0:00:22 > 0:00:29This is the story of the rise to power of the largest wolf pack ever known.
0:00:40 > 0:00:45Going from strength to strength, they're now at a turning point in their lives.
0:00:53 > 0:00:56The balance of power is shifting within the pack.
0:01:01 > 0:01:04The leaders face a take-over challenge
0:01:04 > 0:01:08from within their own family.
0:01:31 > 0:01:37Winter in Yellowstone is six months of temperatures below freezing.
0:01:49 > 0:01:52It can look beautiful,
0:01:52 > 0:01:54but the conditions are fierce.
0:01:57 > 0:02:02This is a time when most animals struggle simply to survive.
0:02:05 > 0:02:10But it is also a time when one animal truly comes into its own.
0:02:13 > 0:02:16This is the time of the wolf
0:02:16 > 0:02:22and wolves are back in Yellowstone National Park after an absence of nearly 70 years.
0:02:24 > 0:02:27American grey wolves are formidable predators.
0:02:29 > 0:02:35They hunt in large packs and bring down prey far larger than themselves.
0:02:36 > 0:02:42Wolves have been nipping at the heels of elk for hundreds of thousands of years.
0:02:48 > 0:02:53In the depths of winter, there will always be the weak, the old, the injured.
0:02:55 > 0:02:59Once targeted, the wolf pack closes in.
0:03:03 > 0:03:10The pack has its prey, but the wolves won't be allowed to eat in peace.
0:03:10 > 0:03:15As the bison stumble across the wolves and their kill, they panic.
0:03:23 > 0:03:30Extraordinary scenes like this disappeared entirely from the American West early last century.
0:03:30 > 0:03:35Millions of bison were exterminated, and the wolf wasn't far behind.
0:03:37 > 0:03:43It was treated as vermin by ranchers and park officials - hunted, poisoned and trapped.
0:03:44 > 0:03:47The Yellowstone wolf was gone.
0:03:53 > 0:03:561995 brought a change in fortune.
0:03:56 > 0:03:59Wolves were brought from the Canadian wilderness,
0:03:59 > 0:04:03to be released back into the park after a 65-year absence.
0:04:07 > 0:04:12Park biologists kept the wolves in pens to get them used to the new surroundings,
0:04:12 > 0:04:16and they had their hands full from the start.
0:04:16 > 0:04:22Even after 10 weeks, the Canadian wolves still had a healthy disrespect for human company.
0:04:26 > 0:04:32The plan to fit radio collars to monitor the wolves' progress and location proved...
0:04:32 > 0:04:34challenging.
0:04:35 > 0:04:39But local officials had more serious worries.
0:04:39 > 0:04:45Once released, would the wolves leave the park and start preying on livestock instead of the wildlife?
0:04:45 > 0:04:49If they did, the project was doomed.
0:04:52 > 0:04:55As the date of the releases approached,
0:04:55 > 0:04:58park biologists, like Doug Smith, really had no idea
0:04:58 > 0:05:02what would happen once the doors to the pens were opened.
0:05:08 > 0:05:09One's out.
0:05:12 > 0:05:15That's two. Two are out. Two out.
0:05:15 > 0:05:21'Many people were tearful. The emotional burden that was lifted off people's shoulders was tremendous.'
0:05:21 > 0:05:23Now, what was going to happen?
0:05:23 > 0:05:27Would this take? Would the wolves go back to Canada?
0:05:27 > 0:05:29What are they going to do?
0:05:30 > 0:05:33In theory, Yellowstone was perfect wolf habitat,
0:05:33 > 0:05:37but no-one really knew whether the wolves would thrive,
0:05:37 > 0:05:40starve, or simply leave the park.
0:05:40 > 0:05:45For biologist Doug Smith, head of Yellowstone's wolf recovery programme,
0:05:45 > 0:05:51the releases marked the beginning of an epic, seven-year scientific adventure.
0:05:51 > 0:05:55'I've been interested in wolves since I was a small boy.
0:05:55 > 0:06:00'I never dreamed that I would be in the position that I am today.
0:06:00 > 0:06:04'And for me, this truly is a labour of love.
