Category Archives: crow diet

February 5, 2022 · 1:11 am

Butts for nuts: can crows do our dirty work (and should they)?

 

It’s no mystery that garbage is one of the most pervasive issues of our time. From oceanic microtrash to seeping landfills, people are trying to work out how to address the world’s garbage crisis with increasingly grand ideas. Corvids have long been associated with garbage, sometimes acting as agents of litter themselves, but one such idea asks if they might offer a solution.

A Swedish start up, Corvid Cleaning, is attempting to train corvids to pick up cigarette butts in exchange for food, as a means of combating the pervasive litter problem across their city. They plan do this through a machine that according to their website, they’ve already successfully ground tested with wild birds.

So, will this work and is it a good idea? In my opinion no and no, for many reasons. This whole idea rests on the premise that corvids are smart, (which they are,) but being smart and being motivated are very different. It’s not an issue of whether crows *can* learn it, but how you keep them engaged over time (the company hopes to save 75% of the city’s current cigarette clean-up costs). Having fed a lot of crows a lot of peanuts, I can tell you that the appeal of unlimited peanuts wanes drastically over time. While there might be an initial rash of participants, or at least a couple highly exuberant ones, there’s a serious question of meaningful sustainability without the introduction of a more desirable (and more expensive) food.

My skepticism here is born both from my experience with crows and the cold hard fact that this has simply never worked before. This isn’t the first time someone has tried this, but the 4th. The first was in 2008, when Joshua Klein delivered his infamous and highly misleading crow vending machine TED Talk. From there the Klein team debuted their Open Source idea for the Crow Box, a build it yourself machine that offered the chance to train wild crows to exchange found coins for food. While the no promises, DIY, community science nature of the project gets a more sound endorsement from me, to date, no one has had success with the final stage of the training process. The idea it seems, makes no cents. Next, in 2017, a Dutch start up called Crowded Cities pitched the exact same idea as Corvid Cleaning, though I assume their proprietary machine was a bit different. By December 2018 though, they tabled the idea, citing a lack of resources and an inability to, “get a clear picture of what the effects would be on crows and the environment.” That same year a French theme park, Puy du Fou, hired a falconer to train some captive rooks to pick up garbage as a stunt for the park. In that case it worked marvelously but of course the stakes are entirely different between wild and captive birds. And in between all those highly profiled efforts have most certainly been the odd successful backyard tinkerer. But what eventually plays out over and over again is that while wild crows can learn to do this, no one has ever been able to scale their success into something meaningful. And I don’t think they ever will.

For a moment though, let’s say that my skepticism here is invalidated; various corvids do consistently use the machine as intended. In fact, their intelligence and understanding of cause and effect renders them quite simply excellent at it. Without the appreciation for the purpose of their activities (cleaning up garbage) the project is liable to create two different kinds of cheaters: those that steal the food out from under the participants and those that resort to collecting their currency straight from the source, before it’s officially become garbage. I’m not sure how likely either of those two scenarios are, and in fact bearing that out is nearly worth keeping quiet and bagging this whole article simply to find out. But there remains at least one more point that compels me to keep going: I have never once seen a proponent of this idea fully tackle the very real health and safety issue at stake here.  

At the smaller end of this question are the issues associated with the maintenance of the machine itself. How do they plan to keep pests and mildew out of the food hopper? Rats would be the most conspicuous problem, but it’s the smaller stuff that might prove the most challenging. In my own hard learned lesson on this, I’ll never forgive myself for infesting my sister’s kitchen with pantry months after leaving behind a forgotten bag of peanuts. And of course like any high calorie food, nuts are liable to spoil especially when unsealed and exposed to the environment. I don’t offer this in denial of the absolutely horrendous things I’ve seen crows gleefully eat, but if you are intentionally creating a crow cafeteria you have a higher obligation to the food you are serving. Especially if you offer on your website that, “Chances are pretty good that it’s possible to put the birds on a better diet and improve their overall health with this solution.”

