Category Archives: Ravens

November 12, 2022 · 7:40 am

How corvids mimic human speech

If you’ve spent much time watching corvids in person or online, chances are you’ve come across one doing a Fred Armisen-level impression of something else. Perhaps it was the Steller’s jay in your backyard tricking you into thinking there was a red-tailed hawk soaring overhead, or maybe you remember the trash talking American crow that invited itself to an Oregon elementary school and delighted children with some crass language. That corvids, like some parrots, starlings, bowerbirds, etc., can mimic is well understood, but have you ever wondered why? Why can a bird talk like a person but a chimpanzee, an animal who shares 98% of our DNA, cannot? The answer boils down to three things: vocal anatomy, the brain, and behavior.

In humans, as with virtually all other terrestrial vertebrates, sound is produced in the larynx aka the voice box. As air passes through the larynx it vibrates the vocal cords, producing sounds. Across different species this system is enhanced or reduced, resulting in the roar of a lion, the grunt of an alligator or that conversation you wish you could have avoided with your coworker. While birds also have a larynx, it doesn’t produce sound. Instead, birds (well, most birds) have a wholly unique structure called the syrinx which sits not at the top of the trachea as the larynx does, but at the bottom, right at the bronchial split. This unique forking anatomy allows some birds to lateralize their sounds, meaning making different sounds on the left or right side, sometimes even at the same time! The repertoire of parrots is further enhanced by their fleshy (for a bird) tongue, which can manipulate air flow and produce more human-like speech.¹ It’s this level of vocal complexity and control that possess birds with the incredible vocal range we hear, whether they use it for mimicry or not. In fact, despite this potential, most songbirds do not mimic, and actually cannot learn new songs after their first year of life.

But while the syrinx explains why some birds can produce human speech sounds, it doesn’t explain why our closest primate relatives cannot, especially given the similarities of their voice box with our own. That’s where the brain comes in. While non-human primates have the correct hardware in their vocal tracts², they’re missing the technology they need in their brains.³ Specially, in the cortical association areas in the neocortex (the part of the brain that’s responsible for our higher-order behaviors). They simply don’t have the neurological control required to mimic human speech (though they do mimic us in other ways). So why do birds?

Unlike in primates, vocal mimicry is a cornerstone of communication and signaling in certain birds. Whether they’re using it to advertise their quality as a potential mate, territory defense, or as a way to bond with partners or group mates, mimicry plays a key role in engaging with those around them. Though the specifics of that engagement may not always be clear. For example, despite persistent online assertions that Steller’s jays mimic hawks either to warn of their presence or to scare competitors, there’s zero evidence in support of either of these. In fact, a study from 2017 found that wild jays almost never do it when predators or competitors are around, and instead do it most often at the beginning of the breeding season in front of their mate.⁴ Which is probably for the best. After all, if corvids chose to really make a habitat of using mimicry to trick other animals we’d likely find ourselves at the top of their target list.

Literature cited
1. Beckers G, Nelson B, and Suthers R. 2004. Vocal-tract filtering by lingual articulation in a parrot. Current Biology 14: P1592-1597
2. W. Tecumseh Fitch, de Boar B. Mathus N, Ghazanfar A. 2017. Monkey vocal tracts are speech ready. Science Advances 2: DOI: 10.1126/sciadv.1600723
3. Dunn J and Smaers J. 2018. Neural Correlates of Vocal Repertoire in Primates. Frontiers: https://doi.org/10.3389/fnins.2018.00
4. Tippin T. 2017. Propensity of predator mimicry in wild Steller’s jays. Humboldt State University, MS thesis

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Filed under Birding, Crow curiosities, Jay behavior, Ravens, Vocalizations

October 2, 2020 · 12:01 am

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.

Two crows with slight variations in bill overhang.

•••

* 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

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

Tagged as bill morphology, bill tip, Crow, parasites, raven

April 16, 2020 · 6:45 pm

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.

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.

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

With 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.

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.

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.

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.

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.

Common raven call (Recording by Davyd Betchkal-Denali National Preserve, Alaska)

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).

Common raven range map

American crow range

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.

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.

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.

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!