0:06:04 > 0:06:07'I love going to work every day.
0:06:07 > 0:06:13'I love trying to figure out what these animals are doing, their stories,
0:06:13 > 0:06:17'their interactions with the other animals in Yellowstone.
0:06:17 > 0:06:21'It's a wonderful opportunity that challenges me in every way.'
0:06:29 > 0:06:36To keep track of the wolves, Doug's team have fitted radio collars to about a third of the animals.
0:06:36 > 0:06:39When the batteries run out, the collars must be replaced.
0:06:48 > 0:06:51After trying different recapture techniques,
0:06:51 > 0:06:57Doug has found darting from a helicopter to be the least traumatic for the wolves.
0:07:08 > 0:07:12While the wolf is sedated, Doug gives it a thorough examination,
0:07:12 > 0:07:15and checks its health before replacing the collar.
0:07:17 > 0:07:24The radio collars have given him an extraordinarily intimate glimpse into the secret lives of wolves.
0:07:29 > 0:07:34The wolves he's come to know best are a pack released in the shadow of Druid Peak in 1996.
0:07:37 > 0:07:40The Druid pack initially seemed to adjust well to Yellowstone.
0:07:40 > 0:07:44But more than a year later, they wandered out of the park,
0:07:44 > 0:07:47and the pack-leader was shot.
0:07:47 > 0:07:52Command of the seven wolves fell to his mate, the alpha female,
0:07:52 > 0:07:55a beautiful wolf, but a violent one.
0:07:56 > 0:08:01A coyote scavenging her kill was in serious trouble.
0:08:02 > 0:08:06'The first alpha female was wolf number 40.
0:08:06 > 0:08:10'She was very aggressive and she ruled with an iron fist.'
0:08:11 > 0:08:16Led by this powerful Dark Queen, the Druids developed a reputation
0:08:16 > 0:08:20for killing wolves from neighbouring packs, as well as coyotes.
0:08:29 > 0:08:36A stranger from a rival pack, a young male known as number 21, entered the Druids' territory.
0:08:38 > 0:08:41He risked his life to court the Dark Queen.
0:08:52 > 0:08:54His gamble paid off.
0:08:54 > 0:09:01Number 21 managed to win her over and became the alpha male of the Druid pack.
0:09:03 > 0:09:06The union of the two wolves did not go unnoticed.
0:09:06 > 0:09:11The Dark Queen's sister, number 42, was watching.
0:09:20 > 0:09:22Known as the Cinderella wolf,
0:09:22 > 0:09:26number 42 was in constant trouble with her sister.
0:09:26 > 0:09:30She was never quite submissive enough to please her leader.
0:09:34 > 0:09:37Vicious put-downs were all too common.
0:09:41 > 0:09:43And then,
0:09:43 > 0:09:46one night, everything changed.
0:09:51 > 0:09:54The Dark Queen was dead,
0:09:54 > 0:09:56probably killed by her own sister.
0:10:03 > 0:10:07The next day, the once-lowly Cinderella wolf
0:10:07 > 0:10:11claimed the den of the Dark Queen for her own pups.
0:10:12 > 0:10:15The Druid pack had a new leader.
0:10:15 > 0:10:19She took her sister's mate for herself.
0:10:21 > 0:10:24And she raised her sister's pups, as well as her own,
0:10:24 > 0:10:26and a third litter as well.
0:10:29 > 0:10:32They had 21 young mouths to feed.
0:10:32 > 0:10:36The Druids took turns babysitting and feeding them all.
0:10:59 > 0:11:03All but one of these pups from three litters grew into adults -
0:11:03 > 0:11:07a remarkable achievement for the Druid pack,
0:11:07 > 0:11:11and a triumphant return of wolves to Yellowstone.
0:11:13 > 0:11:18'I didn't think that 20 out of 21 pups were going to survive.
0:11:19 > 0:11:22'Yellowstone was the ideal place for wolves to be,
0:11:22 > 0:11:26'and they weren't there, and we reintroduced them,
0:11:26 > 0:11:28'and conditions were such
0:11:28 > 0:11:32'that they could have three litters of pups in one pack,
0:11:32 > 0:11:36'and they could have 20 of 21 of those pups survive.'
