0:00:08 > 0:00:13Stretching out before me is the magnificent Yellowstone.
0:00:18 > 0:00:20This is one of the most dynamic...
0:00:22 > 0:00:26..unpredictable and exciting environments on Earth.
0:00:32 > 0:00:34Deep in the Rocky Mountains,
0:00:34 > 0:00:36this vast wilderness
0:00:36 > 0:00:39is home to North America's most iconic wildlife.
0:00:43 > 0:00:46But every year, Yellowstone's animals
0:00:46 > 0:00:48are pushed to their absolute limits.
0:00:51 > 0:00:54Temperatures can swing from minus 40 in winter
0:00:54 > 0:00:57to approaching plus 40 in summer
0:00:57 > 0:01:01and at the heart of this change is the thaw.
0:01:02 > 0:01:06This melt can last several months from March to July,
0:01:06 > 0:01:10and is one of the most dramatic seasonal events on Earth.
0:01:13 > 0:01:17How do the animals cope with such extremes of temperature?
0:01:19 > 0:01:21We're here to find out.
0:01:24 > 0:01:27I'm joined by biologist Patrick Aryee...
0:01:27 > 0:01:30- Whew!- That's intense.
0:01:30 > 0:01:33..and a team of wildlife cameramen and expert scientists.
0:01:37 > 0:01:40I'll be following some of the area's key wildlife.
0:01:40 > 0:01:42We'll be getting to know families
0:01:42 > 0:01:44through their highs and lows, starting right now.
0:01:46 > 0:01:49And I'm looking at the bigger picture,
0:01:49 > 0:01:51understanding the science of the thaw
0:01:51 > 0:01:53during each season, across winter,
0:01:53 > 0:01:56spring and summer.
0:01:56 > 0:01:57That's brilliant.
0:01:59 > 0:02:00Living here is tough.
0:02:02 > 0:02:05The changing climate has brought freak storms,
0:02:05 > 0:02:08flash floods and raging fires,
0:02:08 > 0:02:12making life for the animals even more extreme.
0:02:15 > 0:02:18With unprecedented access to this remarkable place,
0:02:18 > 0:02:21over the next three nights we're bringing you Yellowstone
0:02:21 > 0:02:23as you've never seen it before.
0:02:26 > 0:02:30Welcome to "Yellowstone: The Wildest Winter".
0:02:30 > 0:02:32WOLF HOWLS
0:02:45 > 0:02:47It's early March.
0:02:51 > 0:02:54This is a world blanketed in thick snow and ice.
0:02:57 > 0:03:00And after four long, hard months of winter,
0:03:00 > 0:03:05the animals still have more weeks of brutal cold to endure.
0:03:08 > 0:03:11We are in the north-west of the USA,
0:03:11 > 0:03:142,000 metres up in the Rockies.
0:03:14 > 0:03:18This is an area known as the Greater Yellowstone Ecosystem.
0:03:18 > 0:03:20It's the size of Scotland,
0:03:20 > 0:03:22includes two national parks
0:03:22 > 0:03:26and is bounded on three sides by mountain ranges.
0:03:29 > 0:03:30In this programme,
0:03:30 > 0:03:33we'll be following the lives of animals
0:03:33 > 0:03:37that have to adapt to extreme change,
0:03:37 > 0:03:39as winter turns into spring.
0:03:41 > 0:03:43For many, this is the ultimate challenge...
0:03:45 > 0:03:47..particularly for Yellowstone's biggest,
0:03:47 > 0:03:51and, at this time of year, hungriest carnivores.
0:03:51 > 0:03:54Patrick's heading high up into the mountains on their trail.
0:03:57 > 0:04:02It's amazing to think that somewhere out there are grizzly bears.
0:04:05 > 0:04:08But it's right at the tail end of winter and it's really cold,
0:04:08 > 0:04:11so most of those bears are still going to be hibernating in dens
0:04:11 > 0:04:13deep beneath the snow.
0:04:13 > 0:04:16And, for most, that's a sensible strategy.
0:04:18 > 0:04:21Right now the weather is bitterly cold
0:04:21 > 0:04:24and down to minus 21 Celsius up here.
0:04:24 > 0:04:26It's usually later in March
0:04:26 > 0:04:29that the majority of grizzlies start coming out.
0:04:29 > 0:04:31I'm in the Gallatin Mountains
0:04:31 > 0:04:33in the north-west of Yellowstone.
0:04:41 > 0:04:43Our grizzly expert, Casey Anderson,
0:04:43 > 0:04:46is out here monitoring bear activity.
0:04:46 > 0:04:49- Hello, Casey. How are you doing, man?- Good.
0:04:49 > 0:04:53We're looking for any bears that are emerging from hibernation early,
0:04:53 > 0:04:57and the most likely place to find them is at the higher elevations,
0:04:57 > 0:04:58where grizzlies have their dens.
0:05:01 > 0:05:02Good view, huh?
0:05:02 > 0:05:04Absolutely stunning.
0:05:04 > 0:05:06But it does look completely devoid of life.
0:05:06 > 0:05:09How are we even going to start looking for these bears?
0:05:09 > 0:05:12You're right, there's not much moving around out here.
0:05:12 > 0:05:15Right now the only bear that probably will be out
0:05:15 > 0:05:17is those first big males.
0:05:19 > 0:05:22Casey believes some grizzlies are already leaving their dens
0:05:22 > 0:05:27because of a recent spell of unseasonably mild temperatures.
0:05:27 > 0:05:30So, just a few days ago we had really warm weather,
0:05:30 > 0:05:31it felt like spring.
0:05:31 > 0:05:34It's been so warm you've got to believe the bears are thinking
0:05:34 > 0:05:36it's getting close to spring
0:05:36 > 0:05:39and that can be really bad news, because it's not spring
0:05:39 > 0:05:42and they come out here and winter can hit again
0:05:42 > 0:05:45and that could really be devastating to a lot of animals,
0:05:45 > 0:05:46including the bears.
0:05:48 > 0:05:52Last week, right here, it was 15 degrees warmer than today.
0:05:54 > 0:05:57Now it's back to more typical March conditions.
0:06:03 > 0:06:05Casey, this weather's pretty...
0:06:05 > 0:06:06HE COUGHS
0:06:06 > 0:06:07Whew!
0:06:07 > 0:06:10- This is pretty intense. - That's intense.
0:06:10 > 0:06:13How do the bears cope with this?
0:06:14 > 0:06:17Bears are tough, but this is difficult for them, too.
0:06:23 > 0:06:28Suddenly, Casey sees an opening that could be a bear den.
0:06:28 > 0:06:31- You see, like, these natural rock formations.- Oh, yeah.
0:06:31 > 0:06:34- It's like a little cave.- Yeah.
0:06:34 > 0:06:37It's perched high on a steep slope.
0:06:41 > 0:06:42Not easy going.
0:06:47 > 0:06:49The things I'll do for bears.
0:06:54 > 0:06:58Would that be a good site for a bear to hibernate in?
0:06:58 > 0:07:00The statistics are this -
0:07:00 > 0:07:0470% of bears will dig in a north-faced slope.
0:07:04 > 0:07:08At least 30% of this population does something else,
0:07:08 > 0:07:12and something else is something like this.
0:07:12 > 0:07:16Ready-made, in the sun,
0:07:16 > 0:07:19they can get down in there and trap the heat.
0:07:19 > 0:07:21It's perfect.
0:07:21 > 0:07:23And it's not all one big sleep.
0:07:23 > 0:07:28During hibernation, the pregnant females also give birth.
0:07:28 > 0:07:31It's March now, and those little guys were born two months ago.
0:07:31 > 0:07:35So, just imagine these little guys that big
0:07:35 > 0:07:38and they're going to grow about that big in about another month.
0:07:38 > 0:07:40And then in another month from now
0:07:40 > 0:07:43they're going to pop their heads out, and this is going to be home.
0:07:43 > 0:07:48It's just amazing, think about that, the first view.
0:07:48 > 0:07:49It's a pretty good one.
