Category Archives: Crow curiosities

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.

***

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

Meet Ferdinand

Around this time last year I was both delighted and intrigued when a reader emailed me about a very usual crow showing up in her yard.  Unlike its flock mates this crow was not black, but white and brown, like the kind of milked-down coffee that inspires the comment “would you like some coffee with your cream?”.  Understanding what would cause such a unique coloration in her crow sent me down a most unexpected rabbit hole where the science of what I call ‘caramel crows’ turned out to be somewhat subject to mystery.

Within months of publishing that article, I couldn’t believe my luck to encounter a caramel crow of my own named Blondie.  Whereas the science of their pigmentation may be up for debate, their beauty most certainty is not and I considered myself exceptionally lucky to lay eyes on one in person.

Photos of Blondie from 2017

Now, it seems my perception of their rarity may not have been quite justified as I have since discovered yet a second caramel crow, who I call Ferdinand, in a completely different part of the city.  Unlike Blondie, who lives exclusively in a residential area, Ferdinand’s haunts include a public park.  I won’t give his or her precise location, but if you’re a Seattle native I encourage you to use the clues provided in the text and photos of this post to see if you can find Ferdinand.  If you do use the hashtag #FoundFerdinand to update us on its activities but remember not to give away its precisely location.  This is both to encourage people to get outside and explore on their own, and to protect Ferdinand’s safety.  If seeming him in person is not possible I hope these photos will suffice.  As a last bit of fun feel free to let me know in the comments who you think wore it better, Ferdinand or Blondie.

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Filed under Birding, Crow curiosities, Just for fun

15,000 crows

I had imagined it like a beckoning flood.  A small sputter of water followed with increasing force until a great river finally makes its way.  Rather than water though, the flood I was trying to envision was the ascent of 12-15,000 crows to their nightly roost in Bothell, Washington.

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Witnessing it in person, I found that my water analogy was not entirely accurate.  Rather than being a steady stream with a predictable course, their arrival ebbed and flowed, sometimes leaving the sky lonely with only its fading grey light while other times exploding into seemingly endless black clouds.  They arrived from all cardinal directions, colliding into a mass that could be deafening at close range.  Although the movement of the flock as a whole was more restrained, individually they showed off with spontaneous dives and barrel-rolls.  Soon the light receded completely, and all I could sense was the cacophony of so many crows settling into the willow trees they would call their beds for the evening.

Time lapse of Bothell crow roost I took with my GoPro in December of 2016.  Music by Andy McKeen.

Since that first experience, I have visited the Bothell roost many times, each as awe inspiring as the time before.  This behavior isn’t unique to my region, however.  Cities and rural areas all over the world call themselves home to the upwards of thousands, even hundreds of thousands of crows that may seek their refuge when darkness falls.  Even in the greater Seattle area, Bothell is only one of two roughly equally sized roosts.  This kind of mass sleepover, known as communal roosting, isn’t unique to crows, but it certainly captures our attention in ways most other birds don’t.  So what exactly are the characteristics and functions of roosts?

For all species of corvid, roosts are places where anywhere from a small handful to hundreds of thousands of individuals may converge to spend the night together.  Though roosting occurs year round, it peaks in winter, when territorial pairs are free from the eggs or nestlings that demand all-night attention.  They may occur in wildlands, but more typically occur in cities, where sequestration of heat is higher than in surrounding areas.  Here in Bothell, the roost converges in a wetland outside of the University of Washington’s Bothell campus, but in other areas they may take over the rafters of abandoned buildings or trees dotted within a business district.

Historically Danville, IL hosted North America’s largest roost, a whopping 325,000 birds but I do not know if they remain the contemporary record holder.  The midwest is particularly primed to host such large numbers because many thousands of crows head there during winter from their too cold territories in Canada and because appropriate roosting locations are few and far between.

