How A Woodpecker Pecks Wood, And How Ants Crown A Queen

FLORA LICHTMAN: I’m Flora Lichtman, and you’re listening to Science Friday.

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Today on the show, how do you drill a hole with your head?

NICK ANTONSON: They’re engaging everything from head and neck muscles, which you might expect, all the way down to muscles in their tail and hips.

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FLORA LICHTMAN: If you have heard the hammering of a woodpecker in the woods, you may have wondered, how do they do it? What does it take to whack your head against a tree repeatedly hard enough to drill a hole. Well, a team of researchers wondered that, too, and set out to investigate by putting tiny muscle monitors on eight Downy woodpeckers and watching them with high speed video as they pecked away in the lab.

Joining me now is one of those researchers, Dr. Nick Antonson. He’s an NSF postdoctoral research fellow at Brown University and an author of a report on the work in the Journal of Experimental Biology. Nick, welcome to Science Friday.

NICK ANTONSON: Thank you, Flora.

FLORA LICHTMAN: I love this question, but why this question?

NICK ANTONSON: Yeah, so what we were really excited about with this question, in particular, is all birds peck. But woodpeckers are really special in that they take this to the extreme. And by investigating extreme behaviors, we can figure out what the performance limits are of what things like muscles are actually able to do.

FLORA LICHTMAN: When you say that woodpeckers take it to the extreme, how hard do woodpeckers peck?

NICK ANTONSON: A woodpecker can peck at about 20 to 30 times their body weight. What it feels like if you get pecked by one is it feels like a sharp pinprick. That’s actually really impressive for a bird that weighs about as much as a single AA battery.

FLORA LICHTMAN: Well, I was going to ask. I mean, 20 to 30 times your body weight, is that a lot? When I’m hammering, Am. I hammering as hard as a woodpecker or harder?

NICK ANTONSON: So you would be hammering probably harder than what a woodpecker does. But with the woodpeckers, what’s interesting is it’s all of that hammering force down to a pinpoint. And so that’s what we were really excited to set out to investigate here. It’s so much more than the force that your normal bird pecks with.

FLORA LICHTMAN: So what did you find? What is driving this drilling power?

NICK ANTONSON: I think one of the most stunning things that we found in this study was that it’s muscles across the body of the woodpecker. And so they’re engaging everything from head and neck muscles, which you might expect, all the way down to muscles in their tail and hips as they push forward during these strikes.

FLORA LICHTMAN: I mean, this reminds me of my high school soccer coach, who would often tell us that if we were doing a header, we had to use our whole body.

NICK ANTONSON: Yeah, absolutely. You just build more force that way. And the other thing that was really exciting with this, too, that I’m sure your soccer coach probably also would have recommended, is to grunt while you do it. And so the woodpeckers do that, too, where they’re actually grunting through each one of these strikes.

FLORA LICHTMAN: Can you hear it?

NICK ANTONSON: So you can’t hear it. It, unfortunately, gets masked by the percussion of the drumbeats that they’re making. But we were able to actually measure the respiratory pressure from their respiratory system to tell when these birds were exhaling versus when they were inhaling.

FLORA LICHTMAN: So that’s what you mean by grunt. They did a big exhale?

NICK ANTONSON: Yes, they exhale straight through the strikes, similar to how an athlete like Serena Williams will when she’s striking a tennis ball. What happens is by stabilizing those core muscles while you exhale, you can add extra power to those strikes in all of those instances.

FLORA LICHTMAN: The grunt is making them stronger.

NICK ANTONSON: Yes, so the grunt is actually making them stronger.

FLORA LICHTMAN: Can you make the sound for us, like what you would imagine it to sound like?

NICK ANTONSON: I can give it my best shot. The other thing that’s interesting about it, that I’ll just add to that before I make the sound, because it’ll give some context to the specific sound I’m making, is that they can do this repeatedly, as well, and up to 13 times per second. They can exhale on every single one of the strikes.

