Do crows reduce other songbirds?

A comment I occasionally hear, especially while conducting my research in neighborhoods is, “Ugh, I hate the crows.  All of a sudden we have tons of crows and they’ve scared off all our songbirds!”  This comment always pains me, but I understand that for most people it arises from a genuine concern for songbird abundance and conservation.  First off, as a reminder crows are songbirds themselves; ravens are our biggest songbird.  Semantics aside, I understand that there are many, many bird lovers who just can’t get on the crow bandwagon and when they talk about wanting songbirds at their feeders they mean chickadees, juncos, grosbeaks, etc.  They feel that since the “arrival” of the crows their observations of these other birds have diminished.  So is there anything to this?  Do crows indeed drive down populations of small, “desirable” backyard birds?

I came across this grizzly scene while conducting research in Bellevue.  An adult robin calling frantically while a crow munched on one of its young.  Later that same week I would watch of pair of adult crows chase hopelessly after a cooper's hawk that had taken one of their offspring.

I came across this grizzly scene while conducting research in Bellevue. An adult robin calling frantically while a crow munched on one of its young. Later that same week I would watch of pair of adult crows chase hopelessly after a cooper’s hawk that had taken one of their offspring.

The short answer is: not usually.  Now, let’s be clear, crows will absolutely kill and eat eggs, nestlings and even adult birds if they can get their hands on one.  I once saw a crow take down an adult house sparrow in an attack so quick and dexterous I only realized what had happened after the crow had already started eating its meal.  It’s important to keep in mind, however, that crows are one of many, many animals that are eating the young and adults of other bird species.  Raccoons, squirrels, foxes, hawks, owls, bullfrogs, rats, mice, and of course cats will all gladly eat birds, especially eggs and nestlings.  The vulnerability of young birds is in fact why the breeding strategy of many birds is to have multiple clutches over the course of the breeding season.  Crows themselves are subject to these same predators and very few of their young will make it to adulthood.

Why do we think that crows aren’t responsible for the any observed decrease in feeder birds?  Predator removal studies.  These studies are straightforward and essentially create two populations, a control population that has been unmodified and a second where the predator in question has been actively removed.  Prey abundance or productivity is monitored and compared at the end of the trial.

Recently, Madden et al. published a comprehensive literature review of 42 studies across 9 countries that looked at the impacts of corvid removal on a variety of avian groups including gamebirds, passerines, waders and other ground nesting birds.  They found that in 81% of cases corvid removal made no impact on prey abundance or productivity.  They also found that impacts of corvids on prey species was similar, and no one group was particularly more sensitive than any others.  Of the corvids studied, magpies consistently had the smallest impact on prey productivity, but no difference was found if the study was looking at prey abundance.  So if corvids are such conspicuous avian predators, why doesn’t their removal seem to matter in most cases?

This is explained by idea of compensatory mortality, which is essentially that removing one predator just means that the other predators will account for its absence by eating the prey it otherwise would have.  Kevin McGowan provided a great description for this idea on his site I like to use the analogy of handicapped parking spaces at the mall You drive up to the mall, looking for a parking space in a crowded lot. You can’t find a parking space, but there are four near the entrance that are reserved for handicapped permits only. You complain and think that if only those handicapped restrictions weren’t there, you could park in those spots (common sense). In truth, of course, if those spaces were not reserved they would have been taken long ago, just like all the other spaces in the lot.”  Indeed, Madden et al.  found this to be true.  When they looked at studies that only conducted corvid removal, they found that only 16% of cases saw a difference in prey productivity.  Whereas if all predators were removed the researchers reported that 60% of studies found a significant difference in prey productivity.

What this means for those of us trying to improve the bad reputations of crows and other corvids is that the data is on our side, crows are not usually the problem predators they’re often made out to be (though in a small number of instances they are, and it’s important to acknowledge when that’s the case).  In fact, in 6% of cases the researchers found that corvid presence actually benefited other birds.  So what I suspect is happening when residents ask me why they see fewer birds and if crows are to blame is that crows often follow urban development and it’s possible that what these residents are experiencing is a change in species diversity as habitats are disrupted and modified to make way for new human settlements.  Though it’s also possible they simply don’t know where to look.  It wouldn’t be the first time I’ve listened to folks complain about crows driving away their birds in the presence of yellow-rumped warblers, white crowned sparrows, juncos and chickadees.  Indeed, suburbia is often a great place to enjoy both crows and other smaller songbirds.

