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.

21 Comments

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

21 responses to “Crow curiosities: What do crows eat?

  1. I suppose one of the reasons for crows being thought of as scavengers here in the UK is because the most common species Corvus corone is called the Carrion Crow. I think they are doing a great job if they are getting rid of our refuse. They are not popular with farmers though-one told me recently that crows will peck out the eyes of new born lambs – has this ever been proven?

    • Hi Suzanne, that name does seem like a bit of a trick doesn’t it? Indeed, even Carrion crows are consuming more inverts than actual carrion, though carrion is a more important part of our diet than my local American crows (I can direct you to that paper if you like). Agreed-any amount of undertaking is certainly worth our praise though! I’m afraid the lamb bit is true (actual kills are mostly perpetuated by ravens but some crows as well). The eyes are the softest, most accessible part of most animals so it’s no surprise the birds go for them first. That being said, it doesn’t happen that often.

  2. Interesting thoughts, really nice post. By coincidence I have a half-written post that I plan to complete in the near future which sings the praises of decomposers and scavengers, with a particular focus on urban situations. Crows are one of the examples I use of scavengers because of the amount of human waste food they consume! So why are they not scavengers in that context? Is human waste not “decaying tissue of animals or herbaceous matter”? I appreciate that you’re considering what we might call the “natural” diet of these birds, but even so, the distinction doesn’t seem to me to be so clear cut.

    • Hi Jeff, yes when wildlife biologist talk about scavenging we’re talking about carrion (or plant matter) specifically . I’m afraid leftover Tacobell doesn’t make the cut, especially because so much of the human waste they consume are grain products. But maybe there’s room for a new term, urban scavenger, that would be inclusive of these kinds of critters.

      • It seems to me this is a false distinction from the perspective of the animals, though. Many animals move between the urban, the suburban, the rural and wilderness: it’s all part of the larger landscape in which they find what they need to survive and reproduce. Yes, some aspects of their behaviour may be different in urban areas; but then that’s true of animals that are confined to wilderness – their behaviour may change depending on whether they are foraging inland or at the seashore, for instance.

      • You mean the distinction of ‘urban scavenger’? I agree that the labels we apply to foraging strategies are not as clear cut as we would like them to be. Many animals we think of as ‘herbivores’ will actively kill and eat other animals if they’re in the right place at the right time to do so, for instance. And most ‘predators’ will just as easily steal or eat carrion as they will fresh prey. But calling both crows and turkey vultures scavengers is not an accurate portrayal of their natural histories. Nearly every part of a TUVUs biology is specialized for finding carrion (they’re one of the few birds with a developed sense of smell for example). American crows on the other hand are junk food junkies-that is their “natural” diet. They’re eating Doritos, hot dogs, bread, rotting pumpkins, peanuts, plums, killing and eating small animals, insects, wheat grain, cattle feces, beef jerky, road kill, kettle corn, etc. Although I have no issue with saying crows scavenge, the most accurate description of their diet is omnivore. They’re omnivores that lean on different parts of their diet in different locations. In Mt. Rainier National park they’re eating mostly insects and whatever they can steal from campers. In downtown Seattle, they’re on constant lookout for human refuse. The key, for me, is that in either case they’re not primarily eating carrion. No matter where american crows are they’re an omnivore. I absolutely think you should include them in your post. The only change I would make (not that you asked :)) is to broaden your scope to include omnivores and recognize that in urban situations they’re the ones doing most of the “undertaking” for us. I think this is a really important distinction because it underscores how it’s mostly generalists that do well in urban environments, leaving specialists to get pushed out. Though that point could open another pandora’s box couldn’t it (i.e if house crows can only exist in the presence of people couldn’t they be considered a kind of anthro-specialist) ?!

  3. Very interesting post, Kaeli. Good to hear, once again, that crows are not the scourge of small birds. I believe the outdoor domestic cat has that distinction. Is that true? Or glass windows, perhaps? Did you see the recent article about how corvids and their food caching ways can help with deforestation?
    http://arstechnica.com/science/2016/02/corvids-could-save-forests-from-the-effects-of-climate-change/

    • The most recent pubs I’ve seen have given the title of bird killer to cats, yes. Windows come in second, but remember they’re all beaten out by general habitat loss. I did see that article! Meant to write something up about it but ran out of time. One of these days maybe…

  4. Re crows as scavengers- might we be talking semantics here? We have the people who collect our household waste variously known as the Garbage men, Garbage collectors,Trash collectors,Trash men in the US and here in the UK the Bin Men, Now it’s not considered PC to call them the Bin Men anymore but rather the Refuse collectors perhaps because the former term sounds more degrading? Whatever we call them we would be in a bad way without them.

