Brian Barnes: So, do bears hibernate in the woods? Indeed they do, but since hibernation is best defined by decreases in metabolic rate rather than changes in body temperature, it has not before been demonstrated, especially in bears hibernating under natural conditions. We've now accomplished that and found some surprises.

During hibernation, bears decrease their metabolic rate, their metabolism, to a greater extent, by 75% down to 25% of summer levels, than was expected due to their slighter decreases in body temperature, about five or six degrees Centigrade. This suppression of metabolism allows hibernating bears to save energy and thereby not eat or drink for six to seven months. In fact hibernating bears function pretty much like a closed system, all they need is air. And over the hibernation season females become pregnant and actually lactate, yet they never drink water.

Bears during hibernation enter a state where they are capable of stopping their hearts from beating for 10 to 15 to 20 seconds while they hold their breath for almost a minute, and then the heart beats rapidly again when they inhale and exhale. Measuring body temperature continuously as we have done in captive black bears in Alaska revealed that hibernating bears allow their core body temperature to decrease to no lower than 30 degrees Centigrade, about 86 degrees Fahrenheit. But then they anticipate that and begin to shiver and produce heat and raise their body temperature back up to around 34, 35, 36, not to the normal summer levels.

And then they start to cool again, and this we learned sets up cycles in body temperature that are about two to seven days in length that we'd never seen before in any kind of mammal. Especially unlike those patterns of body temperature in small hibernating mammals like ground squirrels that in the Arctic will allow their body temperature to drop below freezing, adopting temperatures of -2, -3 degrees Centigrade, colder than that of an ice cube, and stay that way for about three weeks before, like other small hibernators, they rewarm for less than a day and then return to torpor. Bears instead maintain higher temperatures and do not arouse regularly.

These are novel findings, since metabolic rate and body temperature have not before been measured together continuously in bears hibernating through the winter under natural conditions. These measurements required a unique facility, a hibernaculum that we've built in Alaska, sophisticated equipment, instruments for telemetry and respirometry that Øivind Tøien designed, and deft surgery by our colleague Dr John Blake, and collaborations with doctors Dale Edgar, Dennis Grahn, and Craig Heller at Stanford University.

Øivind Tøien: Thank you and good afternoon. This study included five American black bears which were nuisance bears captured in south central and interior Alaska by the Alaska Department of Fish and Game. The bears were transported to the Institute of Arctic Biology and placed in structures that mimic a bear's den. The dens were cube shaped, lined with straw for bedding, and were located in the woods away from human disturbance. Each den was equipped with infrared cameras, activity detectors and telemetry receiving antennas. We implanted radio transmitters in each bear that allowed us to record body temperature, heart beats and muscle activity, such as shivering.

On a typical day I would cross-country ski to work and the first thing I would do is to check on the bears, and I would do the same check before commuting each night. The video I am about to show is what the hibernating bear sounds like. The camera has an infrared light source that lets us see in the totally dark den:

[sound of bear snoring and breathing]

Robyn Williams: Yes, that's a bear snoring. But just listen to the gap between snores. Breathing has slowed down almost to a stop.

[sound of bear snoring and breathing]

Øivind Tøien: Notice the long silence between breaths. During that time the bear's heart beats very slowly, sometimes there is as much as 20 seconds between beats. Each time the bear takes a breath, the heart beat accelerates for a short time to almost that of the resting bear in summer. When the bear breathes out, the heart slows down again, and there will be another 30 to 60 seconds before the next breath.

Robyn Williams: Robyn Williams from the ABC in Sydney Australia. Could you tell me, Brian Barnes, why black bears are working for the US Army?

Brian Barnes: Well, we do receive funding support from the US Army Biomedical Research and Materiel Command, and it is along the lines of what other researchers have found, that bears, though they are virtually immobile for five or six months, don't lose much muscle mass and their bones stay calcified and strong, yet that's not what happens with people. And so rehabilitation sciences are very keen to...certainly the army, but all of biomedical medicine, if you are laid up with a broken arm or can't move with bed rest, then it takes many, many months to recover that mass.

Bears don't do that, and they are not particularly active. They do get up every day or two and maybe stretch and turn around and lie down again, but for the most part, as you saw, they're quite immobile, yet somehow they have tricked their tissues, the bones and muscle, to think that they're still doing work. And so we're all very interested in finding out the molecular signals of that.