John Marzluff's newest book which describes the awesome power of suburbia to become a heaven for a huge diversity of birds.  Illustrations by my friend and colleague, Jack Delapp.

John Marzluff’s newest book which describes the awesome power of suburbia to become a heaven for a huge diversity of birds. Illustrations by my friend and colleague, Jack DeLap.

John Marzluff’s new book Welcome to Subirdia, highlights that vast species diversity that can come with suburban development, showing that these types of habitat modifications aren’t doomed to be low diversity.  With a bit of thought on our part, we can create habitats that attract a variety of birds.  Namely, by limiting lawn space, increasing snags, native plants and bushes and keeping our cats indoors, we can expect to see a great variety of birds visiting our feeders, crows included!

Madden, C.F., Beatriz A., Amar, A. (2015) A review of the impacts of corvids on bird productivity and abundance. Ibis: 157, 1-16.

36 Comments

Filed under Crow behavior, crow conflicts, Crow life history, Crows and humans

36 responses to “Do crows reduce other songbirds?

  1. Nikki

    Thanks for the great article Kaeli, I am a avid crow lover and I too have been faced with the same argument. Now you have given me some good points to argue with.

  2. Scott

    I was wondering what was killing the cedar waxwings by the apple trees on our street, as there were numerous kill-sites ( “puddles” of waxwing feathers) Yesterday I found the answer, as I saw a crow ambush a waxwing and kill it. Now I know.

    • Scott, ceder waxwings are one of my favorite migrants and I would certainly grimace at the loss. But a cool predation event to see nonetheless! Where’s there’s one predator there’s usually more and depending on where you live I’d look for a cooper’s or sharp-shined hawk since they’ll be keeping their eyes on the waxwing flocks as well.

  3. Reblogged this on Kaeli Swift and commented:

    Updated with data from a new review of studies looking at impacts of corvid removal on other birds.

    • Mr g kettleborough

      Recently a group of blackbirds (with young) attacked a crow in my garden
      And he had to be rescued , he is ok now and still comes for tit bits and he can now fly ok

      Geoff kettleborough

  4. Pingback: Clever crows! | Jeff Ollerton's Biodiversity Blog

  5. Not so sure — I was feeding small songbirds — now I have only crows patrolling – not a single smaller songbirds
    I always loved crows and still do but — I monitored the facts on my balconies…

    • While personal observations are a key part of good citizen science it’s always important to remember that the plural of anecdote is not data. Individual results may vary but the vast majority of studies (each which incorporate many more individual data points) suggest that corvids do not reduce populations. But keep watching! Look for other sources of decline too, like neighborhood cats, changes in feeders and development.

  6. We have resident crows and a huge population for sparrows, juncos, finches, hummies and flickers.. oh can’t forget the Robins!! All get along or so it seems.

  7. I don’t have anything against crows. We have noticed a pattern. In the winter, we have all kinds of birds in our yard. There are finches, juncos, chicadees, woodpeckers, bewick’s wrens, red-breasted nuthatches, and titmice, to name a few. Sometime in March, a group of crows starts flying around, cawing, and hanging out in the trees. Until late summer, we won’t see any birds but a few crows, some scrub jays, and an occasional California towhee. Does the threat of crow predation send all other birds to another location? Thanks-Valerie

    • Hi Wendy, what you’re describing sounds like seasonal changes. During the winter the small songbirds you mentioned form mixed-species flocks and move about pretty freely. Starting in spring though, the birds start to defend their territories much more fiercely and it can feel like you’re seeing less. They’re also less attracted to feeders which can mean you’re seeing them in less concentrated abundance. So that’s my guess. To answer your question more directly though, while taking a walk through my neighborhood this winter I counted 10 native bird species in a single yard along with a territorial pair of crows. Crows simply don’t take adult birds down often enough to suffice as a predator that would have that immense of non-consumptive effects (i.e. When predator presence changes the spatial use of prey we call that non-consumptive effects). If you make your yard suitable for song birds to hid in (think native shrubs) then they should easily cohabitate with your crow family. Enjoy the birds!

  8. Andrew Poliakoff

    Hi corvidresearch thank you for creating this great area to discuss crows; I’d love to hear what you have to say about two of my anecdotal experiences and how they fall into what is generally understood about crow behavior.

    I live in Northern Virginia. Both of these incidents were roughly the same and both occurred in residential neighborhoods in late Spring. Last year in May I saw a crow in my neighborhood on top of a chimney that was eating something (I didn’t know what at the time) and being attacked by two Brewer’s blackbirds. The crow had to move quickly and landed on a nearby chimney where I could tell that he/she was eating a baby Brewer’s blackbird. The blackbirds gave up at this point.

