Narrator: IN THIS AUSTRALIAN SUBURB, A TURF WAR IS UNFOLDING BETWEEN HUMANS AND KOALAS.

AND THE KOALAS ARE LOSING GROUND.

IT'S AN OUTCOME THAT'S SHAKING UP THEIR SEDENTARY LIVES.

KOALA MALES WILL PROTECT THEIR SHRINKING PATCH OF FOREST AND THE FEMALES THAT INHABIT IT.

WHEN A NEW KOALA SAUNTERS ONTO THE SCENE, TENSIONS EXPLODE.

AS THESE CONFRONTATIONS INCREASE, SCIENTISTS ARE TRYING TO UNDERSTAND KOALA COMMUNICATIONS AND TRACK THEIR MOVEMENTS.

THEY'LL FOLLOW ONE KOALA MOTHER BRINGING UP HER BABY IN A WORLD COLLIDING WITH OURS.

THEY DISCOVER THE FUTURE KOALAS FACE, LIVING IN A SEA OF SUBURBS.

[ BELLOWING ] Narrator: BRISBANE IS A RAPIDLY EXPANDING CITY.

IT'S HOME TO TWO MILLION PEOPLE, WITH NEARLY 1,000 MORE HERE EVERY WEEK.

BUT IN THE OUTSKIRTS OF THIS SUBTROPICAL CITY ARE SOME OF THE BEST EUCALYPT FORESTS IN AUSTRALIA.

THEY PROVIDE REFUGE TO COUNTLESS ANIMAL SPECIES.

PEOPLE ARE THE NEWCOMERS HERE, AND THEY ARE COMPETING WITH ANIMALS FOR THE SAME REAL ESTATE.

ON A TYPICAL BRISBANE MORNING IN JULY, RESIDENTS GO ABOUT THEIR DAILY BUSINESS.

BUT THE LOCALS ARE UNAWARE THAT A SILENT WITNESS SHARES THE SUBURBS.

A FEMALE KOALA WE CALL 'MARY' HAS ALSO MADE THIS NEIGHBORHOOD HOME.

THIS IS THE BOUNDARY WHERE THE WORLD OF PEOPLE AND KOALAS COLLIDES.

INSIDE THESE SMALL URBAN POCKETS OF FOREST, KOALA SOCIETY CAN BE A PLACE OF HIGH DRAMA.

[ KOALAS CALLING ] [ CALLING ] FOR A FEMALE IN THE SUBURBS, THE CONSTANT ATTENTION FROM THE OPPOSITE SEX CAN BE EXHAUSTING, BECAUSE MALE KOALAS WILL ATTEMPT TO MATE WITH HER WHENEVER THEY CAN.

AND MARY KNOWS THE POLITICS AT PLAY.

IF THE DOMINANT MALE CATCHES HER MESSING AROUND WITH A SUBORDINATE, THERE WILL BE TROUBLE.

HER CALL HAS ALERTED THE ALPHA MALE WE CALL 'BUSTER.'

WEIGHING IN AT A BURLY 20 POUNDS, HE IS THE STRONGEST, MOST POWERFUL KOALA IN THE COLONY.

HE HAS EARNED HIS PLACE THROUGH SHEER BRUTE FORCE.

HE MAKES SURE HENRY, THE RIVAL MALE, IS PUT BACK IN HIS PLACE.

ASSERTING HIS DOMINANCE, BUSTER MAINTAINS THE RIGHT TO MATE WITH ALL FEMALES IN THE COLONY.

HENRY RETREATS TO THE SIDELINES.

HIS SNEAKY TACTICS WERE UNSUCCESSFUL THIS TIME.

CALM RETURNS TO THE COLONY AND THE KOALAS GO BACK TO THE BUSINESS OF BROWSING ON GUM LEAVES.

GUM LEAVES ARE HIGHLY TOXIC, AND THIS NOXIOUS DIET WAS ONCE BELIEVED TO SEND KOALAS INTO A DRUNKEN STATE, HALLUCINATING FROM THE TOXIC COMPOUNDS, HIGH IN THE TREES.

BUT LETHARGY IS MERELY AN ENERGY SAVING ADAPTATION TO THEIR POOR DIET.

IT TAKES A LOT OF WORK TO CHEW A LEAF AND KOALAS NEED TO EAT FOR FIVE HOURS A DAY BECAUSE GUM LEAVES ARE LOW IN CALORIES.

DIGESTING A MEAL TAKES OVER FOUR DAYS.

AND MARY IS EATING FOR TWO.

NESTLED IN HER POUCH IS BRUCE, A SIX MONTH OLD JOEY WHO OCCASIONALLY VENTURES OUTSIDE.

FOR THE LAST SIX MONTHS, BRUCE HAS BEEN SUCKLING MILK FROM TEATS INSIDE HIS MOTHER'S POUCH.

BUT NOW, IN READINESS FOR EATING LEAVES, HE MUST CONSUME HER FECES.

FOR THESE CONTAIN 'PAP,' A SECRETION THAT GIVES HIM THE BACTERIA NEEDED TO DIGEST TOUGH EUCALYPTUS LEAVES.

BRUCE IS KEEN TO EXPLORE HIS NEW WORLD.

[ BRUCE SQUEAKING ] HE COMMUNICATES TO HIS MOTHER WITH SQUEAKS AND MURMURS.

[ CONTINUES SQUEAKING ] HE WILL STAY BY HER SIDE UNTIL HE IS A YEAR OLD.