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

Tagged as #CrowOrNo, Crow, crow calls, Crow vs raven, guide, raven, raven calls, Vocalizations

December 31, 2018 · 9:18 pm

2018 research round up

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

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

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

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

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

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

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

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

Image from von Bayern et al. 2018

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

leslie

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

Tagged as Aga, crow calls, Mariana crow, migration, raven calls, tool use, wolves

December 21, 2018 · 4:19 pm

A matter of a pinion

Like all subcultures, the world of corvidphilia comes with its own set of corny jokes and puns. Of these, perhaps none is more well known than the classic: “What do you call two crows?”

“An attempted murder.”

drum

Despite their groan-inducing nature, I consider myself a connoisseur of such jokes. After all, it’s rather flattering that crows are such a cultural fixture that they get their own jokes and cartoons.

Velcrows

There’s one joke though, that I have no choice but to spoil in the name of scientific accuracy. After all, what kind of scientist would I be if I left semi-obscure memes about crows go unchecked?

Pinion

There are many version of the “matter of a pinion” joke but this one is the most cringe-inducing for me because it has the audacity to present itself as scientific fact. The truth is, not only do corvids have far fewer than sixteen primaries, but the entire premise of the joke is simply wrong.

All birds have at least nine primary feathers, but most birds, particularly within the passerines, have ten on each wing. Even outside of passerines, most birds have only ten, though there are exceptions. Flamingos, for example, have twelve, and ostriches have sixteen. Crows and ravens, on the other hand, are in no way exceptional, either from the norm or each other.

American crow wing. Photo c/o the Slater Museum of Natural History.

Common raven wing. Photo c/o the Slater Museum of Natural History.

So, no, the difference between crows and ravens is not, in fact, a matter of a pinion. There’s one thing I do want to point out, though, particularly for you #CrowOrNo players. While it’s true that crows and ravens have the same number of primaries, they do look different enough that in flight you can often identify a bird as either a crow or a raven based on its primaries. Of the ten primaries, there is a handful that is longer and more distinct than the others, making them look kind of like “fingers”. Looking at the wing pictures above, you can see that the crow has five evident finger feathers (feathers 5-9) whereas ravens only have four (feathers 6-9). This difference is a bit easier to detect on birds in flight than on these static wing specimens.

Common raven in flight showing the typical four “finger” feathers.

American crow in flight with five evident “finger” feathers.

So with this in mind, it’s possible that with a little handwaving you can actually get away with saying the difference between a crow and a raven is a matter of a pinion, but by now there’s not much of the joke left since you have to leave off the initial context. A much more scientifically sound version, however, would be to compare crows and song sparrows, which only have nine primaries. “What’s the difference between a crow and a song sparrow?”

“It’s just a matter of a pinion!” And then, as with any good joke, you would explain to your audience the scientific merit of the punchline by describing the technicalities of wing feathers.

Funny right?

Funny

So what’s your favorite corvid joke? Let me know in the comments!

***

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Filed under Birding, Just for fun, Ravens

Tagged as Crow, jokes, pinion, raven

December 21, 2017 · 1:29 am

It’s a wonderful raven’s life

Every year, Jimmy graces our screens as countless people watch him help tell the story of the Christmas classic, It’s a Wonderful Life. I’m talking of course about Jimmy the Raven, though I suppose one could make the same case for Jimmy Stewart. Between the two, however, even Stewart recognized that it was the raven who was the superior colleague, and acquiesced to being referred to as “JS” to stop Jimmy from flying on set every time the director said Stewert’s name.¹

“The raven is the smartest actor on set. They don’t have to make as many retakes for him as for the rest of us.” – Jimmy Stewart, while filming You Can’t Take it With You in 1938²

Among corvid lover’s, Jimmy’s role in It’s a Wonderful Life is surely a memorable delight, but few probably know the full extent of his career and accomplishments.

Jimmy_the_raven_in_It's_a_Wonderful_Life.png

Jimmy in a screenshot of It’s a Wonderful Life.

