Category Archives: Crow curiosities

Bill overhang in corvids

I hardly notice it when I’m in the field because the bird is either too far or too fussy for me to examine the finer details of its beak, but looking at pictures like this I can’t help but notice that little extra bit of bill that sweeps over this raven’s bottom mandible like an awning. It leaves me wondering, what is this overhang for? A why is it more noticeable on some individuals than others?

When we think of birds with curved upper mandibles we are most primed to think of raptors, which have the most conspicuously curved overbite of any group of birds. This shape give them the tearing power they need to breakdown and consume their prey. But upon closer inspection we can see that actually most birds, even some hummingbirds, have a slight* overbite known as maxillary overhang. Among corvids, common ravens have one of the most noticeable overhangs, though they can be quite visible in crows as well. Unlike raptors though, for most other birds this overbite has less to do with food consumption and more to do with hygiene.1

While they can be good at hiding it under those sleek feathers, wild birds are constantly contending with a suite of exterior parasites like gnats, feather lice, and mites. The presence of these parasites, and the speed at which they can cause real harm if left unchecked, is part of the reason birds dedicate so much time and energy into preening. To remove and kill these pinhead sized parasites, birds carefully comb through their feathers, individually plucking up offenders with their bill tip. Even a small (1-2mm) overhang has been show to provide a significant advantage to birds by providing a backdrop against which the lower mandible can pin and damage parasites. Without such an overhang, parasite loads can be as much as 4x higher. By contrast, the overhang doesn’t seem to play any measurable role in foraging success or efficiency.1

Given the largely carrion based diet of common ravens, it’s possible their more visible overhang provides some advantage when it comes to digging into a carcass. Since it hasn’t been tested, however, I can only guess that if some feeding advantage does exist here, it’s slight. This is supported by looking at other carrion specialized corvids, which don’t seem to show a particular bias in longer overhangs relative to their omnivorous or seed eating corvid cousins, and the fact that even within common ravens overhang length is variable.

This common raven doesn’t have a particularly big overhang

To an extent, the longer the overhang the more effective it can be. As anyone who has tried to maintain naturally long nails can attest though, long keratin based appendages are prone to damage and breakage. Bill tips are no different, which explains why there can be so much variation between and within species. The overhang is playing an evolutionary balancing act to arrive at the length that is the most effective and the least vulnerable to damage. That means that not only will some species have shorter or longer overhangs, but individuals within species may, at any point, exhibit more or less obvious tips as due to recent damage. As a result of this variability, I don’t recommend looking to the level of bill overhang as a diagnostic tool for identifying ravens. While it’s certainly useful for crushing bugs, you can’t bank on it being useful for winning that next round of #CrowOrNo.

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* Some corvids have more than simply a slight overbite. Unusually long or misshapen bill tips can be the result of a viral infection called avian keratin disorder. Check here to learn more about AKD in crows.

Literature cited

  1. Clayton DH, Moyer BR, Bush SE, Jones TG, Gardiner DW, Rhodes BB, and Goller F. 2005. Adaptive significance of avain beak morphology for ectoparasite control. Proc. R. Soc. B 272: 811-817

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Filed under Corvid health, Crow curiosities, Diversity, Ravens

The definitive guide for distinguishing American crows & common ravens

For two birds that are surprisingly far apart on the family tree, American crows (Corvus brachyrhynchos) and common ravens (Corvus corax) can be awfully hard to distinguish, especially if you rarely see both together.  But with the right tools and a little practice you can most certainly develop the skill.  Fortunately, there are many different types of clues you can use to tell one from the other, so feel free to use the links to skip around to what interests you.

Physical Differences

Although crows and ravens are superficially quite similar, there are variety of features that can be used to tell one from the other. Overall size can be a good place to start.  This especially helpful if you live in an area where they overlap, but even if you don’t, I find that people who are used to seeing crows take notice when they see a raven in person because it feels ~aggressively~ large.  That’s because ravens, by mass, are about twice the size of an American crow.

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A common raven specimen (top) with an American crow specimen (bottom). On average, ravens are about twice as big as crows, but individually there are certainly large crows and diminutive ravens.

This size difference becomes most obvious is when you look at their face.  Raven’s are much more adapted for consuming carrion than crows are (crows cannot break through the skin of a squirrel) and their bills give the distinct impression that they could, in fact, pluck your eyes from your face with little effort. So if your sense of things is that you’re looking at a bill with a bird attached, then you’re probably looking at a raven, not a crow.

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With practice, judging the proportion of crows’ and ravens’ features, like bill size, becomes easier.

Crow vs. raven measuremntsWith practice, judging relative size becomes easier and more reliable, but for a beginner it may not be useful because it’s so subjective.  Instead, it’s easier to look at the field marks (birder speak for distinctive features) which provide more objective clues.