0:11:39 > 0:11:45Eventually, the Druid Peak pack grew to 37 members -
0:11:45 > 0:11:48almost certainly the largest wolf pack ever known.
0:11:51 > 0:11:56With so many wolves, the Druids became a force to be reckoned with.
0:11:56 > 0:12:01They needed more territory and their howling left no doubt
0:12:01 > 0:12:03they intended to take it by force.
0:12:03 > 0:12:06HOWLING
0:12:16 > 0:12:18THEY ALL HOWL
0:12:24 > 0:12:28'The first thing that happened when the Druid Peak pack grew'
0:12:28 > 0:12:30was they had to get more territory,
0:12:30 > 0:12:33they had to take over more land.
0:12:33 > 0:12:40Unfortunately, all the land in the northern part of Yellowstone was occupied by other wolves.
0:12:40 > 0:12:44So they had to take it aggressively from the nearest pack.
0:12:44 > 0:12:51In the no-man's-land between the Druids' territory and their neighbours',
0:12:51 > 0:12:56Doug and his team found grim evidence of fierce border skirmishes.
0:13:05 > 0:13:07Lots of blood.
0:13:07 > 0:13:11'Territorial skirmishes between wolf packs can be ferocious.
0:13:11 > 0:13:17'In fact, they can be so bad that wolves can die in these boundary skirmishes
0:13:17 > 0:13:21'about who's going to control the different areas of the park.'
0:13:22 > 0:13:27This area right here is a major zone of tension between these two packs.
0:13:27 > 0:13:31Their territorial boundaries pretty much abut here,
0:13:31 > 0:13:37and three wolves have died in three years right along this boundary.
0:13:38 > 0:13:44The Druids almost certainly killed this wolf in pursuit of more prey and more territory.
0:13:44 > 0:13:50But their grey fur shows that time is catching up with the Druids' alpha pair.
0:13:53 > 0:13:56The once-black Cinderella wolf
0:13:56 > 0:14:00and her dark partner have entered their twilight years.
0:14:01 > 0:14:08'I feel a lot of kinship with 42 and 21 because I'm watching them grey,'
0:14:08 > 0:14:11and I'm starting to grey along with them.
0:14:12 > 0:14:18'All this stuff pulls you in a lot of different ways, so I'm bonding with the study subjects.'
0:14:18 > 0:14:22Now seven years old, 42 and 21, the alpha pair,
0:14:22 > 0:14:25have outlived most of their contemporaries,
0:14:25 > 0:14:28but they won't be allowed to enjoy their golden years in peace.
0:14:29 > 0:14:33Trouble comes in the form of number 113,
0:14:33 > 0:14:35a powerful young male, a lone wolf.
0:14:37 > 0:14:41The unique thing about 113 is he's so big,
0:14:41 > 0:14:45and how we referred to him was "that big male wolf".
0:14:45 > 0:14:51In the prime of his life, number 113 has one thing on his mind - a mate.
0:14:51 > 0:14:55But Druid turf is a dangerous place to come courting.
0:14:58 > 0:15:01Caution takes hold,
0:15:01 > 0:15:06and the big male wolf has second thoughts about advancing further.
0:15:06 > 0:15:10And it's 21, the old man of the Druids, who chases him off.
0:15:43 > 0:15:46But the Druid pack has young daughters,
0:15:46 > 0:15:50and the powerful stranger's presence hasn't gone unnoticed.
0:15:56 > 0:15:59She's interested, but nervous.
0:15:59 > 0:16:05A meeting between wolves from different packs is a tense and dangerous affair.
0:16:06 > 0:16:09'These behaviours are quite ritualised.
0:16:09 > 0:16:13'The animal stands very stiffly facing the oncoming wolves.
0:16:24 > 0:16:29'It almost appears as if a wolf is highly nervous
0:16:29 > 0:16:32'and moving in a very kind of mechanical way,
0:16:32 > 0:16:35'probably trying not to do anything wrong,
0:16:35 > 0:16:40'because the slightest mistake could mean death for that wolf.