  5. Suzanne, we are talking semantics but it is crucial to do so. I have no issue with folks referring to them as opportunistic scavengers. Simply to refer to them as scavengers though equates them with a number of animals specially adapted for that strategy. It also doesn’t capture a huge part of their diet which is the active hunting for insects and fresh fruits and veggies. In other words, I love scavengers and crows definitely scavenge, but to truly capture their diet it’s most accurate to call them omnivores. I’ve really liked this conversation with my readers though so thank you for being apart of it!

    • I should add too, that carrion crows ARE a different story. I see them much more like a wolf or lion. Yes, they actively hunt (insects or small mammals) but they’re also getting A LOT of their food from carrion. So they fit the more classic predator/scavenger model in my book!

      • Yes, I think that’s the issue, as biologists we try to fit animals with very complex behaviour into simple categories, and it just doesn’t work. So I agree, the semantics are important, and we need to be nuanced about the context in which we are describing what species do. The urban crows I’m referring to are largely predators, it’s true, feeding on insect larvae in park grasslands as far as I can tell. But they take advantage of any scavenging opportunity they can.

        With regard to your comment that turkey vultures are “one of the few birds with a developed sense of smell”, has there been a recent review of the topic? The last one I saw was quite a few years ago and since then I’ve found a paper from the 60s that seems to show that hummingbirds have a sense of smell, which questions the assertion that bird pollinated flowers are scentless because “birds can’t smell”.

        Keep up the great work 🙂

      • Good catch Jeff, I should have caveated that with *well developed*. Check out Tim Berkhead’s book, Bird Sense for the run down on the latest thoughts on bird olfaction.

      • Christian

        Tthey actively hunt birds, too.
        Saw a group of ~6 carrion crows kill a sick pigeon. Took them 2 minutes. The pigeon lost its head.
        Saw a single crow successfully hunt a young sparrow. The crow took it and flew up to a tree. Later the same morning, (probably) the same crow chased a family of sparrows into thick ivy at a house wall. The crow gave up at one meter distance from the wall.
        Yet, I still see robins, sparrows, wrens etc. at my site.

  6. Great information. Thank you. I’m armed and dangerous now when confronted as I sing their praises.

  7. Carole Strunk

    Cool!

    On Wed, Feb 17, 2016 at 1:08 PM, Corvid Research wrote:

    > corvidresearch posted: “Spoiler alert: They’re not, as so many people > believe, scavengers. 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 ” >

  8. I couldn’t believe the lucky timing one of our neighborhood crows had. We had a couple of bird feeders in our Seattle front yard. One was a wire cage type for suet blocks. It was wintertime. One of my contractors, Mark, just happened to be starting a job for us. When I greeted him at the door, he asked me if I knew there was a crow hanging upside down from the suet feeder. I said ‘oh no’ and ran outside. The crow’s feet were stuck in the wire and it was flapping its wings and trying to free itself to no avail. Mark loves animals. He immediately put on some heavy leather gloves and was able to free the crow. It flew away and hopefully continues to lead a happy life. I took down the bird feeder and threw it away. It may have been a freak accident, but I don’t recommend those types of feeders. Whenever I go to WildBirds Unlimited for more birdfood, I always tell them about those cages and how potentially unsafe they are.

  9. kris0723

    Hi! I recently read crows remembered where they cached their food better than graduate students Amazing memory! What percentage of their stash do you estimate is actually retrieved and eaten by crows? I read on one site, Blue Jays recover only about 30% of their caches. I’m wondering because my neighbor told me she saw a giant rat running off with a peanut in its mouth. Since then, I’ve been feeding the crows only a few unsalted shelled peanuts and one fried egg yolk. I wait and watch the crows take the food, but who knows what happens to the food they don’t eat immediately. I hate to think I’m contributing to the rat population in Wallingford. Hopefully I’m not?

    • Hi Kris, unfortunately rats can be a big problem for bird feeders, particularly in Seattle. If you’re feeding smaller birds, there are ways to address this with feeder style. Like Steller’s Jays, scrub jays or blue jays, crows are not cache reliant species so their recovery rate will likewise be small. You’re doing the right thing by limiting your offerings. Ive found that limiting yourself to just a few nuts a day (or every couple of days) will still keep a city bird interested without fear of bolstering the location population or unintentionally feeding rats. Making sure they’re things that need to be eaten ASAP (like your eggs yolks) is another good way of to make sure they’re being consumed by the intended party.

  10. kris0723

    Hi Kaeli! After all this talk about crows eating human food (even fast food) can crows have weight problems? I’m guessing they don’t have a problem with being overweight, but does eating human food w/preservatives, artificial colors/flavors affect their overall health?

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