0:07:49 > 0:07:52We head off before we disturb any sleeping bears.
0:07:59 > 0:08:03Emerging in these conditions would mean the odds are against them...
0:08:11 > 0:08:15..and 50 miles further east that's exactly what's happened.
0:08:16 > 0:08:19Scientists have tipped off one of our camera teams
0:08:19 > 0:08:23about a grizzly bear that has taken the risk of emerging early.
0:08:25 > 0:08:26It's clearly struggling.
0:08:30 > 0:08:32The warmer weather of a week ago
0:08:32 > 0:08:35has been followed by plunging temperatures and more snow.
0:08:37 > 0:08:39This could make finding food impossible.
0:08:43 > 0:08:47The grizzly finally makes it down from the mountains
0:08:47 > 0:08:48to the valley floor.
0:08:52 > 0:08:54There are plenty of bison here,
0:08:54 > 0:08:57but even a starving bear won't tackle
0:08:57 > 0:08:58these formidable beasts.
0:09:03 > 0:09:06Bears rely heavily on their extraordinary sense of smell
0:09:06 > 0:09:08to find food.
0:09:10 > 0:09:13Their nose bristles with over a billion nerve cells.
0:09:15 > 0:09:17It's their super sense...
0:09:19 > 0:09:22..and it's led this bear to a pond.
0:09:43 > 0:09:48A dip in the sub-zero water could zap his precious energy.
0:09:53 > 0:09:56Grizzlies are superb at catching fish...
0:09:59 > 0:10:01..but it's not fish he's after.
0:10:09 > 0:10:10It's a bison.
0:10:11 > 0:10:14Long dead, frozen all winter
0:10:14 > 0:10:17and now released from its icy tomb.
0:10:21 > 0:10:25This is probably the first meal the bear's eaten
0:10:25 > 0:10:27in over four months.
0:10:28 > 0:10:30It offers a huge protein hit...
0:10:32 > 0:10:34..but he'll need to hang onto it.
0:10:36 > 0:10:39The carcass's smell attracts scavengers.
0:10:43 > 0:10:46These coyotes won't fight the bear -
0:10:46 > 0:10:49he's 15 times their weight -
0:10:49 > 0:10:51but they will harass him for scraps.
0:10:56 > 0:11:00He tries to mask its scent by covering it with grass.
0:11:01 > 0:11:03This will also slow down the bison's decay.
0:11:11 > 0:11:15Having lost up to a third of his body weight during hibernation,
0:11:15 > 0:11:19he's determined to keep these precious nutrients for himself.
0:11:44 > 0:11:46Despite emerging from his den early,
0:11:46 > 0:11:49this lone bear has hit the jackpot...
0:11:55 > 0:11:57..but the stakes are high,
0:11:57 > 0:12:00and the majority of grizzlies won't bother venturing out
0:12:00 > 0:12:03until the consistent warm weather of spring.
0:12:09 > 0:12:12But that still seems a long way off.
0:12:16 > 0:12:19The snow shows no sign of letting up.
0:12:26 > 0:12:30All of the animals here face the same basic challenge -
0:12:30 > 0:12:33finding enough food to survive until spring.
0:12:35 > 0:12:38Our crews are out across the region
0:12:38 > 0:12:42to capture the stories of how the wildlife is coping
0:12:42 > 0:12:44in these last days of winter.
0:12:53 > 0:12:57Yellowstone's elevated position and horseshoe of mountains
0:12:57 > 0:13:01channel and trap the cold air driving in from the north,
0:13:01 > 0:13:04and moisture coming in from the Pacific Ocean.
0:13:06 > 0:13:10This leads to prolonged periods of extreme weather.
0:13:20 > 0:13:22When the snow melts in spring,
0:13:22 > 0:13:27it feeds into a thousand rivers and streams across Yellowstone.
0:13:27 > 0:13:33These 2,500 miles of running water are hugely important,
0:13:33 > 0:13:35not just for Yellowstone,
0:13:35 > 0:13:37but they provide an essential resource
0:13:37 > 0:13:40for millions of people and animals
0:13:40 > 0:13:43right across the Western United States.
0:13:45 > 0:13:49Scientists constantly monitor how much snow is building up here
0:13:49 > 0:13:52during the winter.
0:13:52 > 0:13:54To understand what's going on this year,
0:13:54 > 0:13:57I am joining a team up in the Beartooth Mountains
0:13:57 > 0:14:01in the north-east on their cool commute to work.
0:14:03 > 0:14:06This is possibly the best office I have ever been to.
0:14:06 > 0:14:09THEY LAUGH
0:14:09 > 0:14:11This looks like a pretty good spot.
0:14:12 > 0:14:15Oh, wow.
0:14:15 > 0:14:19It's right at about 205 centimetres.
0:14:19 > 0:14:20OK.
0:14:21 > 0:14:24Lucas Zukiewicz is one of the hydrologists
0:14:24 > 0:14:28who spends the winter carrying out health checks on the snow.
0:14:28 > 0:14:30Our entire history of our snowpack,
0:14:30 > 0:14:31starting mid-October,
0:14:31 > 0:14:33is really in this snowpack here.
0:14:33 > 0:14:35So we're going to dig a hole down into the ground,
0:14:35 > 0:14:38and it's pretty much the coolest layer cake
0:14:38 > 0:14:39that you're ever going to see.
0:14:39 > 0:14:41LAUGHING: I love that.
0:14:41 > 0:14:43I have a feeling that I might be here for months.
0:14:43 > 0:14:45Right, OK. So...
0:15:00 > 0:15:02Yeah, I've hit grass!
0:15:04 > 0:15:05That is so cool.
0:15:05 > 0:15:08I have to say, coming from a country where, you know,
0:15:08 > 0:15:11if you get four centimetres of snow it's newsworthy,
0:15:11 > 0:15:14to look at that and to kind of understand
0:15:14 > 0:15:19that that is a record of your winter, that's quite cool, isn't it?
0:15:19 > 0:15:23It's amazing. And the best part of this job is it's never the same.
0:15:23 > 0:15:25Every year is different.
0:15:25 > 0:15:27It's like hitting the reset button on it every year.
0:15:27 > 0:15:32So it's time for us to analyse what the snowpack can tell us.
0:15:32 > 0:15:35So, looking at it from bottom to top, here,
0:15:35 > 0:15:37we are looking at a time series.
0:15:37 > 0:15:40So we have our early season, October snowfall,
0:15:40 > 0:15:43probably our Thanksgiving and Christmas snowfall
0:15:43 > 0:15:45- that we have here. - You had a white Christmas?
0:15:45 > 0:15:47We had a white Christmas this year, it was great.
0:15:47 > 0:15:50Various measurements enable Lucas and his team
0:15:50 > 0:15:53to work out how much snow is building up here,
0:15:53 > 0:15:55and how dense it is.
0:15:56 > 0:15:59The texture of it here is completely different.
0:15:59 > 0:16:03It feels much more compact, exactly as when we were digging it out.
0:16:03 > 0:16:07The density reflects how much water is contained in each layer
0:16:07 > 0:16:10of the snowpack and that varies
0:16:10 > 0:16:13depending on the temperature when the snow fell.
0:16:13 > 0:16:15Maybe we see some pretty well bonded snow in here,
0:16:15 > 0:16:18which is generally an indication of warm temperatures.
0:16:18 > 0:16:21- OK.- Warm temperatures actually bond the snow pretty well together.
0:16:21 > 0:16:23First of all, we're going to stick one right up here
0:16:23 > 0:16:24on the surface of the snow.
0:16:24 > 0:16:28Measuring the temperature is also key in helping to predict
0:16:28 > 0:16:32when the bulk of the water will flood down into the valleys.
0:16:32 > 0:16:33The next one at 170,
0:16:33 > 0:16:35we are going to stick that right below
0:16:35 > 0:16:36that little crust layer that we saw.
0:16:36 > 0:16:39And these readings also provide clues
0:16:39 > 0:16:43as to why some mammals hibernate deep in the snow.
0:16:43 > 0:16:44Stick it right in the ground.
