Episode 3

KIRK: SUMMER IN YELLOWSTONE.

THIS MIGHT LOOK LIKE AN IDYLLIC TIME OF YEAR, BUT FOR SOME ANIMALS, THIS SEASON BRINGS ITS OWN CHALLENGES.

THIS WOLF HAS 11 HUNGRY PUPS TO FEED.

THE ELK HERDS SHE HUNTED IN WINTER ARE NO LONGER HERE.

THEY'VE MOVED TO HIGHER GROUND TO ESCAPE THE HEAT.

[ELK BUGLING] SHE'LL NEED ALL HER CUNNING TO FIND NEW WAYS TO KEEP HER PUPS FROM GOING HUNGRY.

[SQUIRREL TRILLING] IN YELLOWSTONE, IT'S THE WARMEST SEASON THAT'S THE TOUGHEST FOR SOME TO SURVIVE.

I'M KIRK JOHNSON.

I'VE BEEN COMING HERE TO THE GREATER YELLOWSTONE ECOSYSTEM FOR MY WHOLE LIFE, ONE OF MY FAVORITE PLACES ON THE PLANET.

WHAT MAKES THIS PLACE UNIQUE IS THE EXTREME CHANGES FROM ONE SEASON TO THE NEXT, THE TRANSITION FROM A FRIGID MINUS-40-DEGREE WINTER TO A 100-DEGREE SMOLDERING SUMMER.

THESE DRAMATIC CHANGES PUSH YELLOWSTONE'S WILDLIFE TO ITS LIMITS.

FOR THE PAST 4 MONTHS, I'VE BEEN HERE, FOLLOWING THE THAW.

IN WINTER, I SAW ANIMALS STAVE OFF COLD AND HUNGER.

IN SPRING, THEY SURVIVED STORMS AND RAGING RIVERS.

AND NOW THEIR FINAL CHALLENGE.

SUMMER WILL BAKE THE YELLOWSTONE LANDSCAPE, AND FIRES WILL RIP THROUGH THE TINDER-DRY FORESTS.

[OWL SCREECHES] TO UNDERSTAND HOW THE ANIMALS COPE WITH THE CHANGE OF THE SEASONS, WE'RE GONNA FOLLOW A NUMBER OF FAMILIES TO WITNESS THE THAW THROUGH THEIR EYES.

WE'VE BROUGHT TOGETHER A TEAM OF WILDLIFE CAMERAMEN... OH, NO.

THIS IS NUTS.

SCIENTISTS, AND LOCAL EXPERTS, WHO ARE USING THE LATEST TECHNOLOGY TO RECORD AND ANALYZE THE CHALLENGES FACED BY OUR ANIMAL FAMILIES.

THEY MAKE A MISTAKE, THEY'RE KILLED.

KIRK: SO FAR IN 2016, EVERY MONTH HAS BEEN WARMER THAN USUAL IN YELLOWSTONE.

IF THIS TREND CONTINUES, SUMMER TEMPERATURES COULD REACH A RECORD HIGH, AND THE WILDLIFE WILL HAVE TO ADAPT OR DIE.

BECAUSE YELLOWSTONE IS OVER 600 MILES FROM THE OCEAN AND MORE THAN A MILE HIGH, IT HAS FREEZING-COLD WINTERS AND BAKING-HOT SUMMERS.

BUT IT'S NOT ALL BAD.

THE LAND IS ALREADY STARTING TO DRY OUT, WHICH IS ACTUALLY GOOD NEWS FOR THE BEAVER FAMILY THAT I'VE BEEN FOLLOWING ON THE SNAKE RIVER.

BACK IN THE SPRING, WHEN I WAS LAST HERE, THIS WAS A REALLY DIFFERENT PLACE.

THERE WAS A LOT OF WATER GOING THROUGH THIS RIVER, AND IT WAS PUSHING THE DAMS APART.

BEAVERS DAM RIVERS TO CREATE A POND WHERE THEY LIVE AND FEED, SAFE FROM PREDATORS.

THEIR ENGINEERING CREATES A VALUABLE WETLAND ENVIRONMENT FOR MANY DIFFERENT ANIMALS THAT COME TO FEED ON LUSH VEGETATION AT THE POND'S EDGE AND TO COOL OFF IN THE WATER.

BUT THE THAW THIS YEAR HAPPENED 3 WEEKS EARLY, AND THE DELUGE OF MELTWATER NEARLY WASHED THE BEAVERS' HOME AWAY.

THE FAMILY HAS BEEN BUSY WITH HOME IMPROVEMENTS, AND THEIR PLACE LOOKS GOOD AS NEW.

NOW IT'S SUMMER, THE SNOW IS OFF THE TETONS, AND IT'S LIKE A SERIES OF LAKES BETWEEN THESE DAMS.

I'M REALLY WONDERING, WHERE ARE THE BEAVERS, AND WHAT ARE THEY DOING?

CAMERAMAN JEFF HOGAN HAS CONTINUED TO TRACK THEIR PROGRESS, AND THANKS TO INFRARED CAMERAS HE PLACED IN THEIR LODGE... HOW'S IT GOING?

GOOD.

WE HAVE AN EXCLUSIVE ON SOME EXCITING NEWS.

OH, THERE'S A LITTLE ONE!

WOW.

THAT'S INCREDIBLE.

LOOK AT THAT.

YEAH.

THEY'RE JUST WAKING UP.

A LITTLE YAWN, AND THEN BACK DOWN.

THESE WERE BORN THIS SPRING.

ALL 3 OF THOSE LITTLE GUYS?

YEAH, YEAH.

OH, WOW.

KIRK: DESPITE THE EARLY FLOODS THAT DAMAGED HER HOME, THIS BEAVER MOM HAS GIVEN BIRTH TO 3 LITTLE BABIES KNOWN AS KITS.

I WOULD SAY THEY'RE PROBABLY ABOUT 10 WEEKS OF AGE MAYBE.

KITS ARRIVE WELL-PREPARED FOR THEIR WATERY WORLD.

THEY'RE BORN KNOWING HOW TO SWIM, USING THEIR FLAT TAILS AS RUDDERS, AND THEY HAVE A FULL FUR COAT AND SUPER-SHARP TEETH READY TO PUT TO USE.

JEFF THINKS THEY'RE 10 WEEKS OLD BECAUSE THEY'VE STOPPED DRINKING MOTHER'S MILK, AND THEY ALREADY EAT THE SAME FOOD AS THE ADULTS, VEGETATION AND LOTS OF IT.

JEFF: I'VE GOT ANOTHER CLIP FOR YOU.

KIRK: OH, LOOK AT THIS.

IT'S LIKE ALL THE GROCERIES COMING HOME.

YEAH, FRESH GREEN GROWTH, THE SEDGES AND GRASSES.

SO, OK, THEY'RE JUST HARVESTING THE SHORELINE.

BUT THEN THEY ALSO-- AN ADULT WILL COME IN AND BRING IN A BIG BRANCH.

AND THE LITTLE YOUNG ONES WILL JUST JUMP ON THIS.