BY THEN HE WILL BE SMART TO THE WAYS OF KOALA SOCIETY AND STREET WISE ENOUGH TO NAVIGATE THE SUBURBS.

IN THIS PATCH OF FOREST IN THE BRISBANE SUBURB OF PETRIE, BIOLOGISTS FROM GRIFFITH UNIVERSITY HAVE BEEN STUDYING THE MOVEMENT OF KOALAS FOR TWO YEARS.

CATHRYN DEXTER AND DAVID BLACK WANT TO UNDERSTAND THE SOCIAL DYNAMICS WITHIN A KOALA COLONY THAT'S SURROUNDED BY THE SUBURBS.

Dexter: WE TRACK THE ANIMALS WEEKLY, TRYING TO GET AN UNDERSTANDING OF HOW FAR THEY'RE MOVING AND HOW THEY ARE INTERACTING.

ONE OF THE THINGS THAT WE'RE TRYING TO DO IS CAPTURE MORE KOALAS AND PUT COLLARS ON THEM TO TRACK THEIR MOVEMENTS.

OKAY, IT LOOKS LIKE WE'VE GOT HIM.

Black: LET ME JUST TAKE A GPS... Dexter: YEP, YOU CHECK THAT.

CAN YOU JUST CHECK SOME OF THE DETAILS FOR ME?

YEP.

ALL RIGHT, SO, CAN YOU SEE THE RUMP?

YEP, THE RUMPS GOOD.

SO, GOOD?

OKAY, AND THE... CAN YOU SEE THE COAT?

YEAH, THE COAT'S FINE, THE EYES FINE, THE KOALA'S VERY ACTIVE.

Narrator: THE NEXT STEP IS TO SNARE THIS KOALA AND ADD HIM TO THEIR STUDY, SO A TEAM OF EXPERT CATCHERS HAS BEEN CALLED IN.

THEY USE A COLORED PAPER BAG AT THE END OF A POLE TO COAX THE KOALA DOWN THE TREE.

Black: I'LL BRING HIM DOWN.

BRING HIM BACK TO YOU.

BRING HIM DOWN.

JUST BRING HIM DOWN.

Dexter: THAT'S BEAUTIFUL.

Black: GOOD, WELL DONE, WELL DONE.

OKAY, QUICK!

HANG ON.

PUT IT OVER HIS HEAD, PUT IT OVER HIS HEAD.

NICE WORK, DAVE, NICE WORK.

WELL DONE ON THAT BRANCH, NICE, WELL DONE.

Dexter: EACH AND EVERY ONE OF OUR KOALAS, WHICH IS NOW OVER 70 FOR THIS PROJECT, HAVE A FULL HEALTH CHECK AT THE BEGINNING.

WE GIVE THE ANIMAL A LIGHT SEDATIVE, SO ONCE IT'S ASLEEP WE POP THE NEW COLLAR ON.

Black: WE COLLAR KOALAS BECAUSE WE WANT TO TRACK THEM.

WHEN WE CATCH THEM, WE PUT EITHER A VHF OR A GPS COLLAR ON THEM, SO THEY'LL HAVE EVERY FOUR HOUR FIXES.

AND THIS GIVES US A REALLY CLEAR INDICATION OF HOW THEY'RE MOVING WITHOUT HAVING TO TRACK THEM EVERY DAY.

Dexter: ONE OF THE NICE THINGS ABOUT THIS PROJECT IS NAMING THE KOALAS, AND WE HAVE A LITTLE BIT OF FUN WITH THAT, SO, THE NAMES THAT HAVE COME UP TO ROCK STARS OR MOVIE STARS.

Narrator: THEY'VE CALLED THIS KOALA 'HENDRIX,' AFTER THE LEGENDARY GUITARIST.

Dexter: SO, ONCE THE COLLAR IS FITTED, WE TAKE IT BACK TO THE TREE THAT WE CAUGHT IT IN AND RELEASE IT.

ONCE WE'RE ABLE TO DOWNLOAD THE DATA, IT GIVES US THE INFORMATION OF WHERE THAT ANIMAL HAS MOVED OVER THE PAST FOUR AND HALF MONTHS.

GOOD LUCK, FELLA.

Dexter: FOR ME PERSONALLY TO BE INVOLVED IN A PROJECT LIKE THIS, WHICH IS GOING TO HAVE MAJOR OUTCOMES FOR ROAD MITIGATION, THAT'S ENORMOUSLY SATISFYING.

Narrator: IT'S NOW SEPTEMBER, AND CHANGE IS IN THE AIR.

IT'S THE START OF THE BREEDING SEASON AND BUSTER IS RESTLESS.

HE IS ANXIOUS ABOUT HIS FEMALES BEING UNFAITHFUL, AND HE REMAINS VIGILANT.

HENRY KEEPS HIS DISTANCE BECAUSE HE DOESN'T WANT ANOTHER FIGHT.

BUT JUST WHEN BUSTER IS SURE HE'S ON TOP, THERE'S MOVEMENT BELOW.

AN OUTSIDER WE'LL CALL 'JACK,' HAS ENTERED THE COLONY, SO BUSTER DECIDES TO INVESTIGATE.

JACK IS A FOUR YEAR OLD TRAVELING MALE -- A WANDERER WHO HAS LEFT HIS NATIVE COLONY TO TRY HIS LUCK WITH FEMALES ELSEWHERE.

BUT HE'S NOT WELCOME HERE.

WHEN THERE'S A CONFLICT, KOALAS TALK TO EACH OTHER TO AVOID A FIGHT.