Which brings us now to the most obvious issue: cigarettes are toxic. For example, direct ingestion of nicotine at a concentration of 0.054ml/kg causes rapid death in birds.1 While there’s no way a crow would ingest that much nicotine simply from handling a cigarette butt (even with its mouth), there’s urgent need to understand how repeated handling of cigarette filters might impact these wild animals. And truth be told, I have very little confidence that the people behind these butts for nuts ideas understand the challenges of executing that study, though I would welcome their inquiries.

Earlier I asked two questions: will this work and is it a good idea. I suspect that every iteration of person that has come up with this idea genuinely appreciates corvids for their intelligence, is concerned with the amount of litter created by people, and believes that they’ve hit on an idea that will solve a problem that needs solving. Where I think they go wrong, however, is condensing my question into a single query where whether or not it’s a good idea is simply an artifact of whether or not the idea works. It’s the Silicon Valley mindset applied to wildlife. Ian Malcom warned us against this, and here we are ignoring him yet again.

Which leads to me to what I think is the only good idea that might arise out of a machine that trades treats for garbage. Rather than exploiting wildlife, why not use the money and creativity being invested here to better train people? After all, humans like a good reward-based dopamine hit as much as the next animal. What’s the smallest amount of money that would encourage someone to dispose of their cigarette waste? That’s the start-up I’d rather see. Or better yet, pay people living wages to act as care takers for our communal spaces. Some problems don’t need a grand solution, they simply need our humanity.

Literature cited

  1. Ridpath MG, Thearle RJP, McCowan D, and Jones, F.J.S. 1960. Experiments on the value of stupefying and lethal substances in the control of harmful birds. Annals of Applied Biology 49: 77-101

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Filed under Corvid health, Crow behavior, crow diet, Crows and humans, In the news, Science

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August 26, 2019 · 8:43 am

Dumpster diving is giving crows higher cholesterol—but does it matter?

Whether it’s from actively watching crows, or simply just existing in a city, we’ve all seen it: the overflowing garbage bin with fat-stained wrappers littered at its base, and the crows snapping up each bit of leftover junk like spilled money.  Cheetos, cheeseburgers, fries, nuggets, chips, or pizza, they will devour basically anything fatty and salty with absolute glee.  This behavior is so canonically crow that it’s stapled into our contemporary imagery of these birds.  Take this 12ft statue called “Crow with Fries” by artist Peter Reiquam.

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Photo c/o salishsea

I’d wager that most people don’t think about this behavior beyond simply finding it amusing or annoying, but I suspect that if you describe yourself as crow lover, naturalist, or bird watcher, you’ve been struck with the same thought as me: “This stuff is called junk food for a reason—it’s bad for you.  What’s it doing to these birds?”

Given that anthropogenic foods can account for as much as 65% of an urban crow’s diet, it seems essential to understand what a diet derived from regularly feasting at McDonalds might do to an animal with 0.7% the body mass of a typical human.1  Unfortunately, we could do little more than shrug and speculate as to its effects.  The data for a more informed understanding just didn’t exist.  That is, until today.

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A new study published in The Condor by Dr. Andrea Townsend et al. examines the relationship between urbanization, junk food, and the body conditions of crows.2  To conduct this study, her team blood sampled 140 wild crow nestlings along an urban to rural gradient.  They found that plasma blood cholesterol levels increased in correlation with the amount of impervious surface, which is a typical way we measure urbanization.  This finding suggests that crows in the city have more access to high cholesterol foods and they make haste in gobbling it up.

Correlation is not causation, however, so to confirm this, they ran an additional supplementation study where they provided 10 rural crow parents with 3 McDonalds cheeseburgers 5-6 days a week, and then looked at how their nestling’s blood cholesterol levels compared with unsupplemented nestlings from the same area. They found that eating cheeseburgers most days of the week had a demonstrable effect on the subject’s cholesterol levels.  While this finding may not be raising any eyebrows, the actual logistics of carrying out a study that required buying hundreds of cheeseburgers each week, and sometimes in one order, certainly did.  In one of their more memorable attempts, Hannah Staab called to place an order for 125 pickle-less cheeseburgers, a request to which McD’s staff replied, “Sure, we’ll get right on that.”  When she arrived several hours later to pick them up, however, they hadn’t made any, having been convinced that the call was a prank.  The peculiarities of urban fieldwork never falter.