0:16:44 > 0:16:46In the grass.
0:16:46 > 0:16:49So, we can see here that our snow surface temperature -
0:16:49 > 0:16:51what does that one say?
0:16:51 > 0:16:53I would say minus eight.
0:16:53 > 0:16:55But as we move further down the snowpack...
0:16:55 > 0:16:57- It's warmer!- It's warmer, it's minus three degrees.
0:16:57 > 0:16:59That's mad.
0:16:59 > 0:17:02OK. And if we go even closer to the ground...
0:17:02 > 0:17:03It's almost on zero.
0:17:03 > 0:17:07Yep - so, the ground is generally close to zero degrees Celsius
0:17:07 > 0:17:11through the winter, so the snowpack is also insulating the soil.
0:17:11 > 0:17:13But it also makes sense,
0:17:13 > 0:17:16when you look at something like a grizzly bear
0:17:16 > 0:17:18hibernating in the winter beneath the snow -
0:17:18 > 0:17:22I now understand why it chooses to hibernate there,
0:17:22 > 0:17:23because it's warmer.
0:17:23 > 0:17:25Snow caves are pretty warm.
0:17:25 > 0:17:27That's brilliant.
0:17:27 > 0:17:29This insulating effect
0:17:29 > 0:17:33not only allows bears to hibernate in snow dens,
0:17:33 > 0:17:35it keeps the grass alive.
0:17:35 > 0:17:38Vital food for herbivores
0:17:38 > 0:17:41and whilst it may look just like a white wall,
0:17:41 > 0:17:45we're actually looking at an enormous reservoir.
0:17:48 > 0:17:52When the weather warms up enough to heat the snowpack right through...
0:17:56 > 0:17:59..billions of litres of water run off the mountains
0:17:59 > 0:18:01into the rivers and lakes of Yellowstone.
0:18:03 > 0:18:07Is the timing of the thaw important for you?
0:18:07 > 0:18:10It is, because it affects when we see the bulk of the water
0:18:10 > 0:18:12- move into our river systems.- Right.
0:18:12 > 0:18:14This is our reservoir that we have in our mountains,
0:18:14 > 0:18:17this is how we get our water, this is how it flows through the park.
0:18:17 > 0:18:20So, do you think when the thaw comes,
0:18:20 > 0:18:22it's going to be a normal year,
0:18:22 > 0:18:24or an abnormal year?
0:18:24 > 0:18:25We are slightly below average
0:18:25 > 0:18:28with the snowpack that we have here in place, at this elevation,
0:18:28 > 0:18:30but really it is going to be the next month or two
0:18:30 > 0:18:32and the weather that we experience
0:18:32 > 0:18:35that is going to dictate what we see this year in terms of our thaw,
0:18:35 > 0:18:37and how that impacts the bigger ecosystem.
0:18:39 > 0:18:42It will be interesting to see what happens in the coming weeks,
0:18:42 > 0:18:47as the weather has already proved highly volatile this winter.
0:18:47 > 0:18:49There was a jump in temperatures
0:18:49 > 0:18:53and an unusually warm period at the end of February.
0:18:53 > 0:18:55March has now seen a return to the colder,
0:18:55 > 0:18:58more typical weather for this time of year.
0:19:00 > 0:19:01In recent years,
0:19:01 > 0:19:05Yellowstone has experienced milder winters more often
0:19:05 > 0:19:08and this one appears to be following that trend.
0:19:10 > 0:19:14Patrick has headed south to see how the temperature jumps this year
0:19:14 > 0:19:17are affecting another iconic species.
0:19:21 > 0:19:25Snow is a lot more complex than it looks,
0:19:25 > 0:19:28and for one animal, a bird of prey,
0:19:28 > 0:19:30the precise depth and type of snow
0:19:30 > 0:19:34can literally mean the difference between life and death.
0:19:44 > 0:19:47This is the great grey owl,
0:19:47 > 0:19:50one of the largest owls in the world,
0:19:50 > 0:19:54with a wingspan that stretches up to 1.5 metres.
0:19:57 > 0:19:59It's a winter specialist.
0:20:00 > 0:20:03It survives in some of the coldest forests on earth,
0:20:03 > 0:20:06from Siberia to Scandinavia...
0:20:08 > 0:20:11..to here, in north-west America.
0:20:12 > 0:20:15Researchers believe several hundred great grey owls
0:20:15 > 0:20:18live in the Jackson Hole Valley,
0:20:18 > 0:20:21all within 150 square miles of forest.
0:20:28 > 0:20:30Our cameraman, Jeff Hogan,
0:20:30 > 0:20:34has had a lifelong love affair with this enigmatic bird.
0:20:39 > 0:20:41I've been following and filming the great grey owls
0:20:41 > 0:20:43for just about 30 years now.
0:20:43 > 0:20:46It's still just as exciting and challenging
0:20:46 > 0:20:48as it was the very first day.
0:20:50 > 0:20:54This is a fantastic place for owls to be hanging out.
0:20:54 > 0:20:57I mean, it is mixed aspens and conifer forest,
0:20:57 > 0:20:59along with these meadows,
0:20:59 > 0:21:04provide an incredible habitat for the prey that the owl feeds upon.
0:21:07 > 0:21:09Great greys feed on rodents -
0:21:09 > 0:21:13mainly gophers and voles - that burrow under the snow.
0:21:15 > 0:21:18Their huge facial discs act like satellite dishes,
0:21:18 > 0:21:22directing sound to their ears.
0:21:22 > 0:21:24Their hearing is exceptional.
0:21:26 > 0:21:29They can detect prey from over 100 metres away,
0:21:29 > 0:21:31through snow almost half a metre deep.
0:21:33 > 0:21:36But it's one thing knowing where to pounce,
0:21:36 > 0:21:39another to break through to reach the meal.
0:21:40 > 0:21:42Jeff is out looking for them.
0:21:42 > 0:21:45He's concerned that, with the erratic weather conditions,
0:21:45 > 0:21:48the owls face a big challenge.
0:21:48 > 0:21:53Earlier this week we got a lot of snow, and then the skies cleared,
0:21:53 > 0:21:56so you can look around here and see where the sun is beating down
0:21:56 > 0:22:00on the surface of this snowpack, and it really softens it up.
0:22:00 > 0:22:03It doesn't melt it completely, but it makes it really soft and wet,
0:22:03 > 0:22:06and then at night, when the temperatures plummet,
0:22:06 > 0:22:09it will freeze hard and turn it to ice.
0:22:09 > 0:22:12You can actually see this layer of crust.
0:22:15 > 0:22:17Boy, you can really feel that.
0:22:17 > 0:22:18Ouch.
0:22:18 > 0:22:20This is hard.
0:22:22 > 0:22:25And as the temperatures drop as night approaches,
0:22:25 > 0:22:27this is going to get harder and harder,
0:22:27 > 0:22:31and these owls have to bust through this crust,
0:22:31 > 0:22:34and there may be another foot of snow to get to their prey.
0:22:36 > 0:22:39Jeff hasn't seen any great greys,
0:22:39 > 0:22:42which could mean they've been forced further afield to hunt.
0:22:44 > 0:22:46So, I guess I'm going to have to keep on looking.
0:22:49 > 0:22:53At this time of year, eating enough food is critical.
0:22:53 > 0:22:57If the great grey owls can't hunt, they simply won't lay eggs,
0:22:57 > 0:22:59or even nest this season.
0:23:01 > 0:23:04Their population is already small and vulnerable.
0:23:07 > 0:23:10Biologist Katherine Gura is keen to see how current snow conditions
0:23:10 > 0:23:14might be impacting the owls' ability to feed
0:23:14 > 0:23:16and that involves a simple experiment.
0:23:18 > 0:23:21Katherine, you are stood out here with a ruler, a metre rule,
0:23:21 > 0:23:23and these flasks of water.
0:23:23 > 0:23:25What do these have to do with owls?
0:23:25 > 0:23:29So, this is about the same weight as a great grey owl.
0:23:29 > 0:23:31So, what we're doing is dropping these,
0:23:31 > 0:23:34and we're seeing how far they penetrate the snow.