And so if I were to make the sound, I think it would sound something like, huh, huh, huh, huh, huh. So to us, that sounds like hyperventilation. But to them, this is just well within their respiratory capabilities.

FLORA LICHTMAN: Amazing. How do they deal with kickback? Why don’t they fly backwards after they hit the tree?

NICK ANTONSON: Yeah, so another one of the really exciting things we found is that when these birds are going in for these strikes, the first things they do is they’ll activate the neck muscles that pull the head forward. Then it’s the hip flexors to pull the entire body forward. Then their tail pushes against the tree as a brace.

And then following that, there’s a collection of head and neck muscles on the back of the head that actually stiffen. And so right as they’re going into that strike, they engage those abdominal muscles to exhale and then push their way into the wood. And so they’re not just bouncing off, and their neck’s not just collapsing as they take the force of basically, a car crash. They’re powering their way into the strike. And then they very measurably just pull themselves back out and inhale as they’re pulling themselves back out.

FLORA LICHTMAN: Wow, this sounds like there’s a lot of choreography here, muscle choreography in their bodies to achieve this.

NICK ANTONSON: Absolutely. And we looked at this, as well, specifically with the repetitive strikes that these birds are performing, where they’re pecking multiple times in a row without taking a break. And one of the really striking things that we found in doing that was that the timing of when they’re activating each of these muscles in sequence was incredibly precise. And so there was never a misfire, where one muscle fired out of order where it wasn’t supposed to.

FLORA LICHTMAN: Let’s talk about the experimental setup. Was it difficult to get the woodpeckers to peck in the lab?

NICK ANTONSON: So the woodpeckers are voracious. And so they actually love to peck on any wood that you provide for them.

FLORA LICHTMAN: As many homeowners know.

NICK ANTONSON: As many homeowners know, yes. So in order to collect the data, we had these birds hooked up to their sensors. And those sensors actually went to a custom-made backpack for each bird so that it comfortably rested on their back, so that they could freely move throughout our recording chamber and peck on a variety of woods. So we gave them kind of a charcuterie board of different woods to peck from.

FLORA LICHTMAN: Are there any other special adaptations that a woodpecker has to live this pecking lifestyle?

NICK ANTONSON: Yeah. So I think one of the most exciting other things that we found with the woodpeckers was that they can exhale on every single one of those strikes. They can exhale at a rate of 13 times per second. And then as they’re pulling away with each strike, they can inhale on the order of 40 milliseconds, which is less than the blink of an eye, to take a quick breath in and get ready to oxygenate all of those muscles in their airways between each one of those strikes.

And in birds, this is really only a respiratory adaptation we’ve seen to this point in songbirds. When they’re doing their singing behaviors, they can intersperse these little inspiration breaths between each one of the syllables of their song. And so woodpeckers aren’t very closely related to songbirds. And so it’s really interesting to find that woodpeckers have found a similar adaptation for their pecking behaviors.

FLORA LICHTMAN: While I have you, Nick, I have a very important question. I’ve heard for many years that the tongue of a woodpecker wraps around its brain. And the purpose of that is that it’s a shock absorber. True?

NICK ANTONSON: No. So actually, that, it’s become a very popular science myth.

FLORA LICHTMAN: That’s the second gasp. I’ve gasped twice.

NICK ANTONSON: So what’s interesting about this is their tongues do wrap around their head, but they wrap around the outside of the skull. And so they’re not providing the cushioning to the brain. The brain is still smacking against the front of the skull when they’re doing these repetitive impacts.

What the tongue wraps around the skull for is actually to be a projectile. So they can actually shoot their tongues like chameleons can to spear insects in the holes that they’ve drilled in trees.

FLORA LICHTMAN: To spear them?

NICK ANTONSON: Yeah.

FLORA LICHTMAN: They’re pointy at the end?

NICK ANTONSON: Yes. So at the end of a woodpecker’s tongue, there’s a barb so that they can skewer through those insects.