[KITS MEWING] THEIR LITTLE PAWS ARE JUST LIKE FINGERS.

THEY'VE GOT INCREDIBLE ABILITY TO GRASP.

YEAH.

NOW HE'S JUST CHEWING AWAY.

YEAH.

JUST CHEWING AWAY.

KIRK: IN SUMMER, THE PONDS THE BEAVERS MADE BY DAMMING THE RIVER TURN INTO VEGETABLE GARDENS RIPE FOR HARVEST.

THE WARM SLOW-MOVING WATER IS THE PERFECT ENVIRONMENT FOR THESE PLANTS.

JEFF: IT'S QUITE AMAZING HOW THEY ENGINEER SUCH A, YOU KNOW, PRODUCTIVE ECOSYSTEM.

KIRK: BUT GARDENING IS HARD WORK.

MOM, DAD, AND THE YOUNG BORN LAST YEAR ARE WORKING FULL-TIME BRINGING FOOD TO THE KITS.

AND THEN THERE'S THE CLEANING.

ALL THAT GRASSY BEDDING NEEDS REGULAR WASHING.

SUMMER HAS ITS REWARDS, BUT IT'S NO TIME TO RELAX.

NOW IS THE TIME BEAVERS PREPARE FOR THE WHOLE CYCLE TO TAKE PLACE AGAIN.

SUCH AMAZING LITTLE ENGINEERS.

THAT SAYS DINNERTIME.

OH, YEAH.

AFTER A HARD DAY OF DAM REPAIR, CANAL DIGGING, TREE CHOPPING.

KIRK: IT WON'T BE LONG BEFORE THE KITS WILL BE OLD ENOUGH TO GO OUT AND FIND THEIR OWN FOOD.

BUT THEY'LL NEED TO WATCH THEIR BACKS.

IN SOME PLACES, AS MANY AS HALF OF THE KITS ARE TAKEN BY PREDATORS LIKE WOLVES, COYOTES, AND BALD EAGLES.

IT'S SUCH A CRITICAL TIME FOR THE FAMILY.

JEFF WILL MAKE SURE HE KEEPS AN EYE ON THEM EVERY STEP OF THE WAY.

ALL ACROSS YELLOWSTONE'S WATERWAYS, YOU CAN SEE SIGNS THAT AN EARLY SPRING THAW IS AFFECTING THE COMPLEX WEB OF RELATIONSHIPS BETWEEN PLANTS AND ANIMALS.

AS ICY MELTWATERS FLOWING DOWN FROM THE MOUNTAIN SUBSIDE, STREAMS WARM RAPIDLY IN THE SUN, AND THE SURFACE OF THE WATER BEGINS TO DANCE.

THIS IDYLLIC PICTURE OF YELLOWSTONE MARKS AN EXPLOSION OF LIFE.

THE RISING TEMPERATURES TRIGGER MAYFLIES TO HATCH IN THEIR MILLIONS.

THIS IS THE STARTING GUN FOR AN IMPORTANT EVENT...

THE ARRIVAL OF CUTTHROAT TROUT.

THEY'VE SPENT THE WINTER IN DEEP RIVERS AND LAKES BUT MIGRATE UPSTREAM TO FEED ON MAYFLIES AND SPAWN IN THESE SHALLOW RIVERS.

THIS IS THE LARGEST POPULATION OF INLAND CUTTHROAT TROUT IN THE WORLD.

THE TIMING OF THEIR ARRIVAL AFFECTS OVER 20 DIFFERENT SPECIES OF PREDATORS THAT RELY ON THE PROTEIN-RICH FISH IN EARLY SUMMER.

[BIRDS SCREECHING] TO FIND OUT HOW AN EARLY THAW CAN AFFECT THIS KEY EVENT, I'M HERE CASTING LURES WITH BIOLOGIST CHAD WHALEY.

I'VE GOT A FISH!

CAN WE GET A NET OVER HERE?

NO, HE GOT OFF.

[LAUGHTER] YOU GOT HIM?

NICE.

I CAN'T BELIEVE YOU GOT MY FISH.

HA HA HA!

NICELY DONE.

SWEET.

HOW LUCKY IS THAT?

LET'S DO A LITTLE SCIENCE ON THIS FISH, HUH?

SOUNDS GREAT.

KIRK: EACH TROUT, WE-- WELL, CHAD CATCHES-- IS FITTED WITH A TINY RADIO TRANSMITTER.

CHAD'S TEAM WILL NOW BE ABLE TO TRACK THEIR EVERY MOVE AND IDENTIFY THE EXACT MOMENT THE TROUT LEAVES THE LAKE TO HEAD UPRIVER.

THAT'S AMAZING.

SO THE POOR TROUT LIVES ITS LIFE IN THE LAKE.

WHEN IT WANTS TO GO SPAWN, HE RUNS RIGHT THROUGH YOUR DETECTOR, AND IT GOES "BEEP."

THE FISH WON'T KNOW.

THE FISH DOESN'T KNOW.

THE FISH DOESN'T KNOW.

I MEAN, IT'S A PRIVATE MOMENT FOR THE FISH.

KIRK: SPYING ON THE SECRET SEX LIVES OF CUTTHROAT TROUT MAY SEEM A LITTLE INTRUSIVE, BUT IT'S ALL FOR SCIENCE.

WE'RE GETTING REALLY FUNDAMENTAL DATA ON THE TIMING OF THESE FISH GOING INTO THE STREAMS.

WHAT'S INTERESTING, WE'RE SEEING THAT THE SNOW IS MELTING EARLIER IN THE SEASON EACH YEAR, AND THESE FISHES' ABILITY TO SPAWN EARLIER IS GETTING TESTED.

THE FISH MAY OR MAY NOT BE READY WHEN THE WATER IS CUEING THEM TO BE IN THE STREAM SPAWNING.

KIRK: THE CUTTHROAT TROUT'S ABILITY TO ADAPT WILL BE TESTED BY EARLIER THAWS, LIKE THE ONE THIS YEAR IN YELLOWSTONE, BUT FOR PREDATORS, THE TROUT'S EARLY ARRIVAL IS A BONUS.

THEY HAVE EXTRA TIME TO FATTEN UP.

WHILE THERE'S A LOT OF ACTION HAPPENING IN THE RIVERS, YELLOWSTONE'S LOW-ALTITUDE GRASSLANDS ARE EERILY QUIET.

IN SPRING, HERDS OF ELK AND BISON WERE FEEDING HERE, BUT THEY'VE MOVED ON AS THE GREEN VEGETATION HAS WITHERED IN THE HEAT.

IT'S WHAT WE CALL THE BROWN-UP, AND IT'S ALREADY WELL UNDERWAY.

[ELK BUGLING] THE GRAZERS ARE HEADED FOR COOLER HIGH GROUND, WHERE THERE ARE STILL GREEN SHOOTS.

BY JULY, BISON HAVE ARRIVED AT SUMMER GRAZING GROUNDS ON YELLOWSTONE'S HIGH PLATEAU.

THIS IS THE ONLY TIME LARGE MATURE MALES COME TOGETHER WITH FEMALES.