BUSTER REACTS TO THE ARRIVAL OF THE TRAVELING MALE WITH A GUTTURAL BELLOW.

[ BUSTER BELLOWING ] THIS IS HIS WAY OF SAYING, 'I'M BOSS HERE, GET OUT OF MY TERRITORY.'

JACK REPLIES, 'YEAH? MAKE ME!'

[ KOALAS CONTINUE BELLOWING ] BUT BUSTER IS HAVING NONE OF IT.

HE BELLOWS HARDER, AND AT A DEEPER SOUND FREQUENCY.

THOUGH NOT MUCH LARGER THAN A CAT, HE SOUNDS AS BIG AS A LION.

THE INTIMIDATION TACTIC SEEMS TO HAVE WORKED.

JACK DECIDES TO MOVE ON.

BUT HE STUMBLES ON ANOTHER MALE KOALA.

THESE TWO MALES EMBARK ON A DIFFERENT FORM OF COMMUNICATION.

JACK SMEARS HIS SCENT ON THE TREE, HOPING HIS ODOR WILL INTIMIDATE THE RESIDENT MALE.

ADULT MALES HAVE A SCENT PATCH ON THEIR CHEST, WHICH THEY USE TO MARK THEIR TERRITORY.

THE KOALA WITH THE STRONGEST SMELL WILL WIN THIS TERRITORIAL DISPLAY.

SO, THE RESIDENT MALE IS FORCED TO DEFEND HIS TERRITORY BY SCENT-MARKING BACK.

ONCE JACK CATCHES A WHIFF OF THE RESIDENT MALE'S POTENT SCENT, HE REALIZES RETREAT IS THE BEST OPTION.

BUT TRAVELING MALES DON'T GIVE UP EASILY, AND AS DARKNESS DESCENDS, JACK BIDES HIS TIME, PREPARING TO MOUNT A SURPRISE ATTACK... UNDER THE COVER OF NIGHT, JACK RETURNS TO THE COLONY TO CHALLENGE BUSTER TO A DUEL.

BUSTER FORCES JACK TO THE END OF THE BRANCH.

96% OF ALL MALE-TO-MALE ENCOUNTERS RESULT IN ONE MALE BACKING OFF.

BUT NOT THIS TIME.

FAR FROM CUTE AND CUDDLY, BUSTER TURNS FERAL AND STAGES REPEATED ATTACKS.

JACK HAS NO CHOICE BUT TO RETREAT TO THE END OF THE BRANCH AND ACCEPT HE HAS LOST THIS BATTLE.

[ BELLOWING ] BUSTER DECLARES VICTORY WITH AN ALMIGHTY BELLOW.

HE WANTS ALL THE KOALAS IN THE COLONY TO KNOW HE IS STILL KING.

SIMILAR BATTLES FOR KOALA DOMINANCE ARE BEING PLAYED OUT IN PATCHES OF BUSH THROUGHOUT QUEENSLAND SUBURBIA.

THE LANGUAGE OF KOALAS HAD BEEN A MYSTERY UNTIL TWO BIOLOGISTS FROM THE UNIVERSITY OF QUEENSLAND DELVED DEEPER INTO ITS MEANING.

IN ORDER TO CRACK THE CODE OF KOALA COMMUNICATION, DR. BILL ELLIS AND SEAN FITZGIBBON CONDUCT AN UNUSUAL EXPERIMENT.

Ellis: THE KOALA SOCIAL SYSTEM SEEMS TO BE A LOT MORE COMPLEX THAN WE MIGHT HAVE OTHERWISE THOUGHT.

THE QUESTION REALLY WAS, WHO ARE KOALAS BELLOWING TO?

ARE THEY ADVERTISING?

ARE THEY TRYING TO WARD OTHER MALES OFF?

WHAT EXACTLY IS GOING ON WITH KOALA BELLOWING?

Fitzgibbon: YEAH, WE GOT ONE, BILL.

UP HERE.

Ellis: WE WERE ATTRACTED TO THIS PARTICULAR SPOT BECAUSE WE HEARD A BELLOW.

IT SEEMED LIKE A USEFUL TOOL, RECORDING AN INDIVIDUAL'S BELLOWS AND PLAYING THEM BACK TO FIND OUT UNDER WHAT CIRCUMSTANCES A KOALA MIGHT RESPOND TO A BELLOW.

Narrator: FOR THIS EXPERIMENT, BILL AND SEAN ARE JOINED BY BRITISH ACOUSTIC BIOLOGIST, DR. BEN CHARLTON.

THE IDEA IS TO PLAY BACK THE GUTTURAL CALLS OF MALE KOALAS TO A FEMALE, AND COMPARE HER REACTION TO EACH.

THE FIRST SOUND PLAYED IS THE BELLOW FROM A SMALL MALE KOALA.

THIS IS GOING TO BE PLAYBACK 1.

AND IT'S GOING TO BE A SMALL MALE.

[ PLAYING RECORDING OF KOALA BELLOWING ] Narrator: A HEAD TURN IS A GOOD RESPONSE AS FAR AS THE SCIENTISTS ARE CONCERNED.

[ RECORDING CONTINUES ] NEXT, THEY PLAY A BELLOW FROM A LARGE MALE TO SEE WHAT RESPONSE THEY GET.

[ NEXT RECORDING PLAYING ] COMING DOWN THE TREE TOWARDS THE SOUND SUGGESTS THAT FEMALE KOALAS ARE ABLE TO GAUGE WHICH MALES ARE BIGGER, AND, THEREFORE, MORE ATTRACTIVE, BY THEIR BELLOWS ALONE.