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Prior, or just after roosting crows attend “staging” or “pre/post-roost” areas where they gather in the trees or on the ground by the hundreds or thousands.  Since these staging areas often occur on asphalt or turf where there’s little food or water, their function continues to elude scientists though social or anti-predator implications seem likely.1 A new UW research study is attempting to parse why crows are so vocal during the staging period and what they might be trying to communicate.  Perhaps their findings will shed some much needed light on these events. 

Corvids get different things out of roost itself depending on the species or possibly even the region they live.  For example, for ravens roosts act, in part, as mobile information centers.2  A raven knowledgeable of a food bonanza such as a moose carcass will display to other ravens at first light, and recruit others to the food.  Rather than being a sign of food altruism, this kind of recruitment is often the only way a lone raven can gain access to a large carcass.  Finding and gaining access to an animal carcass is challenging both because its arrival is unpredictable but also because it’s intensely guarded by the pair whose territory happened to claim the animal’s life.  Overpowering a pair takes a small army, so by recruiting other birds, rather than giving up food in the name of helping others, the lone raven actually gains access to a resource it would have otherwise been boxed out of.

American crows on the other hand do not have this need because urban waste and invertebrate filled yards are so easy to come by.  For crows, roosts act in large part as predator protection.  The odds of successfully fleeing an incoming owl are much better when there are thousands of you, rather than just you and your mate.  They may serve other purposes as well though including socialization, mate finding, and thermoregulation.  Lastly, while there isn’t strong evidence of information sharing among crows it would be arrogant to claim we know it doesn’t occur.

How roosts are organized remains largely mysterious.  For example some evidence shows that ravens that come from the same food bonanzas also sleep near each other in a roost,2 whereas other work done on crows suggested that group cohesion is low at roosts.3  Still, other research suggests that while group cohesion from the territory is low,  it’s high leaving the staging area.  So perhaps there is deep rhyme and reason for who they sleep with, it just hasn’t been captured by the questions we’ve so far asked.  One thing is for certain though; the one place you don’t want to be is low in the trees with others above you.  There would be no escaping the white shower raining down throughout the night.

Even the people who share the UW’s campus are sensitive to this reality.  In perfect synchrony with the incoming cloud of birds, the umbrellas bloom like moonflowers.  Here in Seattle, people seem willing to take such measures to coexist with the birds (though I’m sure there are many who only do so only by rule of law).  In other areas though the cultural attitude or resulting damage makes such cohabitation difficult, even deadly.  In the most extreme case, 328,000 crows were killed in 1940 when the city of Rockford, IL elected to dispose of a local roost with dynamite.4  Today, crows are protected under the migratory bird treaty act and cities are usually required to take more creative, non-lethal approaches including noise and light deterrents.

City living doesn’t always lend itself to witnessing the kind of mass animal movements we fawn over when they appear in Planet Earth footage, but that doesn’t mean they are devoid of such spectacles.  The mass micro-migration of thousands of crows is an awe inspiring event,  grand in both scale and the mysteries it contains.  Any corvid or birdwatcher would be remiss to ignore such an opportunity and I encourage everyone to get outside, head to your roost, and watch the magic unfold.

Literature cited

  1. Moore JE, and Switzer PV. (1998).  Preroost aggregations in the American crow, corvus brachyrhyncos.  Canadian Journal or Zoology.  76: 508-512.
  2. Wright J, Stone RE, and Brown N. (2003).  Communal roosts as structured information centers in the raven, Corvus corax. Animal Ecology 72: 1003-1014.  DOI: 10.1046/j.1365-2656.2003.00771.x
  3. Donald F. Caccamise, Lisa M. Reed, Jerzy Romanowski and Philip C. Stouffer
    (1997). Roosting Behavior and Group Territoriality in American Crows. The Auk 114: 628-637
  4. Marzluff, J.M. and Angel, T. 2005. In the company of crows and ravens.  Yale University Press

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Filed under Birding, Crow behavior, crow conflicts, Crow curiosities, Crow life history, Crows and humans

My first caramel crow 

A few months ago I was both bewildered and delighted when someone emailed me some photographs of a brown crow that regularly visited them.  I had never seen such a bird myself, and was eager to arrive at an explanation for the crow’s strange caramel-colored appearance.  If you follow the blog, you know that I came to realize there was little to offer by way of explanation.  Instead, this color abnormality presents a rather fascinating mystery of conflicting opinions and an overall dearth of science.