0:16:40 > 0:16:42'And that wolf knows that.'
0:16:43 > 0:16:48Clearly, the young Druid ladies appear more amorous than aggressive.
0:16:50 > 0:16:53Not so, their father.
0:17:26 > 0:17:29Trespassers are not tolerated by senior Druids.
0:17:30 > 0:17:33Big number 113 is seen as trouble.
0:17:37 > 0:17:42Humbled and submissive, one daughter comes crawling back to her father.
0:17:43 > 0:17:45She may be young, but she's a Druid.
0:17:45 > 0:17:48And the pack still howls as one...
0:17:48 > 0:17:50HOWLING
0:17:50 > 0:17:52..for the moment.
0:17:55 > 0:17:59As winter sets in, the Druid pack faces a dilemma.
0:17:59 > 0:18:04Hunting has been good, but there are simply too many of them,
0:18:04 > 0:18:06and they are constantly hungry.
0:18:08 > 0:18:13They've spotted an injured elk calf, who seeks refuge in an icy stream.
0:18:15 > 0:18:18This catch seems too easy to be true.
0:18:22 > 0:18:26It means getting drenched, and the wolves are not sure it's worth it.
0:18:40 > 0:18:45They move on, leaving the elk calf's fate to snow and ice.
0:18:57 > 0:19:00Winters in Yellowstone are merciless.
0:19:02 > 0:19:05Temperatures can drop to 50 below.
0:19:10 > 0:19:15Vast elk herds are gathering here in the Lamar Valley,
0:19:15 > 0:19:18and the wolves are right behind them.
0:19:21 > 0:19:24Led by the veterans 21 and 42,
0:19:24 > 0:19:29it's time for the pack to turn to the business of hunting.
0:19:29 > 0:19:34This is prime wolf country, full of elk, a favourite prey,
0:19:34 > 0:19:38and they know the local terrain, which gives them an advantage.
0:19:43 > 0:19:50'Wolves, one of the most important ways they hunt is by getting a good look at their prey,
0:19:50 > 0:19:54'so what the Druid Peak pack likes to do is use Lamar Valley
0:19:54 > 0:19:58'and the wide-open space there to get the elk herds moving,
0:19:58 > 0:20:01'and in that way, they can examine the elk.
0:20:05 > 0:20:10'21, the alpha male of the Druid Peak pack, is oftentimes the leader of the hunt.
0:20:10 > 0:20:16'He's the oldest, most experienced, arguably the wisest wolf in the pack,
0:20:16 > 0:20:19'and so he understands what elk can be pursued,
0:20:19 > 0:20:24'but he might not necessarily be the most aggressive wolf in the hunts.
0:20:24 > 0:20:29'He allows some of those younger wolves and their enthusiasm to come forward
0:20:29 > 0:20:34'to take care of the initial stages of the hunt and he'll move in towards the end.'
0:20:36 > 0:20:41With so many wolves, the Druid pack employs a scattergun tactic -
0:20:41 > 0:20:43fanning out to break up the herd.
0:21:07 > 0:21:10Each wolf follows its own target,
0:21:10 > 0:21:16but keeps an eye out in case a fellow Druid is on the heels of an easier mark.
0:21:27 > 0:21:32Like an experienced general, 21 oversees the attack,
0:21:32 > 0:21:36leaving the hard work to the younger troops.
0:21:57 > 0:22:00All it takes is a single stumble.
0:22:03 > 0:22:07The takedown is the most dangerous moment -
0:22:07 > 0:22:11a frightened elk can easily deal a fatal blow with its sharp hooves,
0:22:11 > 0:22:15but the Druids have experience on their side.
0:22:15 > 0:22:18The prey is overwhelmed.
0:22:19 > 0:22:24With so many hunters, the carcass will be quickly stripped to the bone.
0:22:24 > 0:22:27There will be little left for scavengers.
0:22:36 > 0:22:41After a hunt, it's time to restore order in the ranks.
0:22:41 > 0:22:46The alpha-female, 42, demands submission from her daughters.