THAT'S A VERY STRONG RESPONSE.

Ellis: WE'RE PRETTY SURE NOW THAT THE BELLOW IS AN INDIVIDUAL SIGNATURE OF EACH MALE.

THERE'S COMPONENTS IN THE BELLOW THAT INDICATE HOW BIG THE MALE IS, AND SO WE THINK THAT, PROBABLY, FEMALES ARE ABLE TO SELECT LARGE INDIVIDUAL MALES SIMPLY BY THEIR BELLOW.

[ BELLOWING ] [ BARKING ] Narrator: BUT THE COMMUNICATION AND SOCIAL SYSTEM OF KOALAS IS BEING DISRUPTED BY HUMAN ENCROACHMENT.

KOALAS ARE FOUND ALMOST EXCLUSIVELY ALONG AUSTRALIA'S EAST COAST.

200 YEARS AGO, KOALA HABITAT WAS ABUNDANT.

BUT TODAY IT IS SO FRAGMENTED THAT KOALAS CLING ON IN ISOLATED POCKETS.

ONLY A FEW KOALAS SURVIVE IN THE OUTER SUBURBS OF MELBOURNE AND SYDNEY.

BRISBANE IS THE LAST CITY WHERE THEY ARE FOUND IN NUMBERS.

QUEENSLAND FORESTS HAVE BEEN CLEARED AT NEARLY THE SAME RATE AS THE AMAZON.

THREE-QUARTERS OF THE KOALA'S HABITAT IN SOUTHEAST QUEENSLAND HAS BEEN LOST TO AGRICULTURE AND URBANIZATION.

IN JUST A DECADE, KOALA NUMBERS HERE HAVE DECLINED BY TWO-THIRDS.

ON THE MOVE AGAIN, JACK, THE TRAVELING MALE, SEARCHES FOR A NEW HOME.

HE VENTURES INTO A WORLD WHERE THE TREES ARE MUCH FURTHER APART, AND SO HE'S FORCED TO ENCOUNTER HUMAN STRUCTURES ALIEN TO HIS WORLD.

TRAVELERS ARE USUALLY YOUNG MALES THAT ARE YET TO COME OF AGE.

BUT AS THEY GET OLDER, THEY GROW STRONGER.

EVENTUALLY HE WILL HAVE A BETTER CHANCE OF WINNING A BATTLE WITH A RIVAL MALE... IF HE CAN SURVIVE THE STREETS AND SUBURBS.

IT'S OCTOBER, AND WITH THE MATING SEASON IN FULL SWING, JACK MUST FIND A MATE IF HE IS TO FATHER OFFSPRING THIS YEAR.

BEWILDERED BY IT ALL, HE'S NOT SURE WHERE TO GO OR HOW MUCH FURTHER HE MUST TRAVEL TO FIND A FEMALE KOALA.

HE'S BARKING UP THE WRONG TREE HERE.

JACK ENTERS A CONCRETE JUNGLE INSTEAD OF THE KIND HE HAD HOPED FOR.

AUSTRALIANS LOVE SEEING KOALAS IN THEIR NEIGHBORHOOD, THOUGH IT'S RARE TO FIND ONE ON THE STREETS.

KOALAS ARE A PROTECTED SPECIES, SO IT IS ILLEGAL TO TOUCH OR TO PICK ONE UP WITHOUT A PERMIT.

THE SOONER JACK CAN GET OFF THE STREETS AND FIND A REFUGE, THE SAFER HE WILL BE.

THERE ARE FEWER NATIVE TREES IN THE SUBURBS TO SLEEP IN, SO HE HAS TO TAKE COVER WHEREVER HE CAN.

[ DOGS BARKING ] THE PETRIE SCIENCE STUDY SITE IN NORTHERN BRISBANE HIGHLIGHTS A PATCHWORK EFFECT OF FOREST AND SUBURBS.

ANY KOALA THAT VENTURES OUT OF THE BUSH HERE ENDS UP ON THE STREETS.

AND ON THEIR TAIL ARE BIOLOGISTS CATHRYN DEXTER AND DAVID BLACK.

Dexter: THE INTERESTING THING ABOUT PETRIE IS IT'S QUITE GOOD KOALA HABITAT, BUT IT'S RIGHT NEXT TO LOTS AND LOTS OF ROADS.

WE OFTEN FIND THESE ANIMALS PUSHED OUT INTO THE SUBURBS.

Black: WE'RE TRYING TO UNDERSTAND HOW THEIR MOVEMENTS ARE AFFECTED WITHIN SUBURBAN AREAS, HOW HUMAN POPULATIONS ARE AFFECTING THEM, AND WHY THEY MOVE IN CERTAIN WAYS.

GETTING A STRONG SIGNAL FROM OVER HERE, PROBABLY ABOUT 50 METERS AWAY.

Narrator: THE KOALA THE BIOLOGISTS ARE TRACKING IS A MALE CALLED CAPTAIN BOGART.

THE DATA SUGGESTS HE'S ALSO A TRAVELING MALE.

Black: MIGHT ACTUALLY BE BEHIND THESE HOUSES.

HANG ON, I THINK I SEE HIM.

YEP, I'VE GOT THE POINT.

OKAY, TAKE THOSE DETAILS DOWN.

CAN YOU JUST HAVE A LOOK AND SEE... OKAY, SO, CAN YOU SEE THE EAR TAG?

