Short Wave - How Bears Come Out Of Hibernation Jacked

Episode Date: April 30, 2020

Spring is in the air — and so are black bears coming out of hibernation. Rae Wynn-Grant, a large carnivore biologist, explains there's a lot more going on during hibernation than you might expect.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. So a few weeks ago, I was sitting around just gazing outside my window. Leaves are turning green. Daffodils and tulips are popping up and doing their thing. You know, just watching spring blossom in front of me. And when I think spring, I think bears. bears coming out of hibernation. I mean, who doesn't?

Ray, I cannot tell you how excited I am to talk about this because I was like, I know there's some cool physiology going on. I'm going to read as much as I can about this before I talk to Ray so that she's impressed with me. And I couldn't stop writing questions because there's so much. There really is. As you can hear, I was aggressively excited to talk to Ray Wind Grant. She's a large carnivore biologist who studies black bears. Ray finds black bears, let's say

relatable. Oh, I love that they eat and sleep so much. It's like, honestly, they make me feel so close to them because their main, like, drivers in life are about, like, finding a lot of food so that they can sleep for a long time. Same's bears. It turns out. It turns out, that there's a lot more to hibernation than finding a sweet cave and taking a long nap. So today, an in-depth look at hibernation and the unbelievable bear science that makes it possible. I'm Maddie Safaya, and this is Shortwave, the Daily Science Podcast from NPR. So before we really get into it with Ray, let's set some road rules. First of all, we're sticking to American black bears.

And what you need to know is that not all black bears hibernate. It's all about how much food is around. And that changes based on where you live your bear life. Black bears are kind of what we're going to be referring to as habitat generalists. And they're found all over North America. So the bears in Florida and the Everglades don't usually hibernate. Second, there is this scientific debate over whether or not bears truly hibernate. And so like a useful definition of hibernation, basically, is like a physiological state of a significantly decreased metabolism.

Basically, food has dried up. So some animals enter this low energy mode. How low energy these bears are is up for discussion. But Ray is firmly on team bears do hibernate. So if you were to ask me, and I'm willing to take on this debate, I really am officially on the record. I would argue that they are true hibernators because their metabolism changes from such a significant level in order to avoid food scarcity. We're going with Ray on this one. Moving on. If you're a black bear who hibernates and you are about to go literally months without food, there's one thing you got to do to get ready. It's so easy.

You're eating everything you can find everything. You gotta get thick with two seas by any means necessary. It's called optimal foraging theory and it sounds a little complicated but it's so easy to understand also people do it too. And optimal foraging theory suggests

that bear's job is to eat as many calories as possible while expending as little energy as it can. So that's why we see bears in some places eating tens of thousands. of calories of berries, you know, every day.

Wow. Or if a bear lives in a place where there's, you know, rivers and streams and freshwater fish in there, they're eating tons and tons of fish. Like whatever is around them, they're just going to gorge on that because they don't have to travel far and expend a lot of energy to get more food.

Okay, so I'm a bear. I have just worked hard to chub up as fast as I can with the least amount of energy. And I have, like, found the, place that I'm going to hibernate. What, like, what do those places look like? Because I thought they were all, like, deep caves, but that's not necessarily true, right? Well, I, like, one of my personal desires is to find a bear denning in a cave. Like, I want that more than anything, because you grow up with that, right? As, you know, as a kid, you grew up with these stories about

there's a bear in the cave. And, and of course they do. I mean, you know, if a bear comes upon an empty cave, it is 100% going to make its winter den there. But, you know, how many caves are in, you know, a single forest, like usually not many? So outside of the cave example, bears use a lot of different places to create a hibernation den. So hollowed out logs are good ones. If there's, you know, a tree that has fallen down and is easy to kind of dig into a barrel makes space for itself in, you know, in a log, in a tree trunk, you know, sometimes just next to a whole bunch of bushes. And another thing I love about bears is that some of them, you know, in particular, maybe male bears, will sometimes just sit down and then that's, they're done.

You know, it's a cool thing about being a bear is they're top predators, right? They have no natural enemies in their systems. They can feel safe all the time. you know, humans cause huge problems to bears, but they, you know, haven't evolved necessarily to understand that. So they feel like they are big and bad and safe all the time and, you know, can just lay down wherever they want. Love that. Okay. So I know that there are all of these massive changes that happen in the bear body during hibernation. Tell me about some of the coolest ones in your mind.