So, after penning my answer I tucked this bird away in the back of my mind and moved forward with the science more relevant to my PhD.  Namely, testing how different crows across the Seattle area respond to dead crows.

To this aim, I spend my days wandering the neighborhoods of Seattle looking for crow families to use for my experiments.  Since I need lots of data points it means I encounter lots (think hundreds) of individual crows.  And wouldn’t you know it.  Sometimes the twain shall meet.

Its mate first caught my eye because, of course, I was looking for black things, not blond things.  Even after I registered the bird, I instinctively thought pigeon.  But then it called, and I realized what was happening.

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At 60m away with my naked eye, I first mistook Blondie for a friendly pigeon.

I FOUND A CARAMEL CROW!  And not just a caramel crow, but a caramel crow with a mate and three fledglings.  A black mate and three black fledglings.  Which suggests that whatever is going on is either recessive or not genetic.  It also shows that, for at least this one caramel bird, the color abnormality did not prohibit it from successfully reaching sexual maturity or finding a mate.  After speaking with the neighbors, it appears “Blondie,” as they call it, has been in the neighborhood for several years and it’s possible she’s not the only caramel crow, though I never confirmed any others.  Outside of that, I can’t say much more from a scientist’s standpoint that I haven’t said before.  So I’ll simply finish the post with a photo story of Blondie.  Enjoy!

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Meet Blondie

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Blondie and its mate.  Since I discovered this bird after its nestlings had already fledged, I have no way of determining its sex.

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So beautiful in this juniper tree!

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Blondie’s fledglings were typical looking crow kiddos.

The next batch of images are probably one of the most hilarious bits of fledgling dramatics I’ve ever seen.  It is a scene familiar to many parents I’m sure.  Forgive me for taking my scientist hat off, but I couldn’t help but add some anthropomorphic captions.

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Hello parent I am hungry.

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DID YOU HEAR ME, I SAID I’M HUNGRY.

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(whispering) help, parent, I need sustenance for my growing body.

 

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(muffled whispering) please, have mercy, it’s been over 15 minutes since I was last fed.

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MAYBE I’VE ALREADY DIED AND NOW I’M A GHOST IS THAT WHY YOU AREN’T LISTING TO ME???

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I’m sorry.  I’m just hangry.  I love you.

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Cheers to yet another beautiful crow.  Goodbye for now!

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Filed under Birding, Crow curiosities, Just for fun

What’s in a (corvid) name?

Most people know various corvid species by their common names but have you ever wondered what etymologies inform their scientific names? Turns out it’s a pretty fun little exercise to find out!

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Before we get to breaking down individual corvids though, a quick word on scientific names more generally.  Scientific names always have the format: Genus species. Meaning, the first word in the name tells you what genus the plant/animal belongs to and the second tells you the species name specific to that organism. So for example crows, rooks, jackdaws and ravens are all in the same genus so their scientific names will all start with the same word: Corvus. The second word, however, will be unique to each species. This system of binomial nomenclature was first developed by Carl Linnaeus in the 1700’s.  By looking up the roots of an animal’s scientific name we can learn a thing or two about what he, (or whoever named it) was trying to highlight. Then again, sometimes they’re just fans of Beyoncé or Jonny Cash.

One more note: although scientific names are often referred to, informally, as Latin names, their roots may actually pull from many languages.  Though by far the most common languages are Latin and Greek.

As it happens, I have an old book of  root words I inherited from my late grandfather, Richard Swift. Something about having that book in my hands begged for this exploration in a way that having the breadth of the Internet at my fingertips never did. What can I say, a childhood spent in the library of my grandfather’s office has made me a sucker for old, smelly books. So let’s get started!