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So far, these findings tell us little more than what most people could have probably intuited, but they were crucial to laying the foundation for the real clogged heart of this study: Whether any of this is actually a bad thing.  In the final piece, they examined the body condition, and 2-3 year survival of the 140 nestlings sampled along the urban to rural gradient.  They found that cholesterol levels had no detectable effect on survival and were actually correlated with higher indices of body condition (meaning mass adjusted for size), a feature that is sometimes tied to higher reproductive success and survival. In other words, there might actually be a scenario where regularly pigging out on McDonalds doesn’t kill you and is maybe kinda helpful?

Needless to say, this caught everyone off guard, including Dr. Townsend, who told me, “I was surprised that we didn’t detect any negative health effects. I was thinking—based on the human literature—that high-cholesterol birds would have lower survival rates, but we didn’t see any effect of cholesterol on survival.”

So what gives? Is the universe really just this unfair?  While we can’t rule out that the answer is simply, “Yes,” the authors speculated that it’s possible a longer study would bear out health consequences that take more than a few years to accrue. There’s also something to be said for the fact that body condition has complex and not always agreed upon relationship with fitness and survival.3 While some studies show pudgy birds have more resources to produce more offspring and keep on ticking, others find inconsistent support. Alternatively, crows may just not live long enough to see their lifestyle catch up to them.  Future long-term studies will be necessary to fully understand whether crows have truly found a loophole in the junk-food problem. For now however, I’m happy to wish my favorite dumpster divers well, though I’ll hold off placing my own orders.

Literature cited

  1. Marzluff JM, McGowen KJ, Roarke D. and Knight RL. 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.
  2. Townsend AK, Staab HA, and Barker CM. 2019. Urbanization and elevated cholesterol in American Crows. The Condor page 1-20
  3. Milenkaya O, Catlin DH, Legge S, and Walters JR. 2015. Body Condition Indices Predict Reproductive Success but Not Survival in a Sedentary, Tropical Bird. Plos One https://doi.org/10.1371/journal.pone.0136582

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Filed under Corvid health, Crow behavior, crow diet, Crows and humans, New Research

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March 14, 2019 · 3:38 pm

Crow Vocalizations Part I: New Science

If there’s one general area of questioning that overshadows all others that I receive, it’s questions about vocalizations. One caw, five caws, quiet wows, and loud clicks. We can’t help but to ask what it all means, and wonder how we might better understand and connect with crows if only we knew. To the chagrin of virtually everyone that has asked me a vocalization question, however, the answer is almost always a very disappointing shrug of ignorance. So to help you better understand what we do know about crow vocalizations and why it pales in comparison to what we don’t know, I am dedicating two posts to this topic. The first one–this one–will cover a recent study authored by my colleague and former labmate, Loma Pendergraft. Part II will take the form of a vocalization Q&A. So sit back, grab a snack, and get ready to know more, or maybe less, about crow vocalizations than you ever thought you could.

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Why are you yelling at the dinner table?

If you’ve ever fed a crow  you may have noticed that shortly after whatever tasty morsel you’ve offered hits the ground, the receiving crow will give a couple caws. If you’re anything like Loma Pendergraft, your next thought will be, “Why?” Are they inviting family members to the feast? Are they trying to scare off competitors? Do the number of caws mean anything?

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Unlike most crow feeders that have to settle for a disappointingly fruitless Google search for an answer, when Loma first asked this as a graduate student he was in a unique position to test it. After three years of labor, his findings have been published in a new paper entitled: Fussing over food: factors affecting the vocalizations American crows utter around food.1 As I can already feel your anticipation in finally finding out what all those food calls are about let me start with a spoiler; you are probably not going to learn what you had hoped to from this study. But you will learn something invaluable about crow communication and how we study it. So with that out of the way let’s start at the beginning.

Generally speaking, if an animal vocalizes at a food source, it must incur some benefit from that vocalization that outweighs the potential costs. Costs include things like getting your food stolen by a competitor or drawing the attention of predators. Conversely, the benefits may consist of things like being able to share resources with your mate or kin, claiming ownership, or attracting other individuals to help you secure a food source away from another bird.