FLORA LICHTMAN: I love these birds so much. So are they wrapping– Is it just that it’s a convenient place to hold the tongue?

NICK ANTONSON: Yeah, it’s a convenient place to store a really long tongue. With some woodpeckers, their tongues can even be three times the size of their head.

FLORA LICHTMAN: Wow.

NICK ANTONSON: The other thing I’ll mention about this, too, is that the reason that woodpeckers don’t get concussions, or at least as far as we’ve seen so far, is because their brains are small enough that they don’t build the G-force to smack against the front of the skull that would be necessary to cause a concussion.

FLORA LICHTMAN: Is this just a force equals mass times acceleration thing, like small mass equals small force?

NICK ANTONSON: Exactly. The forces that the brain is smacking the front of the skull with aren’t actually enough to cause a concussion because their brains don’t weigh very much.

FLORA LICHTMAN: Gotcha. This is so fascinating. Nick. Thank you so much for taking the time to talk with us today.

NICK ANTONSON: Thank you for having me.

FLORA LICHTMAN: Dr. Nick Antonsson is an NSF postdoctoral research fellow in the Department of Ecology, Evolution, and Organismal Biology at Brown University.

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We have to take a break, but don’t go away. Because when we come back, what does it take to be a royal? Ant, that is. Turns out how ant queens are crowned is a hot topic in entomology circles. Stick around.

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Turning now to another heady creature question, how do ant queens get crowned? This is a royal mystery because– and this is wild. You can take two ant eggs with exactly the same genes, and one can grow up to be a queen and the other a worker. How does that happen?

It turns out that’s a hot topic in the ant world and a recent paper provides some insights. Here to tell us more is study author Dr. Daniel Kronauer, an evolutionary biologist at the Rockefeller University in New York City. Daniel, welcome to Science Friday.

DANIEL KRONAUER: Thank you very much.

FLORA LICHTMAN: You study the social lives of insects. What drew you to this particular anthill?

DANIEL KRONAUER: Well, I’ve been really fascinated by insects since I was a little kid. So I grew up in Germany, in Heidelberg, as you might be able to tell from my accent. And my mom tells the story that she often couldn’t find me during elementary school pickup, because it turned out that I was hunched over in some hedge, watching ants on the floor or looking at a beetle, or something.

When you watch insects, they just look very exotic and almost like on a different planet or some alien creatures. And for me, that was always very fascinating, thinking about how they experienced the world, and how they communicate, and what their behavior means to them, and how they live. And then I made that early childhood fascination my profession.

FLORA LICHTMAN: So your latest study is about how a queen ant becomes a queen, which I take it is kind of mysterious and a little bit of a hot topic in the ant world.

DANIEL KRONAUER: Yeah, so the interesting thing is that in an ant colony, you can start with, say, two eggs that are genetically identical. And depending on how you treat those individuals during the larval stage, when they’re growing up and they feed a lot, they can develop into either a queen, which is very large, lays a ton of eggs, lives quite long, in some species for decades.

Or you can raise it into a worker, which is small, usually can’t lay eggs or doesn’t lay eggs, lives only for a few months often, and performs all the other tasks in the colony. So from one genome, you can make very, very different types of organisms.

FLORA LICHTMAN: Like stem cells.

DANIEL KRONAUER: Exactly. I was about to say, it’s a little bit like you start with a stem cell, and then you make either, say, a neuron or a skin cell. And that’s actually the analogy that you hear a lot when you read about insect societies, the analogy of the insect society as an organism. Or sometimes, people talk about the superorganism.

FLORA LICHTMAN: The superorganism. So do we understand what determines whether that ant egg becomes a queen or a worker?

DANIEL KRONAUER: Yeah, so there’s a lot of research that’s being dedicated to that still. And it has a lot to do with how much food the larva gets. And so the workers can feed a larva more or less food, or they can feed it different types of food. You might have heard of royal jelly in honeybees. So if a larva gets fed a lot of royal jelly, it tends to develop into queen. So ultimately, it has a lot to do with what size the larva reaches and how large it can grow.