    Yesterday I saw roughly the same thing in Old Town Alexandria in a small residential park. This time I saw the crow take the blackbird from the ground and fly with it up to a chimney. Almost 8-10 Brewer’s blackbirds were going absolutely crazy trying to stop the crow for 20 seconds or so and then the gave up; the crow ate the blackbird on the chimney.

    I am writing for two reasons. First, I have Brewer’s blackbirds in my yard here and the babies just emerged a week or so ago and follow the mother (I’m guessing) around in the yard. They are huge for babies, and appear almost bigger than the parents. That’s why I noticed them and what is what is so odd. I understand crows taking fallen babies or defenseless ones from an unattended nest…but…taking a non-injured robust baby off the ground? Is this normal behavior? I ask because the little research I did into this seems to indicate that crows will only eat a bird if it is already physically ‘opened’ because they do not possess the right beak to kill birds. The bird I saw on the ground getting taken did not have that appearance (but I can’t say I was preparing to collect avian data when I turned to see).

    The crows here were decimated (as per my understanding) a decade or so ago by some disease. In the 80’s and 90’s in Northern Virginia there were oooodles of crows (treefull after treefull) and now there are very few. Is it possible that they’re exhibiting strange behavior due to the entire structure of crow communities being lost?

    Thoughts?
    -Thank you, A.P.

    • Hi Andrew, thank you for your kind words. The short answer is that crows are more than capable of killing and opening birds. Most mammals, on the other hand, are a different story because the skin is thicker. Think about it this way; since they are capable of killing each other, smaller birds are no problem. I’ve seen them attack and kill adult songbirds on more than one occasion (both times it was a house sparrow). That being said, they’re not bird eating specialists so while it’s not an unusual behavior it’s also not a common one, if that makes sense. The limitation is their ability to catch birds, not eat them, which is why observations of them eating fledgling are much more common in contrast to adults. On another note, although fledgling are often similar in size to their parents, you might want to google “cowbird fledgling” so see if maybe your big babies are in fact nest parasites. Great observations!

  9. M Hunt

    I appreciate your interest in crows, however, I am currently devastated by the behavior of a family (murder) of crows in my neighborhood. I enjoy hosting sites in my yard for various species of birds, especially the Robin. I have watched a mother Robin spread her wings protectively over her young during a late season snow storm that left her with a half inch of snow over her entire body as she sat through the night keeping the babies alive. This season there is a young pair that worked tirelessly gathering mud from my backyard ( I helped along in this process). They were at the stage where they obviously had chicks and were busy looking for food. The nest was high in a maple tree in my front yard which I was not able to locate visually. Yesterday the attack by the crows began. I knew what they were doing in that tree and watched sadly as one of the crows flew off with a baby clutched in its talons. The mother, father, and I were devastated. I listened to the distress cry from those birds for a half hour and determined that I would do great harm to those crows if they came near another nest. I now understand that crows are protected by law, which is unfortunate, because today they have raided two other Robin nests in close proximity. I have a Robin still nesting near the house and a sparrow in a hanging planter that I am now taken actively protecting from the crows. Make no mistake; I will forcefully clear the area to protect the smaller birds who are being terrorized by this crow family. I can do so without harming the crows, but it will take some vigilance on my part. If they persist I may borrow a cat from friends for a season, and I do hope the cat is successful in returning the favor of nest robbing from the crows. I understand crows can memorize faces and details for several years. I hope they tell each other that they have created an enemy at my address.

    • People have a very difficult time watching baby birds die, understandably. Just the other day I received an email nearly identical to yours, but replace robin babies with crow babies and crow with Cooper’s hawk. The reality is most baby birds will die before the end of the breeding season. I know it’s tempting to think, oh if only I kept x predator away they would live, but this is not the case. They are just eaten by a different predator or fly into a window (something called compensatory mortality). Given that you have three different pairs nesting in your yard I would say your robin population is incredibly robust and I applaud you for creating a space that attracts prey and predator species alike. Given the vitriol you clearly feel for the crows you have attracted I don’t expect you will be moved by this reality and let nature take its course. If you want to manage your yard for individuals that’s your call; both robins and crows are doing very well and I see no harm in your efforts as long as they are within the law. I do urge you however, NOT to use cats. Cats are indiscriminate killers and will harm the biodiversity of your yard, not improve it. Best wishes,