0:23:34 > 0:23:37Because it in turn can show us how easy or hard it is
0:23:37 > 0:23:40for great grey owls to penetrate the snow to get to their prey.
0:23:40 > 0:23:42- Right, Katherine, can I give you a hand?- Absolutely.
0:23:42 > 0:23:43OK, so what do I do?
0:23:43 > 0:23:47So you want to drop that from one metre above the snow.
0:23:47 > 0:23:48- OK.- So that's here.
0:23:48 > 0:23:50- One metre, that's here.- Yeah.
0:23:51 > 0:23:55OK, so it hasn't really gone that far. It's gone about...
0:23:55 > 0:23:5817 centimetres.
0:23:58 > 0:24:01With their prey often underneath twice as much snow,
0:24:01 > 0:24:03this is why the owls are having trouble feeding.
0:24:04 > 0:24:08Our concern is that it's changing the timing of their behaviour.
0:24:08 > 0:24:09So if there's not enough prey,
0:24:09 > 0:24:12I mean, that's probably going to spell disaster.
0:24:12 > 0:24:14- Are you worried about that? - I definitely am.
0:24:14 > 0:24:16I've been working with these owls for years.
0:24:16 > 0:24:19I love watching them throughout their nesting season,
0:24:19 > 0:24:20and it really concerns me
0:24:20 > 0:24:23if they're not going to be able to have enough prey
0:24:23 > 0:24:26to even attempt to nest, or to eventually support their young.
0:24:30 > 0:24:33This year, with the tricky snow conditions,
0:24:33 > 0:24:35the owls appear to be suffering.
0:24:36 > 0:24:39To find out how they're really getting on,
0:24:39 > 0:24:42or indeed if they're around at all,
0:24:42 > 0:24:45Katherine needs to conduct her survey at night.
0:24:47 > 0:24:50The night-time call of the great grey owl
0:24:50 > 0:24:52is one of the early signs of spring,
0:24:52 > 0:24:54and, for scientists, this is the first time
0:24:54 > 0:24:57they'll be able to work out exactly where they are,
0:24:57 > 0:24:59what they're up to, and how they are doing.
0:24:59 > 0:25:03If the great greys are going to be successful in raising chicks,
0:25:03 > 0:25:05they should be out there right now,
0:25:05 > 0:25:08and we hopefully should be able to hear them,
0:25:08 > 0:25:10but the thing is, this year, nothing is certain.
0:25:13 > 0:25:15Jeff has also joined us.
0:25:15 > 0:25:18He's hoping his luck finding owls will change
0:25:18 > 0:25:20under the cover of darkness.
0:25:27 > 0:25:30The survey area covers several square miles.
0:25:30 > 0:25:35Now, my top speed in snow shoes is half a mile per hour.
0:25:35 > 0:25:37This could be a long night.
0:25:41 > 0:25:44All right, this looks like a good spot to stop and survey.
0:25:44 > 0:25:46OK, so what are we going to do?
0:25:46 > 0:25:48So I will do the male territorial call,
0:25:48 > 0:25:50and then we want to be as quiet as possible,
0:25:50 > 0:25:52and we'll listen to see if one responds.
0:25:52 > 0:25:54- Right, so, fingers crossed we get an owl.- OK.
0:25:54 > 0:25:57I'll do my best.
0:25:57 > 0:25:59SHE MIMICS OWL HOOT
0:26:09 > 0:26:10OWL RESPONDS
0:26:10 > 0:26:12Yep, that's it.
0:26:12 > 0:26:14Right here. Yeah, this is great.
0:26:14 > 0:26:17OWL HOOTS
0:26:17 > 0:26:18It's responding.
0:26:20 > 0:26:22So, is that probably a male?
0:26:22 > 0:26:24So, that's a male territorial call.
0:26:24 > 0:26:27So they'll do that, either to attract a mate,
0:26:27 > 0:26:31and also to tell other males that this is his zone, his territory.
0:26:31 > 0:26:32Should I give it a go?
0:26:32 > 0:26:34You should do it.
0:26:34 > 0:26:36HE HOOTS
0:26:36 > 0:26:37No, that's too deep!
0:26:38 > 0:26:39See if he likes it.
0:26:39 > 0:26:41HE HOOTS
0:26:51 > 0:26:53Mine's too manly.
0:26:53 > 0:26:54You've scared it off.
0:26:54 > 0:26:56He doesn't want to get beat up!
0:26:58 > 0:27:01So, given the conditions that we're having this year,
0:27:01 > 0:27:02this is a really good sign,
0:27:02 > 0:27:05- that we can hear the great grey owls.- Mm-hm.
0:27:05 > 0:27:07I was definitely worried, with kind of the hard crust that we have had,
0:27:07 > 0:27:09that they might not be on territory yet,
0:27:09 > 0:27:12but it is a good sign that they're here and defending it.
0:27:12 > 0:27:13OWL HOOTS
0:27:16 > 0:27:17So, there are males out there
0:27:17 > 0:27:20and they're defending their territory.
0:27:21 > 0:27:25Given this year's unpredictable weather, it's a promising sign.
0:27:26 > 0:27:28Jeff and Katherine will continue monitoring,
0:27:28 > 0:27:31and we'll be back to see how the owls are getting on
0:27:31 > 0:27:33later in the season.
0:27:47 > 0:27:48All across the region,
0:27:48 > 0:27:50the challenge for much of the wildlife
0:27:50 > 0:27:52is simply to hang on until spring.
0:27:54 > 0:27:56It may appear that animals like bison
0:27:56 > 0:28:00spend the winter stoically struggling through the snow,
0:28:00 > 0:28:02but there is a respite for some...
0:28:03 > 0:28:07..and it's thanks to a feature that is synonymous with Yellowstone.
0:28:13 > 0:28:17It's famed not just for its landscapes and its wildlife,
0:28:17 > 0:28:19but also for its geology.
0:28:20 > 0:28:23Yellowstone has more geysers than anywhere else.
0:28:23 > 0:28:28In fact, 60% of all the geysers in the world are here,
0:28:28 > 0:28:32and the reason for that is a giant magma chamber,
0:28:32 > 0:28:35literally a pool, a sort of lake of molten rock,
0:28:35 > 0:28:38sitting just below the Earth's crust,
0:28:38 > 0:28:41literally right under my feet here.
0:28:49 > 0:28:52Scientists believe there's enough magma down below
0:28:52 > 0:28:56to fill the Grand Canyon more than 11 times,
0:28:56 > 0:28:58and in West Yellowstone,
0:28:58 > 0:29:02there's plenty of evidence of all this geothermal activity,
0:29:02 > 0:29:06particularly with the dramatic geysers.
0:29:06 > 0:29:11These hot springs intermittently send fountains of water and steam
0:29:11 > 0:29:12into the air.
0:29:14 > 0:29:17It looks a fairly inhospitable landscape,
0:29:17 > 0:29:22but around 200 bison spend the winter living and feeding here.
0:29:22 > 0:29:26These bison are part of what is known as the central herd,
0:29:26 > 0:29:29and they don't need to work nearly so hard to get at the vegetation
0:29:29 > 0:29:31beneath the snow.
0:29:31 > 0:29:35The earth here is warmed by that magma chamber
0:29:35 > 0:29:37bubbling away beneath the crust,
0:29:37 > 0:29:39and that means there's far less snow,
0:29:39 > 0:29:42and the vegetation is much easier to get at.
0:29:44 > 0:29:47But scientists have discovered that these easy pickings
0:29:47 > 0:29:49come at a high price.
0:29:50 > 0:29:53The hot water pushing up from deep underground
0:29:53 > 0:29:58dissolves the chemical compound silica from the volcanic rock,
0:29:58 > 0:30:00and deposits it on the grass.
0:30:01 > 0:30:05Now, silica coats the vegetation around geysers and hot springs,
0:30:05 > 0:30:08and it's a little bit like eating something
0:30:08 > 0:30:11that has been covered in a very fine dusting of ground glass.