Common raven: Corvus corax
Common ravens are the biggest of the corvids (and in fact, the biggest of all the songbirds) so it makes sense their name might be the yardstick by which other corvids are measured. Cora literally translates to “crow, raven” so the common raven’s scientific name essentially just means raven.

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GO, the American crow

American crow: Corvus brachyrhynchos
Turning to American crows, we can see that yardstick I mentioned coming into play. Brachy means “short” and rhynch means “a beak or snout.” So the American crow’s full scientific name basically translates to the “short-beaked crow.”

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Jungle crow, photo c/o Anne Kurasawa

Jungle crow: Corvus macrorhynchos
At this point, the meaning of the jungle crow’s name probably needs no explanation. The bird looks essentially like an American crow but with a more pronounced bill. Macr rhynch = large beak.

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Pied crow, photo c/o Frank Vassen

Pied crow: Corvus albus
Alb means “white.” No mystery here.

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House crow, photo c/o Benjamint444

House crow: Corvus splendens
Splen means “a badge or patch.” With grey sweater they sport, it’s likely the person who named them was trying to highlight this physical distinction.

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Thick billed raven, photo: Ignacio Yufera

Thick-billed raven: Corvus crassirostris
Sometimes, scientific names are precisely their common names. Such is the case here. Crass means “thick” and rostr means “beak.” This is a good example of where we see different languages influencing the names.  In this case, thick-billed ravens got the Latin root, whereas American and jungle crows got the Greek root for beak.

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Rook, photo c/o Pam P.

Rook: Corvus frugilegus
This one is less clear to me. Frugi means “useful, fit” and legus means “lie down; choose; or collect” depending on what language you pull from. My guess is it’s supposed to be ‘collect’ and the name refers to the more specialized bill they have for collecting insects.

Finally,

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The grey or bare-faced crow, photo c/o B.J Coates

The grey crow: Corvus tristis
Trist means “mournful; sad.” I have a feeling I know the backstory for this one but I’ll leave it to my readers to see if they can figure it out. Leave me your best explanation (made up or researched) in the comments!

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Filed under Birding, Corvid trivia, Crow curiosities, Uncategorized

Crow curiosities: Why their feet don’t freeze

With a peanut visible in my gloved hand, we square off.  The crow eyes me from its snow covered perch, weary of such gifts offered by strangers.  Above us a raven castes a disinterested look, croaks, and flies away.  I toss the nut into an empty parking space and the crow descends to quickly collect its prize.  The space between us must be widened before it will comfortably eat however, so I decide to leave the crow to its snack and return to my car.

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Scrunching my feet in my shoes, I’m relieved for the excuse to retreat.  It’s about 10˚F outside and despite the wool socks and insulated boots between my skin and the snow I can tell that my feet are numb from the cold.  Even stashed in my pocket, my gloved hands are having trouble articulating to their full range.  How is it that my extremities lose function even with so much coddling and yet the crows can continue using their bare toes to steady and manipulate food in such cold weather?

To be clear, birds are endothermic, or warm blooded, just like mammals.  In fact, on average, birds run a little hotter than mammals.  And their feet, like ours, requires warm blood both to function and to prevent the tissues from outright freezing and causing cell death.  Yet despite these needs birds can comfortably walk, stand, or even sleep on ice.

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Glassy ice makes cold footing!

To do so, they can take advantage of two important adaptations.   The first is that the size of the arteries carrying blood into the legs and feet is exceedingly small.  Given this high surface to volume ratio, the blood has already lost most of its heat by the time it reaches the feat, and can’t lose much more to the outside world.  The second is that they employ what’s called a counter current heat exchange system.  Essentially, warm blood traveling away from the core and towards the feet via the arteries comes into close contact with colder blood traveling away from the feet and towards the core via the veins. At this point of contact, heat from arterial blood is transferred to blood traveling in the veins. This heat exchange system allows for the tissues in the feet receive just enough heat to prevent cell death, and can reduce heat loss by up to 90%1.