THE HERDS ARE AN IMPRESSIVE SIGHT AND CAN NUMBER UP TO A THOUSAND.

RIGHT NOW, THE GRASSLANDS LOOK LIKE THEY'RE ON FIRE, BUT IT'S NOT SMOKE.

[BISON RUMBLING] AND THIS TIME OF YEAR, IT'S REALLY DRY, AND THE BISON ARE KICKING UP THE DUST AND WALLOWING IN IT.

THEY'RE COATING THEMSELVES TO KEEP THE BUGS OFF THEM, BUT IT'S ALSO THE TIME OF THE YEAR THAT THE MALE BISON ARE THINKING OF SOMETHING ELSE.

[BISON RUMBLING] THE RUT IS ABOUT TO BEGIN.

[BISON RUMBLING] RUTTING IS A FIGHT FOR THE RIGHT TO MATE.

SO DUST BATHS ARE MORE THAN JUST INSECT REPELLENT.

THEY'RE A SHOW OF STRENGTH.

CHURNING UP AN IMPRESSIVE CLOUD CAN BE ENOUGH TO INTIMIDATE A SMALLER OR INEXPERIENCED OPPONENT.

BUT WHEN TWO HEAVYWEIGHTS WON'T BACK DOWN, IT'S LITERALLY A HEAD-TO-HEAD MATCHUP.

HEAVILY MUSCLED NECKS AND THICK SKULLS COVERED IN A MAT OF DENSE HAIR HELP ABSORB THE HEAD-CRACKING COLLISIONS.

ONLY THE WINNER EARNS THE RIGHT TO MATE...

WHICH ENSURES ONLY THE STRONGEST GENES WILL BE PASSED ON.

BUT WHILE BISON ARE ALREADY THINKING ABOUT MAKING THE NEXT GENERATION...

MOST ANIMALS ARE STILL STRUGGLING TO RAISE THIS YEAR'S YOUNG.

FOR YELLOWSTONE'S TOP PREDATOR, THE WOLF, THIS HAS BEEN A REALLY HARD YEAR.

ABOUT 500 WOLVES ROAM ACROSS GREATER YELLOWSTONE, AND THEY RELY ON A SUPPLY OF PREY GRAZING ON THE GRASSLANDS.

THIS YEAR, A MILD WINTER AND SPRING MEANT THAT THE ELK AND BISON WERE WELL FED AND OUTRAN THE WOLVES.

MANY PACKS WENT HUNGRY.

IN SUMMER, THE STAKES ARE EVEN HIGHER BECAUSE THERE ARE YOUNG PUPS TO FEED.

IN THE SOUTH OF GREATER YELLOWSTONE, ONE PACK IS DOING BETTER THAN MOST.

AN AERIAL PHOTO OF THE PINNACLE PEAK PACK REVEALS THEY HAVE 11 PUPS THIS YEAR.

UNUSUALLY, TWO FEMALES HAVE GIVEN BIRTH, A SIGN THE PACK IS DOING WELL AND FINDING PLENTY OF FOOD.

BUT WITH THE ELK NO LONGER AN OPTION, THE WOLVES HAVE TO COME UP WITH A NEW SOLUTION.

CAMERAMAN CHARLIE HAMILTON JAMES IS INVESTIGATING HOW THIS PACK IS FINDING ENOUGH FOOD FOR ALL 11 PUPS.

HE THINKS THE KEY TO THEIR SUCCESS COULD BE DUE TO HUMAN ACTIVITY.

YOU SEE HIM?

[ENGINE STOPS] I WONDER IF SHE'S GONNA LET ME GET OUT.

I'M GONNA GIVE IT A GO.

BEAR WITH ME ON THIS.

WELL, WELL, WELL, WELL, WELL.

HOW BEAUTIFUL IS THAT?

SHE CAN SMELL ME.

MY SCENT IS GOING STRAIGHT AT HER.

SHE KNOWS I'M HERE.

SHE'S NOT BOTHERED AT ALL.

KIRK: IN 20 YEARS OF FILMING, CHARLIE HAS NEVER BEEN THIS CLOSE TO A WILD WOLF.

THIS FEMALE IS FROM THE PINNACLE PEAK PACK.

AND SOMETHING HAS DRAWN HER INTO THIS AREA.

HERE THE GRASS IS STILL GREEN BECAUSE IT'S BEING WATERED OVER THE SUMMER TO IMPROVE GRAZING.

CHARLIE: BECAUSE YOU CAN SEE ALL THESE SPRINKLERS BEHIND HER, BECAUSE THEY'RE WATERING THE GRASS, THIS CREATES AMAZING HABITAT FOR GROUND SQUIRRELS.

THERE'S JUST TONS OF THEM.

KIRK: A HUGE COLONY OF GRASS-EATING UINTA GROUND SQUIRRELS ARE TAKING ADVANTAGE OF THIS ARTIFICIAL OASIS.

USUALLY, BY MID-JULY, THE GRASS WOULD BE TURNING BROWN AND INEDIBLE, AND THE SQUIRRELS WOULD BE HEADING INTO BURROWS TO HIBERNATE.

THIS FEMALE WOLF HAS SPOTTED THE CHANCE OF AN EASY MEAL... AND IT'S CLOSER TO THE DEN THAN THE LARGE ELK HERDS 20 MILES AWAY.

CHARLIE: THEY NEED THESE GROUND SQUIRRELS, BECAUSE THEY'RE TIED TO THEIR TERRITORY.

THEY'VE GOT PUPS HERE.

THEY CAN'T GO ANYWHERE ELSE.

SO THEY HAVE TO FIND FOOD AROUND HERE, JUST TO SURVIVE AND KEEP THOSE PUPS ALIVE.

KIRK: BUT CATCHING THESE BURROWING RODENTS IS TRICKY.

THEY TAKE TURNS AS LOOKOUTS FOR DANGER, BALANCING ON THEIR HIND LEGS TO SEE OVER THE TALL GRASS.

THE SQUIRRELS ALSO HAVE A RANGE OF ALARM CALLS FOR DIFFERENT THREATS.

[SQUIRREL TRILLING] A TRILL MEANS IT'S A GROUND-BASED PREDATOR.

[SQUIRREL TRILLING] THE ENTIRE COLONY DIVE FOR THE SAFETY OF THEIR BURROWS.

CHARLIE: LOOK AT THAT.

SHE'S ON IT.

SHE'S ON ONE.

AH.

KIRK: THIS FEMALE IS PUTTING IN A LOT OF WORK WITHOUT ANY REWARD.

CHARLIE: AH, THERE'S ANOTHER ONE.

THERE WE GO.

THERE'S ONE RUNNING.

AH, WHERE IS IT?

WHERE IS IT?

WHERE IS IT?

A LONG WAY OFF.

KIRK: ANOTHER PACK MEMBER MAY HELP TURN THE TABLES.

WOLVES' REAL STRENGTH IS IN NUMBERS.

CHARLIE: THERE'S ANOTHER ONE.

THERE'S ANOTHER WOLF.

I DON'T KNOW WHICH ONE TO FILM NOW.