0:30:12 > 0:30:16It's enormously abrasive and very, very tough on the teeth.
0:30:18 > 0:30:22The other issue is the high levels of fluoride in the water.
0:30:22 > 0:30:27This chemical is a by-product of historic volcanic eruptions.
0:30:27 > 0:30:31In low doses, such as in toothpaste, it's good for your teeth,
0:30:31 > 0:30:35but here it's so concentrated it actually softens,
0:30:35 > 0:30:38rather than strengthens, the enamel.
0:30:39 > 0:30:43Now, the combination of silica and an excess of fluoride in their diet,
0:30:43 > 0:30:47means that the bison down here lose their teeth
0:30:47 > 0:30:51significantly earlier than the bison up in the north of the park.
0:30:51 > 0:30:54In fact, life expectancy amongst this herd
0:30:54 > 0:30:56is at least five years less.
0:30:57 > 0:31:00So, although these bison have an easier life
0:31:00 > 0:31:02than their snowbound cousins,
0:31:02 > 0:31:05it's definitely a much shorter one.
0:31:07 > 0:31:10Finally, by mid-March,
0:31:10 > 0:31:14other parts of Yellowstone also get a reprieve from deep snow.
0:31:15 > 0:31:18It's melting faster than it's falling.
0:31:22 > 0:31:24Warmer air has come up from the south
0:31:24 > 0:31:27and pushed out the cold front in the north.
0:31:28 > 0:31:33Daytime temperatures rise above freezing, unlocking the rivers...
0:31:34 > 0:31:36..and the animals make the most of it.
0:31:39 > 0:31:42Underwater plants are more nutritious
0:31:42 > 0:31:44than those beneath the snow,
0:31:44 > 0:31:47and are a vital food source for this moose,
0:31:47 > 0:31:50which needs to pile on the pounds fast.
0:31:53 > 0:31:57This muskrat is enjoying the vegetation, too.
0:31:57 > 0:32:01His double layer of waterproof fur keeps him warm and dry,
0:32:01 > 0:32:04even whilst eating on an icy platform...
0:32:06 > 0:32:10..and, when he dives down, his lips seal shut
0:32:10 > 0:32:12behind his big rodent teeth,
0:32:12 > 0:32:16so that he can gather food without swallowing water.
0:32:22 > 0:32:25Even a winter casualty is good news.
0:32:25 > 0:32:30This elk carcass will sustain many scavengers over the coming days...
0:32:31 > 0:32:33..and it may be here
0:32:33 > 0:32:37thanks to Yellowstone's most charismatic predator.
0:32:39 > 0:32:41HOWLING
0:32:52 > 0:32:55SHE GASPS: Oh, my God, look at the wolves!
0:32:55 > 0:32:56This is the most...
0:32:58 > 0:33:00This is the most incredible view!
0:33:02 > 0:33:06What becomes so evident when you see a pack of wolves
0:33:06 > 0:33:09running across the snow like that
0:33:09 > 0:33:13is just how perfectly adapted they are as winter predators.
0:33:15 > 0:33:18There are some things that...
0:33:18 > 0:33:22in life that floor you,
0:33:22 > 0:33:24and seeing a pack of wolves...
0:33:24 > 0:33:29I am completely, completely overwhelmed by the sight!
0:33:46 > 0:33:50To see what effect this year's thaw is having on these animals,
0:33:50 > 0:33:53I'm joining wolf biologist Doug Smith.
0:33:54 > 0:33:57We're on our way up a ridge on Blacktail Butte
0:33:57 > 0:33:58in the Northern Range,
0:33:58 > 0:34:01home to a pack of 11 individuals
0:34:01 > 0:34:05that lay claim to a territory of 250 square miles.
0:34:06 > 0:34:11Doug and his team constantly monitor the wolves in Yellowstone.
0:34:11 > 0:34:15He's concerned that climate change is having an impact on them.
0:34:20 > 0:34:23They just ooze charisma, don't they?
0:34:24 > 0:34:26Even 2km away.
0:34:28 > 0:34:30It's true.
0:34:33 > 0:34:36There's something enchanting and mysterious about them
0:34:36 > 0:34:39that has gone through the ages.
0:34:47 > 0:34:50Usually wolves thrive in the winter.
0:34:50 > 0:34:52They're snow specialists.
0:34:53 > 0:34:55Their feet fan out,
0:34:55 > 0:35:00enabling them to run across deep snow at over 25mph.
0:35:02 > 0:35:06This gives them an advantage over their prey, elk and bison...
0:35:09 > 0:35:11..which struggle with their cloven hooves.
0:35:13 > 0:35:16Wolves generally have even more of an edge in March,
0:35:16 > 0:35:20when Yellowstone's herbivores are weak and hungry...
0:35:25 > 0:35:27..but this year is different.
0:35:28 > 0:35:30By Yellowstone's extreme standards,
0:35:30 > 0:35:352016 has been one of the mildest winters
0:35:35 > 0:35:36ever recorded.
0:35:36 > 0:35:39Temperatures have fluctuated wildly,
0:35:39 > 0:35:42but, overall, they've hovered three degrees
0:35:42 > 0:35:43above the historic average.
0:35:46 > 0:35:49A warmer winter is great for herbivores
0:35:49 > 0:35:50as there's less snow,
0:35:50 > 0:35:53and they're less likely to die of cold...
0:35:56 > 0:35:59..but for their predators, Yellowstone's wolves,
0:35:59 > 0:36:02it can make life a lot more difficult.
0:36:04 > 0:36:07Because this winter has been so mild,
0:36:07 > 0:36:12do you think that that is going to have a big impact on these wolves?
0:36:12 > 0:36:13It certainly could.
0:36:13 > 0:36:15I mean, hard winters wear your prey down,
0:36:15 > 0:36:18and that makes them easier to kill for wolves.
0:36:18 > 0:36:21A mild winter, their prey is going to do a little bit better.
0:36:21 > 0:36:25This winter was warmer and with below-average snowfall,
0:36:25 > 0:36:28and it's early to tell what the effect of that is,
0:36:28 > 0:36:32but we think that wolf food consumption rates, kill rates,
0:36:32 > 0:36:34are down because of that.
0:36:34 > 0:36:37So these milder winters favour the prey,
0:36:37 > 0:36:41and so does that mean fewer pups,
0:36:41 > 0:36:44which leads to smaller packs?
0:36:44 > 0:36:46This change in winter weather could be a huge impact.
0:36:48 > 0:36:51Wolf kill rates are down this year,
0:36:51 > 0:36:54but our camera teams across the region
0:36:54 > 0:36:56have caught some hunts on film.
0:36:56 > 0:36:58Perhaps there will be clues
0:36:58 > 0:37:02as to the problems wolves are facing right now.
0:37:02 > 0:37:05Talk me through what's going on here.
0:37:05 > 0:37:08I mean, that's classic wolf hunting behaviour.
0:37:08 > 0:37:12What wolves are looking for are behavioural cues
0:37:12 > 0:37:15that indicate to them that there's a weak bison.
0:37:15 > 0:37:19- Right.- But what's interesting is, the bison are staying in these areas
0:37:19 > 0:37:22where there's either no snow or little snow,
0:37:22 > 0:37:27- because they've got firm footing and they feel confident.- Yeah.
0:37:27 > 0:37:31And so what the wolves are doing is trying to bump them into a place
0:37:31 > 0:37:35that's more favourable to them, ie, deeper snow.
0:37:35 > 0:37:37- This winter there's less deep snow...- Right.
0:37:37 > 0:37:40..so the wolves are having a harder time.
0:37:40 > 0:37:43Plus, these brown places have forage for the bison to eat
0:37:43 > 0:37:45- so they're going to be healthier. - Yeah.
0:37:45 > 0:37:47That's also bad for the wolves.
0:37:48 > 0:37:53The next hunt involves the wolves' main winter prey, the elk.
0:37:53 > 0:37:55- Now, here's an elk encounter... - Yeah.
0:37:55 > 0:37:56..and this is even more dramatic.
