Category Archives: Crow life history

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

5 reasons to leave baby crows alone 

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

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

2) It’s hard to tell when they’re stressed.  Recently, I saw a video on Facebook of a Steller’s jay fledgling in the care of a very well intentioned 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

Australian magpies are not corvids

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

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

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

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

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

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

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

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

Crow curiosities: Do crows collect shiny objects?

The notion that corvids, especially magpies, have a special affinity for shiny object has been around for more than a century.  In fact to refer to someone as a magpie is to describe them as someone who ‘compulsively collects or hoards small objects’.   This idea is so old hat that it can feel a bit frivolous to even wonder if it’s true.  The trouble with this bit of corvid whimsy, however, is that when we do investigate it, and scientists have, we find there’s no empirical evidence to support it.

'Crow Collects' by Cori Lee Marvin.

‘Crow Collects’ by Cori Lee Marvin.

For instance, one study1 presented both captive and free-living magpies piles of blue or shiny silver screws, rings, and pieces of tin foil near piles of food to which they had been previously habituated.  They found that, rather than thieving and subsequently caching the gleaming objects, the birds were actually more nervous to take food than they had been previously.  In the 64 conducted tests, only two instances of contact between a bird and an object were recorded.

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Experimental set-up for magpie study.

Cornell crow expert Kevin McGowen, elaborates on this general conclusion, suggesting that perhaps the origin of this folklore is pet crows who are attracted to the objects of obvious value to their owner like coins, keys or jewelry.  Speaking personally as someone who has spent countless hours observing hundreds of individual crows in the field, I can also attest to the fact I have never witnessed anything resembling this behavior.  So there you have it, corvids do not, according to the best empirical evidence, show an attraction to, or are otherwise known to collect shiny objects.

And yet…

And yet I still hear anecdotes about this behavior that peak my curiosity.  For instance, once or twice a year I’ll see a headline about crows thieving shiny stones at the expense of bereft family members.  In Jewish culture, it’s tradition to leave a small stone atop a gravestone, as a way to honor the deceased and indicate that they’ve been visited.  For whatever reason, particularly across Ireland, these stones occasionally go for joy rides in the mouths of crows.  In Omagh, Patsy Kerlin who mounts headstones in his town’s graveyard recently told a local reporter that “It seems to be only the black shiny ones they take and a lot of them go missing.”  Even in my own neck of the woods at the University of Washington one of the gardeners at the Urban Horticulture Center regaled John Marzluff and I with his story of how the crows regularly steal the shiny metal placards that identify the center’s plants.

In science, we often like to say “the plural of anecdote is not data”.  This is unequivocally true.  But just because they’re not data doesn’t mean they’re meaningless either.  I’m inclined to believe there’s more to these stories than random chance and I think they are worth exploring.  Perhaps these stories emerge out of confirmation bias, meaning people tend to report theft with respect to shiny things more often because they’re looking to confirm a suspicion they already had about crows.  If so, it would be yet another fascinating example of the extent to which corvids have infiltrated our culture.  Or perhaps this is the work of curious juveniles as has been suggested by my crow colleague Dr. Jennifer Cambell-Smith.  If so, teasing out any evidence of discrimination or bias juveniles are using when selecting objects to explore could give us insight into how they learn about the world, or how our garbage is modifying that behavior.  Or perhaps crows do like to carry off with glossy objects, but for textural, rather than visual reasons.  At least some corvid species swallow small stones to aid in digestion and these stones are most often partially smoothed2.  These ‘grit stones’, however, are considerably smaller (on average only 2.9 mm) than I imagine grave stones are, so perhaps this behavior is evidence of poor grit stone selection among naive birds.

Or maybe it’s none of the above, we simply cannot say.  Which, for me, is exactly why I find these anecdotes so interesting.  While we can rule out that this behavior isn’t a manifestation of corvids’ love for ‘bling’, we can’t exactly explain this behavior either.   It’s yet another item on the shelf along with thieving golf balls and wiper blades where we can’t do much more than offer an educated guess.  So while I’m quick to clarify that crows are not attracted to shiny objects, I’m not dismissive of these anecdotes either.  My friend and colleague David Craig likes to say that every bird has a story, and citizen science is part of sharing that story.  In my book, the story of corvids and their light fingered behavior seems an ideal project for the crow minded bird nerd.

  1.  Shepard, T. V, Lea, S. E. G., and Hempel de Ibarra, N.  2014.  Thieving magpie’?  No evidence for attraction to shiny objects.  Animal Cognition 18: 393-397.
  2. Gionfriddo, J.P., and Best, L. B. 1996.  Grit-use patterns in North American birds: The influence of diet, body size and gender.  The Wilson Bulletin 108: 685-696

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Filed under Corvid mythology, Crow behavior, crow conflicts, Crow curiosities, Crow life history, Crows and humans, In the news