KIRK: THE GROUND SQUIRRELS CAN'T WATCH ALL 3 WOLVES AT ONCE.

[SQUIRREL TRILLS] AND THESE NEWCOMERS ARE TRYING A NEW HUNTING STRATEGY TO OUTWIT THEIR PREY.

[SQUIRREL TRILLING] THERE'S A LOT OF ACTIVITY, AND THEN THEY'LL LIE DOWN.

AND YOU'LL THINK, WELL, WHY ARE THEY SUDDENLY LYING DOWN?

PART OF THEIR HUNTING STRATEGY.

IF YOU LIE DOWN AND ESSENTIALLY JUST WAIT FOR THE GROUND SQUIRRELS TO COME UP TO THEM, YOU KNOW, AND THEY'RE SORT OF DOZING, THEY'RE HALF-SLEEPING, AND A GROUND SQUIRREL COMES UP, AND THEY JUST LEAP UP AND GRAB IT.

KIRK: IT'S WORKING.

[SQUIRREL TRILLS] EVEN THE ORIGINAL FEMALE IS HAVING MORE LUCK.

CHARLIE: WITH ANIMALS, YOU GET THESE PEAK MOMENTS OF ACTIVITY, AND THEY LAST FOR A FEW DAYS OR A FEW WEEKS, AND THEN THEY'RE GONE AGAIN.

AND IT'S...

IT'S INCREDIBLY LUCKY THAT WE'VE BEEN ABLE TO BE HERE FOR THIS PARTICULAR PERIOD OF PEAK ACTIVITY.

I'VE NEVER SEEN IT BEFORE.

I DON'T KNOW IF IT WILL EVER HAPPEN AGAIN, BUT IT'S AMAZING TO WITNESS IT.

KIRK: THESE WOLVES HAVE USED ALL THEIR INTELLIGENCE TO EXPLOIT THE SITUATION.

THE EXTRA FOOD WILL INCREASE THE CHANCES OF THE PUPS SURVIVING.

IT'S INCREDIBLE TO SEE HOW WOLVES ARE ADAPTING TO A LANDSCAPE INCREASINGLY INFLUENCED BY PEOPLE.

SINCE I FIRST CAME TO YELLOWSTONE AS A KID MORE THAN 40 YEARS AGO, I'VE BEEN BACK HERE MANY TIMES, AND I'VE NOTICED CHANGES IN ALMOST EVERY ONE OF THE HABITATS... CHANGES THAT HAVE NO DOUBT RESULTED FROM WARMER WINTER TEMPERATURES.

RISING TEMPERATURES ARE AFFECTING THE COMPLEX CONNECTIONS BETWEEN PLANTS AND ANIMALS THAT HAVE EXISTED HERE FOR MILLENNIA.

SOME CAN ADAPT BETTER THAN OTHERS, AND SMALL CHANGES CAN HAVE A BIG IMPACT.

IT'S PARTICULARLY VISIBLE IN THE HIGHEST, COLDEST PART OF GREATER YELLOWSTONE, IN THE ALPINE ZONE ABOVE 11,000 FEET.

ONE MAMMAL CAN TOUGH IT OUT HERE ALL YEAR ROUND.

IN SUMMER, PIKAS ARE MAKING THE MOST OF THE WILDFLOWERS.

KAITLYN HANLEY IS THE HARDY RESEARCHER WHO STUDIES THEM.

KIRK: LET'S GET OUT OF THE WIND.

KAITLYN: YEAH, OUT OF THE WIND.

KIRK: IT'S, LIKE, HOWLING.

KAITLYN: WELCOME TO THE ALPINE.

KIRK: I WANT TO GET IN HERE.

KAITLYN: YEAH.

KIRK: OH, THIS IS MUCH BETTER.

TELL ME A LITTLE BIT ABOUT HOW EXTREME THE CONDITIONS ARE HERE UP ON THE BEARTOOTH PLATEAU.

KAITLYN: WE'RE AT 11,000 FEET.

SO IT'S PRETTY EXTREME.

WE'RE BASICALLY IN PRIME PIKA HABITAT, WHICH IS A... WHAT WE CALL TALUS.

IT'S A BOULDER FIELD, ROCK FIELD.

YOU HAVE ALL SORTS OF ROCKS AND BOULDERS, AND THEY STAY WITHIN THE ROCKS TO PROTECT THEM FROM THE COLD.

KIRK: AT THIS ALTITUDE, COLD MEANS ANYTHING DOWN TO MINUS 40 DEGREES FAHRENHEIT.

PIKAS EVOLVED IN ARCTIC AND ALPINE CONDITIONS AND ARE WELL ADAPTED TO FRIGID TEMPERATURES.

THEIR ODD APPEARANCE IS ALL ABOUT KEEPING WARM.

[PIKA SCREECHES] THEIR PLUMP, ROUND SHAPE MINIMIZES SURFACE HEAT LOSS, AND THICK FUR COVERS THEIR ENTIRE BODIES... [PIKA SCREECHES] EVEN THEIR TOES.

DO PIKA ACTUALLY SPEND THE ENTIRE WINTER UP HERE?

ALL YEAR LONG, THEY'RE UP WITHIN THE TALUS.

THEY DO NOT HIBERNATE, SO THEY'RE ACTIVE THROUGHOUT THE WINTER.

THEY COLLECT VEGETATION THROUGHOUT THE SUMMER.

THEY'LL GET THESE HUGE HAY PILES UNDER THE ROCKS, AND THEY'LL USE THAT IN THE WINTER SO THEY HAVE A FOOD SOURCE.

THEY'RE BUSY LITTLE BEES.

THAT'S FOR SURE.

[PIKA SCREECHES] KIRK: ALL THIS RUNNING AROUND CAN TAKE ITS TOLL.

THEY'RE SO WELL ADAPTED FOR THE COLD THAT INCREASINGLY WARM SUMMER TEMPERATURES ARE HARD TO TOLERATE.

KAITLYN: THEY ARE VERY SENSITIVE TO HEAT.

IF THEIR BODY TEMPERATURE INCREASES BY JUST ABOUT 3 DEGREES, THEY'RE GONNA OVERHEAT, AND THEY'RE GONNA DIE.

SO THESE ARE BASICALLY ANIMALS THAT ARE REALLY ADAPTED TO A COLD WINTER AND A COLD SUMMER, AND THE QUESTION IS, YOU WARM IT UP...

EXACTLY.

WITH CLIMATE CHANGE, AS TEMPERATURE INCREASES, PIKA WILL MOST LIKELY MOVE UPSLOPE.

HERE IN THE BEARTOOTHS, THE GREAT THING IS, IT'S A PLATEAU, AND SO AT A CERTAIN POINT, YOU GET AN INCREASE IN POTENTIAL HABITAT UPSLOPE.

BUT THEN ONCE THAT'S GONE, THEY HAVE NOWHERE TO BE.

WHERE ARE THEY GONNA GO?

THEY'RE ALREADY ON THE TOP OF THE MOUNTAIN.

THEY'RE RUNNING INTO THE SKY.