Jimmy’s first role was in Frank Capra’s 1938 movie, You Can’t Take It With You, after which Capra cast Jimmy in every one of his subsequent films. As a result, Jimmy is sometimes mistaken as Capra’s pet, though he really belonged to animal trainer Curley Twiford. In fact it was Jimmy riding on Twiford’s bulldog, Squeezit, along with two parakeets that initially caught a director’s attention and launched Twiford’s career as one of Hollywood’s earliest animal trainers.³

To make him more marketable, Twiford trained Jimmy to do a wide variety of things including opening mail, operating a typewriter, lighting a cigarette, flipping magazine pages, and dealing a hand of poker. In the course of Twiford’s career he trained hundred of animals, but it was Jimmy and his subsequent corvids that he marveled at the most. In a remark that will probably surprise no one, Twiford once said that of all the animals he trained, cats were the most challenging and corvids were the easiest, remembering their stunts for ten years.³

To achieve such tricks, Twiford taught Jimmy a sizable vocabulary of 53 words. Since so much of Jimmy’s act (and therefore Twiford’s income) depended on Jimmy’s memory of these words, Twiford had Jimmy insured with a first of its kind “loss of memory” policy.⁴ Lloyds of London, which remains in operation today, wrote the policy–no doubt with ample side-eye from their competitors. No word, though, on if they currently have any avian clients.

Twiford claimed that between 1938 and 1950, Jimmy had appeared in over 1,000 credited and uncredited films.³ IMBD, the contemporary scorekeeper of such things, lists 22 credited appearances, including The Enchanted Valley, God’s Country, and The Secret Garden. He even had an extended roll in The Wizard of OZ, though the scene was later cut.

A deleted scene from The Wizard of Oz

At the height of his career, Jimmy might well have been a household name, even having newspaper articles dedicated to his biography and upcoming films. One such article in 1948 boasted that Jimmy possessed a, “Red Cross gold medal for his 200 hours spent entertaining Wold War Two veterans,” though the article did not specify if it meant the American Red Cross, or some other entity.⁵ Still, neither Rin Tin Tin nor Lassie (both of whom Jimmy worked with^6,7) can claim such an honor, even if its true nature is rather murky .

The Evening News. Harrisburg, Pennsylvania. December 31, 1948. p. 12 (and, no, ravens don’t live until they’re 140 even in captivity.)

Jimmy’s last film was Three Ring Circus, filmed in 1954, nearly 20 years after his first movie. Sadly, his subsequent whereabouts and death are unknown, though I found one article from 1957 that talks about a raven named Jimmy.⁷ For iconic animal actors however, their successors are often named after them and, indeed, an article published in 1958 mentions a raven by the name of Jimmy Jr., so it’s possible that other articles published during that time were really talking about different birds.⁸ Curley Twinford died himself only two years after Three Ring Circus in 1956.

Searching through newspaper databases, it’s incredible to see the amount of attention Jimmy received throughout his career. Like other Hollywood stars, his activities, on-set demands, and pay rate were all the subjects of much ado. He charmed audiences and his costars alike, no doubt leaving impressions of intelligence that would not be widely accepted until much later. It would be nearly another twenty years after his death before corvids such as Jimmy would be federally protected under the Migratory Bird Treaty Act. I can’t say what role, if any, Jimmy played in shaping the public’s perception of these birds, but it’s hard to imagine that such a star left without leaving a mark.

References:

The Cincinnati Enquirer June 7, 1946: pg 17.
Driscoll, C. New York Day by Day. The Choshocton Tribune. Choshocton, Ohio. June 29, 1983: pg 8.
Kohrs, K. and Ross, S. Movie Animal Man. The Salt Lake Tribune. March 26, 1956: pg 109.
Clary, P. Hollywood Film Shop. The Daily Republican. Monongahela, Pennsylvania. November 18, 1948: page 6.
Jim, the Raven, in new flicker. The Evening News. Harrisburg, Pennsylvania. December 31, 1948: p. 12.
Parsons, L.O. Those Film Fauna are Ticklish Detail. Tampa Bay Times, St. Petersburg, Florida. March 17, 1946: pg 79.
Burton, R. Film Shop. Odessa American. Odessa, Texas. April 30, 1957: pg 8.
Performing Raven. The Tribune. Coshocton, Ohio. August 23, 1958: pg 4.

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Filed under Corvid trivia, Just for fun, Ravens

Tagged as famous bird, famous crow, famous raven, It's a wonderful life, jimmy the raven, raven, the wizard of oz