0:37:56 > 0:37:59- Look at that! - This female elk is very healthy,
0:37:59 > 0:38:02and she's actually attacking the wolf,
0:38:02 > 0:38:04- but she won't leave the dry ground. - Yeah.
0:38:04 > 0:38:09Classic example of the importance of snow depth and footing.
0:38:09 > 0:38:14Look at the elk. A healthy elk will always outrun a healthy wolf.
0:38:14 > 0:38:17So, talking to the old-timers who lived here in Yellowstone
0:38:17 > 0:38:23during the 1960s and 1970s, every winter was a deep snow winter.
0:38:23 > 0:38:27It was the rare winter that was not much snow.
0:38:27 > 0:38:30Now, it's the rare winter where you have deep snow.
0:38:30 > 0:38:33It is more common to have shallow snow,
0:38:33 > 0:38:37and that's switching this balance between predators and prey.
0:38:41 > 0:38:44With so few successful hunts,
0:38:44 > 0:38:47scientists have noticed that some of the wolves
0:38:47 > 0:38:50are turning to a summer feeding strategy.
0:38:50 > 0:38:53Instead of working as a pack, they're hunting alone,
0:38:53 > 0:38:56digging into burrows to catch small mammals.
0:38:58 > 0:39:02It's much less rewarding, much harder work,
0:39:02 > 0:39:05and, for this time of the year, definitely unusual.
0:39:09 > 0:39:12The repercussions could be huge.
0:39:12 > 0:39:14The female wolves are pregnant right now,
0:39:14 > 0:39:17and poor feeding may lead to weaker pups.
0:39:17 > 0:39:20We won't know until early summer.
0:39:30 > 0:39:32It's the end of March.
0:39:32 > 0:39:35The signs of spring are getting stronger every day.
0:39:44 > 0:39:45I guess I weigh more than a coyote.
0:39:46 > 0:39:48With temperatures warming,
0:39:48 > 0:39:51many more grizzlies are coming out of their dens.
0:39:51 > 0:39:55Our bear expert, Casey Anderson, is out searching for them
0:39:55 > 0:39:57up in the Gallatin Mountains.
0:39:59 > 0:40:00Sometimes it's not that hard
0:40:00 > 0:40:04to work out where they've passed through.
0:40:04 > 0:40:05Hey, look.
0:40:06 > 0:40:08You can see, right here, it's all kind of worn out,
0:40:08 > 0:40:10you can see these little claw marks.
0:40:14 > 0:40:17Well, sometimes when the bears come out of the den,
0:40:17 > 0:40:18they can be a little mischievous.
0:40:18 > 0:40:20If you look right here,
0:40:20 > 0:40:24one of the first stops the bear had made was this snowmobile seat.
0:40:24 > 0:40:27Just ripping, clawing, biting, just playing, really.
0:40:27 > 0:40:30It's part of living in grizzly country.
0:40:31 > 0:40:35It's never certain when bears will emerge in Yellowstone,
0:40:35 > 0:40:39but this year has been more unpredictable than ever.
0:40:42 > 0:40:46It's been, really, a strange year so far.
0:40:46 > 0:40:49The spring temperature
0:40:49 > 0:40:51has definitely gotten a few bears out earlier.
0:40:51 > 0:40:53We know that one bear has gone down,
0:40:53 > 0:40:55and pulled that bison carcass out of the pond.
0:40:55 > 0:40:57That was a risk worth taking.
0:40:58 > 0:41:00But it was a risk.
0:41:00 > 0:41:03Other early grizzlies may not have been so lucky.
0:41:06 > 0:41:09The adaptations animals make in Yellowstone
0:41:09 > 0:41:12to chime with its extreme seasonal changes
0:41:12 > 0:41:13are finely balanced,
0:41:13 > 0:41:16and in tune not just with temperature
0:41:16 > 0:41:17and degree of snow cover,
0:41:17 > 0:41:20but also with length of day.
0:41:21 > 0:41:24Right up here, there's a long-tail weasel.
0:41:26 > 0:41:28It's running around right up here.
0:41:32 > 0:41:35So, these long-tail weasels, as soon as spring actually is here,
0:41:35 > 0:41:36they will turn brown,
0:41:36 > 0:41:39and they'll be camouflaged for the spring, summer and fall.
0:41:39 > 0:41:42When winter comes again, they turn white, just like this.
0:41:42 > 0:41:45The fact that he's still completely white
0:41:45 > 0:41:47shows that it's very much winter.
0:41:48 > 0:41:52The changing colour is triggered by hours of daylight,
0:41:52 > 0:41:53not by temperature.
0:41:54 > 0:41:57He won't turn brown until next month.
0:41:57 > 0:41:59And just like the fox and the coyotes,
0:41:59 > 0:42:03he's looking for all the rodents that live underneath the snow cover.
0:42:03 > 0:42:06He's just tunnelling down, going and grabbing these things,
0:42:06 > 0:42:07and popping up and eating them.
0:42:08 > 0:42:12But whilst he's still white, if the snow melts too quickly,
0:42:12 > 0:42:15he'll lose his camouflage advantage,
0:42:15 > 0:42:18and could be at risk from predators himself.
0:42:19 > 0:42:23And one mammal who would happily eat him is a fox.
0:42:26 > 0:42:29You can see this, like, little story unfolding here.
0:42:29 > 0:42:33This is a fox doing what they're so good at in winter time.
0:42:33 > 0:42:35A bear's greatest sense is their sense of smell,
0:42:35 > 0:42:38whereas a fox's greatest sense is their sense of hearing.
0:42:38 > 0:42:43And they literally hear a little rodent way down in the snow,
0:42:43 > 0:42:45they'll stop, and you'll see them,
0:42:45 > 0:42:48they'll do this thing where they pitch their head side to side,
0:42:48 > 0:42:50and what they are doing is really triangulating
0:42:50 > 0:42:53and zoning in to the exact location of that rodent,
0:42:53 > 0:42:56and then they just do this giant leap up in the air
0:42:56 > 0:42:59and get this momentum with gravity, and just, poof!
0:43:00 > 0:43:01Right down into the snow,
0:43:01 > 0:43:02and grab that little guy.
0:43:02 > 0:43:04He doesn't even know it's coming.
0:43:04 > 0:43:06He thinks he's down there, all protected.
0:43:06 > 0:43:08Little does he know, up there is a fox -
0:43:08 > 0:43:10a missile coming straight down and getting him -
0:43:10 > 0:43:13and look at that, that's quite a ways down.
0:43:17 > 0:43:20A little vole is a pretty good snack for a fox.
0:43:20 > 0:43:22Whereas for a bear, it's nothing,
0:43:22 > 0:43:24and there's no way it could survive on voles alone through the winter,
0:43:24 > 0:43:26so that's why they choose to hibernate,
0:43:26 > 0:43:29there's nothing out here to eat if you're a big old...
0:43:29 > 0:43:31bumbling-around bear.
0:43:40 > 0:43:43- PATRICK:- Down in the south, there's also still plenty of snow
0:43:43 > 0:43:46in the forest habitat of the great grey owl.
0:43:47 > 0:43:51Cameraman Jeff Hogan has been out night and day tracking them
0:43:51 > 0:43:54to find out whether they're breeding successfully.
0:43:58 > 0:43:59We have an owl.
0:44:00 > 0:44:04Jeff's been hearing and seeing the male owls consistently,
0:44:04 > 0:44:06which is a reassuring sign.
0:44:07 > 0:44:11He'd feared they might have left the area due to a lack of food.
0:44:14 > 0:44:15We're going to set up here.
0:44:17 > 0:44:21This year, the issue has been icy snow.
0:44:21 > 0:44:25It's prevented the great grey owls snow-plunging deep enough
0:44:25 > 0:44:26to catch their prey.
0:44:33 > 0:44:36The owls each need at least one rodent a day,
0:44:36 > 0:44:40and if they don't eat enough now, they just won't breed.
0:44:42 > 0:44:43He didn't catch anything.
0:44:46 > 0:44:49There's something right here underneath him,
0:44:49 > 0:44:50because he's back.
