00:00 Every year, something switches in the brains of these coastal brown bears. Before they hibernate,
00:04 they lose their ability to feel full and pack on hundreds of pounds. In fact, it's become an
00:09 annual competition to celebrate these fat bears. This is 747 in summer 2022, and this is 747 in
00:16 October 2022. In the span of a few months, 747 and other bears like him at remote Katmai National
00:21 Park are gaining 20 to 40 percent of their body weight. And for bears, that's a good thing.
00:30 Fat Bear Week is a celebration of success and resilience in our healthy population of brown
00:38 bears. It is a week-long march-style madness bracket where the public gets to vote on their
00:46 favorite fat bear. Katmai has some of the fattest bears in the world because of a strong sockeye
00:52 salmon population. The salmon run lasts from late June through September, allowing the bears to
00:56 feast. Sockeye salmon are very nutritious food. They're actually pretty high calorie. One sockeye
01:01 salmon will contain anywhere between two to five thousand calories. Bears on average, they might
01:07 catch ten fish per day. If they are consuming the entire fish, they're getting anywhere between
01:12 20,000 and 50,000 calories per day. And salmon is a good source of fat for bears looking to
01:19 pack on the pounds. They're actually going to focus on just the fattiest parts of the fish. So
01:24 the skin, the brains, the eggs and females, they eat that, they strip the skin, they leave it,
01:30 and then some other bears or other animals will pick off those carcasses. There is one particular
01:35 bear, Bear 480 Otis, who was observed on the webcam to consume 45 salmon within a five hour period.
01:44 And bears are catching these fish at Brooks Falls. But why are bears actually fishing?
01:51 It has something to do with a metabolic process called hyperphagia. Hyperphagia is a general term
01:56 that basically denotes overeating. The term can be applied to humans. With bears, it means that
02:00 there is a period of the year right before they go into hibernation, the fall, where they are
02:04 eating just as much as they possibly can in order to try and prepare for hibernation.
02:10 But bears are mysterious creatures. Researchers still don't really understand why bears enter
02:15 this state. There's a few hormones that act as what we call satiety factors that tell the body
02:19 that we're full. A couple of the big ones are a hormone called leptin. And leptin is released by
02:24 adipose tissue. And that is something that helps tell our body like, hey, we've got enough stored
02:29 energy, so you don't need to eat anymore, you're full right now. Another one is called ghrelin,
02:33 that's released by the stomach. And it says, hey, I'm full right now, you should stop eating. So
02:38 their body's not telling them, I'm full. So they'll just keep on eating and eating without
02:43 that feedback telling them to stop. If they are not moving a lot, not working a lot, not using
02:47 those muscles, then that energy is going to be stored because they don't need to use it right
02:51 then. And the way that it's generally going to be stored for bears is in adipose tissue. So we're
02:55 getting a lot of energy that is then being stored as fat as they prepare to go into hibernation so
03:00 they can use that through the winter. Other animals such as hummingbirds enter hyperphagia
03:04 before long migration periods. But for most animals like humans or cats, hyperphagia is
03:10 not a good thing. Overeating can have a lot of negative health impacts, heart disease, diabetes,
03:15 very well known. All of these sorts of things can happen when you've got uncontrolled eating and
03:19 that energy is not being used. Bears then enter a hibernation period and go into dens at Katmai.
03:25 What hibernation really is, it's a reduction in the metabolic rate. So the bear is not necessarily
03:29 asleep. In fact, they still have circadian rhythms where they will be sort of more active during the
03:34 day, less active at night. So they're still awake throughout this entire period. Heart rate during
03:38 hibernation I would think of as being in the 10 to 12 beats per minute. They're just, their
03:42 metabolism has been slowed down, their heart rate slows down, their respiration rate slows down.
03:46 Generally, they're not eating or drinking, urinating or defecating, though there are
03:50 certainly exceptions to that. Unlike some other hibernating animals, bears don't actually see
03:55 too much of a drop in body temperature. So a lot of the animals where hibernation was originally
03:59 defined are some of the smaller mammals, and they will drop their body temperature down closer to
04:04 ambient temperature and hold very close to freezing. But brown bears will have a body
04:10 temperature of around 36, 37 degrees Celsius. And then during hibernation, they're only dropping
04:15 down to maybe 31 degrees Celsius, about a six degree drop in body temperature. Bears can also
04:22 give birth while in hibernation. Usually they give birth from late December up until early February.
04:27 Their metabolic rate will increase, not all the way back up to active state, but it will increase
04:32 quite a bit. And then they give birth and immediately after giving birth, essentially,
04:37 the metabolic rate will drop straight back down to a full hibernation period. And the cubs will
04:41 just kind of climb underneath mom and they'll start nursing while mom continues to hibernate.
04:46 And all that fat that's been stored up helps them to survive a long winter.
04:51 Bears store all this fat going in hibernation so that they have energy so that they can survive
04:55 through the winter. They'll lose between 25 and 40% of their body weight over the winter.
05:00 That's going to be higher for females that give birth. They're going to be closer to the 40%
05:05 range. Just some of the really large males tend to be closer to the 25% range. One interesting thing,
05:10 that fat is not only giving them energy, it's also providing... So the catabolism of fat also
05:15 provides water. So we mentioned that they're not drinking all winter long. This is one way that
05:19 their body is able to get a little bit of water. Since they're losing water constantly through
05:23 respiration and stuff like that, they do need to offset that somehow. And the catabolism of fat
05:26 actually creates water that they're using as well. Doing any of this type of work on bears can be
05:30 very challenging. Hibernation is a fairly well-studied physiological state. Despite that,
05:36 we still don't really know what triggers hibernation. It's really tough to nail down
05:41 precisely individual factors, particularly when a lot of times it's not one factor that's triggering
05:47 it. It's multiple things that are working in concert that might lead to bears changing
05:50 physiological states like this. So who will win this year's fat bear competition? One of those
05:55 big contenders is our reigning champion, 747. He still looks really, really good. When he came out
06:02 of hibernation, I was fortunate enough to see him the first week of June. And I was like, "Oh my
06:07 goodness, this is a bear that lost one third of his body weight." There's some other large males
06:11 that are also looking really good. Number 32, Chunk. There are also some females that are
06:18 in the running for it. Bear 128, Greaser. She is looking really, really good.
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