FLORA LICHTMAN: But who’s determining how much food that larva gets? Are all the larvae getting the same amount of food, and some just get bigger than others and become the queen?

DANIEL KRONAUER: Yes, it’s a bit complex. I think the simplest scenario is that the workers who feed the larvae, they go out. They forage. They bring food back, and then they give the food to the larvae. Those are the ones that decide how much food the larvae get.

And so what a lot of ant species do is that they raise new workers or new queens in separate cohorts. So sometimes, in the spring, you see winged ants that kind of fly around. Those are queen ants, the bigger ones.

FLORA LICHTMAN: Oh, so you can have multiple queens in a generation. It’s not one that’s being picked out.

DANIEL KRONAUER: No, exactly. So most ant colonies, they have, often, one queen in the colony that lays the eggs. But when they raise queens, they raise many, many queens, often hundreds, sometimes thousands. And those queens, they have wings initially, and then they go on a mating flight. Then they mate.

Then the males usually die, and the queens shed their wings. And then they start to dig a little hole in the soil, and they found a new colony. And then you have a new colony that has [INAUDIBLE].

FLORA LICHTMAN: So we know that size is a biggie for determining how that queen program is going to get switched on in an ant. And size is determined by genes and by the environment. But your new study in clonal raider ants shows that it’s not that simple, right?

DANIEL KRONAUER: Yeah, I would say, if you wanted to distill these findings down into one main conclusion, it’s that basically, what the study shows is that there are genes that affect the body size of an individual and therefore, the cast phenotype; and then the genes that affect the relationship between the cast phenotype and the body size. There’s basically two different ways to be a queen. One is to be larger, and one is to have a genotype where queen development sets on that smaller body size.

FLORA LICHTMAN: And when does this queen program initiate? Is it when they’re in the larval stage after they’ve hatched? I mean, when do they know that they’re big enough to be queen-like?

DANIEL KRONAUER: That’s a very good question. And I think there, we still have to do a lot of work. There are some ant species where it’s determined very, very early, during development. You can almost tell at the egg stage.

FLORA LICHTMAN: Oh, wow.

DANIEL KRONAUER: And then there’s other ant species where it’s probably determined pretty late during the larval stage. And it really only becomes clear once the larva enters pupation, basically metamorphosis. So there’s a lot of diversity in ants, I think. And that’s going to be very interesting, too, to study more carefully at the developmental level and at the molecular level.

FLORA LICHTMAN: I mean, is it good to be the queen? Would you want that if you were an ant?

DANIEL KRONAUER: So, yeah, exactly, right. You think of the queen as the one individual in the colony that has all the power. But in ants, that’s not really true. The queen is basically, this individual that just lays eggs and doesn’t do much else. I don’t know.

FLORA LICHTMAN: That sounds horrible.

DANIEL KRONAUER: Exactly. It’s almost like an egg-laying machine, or something. So I don’t know if I would want to be an ant queen.

FLORA LICHTMAN: So I was reading that this is a hot topic in the ant world. Tell me why. What’s the drama around this?

DANIEL KRONAUER: Well, I think it’s just a very interesting question. It’s this extreme case of what people call phenotypic plasticity. A lot of developmental biology, evolutionary biology, is about this question of what’s classically discussed as nature versus nurture.

How much of your existence or your phenotype, the way you are, is determined by the genes you inherited? And how much is determined by the environment you’ve experienced or maybe even chance events? And it’s a really interesting and important question. And I think ants are just very, very well-suited to address those questions.

FLORA LICHTMAN: Daniel, thanks for talking to me today.

DANIEL KRONAUER: Thank you so much for having me.

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FLORA LICHTMAN: Thanks for listening. Don’t forget to rate and review us wherever you listen. It really does help us get the word out and get the show in front of new listeners. Today’s episode was produced by Charles Bergquist. I’m Flora Lichtman. Thanks for listening.

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