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A crow wades out across a frozen Drumheller Fountain in search of scraps

As an additional strategy, you’ll see them protecting their exposed legs under their body feathers, as if they’re incubating them.  This is the same reason you often see winter birds standing on one leg.  By switching back and forth, birds can minimize overall heat loss by reducing the exposure to only a single leg.

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A crow covers its feet while it waits (hopes) for a handout

So while I need special clothing to keep my extremities at a similar temperature range to my core, the physiology of most birds is adapted to simply allowing extremities to exist at near ambient temperatures with no tissue damage.  In other words, rather than crows’ feet not getting cold, their feet simply are cold.  That said, frostbite is still a possibility even in birds, particularly for: nonnative species, birds in wire cages, birds with metal legbands, and birds in unseasonably cold conditions.  If frost bite occurs, early treatment at a rehab facility can prevent long term damage2.

Still, the idea that cold-adapted birds can keep their hearts beating away at around 105˚F even while their feet are exposed to freezing temperatures is marvel of adaptation and thermoregulation!

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Literature cited:

  1. Elphick C, Dunning JB Jr., Sibley DA (eds).  (2001) The Sibley guide to bird life and behavior.  New York: Alfred A. Knopf
  2. Wellehan JFX. (2003). Frostbite in birds: Pathophysiology and treatment.  Compendium 25: 776-781

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Filed under Corvid health, Crow behavior, Crow curiosities

New research on the cause of the AKD outbreak

Since the nineties, Avian Keratin Disorder has been an increasingly common disorder among Alaskan and PNW crows, chickadees (~17% of northwest crows1, ~6% of black-capped chickadees2) and a handful of other species, that causes gross deformities of the beak such as elongation, curvature or crossing.  I’ve written previously about the details of this disease before, but at that time there was little progress in determining the underlying source of the outbreak.  While AKD can be caused by a variety of things, at the scale it’s being observed now scientists questioned if there was a more consistent underlying factor.  Since AKD can cause discomfort or even death (primarily through the inability to feed or preen) understanding what might be the source of this outbreak has clear management and conservation implications.

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An AKD-afflicted American crow in Seattle, WA.

Among the initial suspects were environmental contaminants such as heavy metals, organic pesticides, and toxic environmental pollutants like PCBs, PCDDs, and PCDFs.   Blood work done on afflicted Northwestern crows, however, showed no significant difference in the 30 blood elements tested compared to unaffected adults or juveniles3.  Fortunately, new research may finally be shedding light on what’s going on.

Disease can be an easy thing to rule out if you know what you’re looking for, but new to science pathogens can evade traditional diagnostic techniques.  To account for this, a team of USGS and university scientists conducted a sequencing study comparing pooled RNA of healthy and AKD positive chickadees, crows and nuthatches in attempt to identify a candidate pathogen2.  Their work appears to have paid off, revealing evidence for a new picornavirus (a family of viruses previously known to science) they are calling poecivirus.  Whereas 100% of AKD-affected birds (23 subjects) tested positive only 22% of the 9 control individuals did.

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Alaskan black-capped chickadee with severe AKD. Photo c/o Martin Renner

Given these small sample sizes, it’s too early to throw our hands up in complete relief of having identified the cause of the AKD outbreak, especially since there’s still much to be done in understanding the potential relationship of this new virus to the environment.  Nevertheless, these findings offer some insight and hope that scientists are on the right track.  With more dedicated work we may soon have a much better understanding of this novel pathogen, its link to AKD, and management options moving forward.