  10. Thank you so much for sharing your wonderful blog! My eight year old son and I just started reading and listening to Gifts of the Crow and love it! Thank you for answering my question about the smaller songbirds. We live in Wallingford (Seattle) and we have a bird feeder in the front yard. We used to have a variety of bird visitors: chickadees, sparrows, robins, pigeons, flickers, stellar jays and even three beautiful waxwings (although the waxwings seemed to be plucking spiders from their webs and not interested in the feeder). We LOVE our crow friends. I was worried because since I’ve been feeding the crows more regularly, we haven’t seen hardly any smaller birds. I am glad it doesn’t have much to do with us feeding the crows and the crows presence. We don’t feed them a lot, just one fried egg yolk and a few unsalted Virginia peanuts. And an occasional bite of leftover salmon from Anthony’s or other seafood restaurant we go to. Do crows taste food like we do? Do they taste salty, sweet, spicy, etc? Thank you again!

  11. Vijay Surya

    Crows must be declared as pests and isolated from liveable environment.

  12. Doro

    Hi. I’d be very interested to know if something I just heard is true…that British crows pick out the eyes of other birds. Is this so? Is it true?

    • Hi Doro, I can answer this question but first it would be nice if you could provide a little more context for this hearsay. Where and what exactly was the context in which this was said? That will help make sure I get at the root of what’s being asserted here. Thanks!

      • Doro

        I don’t understand why my replies aren’t showing up now, but I did answer asking if you were being coy? I did provide the context – someone told me that crows were picking out the eyes of other birds, and I asked if it was true that crows do that. Am I not understanding your question?

      • Hi Doro, no I am not being coy. I’m just trying to figure out where this could have come from on behalf of the person who told it to you. For instance did they mean that crows just peck the eyes out and leave the bird blind but alive, akin to how Eleanora’s falcons pull the wings off living birds and store them so they can eat fresh meat later, or did they mean that they just do it for fun akin to dolphins hunting porpoise calves? Or maybe they meant that they’ve seen a crow pick out the eyes of an already dead bird. In any case, there’s no evidence whatsoever of the first two scenarios. The third is entirely possible though. With mammals, the eyes are most typically the first thing they go for because their beaks are not made for breaking the thick skin of something bigger than a rat. This is why they have such a bad reputation among sheep farmers. Eyes are accessible, nutritious soft tissue so once they pluck and consume the meat of a bird kill there’s no reason they wouldn’t fish out the eyes. The other possibility I can think of is that when I’ve seen crows go after small birds their strategy is to kill them by a blow to the head. It’s possible this person mistook a general interest in going after a bird’s head as a specific aim to peck their eyes.
        Cheers,

      • Doro

        Thanks for your response. I’ve never heard of falcons pulling the wings off living birds, and the image of it in my head is horrible. And I’ve never heard of dolphins hunting porpoise calves either – both being indications of my ignorance. I apologise. But you’re answer helps me to understand what you were looking for, and it’s along the same vein as what I was trying to establish in the original conversation about crows.

        Here are a couple of things I was told: In my book all crows are nasty…. They attack small birds nests, and kill baby lambs/ When one of my blond boys was about 2 years old he was out with his Da and he was attacked by one of those, they were going for his eyes. Those critters are no fun/ in Fort McMurray in 1967-9 there was a report of ravens picking out the eyes of young wolves and waiting for them to die.

        I’d never heard of such behaviour and none of the people who made the claims above responded to my request for info that I could check out independently. So when I found your site, I thought you might have the answer. I guess what you’re saying is that the reports are exaggerated – is that fair to say?

      • Well yes and no. They do attack birds nests-they just don’t do it at such a rate in your backyard that we see declines of songbird populations as a result. Everything eats baby birds, it’s sad to see but that’s why they lay so many eggs. They also do peck the eyes (and anus) of young lambs. That’s also a sad sight, but from a foraging perspective it’s a very a good strategy. Nature doesn’t design itself around our sensitivity nor do humans always abide by it. It’s not hard to find evidence of people doing truly heinous things to our food, despite the fact we are capable of holding ourselves accountable for it. The last two though are more exaggerated. Wolf pups are born in dens and do not emerge until they are hold enough to give the crows and ravens chase. I’m inclined to think that one is a exaggeration of the fact they do like to tease wolves by pulling their tails. Finally, in the summer time crows become very defensive around their nests and kids and will dive bomb people who get too close. Although they’ll swoop and occasionally peck the back of the head, they’re not going for the eyes-that’s too risky. A bird in the hand will go for the eyes but this is true of any bird with a long neck and powerful bill. I’ve handled caspian terns before and was surprised when it was over that I had made it with both my eyeballs.