When looking at perched birds, the most helpful attribute is to look at the throat.  Ravens have elongated throat feathers called hackles, which they can articulate for a variety of behavioral displays.  Crows meanwhile have smooth, almost hair like throat feathers typical of other songbirds.

Crow v raven

Even when the feathers are relaxed, the textural differences between the two species throat feathers are apparent. Note that in this photo, the crown feathers of the crow are erect, while the raven’s is not.  The difference in crown shape should not therefor be judged in this comparison.

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When vocalizing or displaying the raven’s hackles become especially obvious.

In addition to the hackles, ravens can also articulate some of their other facial feathers in way crows cannot.  During threat displays for example, ravens will fluff out both the throat hackles and their “ear” tufts.

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For birds in flight, however, it’s often difficult—if not impossible—to clearly see the throat feathers.  Fortunately, the tail offers a reliable field mark in this case.  Whereas crows have a more squared or rounded tail (depending on how much they’ve fanned the feathers) a raven’s tail will have a distinct wedge shape. Additionally, although they are a bit more subtle, there are also some differences in the primary wing feathers.  While both birds have 10 primary feathers, in flight, ravens will look like they have four main “finger” feathers while crows will appear to have five. Ravens also have more slender, pointed primaries relative to crows.

crow vs raven

Vocal differences

With a little practice American crows and common ravens can easily be distinguished by their calls.  The call of a raven can be best described as a deep, hollow croak.  Crows on the other hand, caw.  Of course, they can both make at dozens of other sounds including rattles, knocks, coos, clicks, and imitations. With practice even these can be recognized by species, but that level of detail is not necessary for most identification purposes.

Juvenile common raven yell (Recording by Antonio Xeira-Chippewa County, Michigan)
Common raven water sound (Recording by Niels Krabbe-Galley Bay, British Columbia)
American crow call (Recording by David Vander Pluym-King County, Wasington)
American crow juvenile begging call (Recording by Jonathon Jongsma Minneapolis, Minnesota)
American crow rattle (Recording by Thomas Magarian-Portland, Oregon)
American crow wow call (Recording by Loma Pendergraft King County, Washington)
American crow scolding (Recording by Kaeli Swift-King County Washington)

Geographic/habitat differences

While both American crows and common ravens have wide distributions across North America, there are some key differences in where you are likely to find them.  The most notable difference is that ravens are absent throughout most of the midwest and the southeast.  Crows on the other hand, occupy most American states with the exception of the southwestern part of the country.  The below maps from Cornell’s All About Birds website offer more specific breakdowns (hover over the images to see the caption). Note that the reason the American crow’s west coast range appears to dry up from the Puget Sound north is not due to a lack of crows, but rather because the crow species that occupies the upper half of the North American west coast is not the American crow, but the northwestern crow (Corvus caurinus).  The continued distinction between these two “species” is likely coming to a close, however.  For more on our current understanding of the differences (or lack thereof) between those two species check here.

With respect to habitat, both birds are considered generalists, with ravens erring more towards what one might describe as an “extreme generalist”. Ravens can be found along the coast, grasslands, mountains (even high altitude mountains), forests, deserts, Arctic ice floes, and human settlements including agricultural areas, small rural towns, urban cities (particularly in California) and near campgrounds, roads, highways and transfer stations. Crows meanwhile are more firm in their requirement of a combo of open feeding areas, scattered trees, and forest edges.  They generally avoid continuous forest, preferring to remain close to human settlements including rural and agricultural areas, cities, suburbs, transfer stations, and golf courses.  In cases where roads or rivers provide access, however, they can be found at high elevation campgrounds.

Behavioral differences

There are books that could be (and have been) written on this subject alone, so we will limit ourselves to what is likely to be most essential for identification purposes.

Migration
While common ravens are residents wherever they are found, American crows are what’s called a “partially migratory species” because some populations migrate while others do not.  Most notably, the northern populations of crows that occupy central Canada during the summer breeding season, travel south to the interior United States once the snow-pack precludes typical feeding behaviors

Breeding
Although trios of ravens are not uncommon, and there have been observations of young from previous years remaining at the nest, ravens are not considered cooperative breeders. Crows are considered cooperative breeders across their entire range (though specific rates vary across populations and not much is known about migratory populations).  If helpers are present they typically have between 1-3. So if a nest is very busy with more than two birds contributing to nest construction, feeding nestlings, or nest defense, it’s more than likely a crow’s nest, not a raven’s.

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Common raven eggs left | American crow eggs right

Diet
Although both species consume a host of invertebrates, crows consume a larger proportion of inverts and garbage relative to ravens.  Mammals, especially from carrion, meanwhile make up the largest proportion of a raven’s diet across surveyed populations.  Access to refuse and population location, however, can dramatically shift the dietary preferences of both these omnivores.

