Category Archives: Crow behavior

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

Why crows sunbathe

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

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

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

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

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

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

Literature cited

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

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

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

 

 

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Filed under Crow behavior, Crow curiosities, Crow disease

5 reasons to leave baby crows alone 

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

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

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

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

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

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Killing them with kindness is a real risk.

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

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

Everything you want to know about crow nests

Spring marks one of my favorite times of year.  Cherry blossoms abound, the rain smell sweet and the birds get busy putting their carpentry skills to good use. Starting early March, the silhouettes of crows with bill loads of timber or wads of soft material dot the skies as they shuttle back and forth to their nest tree. Like a townhouse development, these construction projects are over in the blink of an eye and soon, their bill loads of twigs will be replaced by food for their mate and, eventually, their insatiable young. Spotting these nests is both a great way to observe and engage with your local crow family and avoid unpleasant conflicts with protective crow parents.  With a little knowledge and a bit of practice, tracking down your resident crow nest will become one of your favorite spring traditions in no time.

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Nest construction and site selection

Nest construction begins in early March and will continue (as nests fail) through about June. It takes 1-2 weeks to finish a nest after which the female will lay a clutch of 2-6 eggs. Unlike similarly sized squirrel nests (aka: dreys) which are made of leaves, crow nests are made mostly of pencil-width twigs. A new nest is usually about 1.5 ft across and 8-10 in deep.  After the bulk of construction is complete, they’ll line the cup of the nest with soft materials like grass, tree bark, moss, flowers, paper or fur. Once we saw a crow ripping out the hair of an outdoor manakin, no doubt to use as lining material.

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A crow gathers moss off the branches of a big leaf maple to use as lining material.  


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This bird toyed with this branch for a few minutes before rejecting it and letting it fall to the ground.  


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A sidewalk littered with twigs is good evidence that the nearby deciduous tree is a favorite among the local crows to pull branches from.  I’ve only once seen a crow try and retrieve a branch it dropped, so these are all rejects.  

 

Crows will nest in an astounding array of places, from the eaves of skyscrapers to the crooks of well concealed tree limbs. They can tower in the sky or be almost within reach. Most commonly, I see them built close to the trunk in the top third of Doug fir trees, but this is, of course, specific to the PNW.  Both partners participate in nest construction. Helpers will aid to some degree but most of the work is left to the parents.

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Differences among corvids

Crow, jay and raven nests are similar in shape and material but differ in overall size in accordance with the size of the bird. The main standout are magpies,  which build incredible domed-shaped nests the size of a large beach ball.  The nests require so much material, they can take as much as 40 days to build.  Japanese jungle crows are another species of note, as they have a (relatively) new and problematic habit of building nests out of wire hangers and causing massive blackouts.

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A Jungle crow nest in urban Japan. Photo: Götz


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The magpie’s nest is the big clump in the middle of the tree.

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The life of a typical nest is only about 9 weeks (1-2 weeks of building, 6 days of laying, 20 days of incubating and 4 weeks of nestlings) though they are hardy structures and can remain intact in a tree for years.  After the young fledge, the crows will not return to the nest.  Crows will only use a nest once, and generally only fledge one brood a year. They will, however, build on top of an old nest particularly in areas where nest trees are especially sparse like downtown Seattle. This also appears to be more common in the Midwest.

Avoiding conflicts

Most breeding related dive bombs occur as the result of a person being too close to a fledgling, but some crows get feisty around their nest too. Crows in areas where they are less persecuted (like cities) tend to be more aggressive than their rural counterparts. If you know where a nest is and can avoid it, do so and save everyone the aggravation. Otherwise carry an umbrella or paint eyes on the back of a hat. Crows rarely attack from the front so having eyes on the back of your head can be an effective deterrent!

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Putting all this together to actually find nests, is one of the most rewarding moments an urban naturalist or crow enthusiast can have.  Be warned though: crows are wary of potential predators (including people) spying on them and they have a few tricks for throwing you off, so don’t be surprised if a nest location you were certain of turns out to have been a ruse!

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Can you spot the nest? 

Have more questions? Let me know in the comments!

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Filed under Birding, Breeding, Crow behavior, Crow life history, Crows and humans

Why the crow smiles

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

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

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

Literature cited

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

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

I spy with my raven eye…

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

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

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

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

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

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

Literature cited:

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

 

 

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Filed under Crow behavior, crow intelligence, New Research, Raven behavior, Raven intelligence

Crow curiosities: What do crows eat?

Spoiler alert: They’re not, as so many people believe, true scavengers.  Meaning, they’re not mostly eating carrion.  I know what you’re thinking: MIND BLOWN.  Also you might be thinking PBS lied to you, and you’d technically be correct.  So why is this myth so pervasive that even PBS fell victim to its ubiquity?

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An American crow picks at the torn up belly of a rat in a Bellevue neighborhood.  After a few minutes, it had its fill and moved on to other feeding opportunities, leaving most of the rat untouched.  

Well, a huge part of the problem is that like so many words in science, their use in general discourse has parted from their scientific meaning.  Typically we use this word to describe say, grad students at the end of the party stuffing their pockets with the leftovers but, biologically speaking, scavengers are organisms who are specialized to consume, or obtain most of their food, from the decaying tissue of animals or herbaceous matter.  Now don’t get me wrong, the title of ‘scavenger’ can get a bit blurry as Bernd Heinrich argues in his book, Life Everlasting.  Ravens for instance, switch primarily to scavenging during lean winter months.  For most American crows, however, the identity of ‘scavenger’ simply will not do.

Which is really too bad, since the title of scavenger is bestowed with honor given how they make our living on planet earth possible.  I’m not being hyperbolic when I say thanking the undertakers of our ecosystem should be part of everyone’s pre-meal ritual, but perhaps that argument should be saved for another post.

As for crows, carrion makes up only a very small part of their diet.  In Seattle, roadkill accounts for <5% of crow food, and in wildland areas carrion accounts for even less1.  Crow beaks aren’t even strong enough to break through the skin of a grey squirrel, though they will usually give it a try.

So what are they eating?  Mostly human refuse (no surprise) and invertebrates.  In fact human garbage (meat, grain products and veggies) account for about 65% of their diet in urban areas, whereas in wildland areas it’s roughly split between garbage and inverts (35% and 35% respectively)1.

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Crows spend much of their time patrolling lawns looking for invertebrates

 

These data correct another common misconception about crows: they’re not mostly eating the eggs and nestlings of other birds.  In fact, crows only account for 1 of 20 observed nest predators in WA and have been found to have a nonsignificant, negative relationship between abundance and rate of predation in experiments using artificial ground nests, shrub nests, and canopy nests1.

So there you have it, American crows are neither true scavengers nor meaningful nest predators. They’re primarily omnivores with an emphasis on human refuse and invertebrates.  So the next time you see one patrolling your grassy lawn remember; they’re busy trying to bring home the bacon.  Er, bugs.  Well, probably bugs, but preferably bacon provided you were crazy enough to throw some out.

Literature cited

  1.  Marzluff, J.M., McGowen, K.J., Roarke, D. and Knight, R.L.  2001.  Causes and consequences of expanding American crow populations.  in Avian ecology and conservation in an urbanizing world (J.M. Marzluff, R. Bowmanm and R Donelly, eds).  Kluwer academic Press, norwell, Ma.

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Filed under Crow behavior, Crow curiosities, crow diet, Crow life history