0:22:59 > 0:23:05The success of the Druids has had an impact not only on the elk, but on the wolf's cousin -
0:23:05 > 0:23:07the coyote.
0:23:09 > 0:23:15Continually harassed by wolves, its numbers have fallen by half in the Lamar Valley.
0:23:38 > 0:23:41Once the Druids were infamous for killing coyotes,
0:23:41 > 0:23:43but no longer.
0:23:43 > 0:23:47This young wolf wants a playmate, however reluctant.
0:23:53 > 0:23:58The two creatures understand a common body language.
0:23:58 > 0:24:02The coyote knows that this is a game, and not game over.
0:24:14 > 0:24:17Although the Druid pups are ten months old,
0:24:17 > 0:24:18nearly full-grown,
0:24:18 > 0:24:22their puppyish curiosity and appetite for play
0:24:22 > 0:24:24are still very much alive.
0:24:33 > 0:24:37Play lets young wolves establish their status in the pack -
0:24:37 > 0:24:40a constantly-shifting power struggle.
0:25:01 > 0:25:04But while the pups play, there is trouble stirring.
0:25:08 > 0:25:11The pack has reached a critical size.
0:25:11 > 0:25:14It can no longer feed everyone.
0:25:14 > 0:25:17It's time for the yearlings to strike out on their own,
0:25:17 > 0:25:22and the rest of the pack can't emphasise the point strongly enough.
0:25:57 > 0:25:59Shunned by his own family,
0:25:59 > 0:26:03this outcast will have to make his own way in the wilderness.
0:26:04 > 0:26:08If he's lucky, he'll find a young female and start a new pack.
0:26:08 > 0:26:13If he's unlucky, he may be killed by a rival pack or starve.
0:26:23 > 0:26:27In the late afternoon, one of the Druid daughters is restless,
0:26:27 > 0:26:30and with good reason.
0:26:37 > 0:26:40113, the lone male, is back again,
0:26:40 > 0:26:42and looking for a mate.
0:27:20 > 0:27:26In this moment, the first steps in the formation of a new alliance have been taken.
0:27:33 > 0:27:36And as day gives way to night,
0:27:36 > 0:27:40there is a clear declaration that a new pack is born.
0:27:46 > 0:27:50Under cover of darkness, another Druid female
0:27:50 > 0:27:53approaches the big male stranger...
0:28:00 > 0:28:03..and then an adolescent male.
0:28:06 > 0:28:10A new force is gathering, but it's still on Druid territory.
0:28:21 > 0:28:27The morning finds old 21, the alpha-male, leading the remaining Druids on border patrol.
0:28:31 > 0:28:35This is not a good time for the new pack to be caught out in the open,
0:28:35 > 0:28:38and a very bad time to be caught mating.
0:28:41 > 0:28:44Mother and Father suspect nothing as yet.
0:28:46 > 0:28:48The new gang spots the patrol.
0:28:48 > 0:28:50It's definitely time to leave.
0:28:53 > 0:28:57At the top of the ridge, a team of Druids seals off an escape route.
0:29:01 > 0:29:04The big male stranger takes no chances.
0:29:04 > 0:29:07He leads his band of recruits into no-man's-land.
0:29:08 > 0:29:14On the way out of the valley, he's joined by several more Druid deserters.
0:29:18 > 0:29:22Travelling along the disputed border between rival wolf packs,
0:29:22 > 0:29:25the young gang of six heads south,
0:29:25 > 0:29:29further into the heart of the park to try their fortunes there.
0:29:30 > 0:29:35The loyal Druids reaffirm their ownership of this part of Yellowstone.
0:29:46 > 0:29:48To follow the wolves of the interior,
0:29:48 > 0:29:52Doug and his team are also headed deep into the backwoods of the park,
0:29:52 > 0:29:54far off the beaten path.
0:30:16 > 0:30:21Deep in the heart of Yellowstone is where winter hits hardest.
0:30:23 > 0:30:26There is no comfort to be found in these parts.
0:30:47 > 0:30:51During their study, the scientists have observed that predator and prey
0:30:51 > 0:30:55actually communicate with each other during a hunt.