Flight
Because ravens consume a lot more carrion, which is unpredictable in its availability and location, they spend a great deal more soaring than crows do.  So if you see a black bird cruising the sky for more than a few seconds, it’s most likely a raven.  Ravens are also unique from crows in that they barrel roll to advertise their territory.  So if you see a  barrel rolling bird, there’s a better chance it’s a raven.

Interactions
In places where they do overlap, interactions between the two are often antagonistic, with crows acting as the primary aggressors in conflicts.  Ravens will depredate crow nests if given the chance.

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A raven defends itself from a crow by rolling upside down.  Someday I’ll get a better photograph…

Genetic differences

Throughout most of our history, we have used external cues like appearance, voice and behavior, to sort one kind of animal from another.  Now that we have access to a plethora of genetic tools, however, we can ask a new level of the question “what’s the difference between an American crow and a common raven.”

To put it simply, American crows (Corvus brachyrhynchos) and common ravens (Corvus corax) are different species in the same genus, just like lions (Panthera leo) and tigers (Panthera tigris).  Species and genus refer to different levels of the taxonomic tree, where species represents the smallest whole unit we classify organisms.  The issue of species can get complicated quickly, however, so I’ll direct you here if you want to learn what a mess it really is.  Most important thing to appreciate now, is that if you want a quick, back of the envelope way to evaluate if two animals are closely related, look at the first part of their latin binomial (scientific) name.  If they share that part then they’re in the same genus (ex: crows and ravens belong to the genus Corvus).  If they don’t (ex: American crow is Corvus brachyrhynchos and the Steller’s jay is Cyanocitta stelleri) then they are more distantly related. 

Within the Corvus genus, however, there is still a ton of evolutionary space available.  In fact, to find the closest shared relative of common ravens and American crows you’d need to go back approximately 7 millions years.  Although they are more visually distinct and don’t overlap geographically, American crows are more closely related to the collard crows of China, or the carrion crows of Europe, than they are to common ravens.

Crow phylogeny

Image from Jønsson et al. 2012

Laws and protections

US laws
In the United States, both American crows and common ravens are protected under the Migratory Bird Treaty Act.  This means that, like with nearly all native birds species, you cannot kill, possess, sell, purchase, barter, transport, or export these birds, or their parts, eggs, and nests, except under the terms of a valid Federal permit. It is this law that prohibits the average person from keeping these birds as pets, and requires that rescued crows be turned over to a licensed professional.  The MBTA also prohibits the civilian hunting of ravens under any circumstance.  Under 50 CFR 20.133, however states are granted an exception for crows, wherein with some restrictions, states can designate regulated hunting seasons.

In addition, under 50 CFR 21.43 of the Migratory Bird Treaty Act, you can also kill crows without a license and outside of the regulated hunting season if they are in the act of depredating crops, endangered species, or causing a variety of other destructive issues.  You can obtain the specifics of the Depredation Order here.  Such lethal control must be reported to Fish and Wildlife to remain within the law. No such depredation exceptions exist for ravens. 

Canadian laws
In contrast to the US, no corvids receive federal protections in Canada.  Crows and ravens may receive provincial protections, however.

Concluding thoughts

Before we pack it up, I want to leave you with one last useful piece of information.  This whole article was dedicated to the question of how American crows are different from common ravens.  Hopefully, you’re walking a way with a solid understanding that these animals are in fact different morphologically, behaviorally, and genetically. Asking if American crows are different from common ravens is a different question, though, than asking if “crows” are different than “ravens”.  Because while that first answer is a hard, “yes,” there is no one thing that initially classifies a bird as either a type of raven or a type of crow.  Generally ravens are bigger and have those elongated throat feathers, but there are plenty of crow named birds that could have been named raven and vice versa. So proceed cautiously and consider the specific types of birds the question’s author is referring to before offering specific answers.

If you want to continue to hone your skills I invite you to play #CrowOrNo with me every week on twitter, Instragram and facebook, all at the @corvidresearch handle.  While it’s not to quite this level of detail, I promise it will help advance your ID skills and introduce to to more of the world’s fantastic corvids. For a head start, keep this charming and informative guide illustrated by Rosemary Mosco of Bird and Moon comics handy!

raven vs crow

 

Reference literature
Jønsson K.A., Fabre P.H., and Irestedt, M. (2012).  Brains, tools innovations and biogeography in crows and ravens.  BCM Evolutionary Biology 12
https://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-12-72

Freeman B.G. and Miller, E.T. (2018).  Why do crows attack ravens? The roles of predation threat, resource competition, and social behavior.  The Auk 135: 857-867

Verbeek, N. A. and C. Caffrey (2020). American Crow (Corvus brachyrhynchos), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.

Boarman, W. I. and B. Heinrich (2020). Common Raven (Corvus corax), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.

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Filed under Birding, Corvid diversity, Crow behavior, Crow curiosities, Raven behavior, Ravens, Taxonomy, Vocalizations, Wildlife

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