YEP, IT'S DEFINITELY CAPTAIN BOGART.

[ DOGS BARKING ] OKAY.

ALL RIGHT, I CAN'T BELIEVE IT'S SITTING IN THAT BACKYARD WITH THAT DOG.

Dexter: WE GET THEM SITTING IN PEOPLE'S BACKYARDS WHERE YOU JUST WOULDN'T THINK THAT THEY'D WANT TO LIVE.

YOU THINK THAT THEY GENERALLY SHOULD BE BASED IN THE BUSH, BUT WE FIND THEM QUITE FREQUENTLY OUT IN THE SUBURBS.

THEY'VE RANGED QUITE A WAY FROM WHERE THEY SHOULD BE.

Narrator: DAVID HAS BEEN COLLECTING HOME VIDEO FOOTAGE FROM RESIDENTS WHO'VE COME INTO CONTACT WITH KOALAS IN THE SUBURBS, AND SOME OF WHAT THEY'VE SEEN IS RATHER BIZARRE.

Black: I REALLY FIND IT FASCINATING HOW THE KOALAS ARE RELATING TO THE SUBURBS.

[ DOG BARKING IN VIDEO ] I'VE SEEN KOLAS IN BACKYARDS WHERE DOGS HAVE KILLED KOALAS BEFORE -- REALLY HEARTBREAKING.

IN THE SUBURBS YOU SEE REALLY STRANGE BEHAVIORS.

YOU'LL SEE THEM IN REALLY STRANGE TREES AND GOING THROUGH BACKYARDS OF HOUSES.

THERE'S SO MANY RISKS THAT THEY'RE TAKING TO GO INTO THIS SUBURBAN ENVIRONMENT.

YOU REALLY GET A FEELING FOR HOW THREATENED THEY ARE IN THEIR EVERYDAY LIVES.

Narrator: LIVING IN THE CITY COMES WITH ITS CHALLENGES.

KOALAS MAY HAVE STARTED LIFE IN THE SLOW LANE, BUT FREEWAYS NOW INTERSECT THEIR BUSHLAND HOME.

OVER ONE-THIRD OF ALL KOALA DEATHS IN SOUTHEAST QUEENSLAND ARE FROM VEHICLE IMPACT.

OVER 100 ARE KILLED ON THE ROADS HERE EVERY YEAR.

THE GRIFFITH UNIVERSITY BIOLOGISTS ARE HELPING KOALAS TO MOVE FREELY WITHOUT HAVING TO INTERACT WITH BUSY ROADS.

THEY ARE PLANTING TREES ON BRIDGES TO LINK KOALA CORRIDORS AND ADAPTING UNDERPASSES TO ENCOURAGE KOALAS TO GO UNDER THE ROAD.

Dexter: CARS ARE THE NUMBER-ONE DIRECT KILLER OF KOALAS.

THE FUNDAMENTAL QUESTION WE'RE TRYING TO ANSWER IS, DO KOALAS USE UNDERPASSES THAT HAVE BEEN DEVELOPED FOR THEM?

Black: WE REALLY WANTED TO GET VISUAL PROOF THAT THEY WERE CROSSING THESE STRUCTURES, SO WE SET UP CAMERAS AT EVERY POSSIBLE LOCATION THAT THEY COULD BE CROSSING.

I HAD -- YEAH, NO EXPECTATION, BUT, I MEAN, IT WOULD BE FANTASTIC TO SEE A KOALA -- BUT SUCH A LONG SHOT.

Narrator: IT'S EARLY MORNING IN THE KOALA COLONY, AND THE MALES ARE BECOMING ACTIVE.

MARY AND BABY BRUCE ARE ENJOYING BREAKFAST.

NOW NINE MONTHS OLD, BRUCE SPENDS MUCH OF HIS TIME EATING GUM LEAVES.

HIS LIFELONG BOND TO THE EUCALYPT FOREST HAS BEGUN.

HE CAREFULLY SNIFFS EACH LEAF AND STALK TO AVOID THE MOST TOXIC.

KOALAS ARE FINICKY ABOUT WHICH LEAVES TO EAT.

DESPITE THERE BEING OVER 600 TYPES OF EUCALYPT, ONLY FIVE OR SIX SPECIES COMPRISE THE BULK OF THEIR DIET.

BRUCE STILL RELIES ON HIS MOTHER FOR MILK, AND WILL REGULARLY POP HIS HEAD BACK IN THE POUCH FOR A DRINK.

AT THIS AGE HE BECOMES ADVENTUROUS, AND WILL WANDER AWAY FROM MUM TO EXPLORE HIS NEW WORLD.

BUT THERE ARE MANY SCARY SIGHTS AND SOUNDS NEARBY.

SO HE DECIDES IT'S BEST TO BE BY HIS MOTHER'S SIDE WHERE IT FEELS SAFE AND WARM.

IT'S NOVEMBER, AND STORM CLOUDS ARE BREWING.

IT'S THE BEGINNING OF THE SEVERE WEATHER SEASON IN SOUTHEAST QUEENSLAND.

THIS TIME OF YEAR, FOUR INCHES OF RAIN CAN FALL IN SINGLE DAY, DRENCHING THE KOALA COLONY.

ALL THE KOALAS CAN DO IS SIT OUT THE STORM.

THE FUR ON THE KOALA'S BOTTOM IS DENSELY PACKED TO PROVIDE A CUSHION FOR THE HARD BRANCHES AND INSULATION FROM THE WET AND COLD.