0:30:55 > 0:30:57Over countless numbers of years,
0:30:57 > 0:31:03elk have developed signals that advertise their strength and fitness to wolves,
0:31:03 > 0:31:08and wolves have developed the ability to guess when the elk are cheating.
0:31:09 > 0:31:15These elk are signalling that they're strong by energetic and exaggerated trotting.
0:31:21 > 0:31:23It's a tactic to say,
0:31:23 > 0:31:27"Don't bother chasing me because I can outrun you."
0:31:34 > 0:31:38Sometimes the wolves will call their bluff,
0:31:38 > 0:31:40and continue to chase the elk.
0:31:40 > 0:31:44It won't be long before any weakness will be found out.
0:32:06 > 0:32:10Elk and wolf are much more evenly matched than might appear,
0:32:10 > 0:32:14and standing its ground when surrounded by a pack of hungry wolves
0:32:14 > 0:32:17turns out to be a winning strategy,
0:32:17 > 0:32:19if the elk can hold its nerve.
0:32:29 > 0:32:32'Wolves can be killed by their prey.
0:32:32 > 0:32:36'And we've had six wolves die in Yellowstone because of their prey -
0:32:36 > 0:32:40'five by elk, one by a moose -
0:32:40 > 0:32:46'so wolves have to be very, very careful at what they kill.'
0:32:47 > 0:32:51Stand-offs like these can go on for hours.
0:32:51 > 0:32:55If the elk can resist the urge to make a break for it,
0:32:55 > 0:32:57the wolves will often give up.
0:32:59 > 0:33:04The wolf's strength lies in killing animals that are already running.
0:33:04 > 0:33:07A passing group of bison is too tempting to resist.
0:33:21 > 0:33:25The Yellowstone winter finally loosens its grip,
0:33:25 > 0:33:28and gives way slowly...
0:33:28 > 0:33:30to spring.
0:33:32 > 0:33:36The winter has culled the weak and the old -
0:33:36 > 0:33:38only the fittest have survived.
0:33:47 > 0:33:51Today, Doug is out with David Mech and Rolf Peterson,
0:33:51 > 0:33:54both veterans of wolf research.
0:33:54 > 0:33:58They're looking for a bison carcass that was spotted from the air.
0:34:05 > 0:34:10Doug and his team meticulously document every wolf kill they find
0:34:10 > 0:34:13and conduct a death-scene forensic investigation.
0:34:13 > 0:34:15OK.
0:34:15 > 0:34:18There's an extra tooth right there.
0:34:18 > 0:34:20Oh, yeah, right there.
0:34:20 > 0:34:24An impacted and infected tooth may have caused this animal's downfall.
0:34:25 > 0:34:29Wolves may be able to sniff out decay in a rotting tooth.
0:34:29 > 0:34:32Oh, and that stuff smells, actually.
0:34:32 > 0:34:35If wolves can detect abnormalities by smell,
0:34:35 > 0:34:38they could sure smell that.
0:34:38 > 0:34:43The researchers suspect more than just a toothache as the cause of the bison's death.
0:34:43 > 0:34:49By sawing apart one of its bones, they can examine the condition of the marrow.
0:34:51 > 0:34:53- Look at that!- Wow!
0:34:53 > 0:34:57There's no fat in there whatever.
0:34:57 > 0:34:59I mean, it's water, it's water.
0:34:59 > 0:35:03No fat in the marrow means the animal was starving.
0:35:03 > 0:35:06It would've been dead even if the wolves hadn't killed it.
0:35:06 > 0:35:10- It couldn't go anywhere. - The wolves did it a favour.
0:35:12 > 0:35:15The spring thaw has thinned the ice.
0:35:26 > 0:35:30The bison will find escape impossible.
0:35:44 > 0:35:48Ravens are the first to discover a carcass.
0:35:52 > 0:35:55Coyotes aren't far behind.
0:36:08 > 0:36:12He's earned the right to have the first go at the soggy carcass...
0:36:23 > 0:36:26..not that it's going to be that easy.