Yeah. So, you know, maybe this is because I have. have a preschooler and so we are like just about a year or so past like potty training so this might be on my mind a lot but I think one of the coolest things is that bears will recycle their own waste during hibernation so they they don't you know like urinate or defecate at all during this time period it just is recycled in their bodies but but that allows them to you know essentially like not lose hydration or not lose, you know, a certain amount of nutrients during hibernation, which is, it's just tremendous. I mean, it's so efficient.

It's so efficient, it's really amazing. It's just like a beautiful, efficient biological system, you know? Mm-hmm. Mm-hmm. Yeah. It's, oh, gosh, I could just keep going, but it's really cool. Yeah, yeah. So, okay, probably one of the most ridiculously cool things about their physiology in this state is that

Although bears lose a lot of body weight during hibernation, they don't actually lose a ton of like muscle mass or or bone strength, like way less than humans would if we didn't move for three months. Right. I mean, that's wild, Ray. Well, it's because they get so fat. It's like, I mean, so, you know, what is so, I think what is what is interesting, you know, as a human being, especially in like American society is that we associate fat. with something bad, right? Like if people get too fat, you know, we might encounter a lot of health problems. But for bears, being fat makes you actually more ecologically fit. And sometimes they're putting on, you know, hundreds and hundreds of pounds just to prepare for hibernation. And so,

if they do that, then of course, they're not losing muscle mass when they hibernate. They are not losing, you know, losing bone density. They're just burning that fat, recycling their waste, like doing this slow burn all winter and then emerging, you know, as healthy as ever. Yeah. This brings me to one of the wildest bear things that is blowing my bear mind is that some mama bears give birth during hibernation. Yes. So all mama bears give birth during hibernation unless they live in a place where they don't hibernate. Yeah. So, you know, in the ecology community, we essentially do this thing where we assign a birth date to every animal that we encounter. And all black bears have a January birth date, all of them.

So for the most part, you can assume that any black bear you've ever seen ever in your life and ever will was born in January. And in most parts of North America, that's a time of hibernation. You know, from the few studies where we've been able to witness, you know, a hibernating female bear giving birth, which is few, we've been able to see her show some obvious signs of labor, right? So she's like awake. She's not loving it, but she's giving birth to, you know, a couple of very, very, very small cubs. So they grow, you know, from one pound to, you know, like 10 pounds or so. And, you know, all in the den while the mother is, you know, doing her best to get some rest.

but, you know, she's got like a litter full of kiddos with her. So it's not, you know, those winters as she gives birth, they're not the most restful periods of hibernation. Gotcha, gotcha, gotcha. Yeah, no, I mean, the kids are around. Oh, yeah. She's like nurse, but I'm trying to hibernate, so keep it down. Yeah.

So, Ray, I'll start this question by asking that you still respect me as a person as a scientist after I ask it. I have read that they take kind of an epic post-hybernation poo. Is that right? So, I mean, you can imagine, right? I mean, it's not so far-fetched that after like holding it for, you know, half the year, you might really want to get rid of that stored up, you know, waste in your body. And so the answer is yes, yes.

They, you know, they are all about cleansing their system, you know, kind of doing a spring cleaning, if you will. I will. But that does happen. And it allows their body, again, to kind of just get rid of that waste that they were recycling within them for a while and, you know, get some fresh water, get some fresh food and start the metabolism, you know, back up. Yeah. So what is, what's the coolest part of all of this to you? Like, what gets you jazzed about this? You know, I love the way, I love watching patterns and cycles, you know,

happen in nature. It gives me somehow this sense of comfort that the natural world is taking care of itself. And I think that humans can can learn a lot from it. So even in like a fairly, you know, forgive me from kind of leaving the scientific realm, but in almost like a spiritual way, I've always appreciated winter as a time of like shutting down and solitude and, you know, maybe inner change as opposed to like outward growth. And so I really love seeing that in bare hibernation and especially doing it over and over year after year, you know, this need to conserve and to be still for a portion of the year in order to be super productive and active and other parts of the year. And so I would definitely argue that is my all-time favorite thing is just, you know, that predictability of it

makes me feel so comfortable and makes me feel like nature is just going to keep doing its thing, especially if we don't get too much in the way. Ray Wynn Grant is a National Geographic Explorer and a wildlife ecologist. Today's episode was produced by Rebecca Ramirez, clearly the apex predator of Shortwave. It was edited by Viet Le and fact-checked by Emily Vaugh. I'm Maddie Safaya, and you've been listening to Shortwave from NPR. Oh, and speaking of which, if you've been liking what you're hearing, go ahead and subscribe to our podcast. That way you get episodes as soon as they drop.

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