation I’ve found that many birds do indeed respond to these people when they see them in the future.  While that’s certainly cool in and of itself, what makes it interesting from the perspective of their calls is that although their alarm call in this instance does not sound different to me, they almost never draw the crowds the initial stimulus day does.  It’s almost as if the hawk or dead crow is a neighborhood problem but a dangerous person is only the territory holder’s problem.  Is the caller advertising this distinction and intentionally not drawing in the other birds or are the others making that choice themselves?  I have no idea.  But there’s no arguing that there’s a level of complexity there worth investigating.

As for the story on my Jaws loving bird.  This afternoon I was returning to a field site I had, just the previous day, tested the stimulus I described above on.  While I was walking through the woods on my way there I noticed a shadow occasionally passing above me.  Finally I saw my stalker: A crow who I can only assume had spotted me and was hoping I’d offer some food before we actually arrived at the now tainted feeding site.  Once we arrived I threw my food out and, unsurprisingly, was not greeted by eager feeding.  Instead the bird merely perched in the tree and stared wishfully at the food it was too nervous to eat.   After a few minutes I started to hear an inexplicable noise.  A very low duh-nuh.  Duh-nuh.  The field site is located on the edge of a residential street and at first I assumed it was some kids, maybe just playing or perhaps intentionally trying to mess with me.  It was clearly the intro to the Jaws theme song.  But the more I listened, I realized there were no kids around and the sound was coming from the wrong direction to be made my a person.  With some careful watching I realized that, although I could not perceive it to be moving its bill, my perching crow bowed its head in perfect unison with the sound.  It became clear it was the sound’s author.  In all my time watching these birds I have never heard anything like it.  Have you?  You can listen to it here, but be warned it’s pretty quiet so turn your sound up.

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Filed under Crow life history