Tag Archives: crow behavior

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

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

Crows caught play wrestling

I’ve posted before about the generals of crow play behaviors, and it’s something I’m routinely delighted with as the kids of late summer start testing the limits of their world and their peers.  Adult play (or what I’m fairy confident are adults) is something I’ve encountered far less often, however.  Even more rare is a camera on hand to capture what’s usually a rather fleeting behavior.

You can imagine my excitement then, when yesterday not only was I present to witness either two adults or one adult and one subadult play wrestling in the grass but I also had a camera already rolling.  Granted the footage isn’t great (it’s an old camera and they were far away) but you can make out enough to see what’s happening.

Here’s a play by play of them moments leading up to and during the event.

  • I had been following a family group of three, presumably composed of two territorial adults and one subadult based on mouth lining color and general behavior (allopreening).
  • Two of them were foraging when they joined together and began to roll in the grass.
  • No audible calls were given, which I would expect if it had been a malicious attack.
  • You can see moments where one crow appears to have the upperhand and then willingly falls to its side to allow a shift in power and continue the play.
  • The roughhousing only stopped after the third bird flew overhead and gave a short loud ‘caw’.
  • After they disentangled they continued foraging near each other rather then taking chase, another indication that is was mutual and fun rather than antagonistic.

Pretty cool right?!

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Filed under Crow behavior, Field work, Just for fun, Uncategorized

The science of crows and death

Curious to read my popular science take on our recent publication on how crows behave around their dead?  Check out my latest article for Biosphere.  Then check out all the other awesome authors and contributors to my favorite popular science publication.  You won’t regret it.  (And congrats to GO for making the article cover!  She’s such a gorgeous bird…)

Read the full article here

Biosphere

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Filed under Crow behavior, Kaeli in the media, New Research, women in science

Baby crow detective work

By now, most of us have come across these images of  “baby crows” so often it induces more of a yawn than a fit of aggravation.
Image-1If, somehow, these images are new to you feel free to check out my post fully debunking them, as I will not dedicate any further time to them here.   But there’s a new photo circulating social media, and it makes for a much more compelling crow doppelganger;

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You’ve got three, black, altricial baby birds in a nest and really, they’re not terribly un-crow like.   It doesn’t make you a complete crow rookie to make this mistake, but there are some key things wrong here.  And this is the moment where, as a scientist, these photos elevate from being simply another source of annoying misinformation (which, they are) to the kind detective work that childhood doctor visits fostered a deep love for.  Because, not unlike my favorite activity in the Highlights magazines I anxiously parsed through in those waiting rooms, there are 4 things that are different between these two photos and it’s up to you to find them.  So take a minute and see what jumps out at you….

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Figured it out (or given up)?  The first thing to know is that all bird species are very specific in terms of both nest materials and nest construction.  Sure, some birds can happily use some ribbon in place of straw (like orioles) or build nests in old shoes just as easily as in gutters (like bewick’s wrens) but the basic style is always the same.  Robins will always use mud as a binder and bushtit nests will always look like cozy sleeping bags made of moss.  Knowing that, the material used in the nest on the right should jump out as a red flag.  Of course you’ll find crow nests with a bit of string, fabric or grass (especially for lining) but the bulk of the nest is always made of pinky-wide sticks.   Really, you need look no further at this point to know immediately that the photo on the right is an impostor but let’s keep going because it’s fun.

Next let’s look at the babies themselves, which is where the three remaining differences are.  Two of them are color-coded, did you catch them?  Ah yes, gape and eye color.  See that brightly colored area on the corner of the bird’s developing beak?  That’s called the gape, and the bright color that flashes when they open their mouths is a powerful signal that tells parents to “insert food here”.  Crows have bright pink gapes, whereas these other birds have yellow gapes.  Our other color coded giveaway is the eyes.  Granted the lighting is not great, but it’s clear that the crows on the left have light blue eyes whereas these other birds have dark eyes.  In some species of crow the babies are born with brown eyes that turn blue as they age, but such is not the case with our American crows and you can expect that nestlings will always have blue eyes.  The last clue, which takes more expert level knowledge to notice, is the bill shape.  The birds on the right have a slightly more embellished curve to the bill than a typical crow chick.

The final mystery, of course, is what the birds on the right actually are.  Unfortunately, I failed to track down the original poster, but as best I can tell they’re black drongo chicks.  Black drongos are members of the drongo family (Dicruridae) and are native to Southern and Eastern Asia.  Here’s another photo I found that looks consistent with the previous one.  If any drongo experts read this blog though and want to correct me, I’d love to hear from you!

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Filed under Birding, Crow life history

Help, I’ve found a baby crow!

You’re walking down the sidewalk when suddenly you notice a waddling little mass of black feathers trying awkwardly to hide under a bush or car.  When you begin to approach the young crow, it simply stares up at you or perhaps continues on its poorly planned waddle down the sidewalk or worse, into traffic. Clearly this baby crow cannot fly and has a habit of making bad decisions.  Your instinct (and perhaps the opportunity to interact with a baby animal) are tempting you to intervene and “save” this young crow who seems ill prepared to be out of the nest.  What should you do?

Does this baby scrub jay need to be taken to a rehab facility?

This baby scrub jay was found running around the grounds of an apartment complex.  Should it be taken to the rehab facility?

The answer, almost always, is to ignore your instincts and good intentions.  I’ve had many friends and colleagues who are either licensed wildlife rehabbers or who spent summers volunteering with their local rehab facilities, that can attest to the dozens of animals that get brought in during the spring and summer by well intentioned folks who assumed that simply finding such a vulnerable baby meant it needed help.  In many of these cases, these animals did not need help and now they’ve been separated from their parents or mother and stand a much lower chance of surviving once they’re released from the rehab facility.  So how do you avoid making the same error?

First, understand that corvid babies very often leave the nest before they are completely flighted (usually by about 7-10 days).   Evolution has taught them that it’s better to be flightless but still mobile on the ground than trapped in the nest where they stand no chance of escape, should they be located by a predator.  During this time they are still in the care of their parents who will continue to feed and defend them.  So finding a flightless baby crow or jay is totally normal between late May and July.  Perhaps it would be helpful to gently herd the fledgling away from traffic and under the safety of a bush but, outside of that, most baby corvids do not need your help and are better off (less stressed) if you give them a wide girth. The baby jay in the above picture was captured so it could be color-banded, and then was released under a bush where its parents quickly attended to it.

Simply knowing this piece of corvid biology will lay to rest the concerns for most situations you may find yourself in this summer.  For babies that are naked, are bleeding or have drooping wings, or are within reach of a dog or cat, etc., the following flow chart is excellent and will help navigate the situation (I’ve thrown in the mammal one too just for fun).

Help, I’ve found a baby bird
Help, I’ve found a baby mammal

The main thing to remember is; as long as the baby is mostly feathered and being attended by its parents, it’s just where it needs to be.  Only if it’s trapped in a storm drain, naked, injured, cornered by a cat, or after several hours has not been visited by its parents is it appropriate to intervene.  Even in most of those cases, simply creating a makeshift nest out of a basket and securing it to a tree, or placing the baby in a bush and leaving the area, is much better than taking it away to a facility.  So use your best judgment this summer and remember; if you feel your situation is unique and has not been addressed by the flow charts provided, give a rehab facility a call and let them help you decide if an animal needs to be removed before you make the mistake of taking babies away from their parents.

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A recently fledged juvenile waits for mom or dad to return with food.

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Filed under Crow behavior, Crow life history