STILL, IT'S NOT MUCH FUN BEING OUT IN THE RAIN.

ONCE THE RAIN STOPS, MARY AND BRUCE NEED TO EAT TO MAKE UP FOR LOST TIME.

KOALAS SPEND ONLY FIVE HOURS A DAY BEING ACTIVE, AND 19 HOURS A DAY RESTING OR SLEEPING.

SO EVERY WAKING MOMENT COUNTS -- AND FEEDING IS ALWAYS THE HIGHEST PRIORITY, COME RAIN OR SHINE.

AS FOREST IS CLEARED THROUGHOUT SOUTHEAST QUEENSLAND, THE KOALA'S HABITAT IS REDUCED TO SMALL ISLANDS OF BUSH AMIDST A SEA OF SUBURBS.

JACK WILL NEVER EXPERIENCE THE NATIVE BUSH HIS ANCESTORS KNEW.

INSTEAD HE WILL CONTEND WITH ALL THE STRESSES OF LIVING IN SUBURBIA.

TRAVELING KOALAS ARE KNOWN TO ROAM FOR UP TO SIX MILES TO FIND ANOTHER COLONY.

BUT IN SUBURBIA TODAY, THE REMAINING GUM TREES NEEDED FOR FOOD CAN BE FEW AND FAR BETWEEN.

AND TO MAKE MATTERS WORSE, JACK HAS UNWITTINGLY STUMBLED INTO ANOTHER MALE'S TERRITORY.

THE RESIDENT MALE ISN'T KEEN ON VISITORS.

HE MAKES SURE THE TRAVELER KNOWS HE IS NOT WELCOME.

THE RULES OF THE JUNGLE STILL APPLY, EVEN IN AN URBAN JUNGLE.

AND JUST LIKE IN THE BUSH, MALES MUST CONFRONT EACH OTHER TO SORT OUT THE PECKING ORDER.

JACK HAS BEEN CAST OUT ONCE MORE.

HE'S NOW FORCED TO CROSS WATER TO GET AWAY FROM THE OCCUPIED TERRITORY.

KOALAS CAN SWIM IF THEY HAVE TO, BUT THEIR BODIES ARE DESIGNED FOR CLIMBING TREES AND NOT FOR MOVING THROUGH WATER.

BUT THE YOUNG TRAVELER IS PERSISTENT FOR GOOD REASON.

WHILE ALPHA MALES DOMINATE IN SIZE, CHANCES ARE HE WILL FIND FEMALES BY SNEAKING IN UNDER THE GUARD.

BIOLOGISTS CATHRYN AND DAVID HAVE OFTEN SEEN THIS KIND OF TERRITORIAL DISPUTE PLAY OUT AMONGST THE KOALAS THEY'VE BEEN STUDYING.

THEY WERE TRACKING TWO KOALAS.

ONE WAS THE YOUNG MALE, HENDRIX, THEY PUT A COLLAR ON A FEW MONTHS AGO.

THE OTHER WAS AN ALPHA MALE CALLED JAMES.

THEIR PECKING ORDER WAS CLEAR.

JAMES HAD ACCESS TO THE BEST TREES AND WAS PREVENTING HENDRIX FROM USING THEM.

THEN EVERYTHING CHANGED.

JAMES BECAME DISEASED, AND SO WAS CAUGHT AND TAKEN TO AN ANIMAL HOSPITAL WHERE HE REMAINED FOR TWO AND A HALF MONTHS.

WHILE JAMES WAS ABSENT, HENDRIX TOOK OVER HIS TERRITORY.

WHEN JAMES WAS EVENTUALLY RELEASED BACK INTO THE WILD, HE WAS IMMEDIATELY PUSHED OUT OF THE FOREST BY HENDRIX AND FORCED TO LIVE IN THE SUBURBS.

Dexter: THE INTERESTING THING IS NOW, HENDRIX, WHO WAS THE YOUNG CHALLENGER, WAS NOW SITTING IN TREES WHERE JAMES HAD ONCE SAT.

OBVIOUSLY, JAMES HAD TO FIND SOMEWHERE ELSE TO GO, HE'S HAD TO CROSS QUITE A NUMBER OF ROADS AND NEGOTIATE FENCES, DOGS, ALL SORTS OF THINGS.

IT WAS ONLY A COUPLE OF WEEKS AGO AND HE WAS STILL SITTING IN THAT BACK YARD.

Narrator: THE SIGNIFICANCE OF THIS DISCOVERY IS THAT IT SHOWS HOW QUICKLY COLONY DYNAMICS CHANGES WHEN A DOMINANT MALE IS REMOVED OR INCAPACITATED BY DISEASE.

ALTHOUGH IT SEEMS AT ODDS WITH THE ANIMAL'S CUTE AND CUDDLY IMAGE, THE SEXUAL TRANSMITTED DISEASE CHLAMYDIA IS RAMPANT IN KOALA POPULATIONS ACROSS QUEENSLAND.

NOW IT APPEARS HENDRIX HAS SUCCUMBED.

ARE WE GONNA TRY THE, UM, OTHER ONE NOW?

THE SICK ONE?

WE WERE JUST GONNA LOOK AT IT FIRST, AND THEN WE'LL SEE IF IT'S... Man: STRAIGHT DOWN... Black: SO, WHEN WE FIND A DISEASED KOALA, WE TRY OUR HARDEST TO CAPTURE IT AS QUICKLY AS POSSIBLE AND GET IT TO THE AUSTRALIA ZOO WILDLIFE HOSPITAL, BECAUSE THAT WILL GIVE IT THE BEST CHANCE OF SURVIVING.