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To try and determine what, if any, of these might motivate the calls that crows produce, Loma conducted three experiments. In the first, he attempted to look for patterns in their vocal behavior by categorizing and quantifying the calls given around food of varying amounts. For example, perhaps for an amount of food small enough as to be consumable by one crow they keep quiet, but for a significant amount they have a specific three-note “I found food” call to alert their mate. In Experiment 2, he ground-tested his ideas about how he was interpreting the calls from Experient 1 by doing playback. Essentially, he wanted to show that if he thought a three-note call was used to attract a mate, then by playing it back the mate should come in. Finally, in Experiment 3 he tested whether the different calls he had recorded had any effect on the listener’s ability to find the food.

To conduct these tests, Loma used wild crow pairs that he located all around Seattle. To prevent the birds from learning his face, he used a variety of sometimes hilarious disguises.  He fed each pair three different amounts of food over the course of three trials: 1 peanut, 5 peanuts or a bountiful 25 peanuts. To try and suss out both if there were any patterns in calls given around food and if calls varied with the amount of food, he recorded their behavior before and after feeding them, and then used vocal analysis software to detect patterns in call structure.

What he found was that, unlike the grand reveal we were all hoping for, few clear patterns emerged from the call data. When crows are around food, they give shorter calls than they did before, and their calls around only a single peanut are longer than when they are around a more substantial amount of food. But in all the other areas where you might expect some pattern to emerge; call rate, peak frequency, the number of syllables, etc., none did.

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Still, the fact that they give short calls around food is suggestive of something, so Loma attempted to determine in Experiment 2 if these short calls are used to either attract birds in or repel them away by playing back those short calls and watching for how the birds responded. The resulting response was more of a whimper than a bang. Or maybe I should say more of a short call than a bang. Because outside of matching the short calls with their own short calls, the crows hardly changed their behavior. Even in Experiment 3 where he looked for whether specific calls aided in the listener’s ability to locate the food, he came away still puzzled. Crows were only able to locate food in 38% of cases and were no better than when played the control chickadee calls.

A cynic may walk away from these findings feeling as if nothing has been gained; that we know little more about what crows are saying around food than we did before. While it’s true we may not have learned much about what they are saying, this study did reveal something important about what they are not saying. Because while Loma found few patterns once the food was down, he did discover that crows give longer calls in the absence of food and that those medium calls prompted territorial behavior when played back. The implication is that crows do not give territorial calls around food, perhaps to avoid risking its discovery by adversaries.

In addition, while it makes for a less compelling headlines, failing to support our hypotheses offers fundamental insights and lays the groundwork for future studies to keep pressing forward. In this case, Loma and his coauthor John Marzluff question whether the difficulty of detecting clear patterns in “x” vocalization leading to “y” behavior is because crows encode so much context-specific information in their calls. In fact, a previous study on American crows found that acoustic variation can indicate the caller’s sex and identity.2 Perhaps the reason we have so much difficulty in mapping out the world of crow communication is that, unlike a crow, we fail to detect all of the information they can ascertain and use to determine how to respond.

So, yes, in some ways we are no closer to Dr. Doolittling the crows than we were before. Instead, we are left with the more compelling reality that our inky friends likely posses an incredibly rich and complex vocal system. For me, this continued mystery only serves to endear them further. After all, do any of us love these birds because we find them straightforward and predictable? I doubt it.

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Want to learn more about Loma’s research or this study in particular? Don’t forget to head over to his blog.  There you can drop him a line with more crow questions or to request his new paper in full.  He did so much more than I summarized here, it’s really worth a full read!

Literature cited

  1. Pendergraft LJ T and Marzluff JM. (2019). Fussing over food: factors affecting the vocalizations American crows utter around food. Animal Behaviour 150: 39-57
  2. Mates EA, Tarter RR, Ha JC, Clark AB, and McGowen KJ. (2014). Acoustic profiling in a complexly social species, the American crow: caws encode information on caller sex, identity and behavioural context. Bioacoustics 24 

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Filed under Crow behavior, crow diet, Crows and humans, New Research, Science, Vocalizations

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February 17, 2016 · 6:24 pm

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

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