KIRK: SCIENTISTS HAVE ALREADY SEEN PIKAS DISAPPEAR FROM A THIRD OF THEIR FORMER STRONGHOLDS IN THE WARMER STATES TO THE SOUTH.

[PIKA SCREECHES] BUT YELLOWSTONE'S PEAKS STILL PROVIDE SANCTUARY... AT LEAST FOR NOW.

DOWN IN THE VALLEYS, ONE OF OUR ANIMAL FAMILIES IS ALSO FEELING THE HEAT.

IN THE FIRST WEEK OF JULY, NO RAIN HAS FALLEN AT THE SNAKE RIVER, WHERE THE BEAVERS HAVE MADE THEIR HOME.

COMBINED WITH THE EARLY SNOWMELT, HYDROLOGY DATA SHOW THE RIVER IS RUNNING 20% BELOW ITS AVERAGE FOR THIS TIME OF THE YEAR.

IF THE LEVEL OF THE BEAVERS' POND DROPS TOO LOW, IT COULD EXPOSE THE ENTRANCE TO THEIR LODGE, WHICH IS USUALLY UNDERWATER, AND MAKE THEM EASY PICKINGS FOR PREDATORS.

JEFF'S WATCHING CLOSELY TO SEE HOW THEY REACT.

JEFF: OH, LOOK!

WOW!

THAT'S MOM.

KIRK: IT LOOKS LIKE MOM HAS MADE A DECISION.

JEFF: SHE'S GOT ONE OF THE KITS IN HER MOUTH.

SHE'S HEADING TOWARDS THE DAM.

KIRK: SHE'S MOVING HER KIT OUT OF THE POND, MAYBE TO SEARCH FOR A NEW HOME.

JEFF: OH.... SHE SWAM UP TO THE DAM, PICKED HIM UP IN HER MOUTH WITH HER HANDS, WADDLES, POOH, THREW HIM OVER.

AND THERE THEY GO.

I'M GONNA GO CHASE THEM.

KIRK: I'VE HEARD OF KITS BEING MOVED BEFORE, BUT WITH SUCH YOUNG ONES, IT'S A BIG RISK.

OUT IN THE OPEN, KITS ARE VULNERABLE TO PREDATORS LIKE BALD EAGLES.

HERE THEY COME.

KIRK: THE BEAVER FAMILY HAS A LARGE TERRITORY, WITH 5 DAMS AND PONDS ALONG THIS RIVER.

JEFF: SHE'S GONNA CRAWL OVER THIS NEXT DAM.

OH, THIS IS INCREDIBLE.

KIRK: AFTER TRAVELING 300 YARDS AND CROSSING 3 MORE DAMS, THE MOTHER LEADS HER KIT UP A TRIBUTARY THAT COMES OFF THE MAIN RIVER.

THEY'RE GONNA CLIMB RIGHT UP THROUGH THIS CASCADING STREAM, WADDLING UP THROUGH THE STONES.

YOU CAN SEE THAT THE BEAVERS DON'T DO QUITE SO WELL ON LAND, ESPECIALLY THESE RIVER ROCK.

THEY DO SO MUCH BETTER IN THE WATER.

UNREAL.

I'VE NEVER SEEN THIS, EVER.

AND THERE THEY GO.

KIRK: LATER, AT NIGHT, JEFF CHECKS HIS CAMERA IN THE LODGE.

JEFF: LET'S SEE.

KIRK: IT REVEALS THE FEMALE HAS MOVED ALL THE KITS.

NOW JEFF IS ON A MISSION TO FIND OUT WHERE THE BEAVERS HAVE GONE, IF THE KITS SURVIVED, AND WHETHER THIS HUGE GAMBLE PAYS OFF FOR THE BEAVER FAMILY.

CLIMATOLOGISTS STUDYING YELLOWSTONE HAVE CHARTED TEMPERATURES INCREASING BY NEARLY A THIRD OF A DEGREE EVERY DECADE.

THE IMPACT OF YELLOWSTONE'S WARMING CLIMATE ISN'T JUST FELT BY INDIVIDUAL ANIMALS, SOME OF WHOM CAN ADAPT.

IT AFFECTS THE ENTIRE SYSTEM.

THESE PATCHES OF GOLD MAY LOOK LIKE THE FIRST SIGNS OF AUTUMN, BUT THESE TREES ARE ACTUALLY DYING.

WARMER TEMPERATURES HAVE CAUSED A MORE INTENSE INFESTATION OF PINE BEETLES, USUALLY KEPT UNDER CONTROL BY HARSH WINTERS.

BY FEASTING ON THE SOFT TISSUE UNDER THE BARK, THESE TINY CREATURES ARE KILLING THE TREES.

UP TO 80% OF MATURE WHITEBARK PINE TREES IN YELLOWSTONE ARE NOW INFESTED.

IT'S BAD NEWS FOR GRIZZLIES, WHO EAT THESE PINE NUTS AS A VITAL SOURCE OF PROTEIN.

THEY'RE BEING FORCED TO LOOK ELSEWHERE FOR FOOD.

WE'RE IN THE GALLATIN MOUNTAINS NORTH OF YELLOWSTONE RIGHT NOW, AND THIS MEADOW IS ABOUT 7,000 FEET ABOVE SEA LEVEL.

THE MEADOW ITSELF IS REALLY IMPORTANT FOR THE BEARS IN THE SUMMER.

THERE'S LOTS OF FOOD FOR THEM HERE, AND THEY'RE SHARING THE FOOD WITH THE COWS.

[COWS MOOING] IT'S REMARKABLE BEHAVIOR, AND BEAR EXPERT CASEY ANDERSON HAS BEEN INVESTIGATING WHAT MAKES THIS MEADOW SO UNIQUE.

HOW MANY BEARS HAVE YOU SEEN AT ONE TIME IN THIS MEADOW?

OVER 20.

20 GRIZZLY BEARS IN THIS MEADOW AT ONE TIME.

DEFINITELY THE GREATEST CONGREGATION OF BEARS IN THE LOWER 48 RIGHT THERE IN THE MEADOW, AND THERE'S A DUDE OUT THERE WITH COWS.

THAT'S AMAZING.

THEY DON'T CARE ABOUT THE FENCES.

THEY DON'T CARE ABOUT THE COWBOYS.

ALL THEY CARE ABOUT IS HOW MUCH FOOD THEY CAN EAT.

BUT I'VE DRIVEN PAST A LOT OF MEADOWS OUT HERE.

WHAT ABOUT THIS ONE THAT MAKES IT SO SPECIAL, DO YOU THINK?

THERE'S THIS ROOT OUT HERE, A CARAWAY PLANT, THAT ACTUALLY CAME IN WITH THE LIVESTOCK.

IT'S ACTUALLY AN INTRODUCED SPECIES NOT NATIVE TO THE AREA THAT HAS THIS BIG TUBER, JUST HUGE, ALMOST LIKE A CARROT, AND IT'S ALL OVER OUT THERE, AND SO IT'S A GREAT FOOD SOURCE FOR THEM TO FATTEN UP ON-- TONS OF CALORIES.