Literature cited

1.  Van Hemert C, & Handel CM. 2010.  Beak deformities in Northwestern crows: Evidence of a multispecies epizootic.  The Auk 127: 746-751.  doi: http://dx.doi.org/10.1525/auk.2010.10132

2. Zylberberg M, Van Hemert C, Dumbacher JP, Handel CM, Tihan T, and DeRisi JL. 2016. Novel picornhttps://wordpress.com/post/corvidresearch.wordpress.com/3363avirus associated with Avian Keratin Disorder in Alaskan birds.  mBio 7 doi: 10.7589/2015-10-287

3. Van Hemert C, Handel C. 2016.  Elements in whole blood of Northwestern crows (Corvus caurinus) in Alaska USA: No evidence for an association with beak deformities.   Journal of Wildlife Diseases 52:713-718 doi: http://dx.doi.org/10.7589/2015-10-287

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Filed under Birding, Corvid health, Crow curiosities, Crow disease, Crow life history, Ecosystem, Uncategorized

Why crows sunbathe

With its bill agape, I watch as the crow fans out awkwardly across the cedar shingles. Pressing the camera to my face I snap a couple photos, pleased to finally capture on film a moment I so often encounter in the field.  Unlike the crow, who’s keeping a watchful eye on the sky, I’m completely taken with my admittedly creepy behavior.  Until, of course, I hear the stiff “Excuse me, can I ask what you’re doing?” from the driver’s window as the homeowner’s minivan pulls up behind me.

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Fortunately for me, crow curiosity isn’t hard to come by and quickly the homeowner is as taken with watching this bird as I am.  “So, what is it doing up there?  I see them like this on my roof all the time” he asks after I give him my credentials.  It is a rather odd sight.  It’s nearly 90˚ and the crows is sitting in direct sunlight, mouth open, head cocked and wings outstretched like it’s injured.  Rather than escaping to shade, it’s joined by its fledgling and together they bake their bodies in the hot sun for a few minutes before gathering themselves and carrying on down to the grass to forage.

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Although the specifics can vary slightly, this general kind of posture can be observed across hundreds of bird species, even those you might not expect to have much opportunity for it like owls.  Often it’s used to dry wet feathers or warm up on a crisp winter morning but, given that they do it even when it modestly heat stresses them, it must have some other physiological benefits beside thermoregulation.

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There are a handful of other reasons that birds may sunbathe, but the big picture is that applying intense heat to feathers is critical to maintaining them in good condition.  For example, sunlight exposure has been shown to suppress feather degradation caused by the bacteria Bacillus licheniformis 1.  Heat also helps control ectopatasites, possibly by making them more mobile and easier for birds to remove2.  Lastly, sunning may relieve discomfort caused by molting and promote vitamin synthesis3.

So, far from being a signal of distress or heat exhaustion, observing this posture in crows is like watching them ruffle around in a puddle. It’s a routine, and important part of their self care regimen. Plus, everyone knows a few minutes in the sun just plain feels nice.

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Photo c/o Kathy Brown.  Find more of her great photos on Instagram @kat2brown

Literature cited

1. Saranathan, V., and Burtt, E.H. Jr. (2007).  Sunlight on feathers inhibits feather-degrading bacteria.  The Wilson Journal of Ornithology 119: 239-245

2. Blem, C.R., and Blem, L.B. (1993).  Do Swallows sunbathe to control ectoparasites? An experimental test.  The Condor 95: 728-730

3. Potter, E.F., and Hauser, D.C. (1974) Relationship of anting and sunbathing to molting in wild birds.  The Auk 91: 537-563

 

 

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Filed under Crow behavior, Crow curiosities, Crow disease

5 reasons to leave baby crows alone 

Those blue eyes, that awkward gate, their seemingly constant precariousness, they’re all calling to you to intervene. Here are 5 reasons second guessing that instinct might be in the bird’s best interest.

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1) The vast majority don’t need your help. It’s totally normal for baby crows to be on the ground and flightless as long as they’re covered with feathers and appear otherwise alert and mobile. Even nestling crows are usually on the ground on purpose. Not because they are ready, but because their parents have intentionally rejected them for one reason or another. They will die and that’s ok. Part of coexisting with wildlife is giving them the agency to be wild. The story is different of course for species where the survival of individuals may mean the difference between population survival and extinction, especially because these situation are almost always driven by human activity.