0:44:50 > 0:44:52He's going to make another attempt.
0:45:02 > 0:45:03Oh, he jumped.
0:45:08 > 0:45:10Oh, he's on the ground now.
0:45:14 > 0:45:16I don't think he got anything.
0:45:19 > 0:45:21He just flew up with nothing.
0:45:22 > 0:45:26I've been here since dawn and he hasn't caught anything yet today.
0:45:30 > 0:45:33It appears the owls are still struggling.
0:45:34 > 0:45:37Then, at last, a sign of hope.
0:45:39 > 0:45:40A female arrives.
0:45:44 > 0:45:47This could get exciting. We've got two great greys right here.
0:45:47 > 0:45:52Following one bird is pretty exciting, but to have two birds...
0:45:55 > 0:45:58..it's amazing, it really is amazing.
0:45:58 > 0:45:59Let's see what goes on.
0:45:59 > 0:46:01Oh, here, he's flying in.
0:46:01 > 0:46:02Oh!
0:46:05 > 0:46:07Mating. Mating!
0:46:07 > 0:46:09Oh, my.
0:46:12 > 0:46:14I've never seen this before.
0:46:17 > 0:46:19This is great news.
0:46:20 > 0:46:23It's incredible, absolutely incredible.
0:46:24 > 0:46:27For the end of March,
0:46:27 > 0:46:29courtship, mating.
0:46:31 > 0:46:34The next step is nesting.
0:46:42 > 0:46:46Eventually, the pair choose to nest on an old, broken spruce trunk.
0:46:49 > 0:46:53How many eggs are laid will depend on how much food the owls consumed
0:46:53 > 0:46:55earlier in the season.
0:46:56 > 0:46:58On average, they lay four,
0:46:58 > 0:47:01but this year, it could be less.
0:47:01 > 0:47:03We'll be following them to see what happens.
0:47:36 > 0:47:39It's now April and the temperatures are warming up.
0:47:39 > 0:47:42This is Jackson Lake in the Tetons,
0:47:42 > 0:47:45and normally it would be frozen well into May,
0:47:45 > 0:47:47but already the ice is breaking up.
0:47:50 > 0:47:53The arrival of the melt is a tipping point
0:47:53 > 0:47:55for the wildlife of Yellowstone,
0:47:55 > 0:47:58and this year, after an extremely mild winter,
0:47:58 > 0:48:01it's three weeks early.
0:48:01 > 0:48:05At long last, though, it's official - spring is here.
0:48:07 > 0:48:11As the days get longer, the sun is higher in the sky,
0:48:11 > 0:48:16and its increased energy melts the snow and raises daily temperatures.
0:48:17 > 0:48:19Although there's still snow on the ground,
0:48:19 > 0:48:24the warming temperatures are actually changing the shape
0:48:24 > 0:48:26of the crystals within the snowpack.
0:48:26 > 0:48:30Now, they've turned into tight little balls,
0:48:30 > 0:48:32and there's a lot of water in between them,
0:48:32 > 0:48:34so the packs become a lot slushier.
0:48:34 > 0:48:36It's literally at melting point.
0:48:38 > 0:48:41All this snow is just water in waiting.
0:48:41 > 0:48:44Millions of tonnes will gradually melt,
0:48:44 > 0:48:48flooding into the lakes and rivers of north-west America.
0:48:50 > 0:48:53It's a process that will continue until July.
0:48:54 > 0:48:57It's the valleys that lose their snow first,
0:48:57 > 0:49:02and then, finally, the mountain peaks release their huge reservoir.
0:49:08 > 0:49:12Soon, these warmer temperatures will lure the last male grizzlies
0:49:12 > 0:49:14out of hibernation...
0:49:15 > 0:49:17..and, with the snow retreating,
0:49:17 > 0:49:20plants, too, are bursting into life -
0:49:20 > 0:49:23a nutritious feast for hungry bears.
0:49:26 > 0:49:30Patrick's back in the Gallatin Mountains with Casey Anderson
0:49:30 > 0:49:32to find out why a top predator
0:49:32 > 0:49:35sometimes chooses the vegetarian option.
0:49:38 > 0:49:39Look right here.
0:49:40 > 0:49:42This is biscuit root.
0:49:42 > 0:49:44This is a grizzly favourite.
0:49:46 > 0:49:47Bears are omnivores.
0:49:48 > 0:49:51They don't just survive on meat.
0:49:51 > 0:49:56Their diet also includes insects, fungi, and lots of vegetation.
0:49:57 > 0:49:59Many bears time their emergence
0:49:59 > 0:50:03to coincide with biscuit root coming into flower.
0:50:03 > 0:50:05So, that is what they're looking for, right there.
0:50:05 > 0:50:08This bit of root at the bottom.
0:50:08 > 0:50:09There's tonnes of calories in it.
0:50:09 > 0:50:12So how much biscuit root do they have to get through?
0:50:12 > 0:50:15I've watched them eat hundreds if not thousands of these roots.
0:50:15 > 0:50:17- What does it taste like? - You tell me.
0:50:19 > 0:50:22I was afraid you were going to say that, but I'm up to the challenge.
0:50:22 > 0:50:23Bottoms up.
0:50:27 > 0:50:30- It's like carrots.- Yeah.
0:50:30 > 0:50:32Yeah, like a kind of starchy carrot.
0:50:32 > 0:50:35Yeah. To be honest with you, when I'm hiking around out here,
0:50:35 > 0:50:37sometimes I look in my backpack and see what I have for lunch,
0:50:37 > 0:50:38and I look on the ground, and I'm like,
0:50:38 > 0:50:41"I'm going to go grizzly-style here and start digging away."
0:50:43 > 0:50:45As they put on weight after the winter,
0:50:45 > 0:50:47and more grizzlies come out,
0:50:47 > 0:50:49they begin to communicate with each other.
0:50:50 > 0:50:54Each male can have a home range of over several hundred square miles,
0:50:54 > 0:50:58and they need to work out who else is out there on their patch.
0:51:00 > 0:51:04So, this is an old backcountry camp in here,
0:51:04 > 0:51:05people come up and camp from time to time,
0:51:05 > 0:51:07there's a little tent over here,
0:51:07 > 0:51:09and this old outhouse,
0:51:09 > 0:51:11that tree right next to it is the rub tree
0:51:11 > 0:51:14where these big males will rub their back
0:51:14 > 0:51:16and urinate all over the place, right by the outhouse.
0:51:16 > 0:51:18So it's a bear toilet?
0:51:18 > 0:51:20It really is.
0:51:20 > 0:51:23- Look, see these big claws right here.- Wow.
0:51:23 > 0:51:25And look right here, Patrick,
0:51:25 > 0:51:28where the sap has stuck all the hair...
0:51:28 > 0:51:31- Oh, yeah.- ..stuck to the tree. All down to here.
0:51:32 > 0:51:34So, all this here,
0:51:34 > 0:51:36this is...
0:51:36 > 0:51:37- bear hair.- Yeah.
0:51:37 > 0:51:39So, what they do, they come over,
0:51:39 > 0:51:42and they just usually come up and put their back on the tree,
0:51:42 > 0:51:44and they'll rub their scent all over it,
0:51:44 > 0:51:48and they reach up and grab like this, and they bite the tree.
0:51:48 > 0:51:51Then they drop down, particularly the males,
0:51:51 > 0:51:54and they do this thing that I call the cowboy walk.
0:51:54 > 0:51:56So, they just stick it and they twist their feet like this.
0:51:56 > 0:51:58PATRICK CHUCKLES
0:51:58 > 0:52:01They have real rigid legs, and they're just really twisting.
0:52:03 > 0:52:07So each bear that comes to this tree will step in that same exact spot.
0:52:07 > 0:52:08And they do it over and over again.
0:52:08 > 0:52:11It leaves these big divots in the ground.
0:52:11 > 0:52:12So, if you're a smaller bear
0:52:12 > 0:52:15and you really have to reach for that next foot divot,
0:52:15 > 0:52:17you know there's a bigger bear in town.