YOU KNOW, THE CARBOHYDRATES IN THAT IS AMAZING.

KIRK: THIS HAS BECOME A VITAL FOOD SOURCE FOR THE BEARS, AND MANY OF THE RANCHERS IN THIS VALLEY GO OUT OF THEIR WAY NOT TO DISTURB THEM AS THEY TRY TO PILE ON ENOUGH FAT TO LAST THEM THROUGH 5 MONTHS OF HIBERNATION.

CASEY: YEAR AFTER YEAR, YOU SEE THESE SAME BEARS AND GET TO KNOW THEM, AND WE'RE JUST ALWAYS WATCHING THEM.

"OH, THERE'S THAT BIG BOAR AGAIN, AND THERE'S THAT FAMILY GROUP," AND THEY ALL KEEP COMING IN, AND SOMETIMES THERE ARE SURPRISES, AND THIS YEAR THERE'S BEEN SOME AMAZING SURPRISES.

REALLY?

YEAH.

KIRK: AND TODAY IS NO EXCEPTION.

TWO VERY SPECIAL BEARS HAVE ARRIVED.

THESE YEARLINGS ARE ORPHANS.

SADLY, THEIR MOM DIED LAST AUTUMN.

WOW.

THOSE GUYS ARE GREAT.

THIS IS BY FAR MY FAVORITE GRIZZLY BEAR SIGHTING OF ALL TIME.

REALLY?

YOU'VE SEEN A LOT OF GRIZZLY BEARS, TOO.

I HAVE.

AND YOU THINK OF WHAT THEY'VE ENDURED OUT HERE.

KIRK: USUALLY, CUBS STAY WITH THEIR MOTHER FOR UP TO 3 1/2 YEARS.

EVEN WITH HER PROTECTION, ONLY ABOUT 30% OF CUBS SURVIVE IN GREATER YELLOWSTONE.

HOW BIG WOULD THEY HAVE BEEN WHEN THEIR MOM DIED?

LIKE, YOU KNOW, THE SIZE OF A COCKER SPANIEL.

YOU KNOW, THESE LITTLE TINY GUYS.

THAT'S INSANE.

OH, MAN, LOOK AT THAT.

IT'S REALLY AMAZING HOW THOSE GUYS SURVIVED THAT WINTER AND DEN TOGETHER AND THEN WENT THROUGH THAT SPRING AND THE WHOLE THAW AND THEN LEARNED HOW TO EAT FOR THEMSELVES, FIGURE IT OUT, DODGED ALL THE PREDATORS, AND HERE THEY ARE, LOOKING REALLY GOOD.

IT'S ONE IN A MILLION.

I'M REALLY IMPRESSED AT HOW CLOSE.

THEY'RE JUST LIKE A LITTLE TEAM, JUST GOING SIDE BY SIDE.

I THINK THAT'S THE FACTOR THAT KEPT THEM ALIVE, IS...THAT'S IT, THAT THEY HAVE EACH OTHER.

THEY'VE GOT EACH OTHER.

ON THIS WORKING RANCH, THERE ARE LOTS OF UNUSUAL SIGHTS... AND SOUNDS.

[WHIP CRACKS] WITHOUT THEIR MOTHER TO TEACH THEM, IT'S HARD FOR THE CUBS TO KNOW WHAT IS DANGEROUS AND WHAT IS NOT.

CASEY: YOU FIND YOURSELF REALLY WORRYING ABOUT THEM, BECAUSE THEY DON'T HAVE THAT NOTORIOUS MAMA GRIZZLY LOOKING OUT FOR THEM.

SOMETHING'S GOT THEM... KIRK: YEAH, THEY'RE MOVING AROUND AND JUMPING UP AND DOWN NOW.

SEE, THE ONE IN THE BACK IS DEFINITELY NOSING, SMELLING SOMETHING ON THE WIND.

THEY OBVIOUSLY SENSE SOMETHING IN THAT DIRECTION.

I THINK THAT THESE TWO HAVE PROBABLY BEEN CHASED PROBABLY ONCE A DAY BY SOMETHING, WHETHER IT'S ANOTHER GRIZZLY, A PACK OF WOLVES.

[COWS MOOING] KIRK: THE DANGERS HERE DON'T COME FROM CATTLE OR THE RANCHERS.

THE ATMOSPHERE OF MUTUAL TOLERANCE IS STRIKING.

BUT ADULT MALE GRIZZLIES ARE A RISK TO THE ORPHANS AND COULD KILL THEM.

SO THEY'VE TAKEN TO AVOIDING THE OTHER BEARS.

THE BEARS GENERALLY KNOW TO STAY AWAY FROM THE ROAD, BUT NOT THESE YOUNGSTERS.

CASEY: YEAH, THIS PROXIMITY TO THE ROAD AND TO US... MAYBE HAS SOMETHING TO DO WITH WHY THEY'RE HERE, YOU KNOW.

OTHER BEARS AND WOLVES AND THINGS WOULDN'T BE IN THIS AREA.

THERE'S PLENTY OF GOOD FOOD RIGHT HERE ON THE FENCE LINE THE OTHER BEARS WON'T EAT.

AN AMAZING STRATEGY.

YOU KNOW, TO SURVIVE A WINTER, A SPRING, AND GET INTO THE SUMMER LIKE THIS IN YELLOWSTONE COUNTRY, YOU'VE GOT TO BE TOUGH, AND THEY HAVE MADE IT.

SO I THINK THEY'VE GOT A GOOD SHOT.

KIRK: THERE ARE OVER 700 BEARS IN GREATER YELLOWSTONE, AND AS SOME FOODS LIKE THE WHITEBARK PINE DIE OFF, THEIR SURVIVAL WILL INCREASINGLY RELY ON HUMANS SHARING SPACES LIKE THIS RANCHLAND.

I'M SURE IT WON'T ALWAYS RUN SMOOTHLY, BUT I HOPE I'LL BE BACK HERE FOR MANY YEARS TO COME.

YELLOWSTONE HASN'T REACHED ITS RECORD TEMPERATURE OF AROUND A HUNDRED DEGREES THIS YEAR.

BUT CLIMATE DATA HAVE REVEALED THAT JULY HERE WAS THE SEVENTH MONTH IN A ROW WITH ABOVE-AVERAGE TEMPERATURES.

RELENTLESS HEAT AND EARLY THAW ARE A DANGEROUS COMBINATION, INCREASING THE CHANCES FOR FOREST FIRES.

[THUNDER] A SINGLE SPARK COULD SET THIS LANDSCAPE ALIGHT.

EVERY SUMMER, AN AVERAGE OF 26 FOREST FIRES ARE STARTED BY LIGHTNING ACROSS YELLOWSTONE PARK.

THIS YEAR COULD BE WORSE.

[LOUD THUNDER] OUR CREWS ARE OUT FOLLOWING UP ON REPORTS OF FOREST FIRE.

FLAMES CAN REACH HEIGHTS OF 150 FEET, EXCEED 1,500 DEGREES FAHRENHEIT, AND RIP THROUGH THE LANDSCAPE AS FAST AS THE AVERAGE PERSON CAN RUN.