2) It’s hard to tell when they’re stressed.  Recently, I saw a video on Facebook of a Steller’s jay fledgling in the care of a very well intentioned person.  She was giving it gentle strokes with her fingertips, each touch resulting in the young bird turning its head towards its back and opening its mouth.  The comment thread filled with ooo’s and awww’s and general comments of encouragement or gratitude for her actions.  For me it was like watching an alien attempt to care for a human child, the child recoiling and screaming while its caretakers congratulated themselves on how kind they were being.  Having handled baby corvids before, I know what that kind of posturing means, it means “I’m scared and stressed.”  To an untrained eye though, it may not look much different than the kind of gaping that means ‘feed me.’  Being stressed to death is a reality for young, or even adult animals, so any handling best be done by experts whenever possible.

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3) It’s illegal to rehab crows without a license. You can provide temporary care until you can get them to a licensed facility, but do not attempt to rehab them on your own.  Mistakes like the one I just described are a prime example of why the law seeks to protect animals by ensuring they are only raised or rehabilitated by experts.  For more information on how to handle them until you can get them to a facility visit my previous post.

4) Imprinted crows do not survive well in the wild.  Even if baby crows are receptive to being treated like a pet, doing so is both a legal violation and I would argue a violation of their right to be a wild animal with a healthy fear of people.  Of all my daydreams, at the top of the list is having a wild but imprinted crow that follows me around.  I even have a name picked out.  This fantasy of mine will forever remain just that, however, because it’s too dangerous to allow a crow to become that comfortable with people.  All it would take is one cranky neighbor with a pellet gun and it would be over.  Not to mention being imprinted on people, instead of crows, denies them access to skills and relationships with other crows that will help them survive into adulthood. 

5) It may do more harm than good.  The conventional wisdom suggests “well, worse case scenario is I try and rehab this baby crow and it dies, which it would have done anyway so really, nothing’s been lost.”  The more we study death in social animals the more we are beginning to realize there may be a cost to prematurely removing ailing or dead animals from their groupmates.  Being able to interact with their dead may serve an important role for social animals, and denying them this opportunity may have serious implications in their ability to process that death.  So be thoughtful about how slim the chance of survival is.  It might be that the kindest, most responsible action is no action at all.

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Filed under Corvid health, Crow behavior, Crow curiosities, Crow life history, Crows and humans, Uncategorized

Australian magpies are not corvids

Ah the Australian magpie.  With its glossy tuxedo plumage, heavy bill, and charismatic reputation it’s no wonder it’s a favorite among corvid lovers.  Why then, do scientists keep insisting that it’s not, in fact, a corvid?  This insistence of ours can feel arbitrary, even perhaps insulting, to a bird that superficially looks and acts like the corvids we know.

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A still frame from the infamously cute video of an Aussie magpie and a puppy play-wrestling together.  

To address this question, corvid expert and my colleague, Jennifer Campbell-Smith, recently penned a terrific piece to lay the confusion to rest.  I recommend everyone take the time to read it in full.

If you do not have time, the short version of the story is that physiologically, Australian magpies, like the other butcherbirds they are classified with, lack the nasal bristles indicative of corvids.  Genetically, DNA work done in the late 80’s also showed that, while they share a common ancestor, are are phylogentically  distinct from other corvids.  There has been some back and forth since then on the details, but there’s no scientific evidence that we should be lumping them in with corvids.

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The nasal feathers are those thin, wire like feathers covering the base of the bill on the crow to the right, but conspicuously absent on the Aussie magpie to the left.  Australian magpie photo: Guy Poisson

Why this bums so many corvids lovers out is a curious mystery to me.  Personally, I find the convergent evolution with respect to both appearance and behavior much more interesting than if we simply made a taxonomic mistake.  As for whether corvid lovers should continue to find joy and fascination in observing these birds well, I’ll direct you to this video and let you be the judge.

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Filed under Being a scientist, Birding, Crow curiosities, Crow life history, Taxonomy