SO, 119, HE IS... Dexter: IT'S A PRETTY DISTRESSING SITUATION BECAUSE YOU'VE BECOME ATTACHED TO THOSE ANIMALS AND YOU KNOW THAT YOU HAVE TO DO SOMETHING ABOUT IT.

I JUST THOUGHT I'D GIVE HIS MOUTH A LOOK, GIVE HIM A GENERAL QUICK CHECK OVER.

Dexter: WE CHECK THE CONDITION OF THE ANIMAL, WE CHECK THE COAT, THE EYES.

OH, HE'S BREATHING AND HE'S... RIGHT, THAT WAS AT 94.

Dexter: THE OTHER THING THAT WE DO IS A BODY SCORE, AND THAT'S DONE BY CHECKING THE BACK OF THE SHOULDER BLADES THERE, MAKING SURE THERE'S A NICE SORT OF THICKNESS IN THE MUSCLE THERE, AND THAT GENERALLY GIVES YOU AN INDICATION OF HOW HEALTHY THAT ANIMAL IS.

Narrator: HENDRIX WAS FOUND TO HAVE A MILD CASE OF CHLAMYDIA, AND WAS TREATED AND RETURNED WITHIN A FORTNIGHT -- BEFORE JAMES HAD A CHANCE TO RE-INVADE HIS OLD STOMPING GROUND.

LEFT UNTREATED, CHLAMYDIA WILL CAUSE CONJUNCTIVITIS AND BLIND THE ANIMAL.

IT CAN ALSO LEAD TO WET-BOTTOM, A URINARY TRACT INFECTION THAT DISCOLORS THE FUR ON THE KOALA'S REAR.

A NEW VACCINE FOR CHLAMYDIA IS BEING TRIALED AND IT IS HOPED THAT THIS WILL REDUCE THE SPREAD OF THE DISEASE.

CHLAMYDIA MOVES THROUGH THE KOALA POPULATION BY SEXUAL ACTIVITY.

BUT REGARDLESS OF THE THREAT OF DISEASE, WHEN THE FEMALE IS IN ESTROUS AND IN THE MOOD, THERE'S LITTLE STOPPING TREETOP ROMANCE.

THROWING HER HEAD BACK AND FORWARDS IS A SIGN THAT THE FEMALE HAS STARTED OVULATING.

MATING ONLY LASTS A FEW MINUTES, AND THEN BUSTER IS OFF.

[ GRUNTING ] MALE KOALAS PLAY NO ROLE IN PARENTING.

OTHER MALES ARE HANGING AROUND, BUT THEIR CHANCES OF GETTING LUCKY ARE THWARTED IN MORE WAYS THAN ONE.

APART FROM GUARDING THE FEMALE FROM THE ADVANCES OF ANY OTHER SUITORS, BUSTER HAS SECRETED A GELATINOUS PLUG THAT GLUES HER GENITAL TRACT TOGETHER -- A FINAL ATTEMPT TO ENSURE SHE BECOMES PREGNANT WITH HIS YOUNG.

THE BREEDING HABITS OF KOALAS ARE BEING STUDIED IN DEPTH BY BIOLOGISTS BILL ELLIS AND SEAN FITZGIBBON, AND RECENTLY THEY MADE AN IMPORTANT DISCOVERY.

Ellis: THE SURPRISING THING THAT WE FOUND WAS THAT LARGE RESIDENT MALES WITHIN THE POPULATION WERE ONLY SIRING ABOUT 50% OF THE OFFSPRING.

YOU HAD THESE TRANSIENT MALES THAT TENDED TO COME AND GO, AND, LO AND BEHOLD, IT WAS THESE TRANSIENT MALES THAT WERE SIRING THE OFFSPRING AT OUR SITE.

YEAH, SO I WONDER IF THE OTHER BOYS KNOW YOU'RE HERE, EH?

YEAH, FEW POUCH YOUNG AROUND.

HE COULD BE THE PROUD OWNER OF SOME OF THEM.

YEAH.

Narrator: THE TRAVELING MALE IS IMPORTANT FOR MAINTAINING GENETIC DIVERSITY.

BUT WHEN HABITAT IS CLEARED, THE KOALAS LIVING IN THE REMNANT BUSH BECOME OVERCROWDED -- AND INBREEDING OCCURS.

AT COOMERA IN SOUTHEAST QUEENSLAND, A NEW SUBURB HAS BEEN BUILT AROUND A SMALL REMNANT OF ORIGINAL FOREST.

SO AS MANY AS 15 KOALAS LIVE INSIDE AN AREA THAT WOULD NORMALLY SUPPORT ONLY A FEW.

BILL AND SEAN STUDIED SIX OF THESE KOALAS AND FOLLOWED THEIR MOVEMENTS FOR FOUR MONTHS TO SEE HOW THEY WERE AFFECTED BY OVERCROWDING.

LIKE CATHRYN AND DAVID'S STUDY, THEY FOUND MALES WERE BEING PUSHED OUT OF THE FOREST AND ONTO THE SURROUNDING STREETS.

Ellis: THERE'S JUST NOT ENOUGH SPACE IN THERE FOR THE KOALAS THAT NEED TO LIVE IN THIS AREA.

NOW, IF THERE'S THAT MANY KOALAS CRAMMED INTO A SMALL AREA, THEY'RE UNDER A LOT MORE PRESSURE, WHICH EXPLAINS WHY IN SOME OF THESE CROWDED, ISOLATED FRAGMENTS, WE DO SEE A LOT OF DISEASE.