      • Doro

        Thanks for your response. Appreciated. I’m becoming increasingly interested in this topic. As I was trying to find an answer (before I found your site), I came across the following. Would you mind giving me your interpretation on them?
        https://www.realagriculture.com/2015/07/livestock-predation-turns-ravenous/
        http://barrie.ctvnews.ca/ravens-attack-and-kill-livestock-in-grey-bruce-1.2507458
        http://www.owensoundsuntimes.com/2015/07/24/raven-attacks-on-calves-in-chatsworth
        I don’t see any evidence to indicate if these are animals who have been taken from their mothers as often happens in the cattle industry, but I’d be interested to have your take on these. Many thanks in advance.

      • Look legit to me-eyes and anus are good signs of an avian scavenger. I’m not a rancher but from what I can tell domestic cows and ewes just aren’t biologically equipped to chase off looming ravens. Meaning, I don’t think it makes any difference if the young are with mothers or not, their mothers simply don’t do anything about it. I do wonder though, if wild bison and big horn have the same issues, or if because they are co-evolved with this species they are more equipped to watch for and respond to attempted predation events on calves by ravens. I’ll have to ask some of the big game biologists I know. Again though, I’m not a rancher. Perhaps domestic farm animals do try and protect their young from these kinds of attack but just aren’t very successful.

      • Doro

        Hmmm…now I’m getting confused. My understanding of your earlier reply was that reports of them pecking out the eyes of live calves or lambs were exaggerated, allowing for the possibility of “down” calves or lambs being attacked. Your most recent reply seems to suggest that this is to be expected.

        I’ve looked up some more info:

      • I’m not sure what gave you the impression that I thought this (meaning, specifically, pecking lamb’s eyes) was an exaggeration? I said explicitly that they do peck the eyes and anuses of lambs (and I’ll include now, calves). That they peck the eyes of other kinds of more dangerous critters (wolf pups, humans, etc.) is an exaggeration. Does that help? Maybe the confusion is that clarifying if you’re talking about ravens or crows is really important here. Ravens are much more powerful birds than crows so they are actually quiet capable of killing a young mammal under the right circumstance. Crows are not. You started by asking about crows, so most of my answers have been provided with respect to what crows do, not ravens. But it seems maybe now you’re more interested in raven behavior. The video above is of ravens. They could easily pull the eyes and peck to death a young lamb. This would be much more difficult for crows, who would be limited to the eyes and then waiting for it to die and be ripped open by something larger.

      • Doro

        My mistake. I apologise. And yes, you’re right. As far as the crow/raven aspect goes each time I plug in “crow” I get feedback on either both crows and ravens or else just ravens, so I’m unsure if the information is applicable to both or not.

        You may or may not be interested to know that my provincial department of natural resources said that they believe the claims of crows pecking out calves eyes are probably the result of poor animal husbandry. That weak or sickly youngsters may be left unattended, or without a cow to defend them, and since they’re weak, and crows are opportunists, they go after them.

        Again, my apologies for getting your previous answer turned around. I really appreciate the time you’ve taken to help me get this figured out.

      • Hi Doro, yes that’s a common and understandable source of confusion. Not everything will apply to both but that’s just not always made clear, unfortunately. Fascinating that that’s what brings you to ask this question! I’d be very interest in any final report your office publishes on the topic. Animal husbandry issues are a big source of contention here in the states too, particularly as it relates to wolves and cattle/sheep. Range riding is a tough job, but I imagine it could be just as useful for preventing injuries from corvids as it is effective at stopping predation events by wolves.
        Cheers

  13. Jon

    Ridiculous article, masquerade of a scientific paper. The crows are very vicious and work in gangs killing every other small birds, and chasing even bald eagles out of their area (I witnessed such chase in the Vancouver area for many times). The crows population should be kept in check.

  14. Animal murdering a hole

    I was just driving and hit a finch. Accidently of course, I stopped when I had the chance to see if he was still alive. Upon my arrival a crow grabbed it in it’s beak and flew away with it. I was pretty shocked and it lead me to this. Poor little birdie. 😦

  15. Fabulous article and u have really given me ammunition for my argument to try and educate people who hate crows and Maggie’s! Thanks so much, and I feel much better about the new crows and Maggie’s in my garden…!

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