0:37:16 > 0:37:19This is not one of his better days.
0:37:43 > 0:37:46Springtime in Yellowstone is fickle.
0:37:47 > 0:37:52In the Lamar Valley, the blink of an eye and winter is back again.
0:37:52 > 0:37:56A mother grizzly and her cub have emerged from their winter den
0:37:56 > 0:37:59only to be greeted by driving snow...
0:38:00 > 0:38:02..and something more sinister -
0:38:02 > 0:38:04Druids.
0:38:07 > 0:38:12There is no love lost between Yellowstone's top predators.
0:38:21 > 0:38:25Wolves and grizzlies have been known to kill each other's young.
0:38:26 > 0:38:32You'd think an aggressively protective mother bear would be best left alone.
0:38:36 > 0:38:41She could break a wolf's back with a single swipe of her paw.
0:38:43 > 0:38:47But she can't risk straying more than a few yards from her cub.
0:39:03 > 0:39:08Finally, the Druids lose interest in bear-baiting
0:39:08 > 0:39:11and the mother and cub can go their own way.
0:39:25 > 0:39:29After several false starts, spring has taken winter's place.
0:39:58 > 0:40:03With the cloak of winter lifted, the Lamar Valley is barely recognisable.
0:40:05 > 0:40:09There are newcomers here, just getting to know the place.
0:40:20 > 0:40:24The Druids have made it through the winter in fine form -
0:40:24 > 0:40:27old 21 and 42 still at the helm.
0:40:27 > 0:40:31At this time of year, the pack splits up -
0:40:31 > 0:40:35the wolves won't need to hunt as a large team,
0:40:35 > 0:40:37now their prey is elk calves.
0:40:46 > 0:40:48And it's not just wolves -
0:40:48 > 0:40:51every predator is drawn to them.
0:40:55 > 0:41:01'There may be competition between wolves and grizzly bears for elk calves.
0:41:01 > 0:41:04'But it's interesting, because one day
0:41:04 > 0:41:06'in Lamar Valley this spring,
0:41:06 > 0:41:10'our team observed two elk calves killed by wolves,
0:41:10 > 0:41:12'two killed by grizzly bears'
0:41:12 > 0:41:15and two killed by coyotes.
0:41:15 > 0:41:20Black bears, cougars, eagles also take elk calves.
0:41:20 > 0:41:24'So one of the next studies that we're trying to initiate
0:41:24 > 0:41:28'is understanding predation on elk calves.'
0:41:47 > 0:41:51The calves are nimble and quick, even at this young age.
0:41:51 > 0:41:56A grizzly is surprisingly fleet for its size.
0:41:56 > 0:41:59It can reach a top speed of 30 miles an hour.
0:42:22 > 0:42:25Grizzlies have young to feed too.
0:42:36 > 0:42:42The reintroduction of wolves to Yellowstone, though, hasn't been welcomed by everyone.
0:42:47 > 0:42:52Local sports-hunters, for one, don't like competing with the wolves.
0:42:54 > 0:42:57But despite the return of a top predator to the park,
0:42:57 > 0:43:02the scientists report elk numbers seem to be holding steady.
0:43:23 > 0:43:26But the controversy has spread beyond the park.
0:43:26 > 0:43:32Nearly half of the wolves now live outside Yellowstone, where they are not welcome.
0:43:32 > 0:43:35Ranchers feared loss of their cattle,
0:43:35 > 0:43:39but after seven years, the true losses have been far lower
0:43:39 > 0:43:41than many ranchers had predicted.
0:43:47 > 0:43:54The days are growing longer, and the Druids are away patrolling the furthest reaches of their territory.
0:43:57 > 0:44:03Doug and his team use this opportunity to study the Druids' vacated winter home.
0:44:07 > 0:44:09'Den sites are treasures.
0:44:10 > 0:44:14'You get a view into the wolf's world, you know,
0:44:14 > 0:44:18'it's just like going to your house after you've moved out.'
0:44:20 > 0:44:22OK. Oh, yeah, it goes back aways.
0:44:22 > 0:44:26- Can you see the main chamber at the end?- I can.