BY MID-AUGUST, 5 MAJOR FIRES HAVE TAKEN HOLD AND ARE RAGING ACROSS GREATER YELLOWSTONE.

IN THE BEARTOOTH MOUNTAINS, WILDLIFE CAMERAMAN JEFF HOGAN... JEFF: OH, NO.

THIS IS NUTS.

KIRK: IS FILMING A FOREST FIRE THAT IS CONSUMING A HUGE AREA OF FOREST AND HEADED STRAIGHT TOWARDS THE FAMILY OF GREAT GRAY OWLS HE'S BEEN FOLLOWING SINCE SPRING.

JEFF: THIS FIRE IS HUGE, AND IT'S RAGING, AND IT'S...IT'S RIGHT IN THE BACKYARD OF OUR GREAT GRAY OWL FAMILY.

THIS IS REALLY A THREAT.

[OWL SCREECHES] KIRK: SO FAR, OUR CHICKS HAVE BEATEN ALL THE ODDS.

THERE WAS JUST A 20% CHANCE ALL 3 WOULD MAKE IT OUT OF THE NEST.

JEFF: OH, HE'S GONNA GO.

HE'S GONNA GO.

JUMP.

JUMP.

OH, WOW.

KIRK: JEFF THOUGHT THEIR BIGGEST CHALLENGES WERE OVER... [OWL SCREECHES] BUT NOW HE'LL HAVE TO WAIT UNTIL THE FIRE HAS DIED DOWN TO SEE IF THE CHICKS HAVE SURVIVED.

FOREST FIRES ARE A BIG DANGER IN THIS SEASON.

THEY CAN BE QUITE DEVASTATING, BUT THEY ALSO MAKE THIS LANDSCAPE WHAT IT IS.

FIRE IS PART OF THE FOREST'S NATURAL CYCLE.

IT BRINGS GROWTH.

WITH NO CANOPY FOR SHADE, SUNLIGHT CAN REACH THE FOREST FLOOR.

FERTILE ASH MIXED WITH RAIN SPROUTS GREEN SHOOTS... AND LIFE MOVES BACK IN.

SOME PLANTS HAVE EVEN EVOLVED TO BENEFIT FROM FIRES.

THE LODGEPOLE PINE HAS CLOSED CONES, AND THEY ONLY OPEN UP AND RELEASE THEIR SEEDS WHEN FOREST FIRES HEAT THEM.

FIRES ARE A NATURAL PART OF LIFE HERE, BUT THIS YEAR WAS UNUSUAL.

BY LATE AUGUST, THEY HAVE BURNT NEARLY 100 SQUARE MILES, MAKING THEM THE MOST DESTRUCTIVE IN NEARLY A QUARTER OF A CENTURY.

LARGE-SCALE FIRES USED TO SWEEP THROUGH THE PARK AROUND EVERY 300 YEARS.

BUT SCIENTISTS NOW BELIEVE THAT THE WARMING CLIMATE COULD INCREASE THEIR FREQUENCY DRAMATICALLY.

THEY COULD DESTROY THE OLD-GROWTH FOREST THAT COVERS 40% OF YELLOWSTONE AND IS HOME TO THE FRAGILE POPULATION OF GREAT GRAY OWLS.

SO, JEFF'S OUT HERE SOMEWHERE LOOKING FOR THE OWL CHICKS.

I'M LOOKING FOR JEFF.

BUT THIS FOREST IS FULL OF GRIZZLY BEARS, SO KEEP WITH ME.

JEFF IS SCOURING THE AREA AT THE EDGE OF THE BURN FOR ANY SIGNS, AND I FINALLY CATCH UP WITH HIM FOR AN UPDATE.

HEY, JEFF.

HOW'S IT GOING, MAN?

GOOD TO SEE YOU.

SO, WHAT'S GOING ON WITH THE FIRE?

YOU KNOW, IT JUST STARTED UP ONE DAY AND JUST TOOK OFF.

IT WAS PRETTY THREATENING.

IT WAS SCARY.

AND IT WAS COMING RIGHT TOWARDS US, MEANING MYSELF AND THE OWLS.

SO, WHAT?

HOW DO YOU FIND THEM NOW?

I'M OUT LOOKING.

I'M OUT LISTENING.

I CALL FOR THEM A LITTLE BIT.

I LOOK FOR SIGN, WHITEWASH ON THE GROUND UNDER MAYBE SOME SORT OF FAVORABLE PERCH.

LET'S GO SEE IF WE CAN FIND THEM, HUH?

ALL RIGHT, MAN.

YOU GOT IT.

KIRK: JEFF AND I ARE SPLITTING UP TO DOUBLE OUR CHANCES.

[IMITATING OWL CALL] KIRK: THERE ARE SIGNS AROUND THAT THE OWLS MIGHT HAVE MADE IT.

A FEATHER.

APPEARS TO BE A GREAT GRAY FEATHER, A DOWNY FEATHER.

COULD BE...

THIS COULD BE GOOD.

NOW, THIS IS A GREAT SIGN RIGHT HERE.

ALL OF THIS WHITE IS OWL POO.

KIRK: THEY'RE DOWN HERE SOMEWHERE, WE THINK.

IT'S JUST A MATTER OF WAITING TO HEAR THEM CHIRP.

BUT BY THE END OF THE DAY, STILL NO SIGHTINGS OF THE OWLS THEMSELVES.

THERE'S SO MUCH GROUND TO COVER.

EVENTUALLY, JEFF CALLS IN HELP FROM PHOTOGRAPHER AND EXPERT ANIMAL TRACKER DAN HARTMAN.

[OWL SCREECHES] AFTER 4 DAYS OF SEARCHING, HE FINALLY HEARS AN ADULT GREAT GRAY... [OWL SCREECHES] AND CLOSE BY, ONE OF THE CHICKS.

[OWL SCREECHES] AFTER ANOTHER FEW MINUTES WATCHING AND LISTENING, HE SPOTS THE OTHER TWO CHICKS.

THEY'VE ALL SURVIVED... AND ARE EVEN MAKING THEIR FIRST ATTEMPTS AT HUNTING.

THE OWL CHICKS HAVE ALL MADE IT THROUGH THEIR FIRST SUMMER.

BUT WE STILL DON'T KNOW THE FATE OF THE BEAVER MOM AND HER 3 KITS THAT ABANDONED THEIR LODGE.

I'M CATCHING UP WITH JEFF ON A TRIBUTARY OF THE SNAKE RIVER, WHERE THE FLOW OF WATER IS BETTER AND LOCAL WILDLIFE HAS BEEN ATTRACTED TO WHAT LOOKS LIKE A NEW BEAVER POND.

[BIRD CALLS] WE'VE GOT FRESH BEAVER SIGN.

LOOK AT ALL THOSE LEAVES STILL ON THE BRANCHES.

RIGHT.

AND YOU'LL SEE ALL THE WAY ACROSS.

THIS IS ALL NEW.

THIS IS THE LAST FEW WEEKS.

THE WATER'S TOPPING THE DAM, RIGHT?