In our university we have micro arrays and genetic resources to look at differential gene expression in black bears as well as ground squirrels. And we hope by following those changes that will get clues to what biochemical pathways have been altered. And then the trick would be to find drugs that would emulate those same changes in people.

Robyn Williams: So which patients do you think could most benefit?

Brian Barnes: We are often asked what's the lowest-hanging fruit for payoffs from hibernation research, and I guess these days I would say it's probably going to be in bone maintenance, the fact that not just hibernating bears but actually ground squirrels as well have now shown that they preserve the strength of the bones, the calcium concentrations, throughout these seven-, eight-month periods when they are just sitting in a nest. There seems to be some biochemistry and endocrine differences, particularly in black bears, that are being discovered now that could pay off for people to prevent osteoporosis.

Robyn Williams: Yes, you mentioned that in connection with space travel as well. It's famous that people in spaceships tend to lose calcium and so on and get the osteoporotic effect. In what way are you following that up?

Øivind Tøien: Well, in the space station, for instance, they will have an exercise regime where they try to maintain the body, including muscle and bone, but because of the zero gravity field, the bones do not get loaded and thereby they actually still lose a lot of bone mass.

Robyn Williams: And somehow the bears manage to do this without an exercise machine, just lying there.

Øivind Tøien: Yes, just sitting in the den, they have minimal activity, probably a few minutes per day, where they will rise up, scratch a little bit, rearrange bedding before lying down again, and they are still for another...it could be a day or a couple of days before they move much again.

Robyn Williams: Brian, you mentioned those squirrels, they go down to even subzero temperatures. That's amazing.

Brian Barnes: Yes, they supercool their body fluids, that's called. It's a meta-stable state of water in this case in the fluids of their body which should freeze but doesn't in the absence of what's called an ice nucleator, and in fact if you take one of these squirrels and poke through its skin with an icicle it will start the crystallisation process off and they will freeze and die. So somehow they are able to prevent that from happening both internally and externally.

I want to follow up on this question about bones and muscle. What to do next? And we are planning experiments to see whether bears and squirrels can also prevent the loss in mass during the summer. Do they transform to enter a hibernation-ready state that protects them from that, or at any time of year could you put them into a box and they'd be fine? And we haven't done those experiments yet, and the challenge is how do you create disuse in a summer-active animal?

Robyn Williams: But one rather intimate question, how did the bear get pregnant and sit there in the burrow for all that time? Obviously it didn't get pregnant in the burrow, so what happened?

Øivind Tøien: Yes, there is no males around but bears have what is called delayed implantation, which means that even if they have been together with a male bear in summer, it takes several months before the embryo then starts to grow.

Robyn Williams: Kangaroos do that too, don't they?

Brian Barnes: They invented it. In fact they'll have three going at once, the kangaroos do, but bears and skunks and cats all have this deal where the egg will become fertilised but stay in the oviduct and not descend into the uterus until there is a trigger, which in this case may be the shortening days that bears experience when they are in hibernation. So they don't technically become pregnant until they are in hibernation.

Robyn Williams: Do you have, as rumour has it, dinosaurs in Alaska?

Brian Barnes: Not today, not currently, but there is fossil evidence...

Robyn Williams: Not even politically?

Brian Barnes: Well, even she's gone. But evidence shows that there were dinosaurs in northern Alaska 65 million, 85 million years ago when, interestingly enough, the continent of North America and the Alaska part of it was closer to the North Pole than it is today, and it was much warmer then. It was obviously green and these dinosaurs were feeding during the summer from the plant growth. But what did they do in the winter? Because even 65 million years ago the Earth was still off-kilter and we had seasons, and so there had to be a long period of no sunlight in which those plants would have died.

So we're interested, as hibernation physiologists, because if you think about the choices that a dinosaur might have, they could migrate, they could move south as the caribou do. But it's thought that they didn't, they were smaller body sized, and some of the fossils show young who are at an age that they would have been in the winter and how could they accompany their parents. So we think what they might have done is hibernated. Marsupials do it, even echidnas, and it's throughout the whole radiation of mammals and even some lizards, extant today, fatten and then tuck in during the winter and drop their metabolism. And so it is an intriguing possibility that Alaskan dinosaurs were the original hibernators.

Robyn Williams: Fascinating, thank you both.

Brian Barnes: You're welcome very much.

Robyn Williams: And now they're looking dinosaur bones to check them for growth rings that might tell the hibernation tale. Professor Brian Barnes with his Norwegian colleague Øivind Tøien, both from the University of Alaska in Fairbanks.