0:44:26 > 0:44:30They've found that females make dens in caves, dig under tree-roots,
0:44:30 > 0:44:33and even take over beaver dams.
0:44:33 > 0:44:37It's a narrow entryway with a big chamber at the end.
0:44:37 > 0:44:40It might go at least 16 feet -
0:44:40 > 0:44:44an entrance that probably a grizzly bear couldn't get down,
0:44:44 > 0:44:47but a chamber that was pretty roomy and comfortable.
0:44:49 > 0:44:55The Druids themselves are now long gone, spending the summer at a rendezvous site.
0:44:59 > 0:45:05Their two-month-old pups stay here, making the most of the lush period of sunshine,
0:45:05 > 0:45:08while most of the pack hunts.
0:45:11 > 0:45:16There are plenty of new sights and smells to investigate,
0:45:16 > 0:45:21and an attentive babysitter nearby to make sure things don't get out of hand.
0:45:25 > 0:45:27For the next few summer months,
0:45:27 > 0:45:31the rendezvous site will be the focal point of their young lives.
0:45:31 > 0:45:35Though adults often go their separate ways to hunt,
0:45:35 > 0:45:39they return to the rendezvous site to feed the pups,
0:45:39 > 0:45:42and keep in contact with the rest of the pack.
0:45:44 > 0:45:47A new litter of wolf pups is welcome,
0:45:47 > 0:45:54but Doug knows the time will soon come when there will be some sad losses from the Druid pack.
0:45:54 > 0:45:58'42 has been there since the beginning
0:45:58 > 0:46:00'and 21 came on the scene early.
0:46:02 > 0:46:05'They are the thread through that whole story,
0:46:05 > 0:46:10'and that thread is getting short, and it could end soon.
0:46:11 > 0:46:15'It will be a sad day for me,
0:46:15 > 0:46:19'and it will be a sad day for the story of Yellowstone wolves.'
0:46:21 > 0:46:24The sadness of those inevitable losses
0:46:24 > 0:46:27should be balanced by the scale of the achievement.
0:46:27 > 0:46:31'I think the reintroduction of wolves to Yellowstone
0:46:31 > 0:46:35'is one of the scientific opportunities of the century.
0:46:35 > 0:46:38'To be a part of this from the beginning
0:46:38 > 0:46:43'and document how this system will change because of the reintroduction
0:46:43 > 0:46:46'of a top carnivore that belongs here
0:46:46 > 0:46:51'is a huge scientific opportunity that needs to be done.'
0:46:53 > 0:46:58And now a new chapter has opened in Yellowstone's history.
0:47:00 > 0:47:05Doug has been anxious to find out what happened to the big young wolf
0:47:05 > 0:47:09that ran off with the Druid's adolescent daughters.
0:47:09 > 0:47:12Although number 113 has been collared,
0:47:12 > 0:47:14his radio transmitter only works occasionally
0:47:14 > 0:47:16so he's been hard to track.
0:47:18 > 0:47:21One day, at the edge of the Druids' territory,
0:47:21 > 0:47:24Doug spots a group of pups he hasn't seen before.
0:47:26 > 0:47:29And watching over them is 113,
0:47:29 > 0:47:31no longer a renegade wolf,
0:47:31 > 0:47:35but a busy father with his young family.
0:47:38 > 0:47:40With the arrival of the pups,
0:47:40 > 0:47:43this group is now officially a pack in its own right,
0:47:43 > 0:47:46and 113 is their alpha male.
0:47:53 > 0:47:57A chapter is ending for the aging leaders of the Druids,
0:47:57 > 0:48:00but it's just beginning for this pack,
0:48:00 > 0:48:02too new to even have a name.
0:48:02 > 0:48:06Future skirmishes over Yellowstone territory are inevitable.
0:48:07 > 0:48:10As these young wolves face the future,
0:48:10 > 0:48:13this is their battle cry.
0:48:13 > 0:48:15HOWLING
0:48:27 > 0:48:30Subtitles by Sarah Aitken BBC Broadcast 2004
0:48:30 > 0:48:33E-mail us at subtitling@bbc.co.uk