AND YOU KNOW, LIKE THIS HERE...

THEY'LL EAT THE BARK OFF IT, AND THEN THEY'LL USE IT FOR BUILDING MATERIALS.

WE'VE GOT A BEAVER RIGHT HERE.

HERE HE COMES.

HERE HE COMES.

OH, THAT'S AWESOME.

HE'S MOVING FAST.

HE'S GOING STRAIGHT FOR THE DAM.

THIS IS REALLY GREAT.

WE'RE LOOKING AT A NEW DAM, AND THERE'S THE BEAVER RIGHT THERE.

THIS IS ONE OF THE ADULT BEAVERS FROM OUR FAMILY.

IT MIGHT EVEN BE DAD.

THIS BEAVER'S ACTUALLY WORKING ON THE DAM.

HE'S RIGHT THERE.

OH, HERE HE IS.

HE'S JUST EXCAVATED MUD AND STONES FROM THE BOTTOM, AND NOW HE'LL PATCH UP THE LODGE WITH IT.

HE'S COMING RIGHT HERE.

AH, THIS IS SO COOL.

NOT ONLY IS HE RAISING THE WATER LEVEL BY BUILDING THE DAM UP HIGHER, BUT HE'S MAKING THE POND DEEPER BY EXCAVATING.

KIRK: THE BEAVERS ARE STRENGTHENING THE DAM WITH LARGE ROCKS AND PLUGGING HOLES WITH MUD AND WEEDS TO CREATE A DEEP, WIDE POND.

NOW THEY CAN ACCESS ALL THE FOOD AND BUILDING MATERIALS THEY NEED WITHOUT VENTURING ONTO DRY LAND, WHERE THEY'RE VULNERABLE.

JEFF: THIS IS RARE.

RARELY DO YOU SEE THE VERY EARLY STAGES OF A WHOLE NEW BEAVER POND LIKE THIS WITH A LODGE.

KIRK: THIS IS REALLY, REALLY GREAT.

THEY'VE SURVIVED THE WINTER, THEY'VE SURVIVED THE SPRING, AND NOW THEY'RE BUILDING A BRAND-NEW DAM, THEY'RE EXPANDING THEIR EMPIRE.

JEFF: AND WE HAVE A LITTLE BEAVER RIGHT THERE.

THERE'S WHERE OUR KIT-- THAT'S A KIT.

KIRK: THAT'S A BABY.

JEFF: IT'S THE FIRST TIME I'VE SEEN THEM OUT LIKE THIS THIS YEAR.

KIRK: HA.

IT'S INCREDIBLE.

IT'S SO GREAT TO SEE THE LITTLE KIT SWIMMING AROUND.

YEAH.

MYSTERY SOLVED.

YEAH, THEY'RE NOT IN THEIR OLD HOME.

THEY'RE IN THEIR SUMMER HOME.

GREAT NEW LITTLE VACATION SPOT THEY'VE GOT HERE.

I KNOW.

IT'S LIKE THEIR DREAM HOUSE.

KIRK: THE LOW WATER LEVELS PROBABLY TRIGGERED THIS MOVE, AND THEIR RISKY GAMBLE PAID OFF.

THE DEEP POND, THE NEW LODGE, AND PLENTY OF FOOD IS EVERYTHING THE KITS WILL NEED TO THRIVE.

IN JUST A FEW WEEKS, ONE BEAVER FAMILY HAS TRANSFORMED THIS AREA, AND IT'S BENEFITING ALL THE WILDLIFE.

WHOA!

SANDHILL CRANES, MAN.

[CRANES CALLING] UNBELIEVABLE.

JEFF: IT'S INCREDIBLE, THE SPECIES THAT YOU FIND DOWN HERE.

WOW!

I'VE NEVER BEEN THAT CLOSE TO A SANDHILL CRANE BEFORE.

BEAVERS REALLY ARE INCREDIBLE.

THEY ADAPT AND SHAPE THE LANDSCAPE TO SUIT THEIR NEEDS, AND IT IS ON SUCH A HUGE SCALE THAT ONLY HUMANS HAVE BEEN ABLE TO SURPASS IT.

GOT A GREAT BIG NEW DAM HERE.

THERE'S FOOD EVERYWHERE.

FOR THESE BEAVERS, LIFE IS GOOD.

OVER THIS SHOW, WE'VE SEEN HOW OUR DIFFERENT ANIMAL FAMILIES HAVE FARED THROUGH THE WINTER INTO THE SPRING AND THE SUMMER AS THE GREAT THAW PROCEEDED.

THE MILD WINTER MEANT THE WOLVES STRUGGLED TO HUNT STRONG, WELL-FED PREY, AND MANY WENT HUNGRY.

BUT IN THE SUMMER, THEY USED THEIR CUNNING TO FIND FOOD AND KEEP THEIR PUPS ALIVE WITH A LITTLE HELP FROM HUMAN ACTIVITY.

THE BEAVERS SURVIVED THE EARLY SPRING RUNOFF AND WERE ABLE TO BUILD A NEW HOME TO RAISE THEIR 3 KITS.

[OWL SCREECHES] OUR GREAT GRAY OWL CHICKS BEAT ALL THE ODDS AND FLEDGED... [OWL SCREECHES] INCREASING THE CHANCES FOR THIS VULNERABLE POPULATION.

[OWL SCREECHES] THE GRIZZLY BEARS' RACE TO FATTEN UP STARTED EARLY WITH THE MILD WINTER CONDITIONS.

THE MOIST SPRING REVEALED A BOUNTY OF FOOD.

BUT BY THE SUMMER, THEY HAD TO USE ALL THEIR INTELLIGENCE TO SURVIVE.

THE STORIES THAT WE'VE BEEN FOLLOWING ARE ALL PART OF A MUCH BIGGER PICTURE, THE PICTURE OF HOW YELLOWSTONE'S CLIMATE IS CHANGING.

I THINK WHAT WE DO KNOW IS ALL OF IT'S GONNA CHANGE, AND IT'S CHANGING PRETTY RAPIDLY, AND WE DON'T REALLY KNOW HOW IT'S GONNA CHANGE.

WATCHING LIFE EVOLVE WITH THAT GOING ON HAS GOT ME SCARED STIFF.

IT'S REALLY AMAZING TO WATCH A PLACE THAT'S THIS BEAUTIFUL AND COMPLEX AND FULL OF SO MANY AMAZING ANIMALS AND PLANTS CHANGE OVER THE COURSE OF MY LIFETIME, AND IT REALLY MAKES ME THINK, WHAT'S GONNA HAPPEN NEXT?

THE ANIMALS HERE HAVE SHOWN AN INCREDIBLE ABILITY TO ADAPT TO CONSTANT CHANGES IN TEMPERATURES.

WHAT WILL HAPPEN IF THE CLIMATE CONTINUES TO GET WARMER?

NO ONE CAN SAY.

WE DO KNOW THAT THERE WILL BE WINNERS AND LOSERS.

WE CAN ONLY HOPE THAT THE WILDLIFE HERE WILL CONTINUE TO THRIVE.