0:52:17 > 0:52:20This is a well-known rub tree.
0:52:20 > 0:52:21We're setting up a camera
0:52:21 > 0:52:24to see how many of the big males are out there.
0:52:25 > 0:52:27- See this right here?- Right.
0:52:27 > 0:52:28It's going to take a recording,
0:52:28 > 0:52:30and it's going to text me to my cellphone.
0:52:30 > 0:52:32- No way.- Yeah, real-time.
0:52:32 > 0:52:34So, as soon as a bear's there, I'm getting a text.
0:52:34 > 0:52:37So, hang on. You're going to get a text from a bear?
0:52:37 > 0:52:40Exactly, that's exactly what's going to happen.
0:52:47 > 0:52:51A few days later, Casey's called me in to look at the results.
0:52:51 > 0:52:55Right, what have we got? Let's take a look and see what it's caught.
0:52:55 > 0:52:56Uh-oh!
0:52:56 > 0:52:57THEY LAUGH
0:52:59 > 0:53:01That's just brilliant.
0:53:01 > 0:53:02That is an elk.
0:53:02 > 0:53:06A cow elk. So, this is something that always happens.
0:53:06 > 0:53:09You set up your camera trap, you think you've got the right angle,
0:53:09 > 0:53:12and then one of the animals comes along and wants to change the angle.
0:53:12 > 0:53:15- Oh, man!- It's giving it a good go. - She's kicking it.
0:53:15 > 0:53:18I think it shows their playfulness.
0:53:18 > 0:53:20They come over to something new, curious, and it's like...
0:53:22 > 0:53:25"I think I'm going to play a little soccer with it."
0:53:25 > 0:53:26That's just great.
0:53:26 > 0:53:29Let's have a look at a couple of the other clips.
0:53:30 > 0:53:33Whoa, first clip!
0:53:33 > 0:53:35- Exactly what we wanted.- Wow.
0:53:35 > 0:53:37That's a big male.
0:53:37 > 0:53:38I guess it's what we would expect,
0:53:38 > 0:53:39this time of the year,
0:53:39 > 0:53:42that these big guys will be the first ones coming out of the den.
0:53:42 > 0:53:44The females and the cubs are still up high.
0:53:44 > 0:53:48Casey, Casey, this is a huge bear.
0:53:49 > 0:53:51Remember when we set this camera trap,
0:53:51 > 0:53:54- we were anticipating that we would get the whole bear, but...- Mm-hm.
0:53:54 > 0:53:56- Just missing the head. - He's bigger than that.
0:53:56 > 0:53:59He stands at 2.5 metres tall.
0:53:59 > 0:54:03He's giving it a real bear hug!
0:54:03 > 0:54:05That's a bear hug, for sure.
0:54:05 > 0:54:06Wow. And there we go,
0:54:06 > 0:54:09doing that kind of cowboy walk you were talking about, right?
0:54:09 > 0:54:11Really trying to grind in his scent,
0:54:11 > 0:54:12leave those marks.
0:54:12 > 0:54:14That cowboy walk.
0:54:14 > 0:54:17That means one thing - "I'm in town and I'm the boss."
0:54:17 > 0:54:19But what are they picking up,
0:54:19 > 0:54:22and how do you think that affects their behaviour?
0:54:22 > 0:54:25Well, as they emerge, it's the beginning of the mating season,
0:54:25 > 0:54:28so it's important for males to know if there's a bigger male around.
0:54:28 > 0:54:30- It's like... - HE SNIFFS
0:54:30 > 0:54:31.."Oh, this big dude's here,
0:54:31 > 0:54:34"maybe I don't want to be here," and they'll go the other way.
0:54:34 > 0:54:37Equally for the females, they want to know, you know,
0:54:37 > 0:54:39who's going to be the father of their next offspring.
0:54:39 > 0:54:42- Yeah.- If there's any big tough guys around.
0:54:44 > 0:54:46Although the unusual weather a few weeks ago
0:54:46 > 0:54:49had brought some of them out of hibernation early,
0:54:49 > 0:54:51these males appear fighting fit.
0:54:55 > 0:54:59Spring is in the air, and the bears are getting frisky.
0:55:05 > 0:55:08But they're not the only males getting boisterous.
0:55:10 > 0:55:12These elk are shedding their antlers.
0:55:12 > 0:55:15New ones will regrow over the next few months,
0:55:15 > 0:55:18ready for the autumn rutting season.
0:55:21 > 0:55:25But perhaps the biggest male show-offs are down in the south,
0:55:25 > 0:55:30and Kate has a front-row seat for their fabulous performance.
0:55:30 > 0:55:32WITTERING
0:55:36 > 0:55:39It's mating season for the sage grouse.
0:55:41 > 0:55:44They really like to make a proper song and dance about it.
0:55:44 > 0:55:46GROUSE WITTERS
0:55:57 > 0:56:00That sound... It's really difficult to describe.
0:56:00 > 0:56:02It's like a sort of...
0:56:02 > 0:56:03popping and a drumming.
0:56:06 > 0:56:11It's that, combined with these wonderful, very showy
0:56:11 > 0:56:13puffed-up white chests,
0:56:13 > 0:56:17and those fanned-out black tail feathers,
0:56:17 > 0:56:19that will attract the females.
0:56:19 > 0:56:21Ooh, there's one.
0:56:21 > 0:56:23And they will literally do a fly-past -
0:56:23 > 0:56:25they'll sort of fly over and look down
0:56:25 > 0:56:27and go, "Oh, yeah, I don't mind the look of that one,
0:56:27 > 0:56:29"I'll give that one a go."
0:56:29 > 0:56:33Greater Yellowstone is a stronghold for the sage grouse,
0:56:33 > 0:56:35a species under threat.
0:56:35 > 0:56:38Once numbering tens of millions,
0:56:38 > 0:56:41there are now just a few hundred thousand of these birds left.
0:56:41 > 0:56:44Many of them rely on Yellowstone,
0:56:44 > 0:56:48where there's still plenty of their habitat - sagebrush.
0:56:49 > 0:56:51It is now around 11 degrees,
0:56:51 > 0:56:53perfect for breeding.
0:56:56 > 0:57:00But success will depend on how the thaw progresses.
0:57:00 > 0:57:04Chicks won't do well if the temperatures soar too quickly.
0:57:08 > 0:57:12So far during the thaw, some of our animals have done well,
0:57:12 > 0:57:14and some haven't.
0:57:19 > 0:57:21The jumping around in temperature
0:57:21 > 0:57:23at the end of winter confused some bears
0:57:23 > 0:57:26and made life difficult for the owls.
0:57:27 > 0:57:31One of the mildest winters on record and a lack of snow
0:57:31 > 0:57:34prevented the wolves hunting successfully,
0:57:34 > 0:57:39yet the elk and bison emerged from the season in high numbers,
0:57:39 > 0:57:42and with plenty of fighting spirit.
0:57:44 > 0:57:46Soon this landscape will be transformed
0:57:46 > 0:57:49from brown and barren to lush and green,
0:57:49 > 0:57:53but the arrival of spring doesn't necessarily mean
0:57:53 > 0:57:56that life will get easier for our animal families.
0:57:56 > 0:57:58All those newborn youngsters
0:57:58 > 0:58:01will mean that there's lots of competition for food,
0:58:01 > 0:58:03and the predators will be ever present,
0:58:03 > 0:58:05on the lookout for the young and the vulnerable.
0:58:07 > 0:58:10Will the grizzly bear cubs find enough food to eat
0:58:10 > 0:58:13when they venture out into the big, wide world?
0:58:15 > 0:58:17We join a beaver family,
0:58:17 > 0:58:20but will they deal with the deluge?
0:58:20 > 0:58:23The water level is so much higher.
0:58:23 > 0:58:26After a difficult winter for the wolves,
0:58:26 > 0:58:28will their luck turn?
0:58:29 > 0:58:32And there is a nest of great grey owl chicks,
0:58:32 > 0:58:34but will they all survive?
0:58:34 > 0:58:36Oh, he is struggling.