Narrator: ONE OF THE KOALAS THAT BILL AND SEAN TRACKED WAS A MATURE MALE CALLED HOUDINI.

SO, THIS IS WHERE WE WERE EARLIER.

YOU CAN SEE HE'S DEFINITELY COME THROUGH ONE OF THESE FENCES.

Narrator: HOUDINI OCCUPIED A SMALL PATCH OF TREES BETWEEN A ROAD AND SOME HOUSES, AND THEN TRIED TO MOVE INTO THE CENTRAL BUSH AREA.

BUT THIS WAS ALREADY CROWDED, SO THE RESIDENT MALE KOALAS PREVENTED HOUDINI FROM ENTERING NOT ONCE, BUT FOUR TIMES.

SO HOUDINI WAS FORCED TO SETTLE FOR A LIFE IN THE MEDIAN STRIP.

Fitzgibbon: HE SCOOTED ACROSS THE OTHER ROAD HERE, JUST BRIEFLY IT LOOKS LIKE, BUT BY AND LARGE HE'S JUST HANGING IN THAT TINY LITTLE PATCH THERE.

Ellis: KOALAS OBVIOUSLY HAVE A REALLY COMPLEX SOCIAL SYSTEM, AND I THINK THERE'S NO DOUBT THAT WHAT WE'RE DOING IN THEIR ENVIRONMENT IS BREAKING THAT SYSTEM DOWN.

YEAH, IT'S PRETTY CLEAR IN SOUTHEAST QUEENSLAND THAT URBANIZATION IS THE BIGGEST THREAT THAT THEY FACE.

Narrator: KOALAS ARE BARELY HANGING ON.

MARY AND BRUCE ARE ON THE MOVE.

KOALAS LIKE TO CHANGE FOOD TREES REGULARLY, BUT IT'S NOT SO EASY WHEN YOU ARE CARRYING AN EIGHT POUND BABY ON YOUR BACK.

BRUCE IS NOW 12 MONTHS OLD AND GETTING TOO BIG TO CARRY FOR LONG.

SO, HE WILL WANDER AWAY FROM MUM TO EXPLORE FOR HOURS ON END.

AT THIS AGE HE IS NEARLY FULLY INDEPENDENT.

MARY IS NOT PRODUCING MILK ANYMORE AND WON'T SUCKLE HIM AGAIN.

SO, BRUCE SURVIVES EXCLUSIVELY ON A DIET OF GUM LEAVES.

BUT HE IS NOT YET THAT GOOD AT GETTING THEM DOWN THIS THROAT.

LIKE HIS MOTHER, HE WILL SURVIVE ON NOTHING BUT EUCALYPT LEAVES THROUGHOUT HIS EXPECTED LIFE SPAN OF 12 YEARS.

SEVERAL MONTHS HAVE PASSED SINCE JACK, THE TRAVELER, SET OFF DETERMINED TO FIND A HOME OF HIS OWN.

HE NOW HAS HIS SIGHTS SET ON RETURNING TO THE COLONY WHERE HE WAS OUSTED SIX MONTHS AGO.

HE HAS BECOME OLDER AND TOUGHER -- MORE CONFIDENT TO NAVIGATE THE WORLD AROUND HIM.

[ LOWING ] EVEN THE OPEN FIELDS AND LARGE ALIEN-LOOKING CREATURES DON'T INTIMIDATE HIM.

JACK IS DETERMINED TO HOLD HIS COURSE AND BRAVE ENOUGH TO CROSS THEIR PATH.

SUCH TENACITY HAS EVEN SURPRISED KOALA SCIENTISTS, WHO NOW HAVE SOME ASTONISHING RESULTS FROM THEIR TRACKING DATA.

SIX MILES AWAY FROM PETRIE, THE BRUCE HIGHWAY IS THE MAIN FREEWAY IN QUEENSLAND.

IT'S HARD TO BELIEVE THAT A KOALA WOULD EVER TRY TO CROSS SUCH AN ACTIVE HIGHWAY, BUT THAT'S WHAT BIOLOGISTS CATHRYN DEXTER AND DAVID BLACK HAVE COME TO INVESTIGATE.

Dexter: ONE OF THE THINGS THAT WE UNDERSTAND ABOUT ROADS IS THAT THEY ARE BARRIERS, AND YOU WOULD SUSPECT A SIX LANE HIGHWAY TO BE A MAJOR BARRIER TO AN ANIMAL.

OKAY, YEP, HE'S IN THE CROOK OF THE TREE THERE.

SO CLOSE TO THAT ROAD.

Dexter: WELL, THEY DON'T SEEM TO HAVE ANY SORT OF CONCEPT OF A BUSY ROAD TO A NON-BUSY ROAD -- THEY SEEM TO BE DRIVEN TO GO IN A DIRECTION, AND THEY JUST GO.

Narrator: THEY'VE TRACKED CAPTAIN BOGART CLOSE TO THIS BUSTLING SPOT, AND ARE NOW RETRACING HIS STEPS TO UNDERSTAND HOW HE ARRIVED AT THIS PLACE.

Black: SO, YEAH, WITH CAPTAIN BOGART, SO, ONCE WE WERE ABLE TO GET HIS GPS COLLAR OFF, DOWNLOAD THE DATA, AND UNDERSTAND HIS MOVEMENTS, WE WERE REALLY ABLE TO SEE THAT HE'D DONE THIS MASSIVE WALK.

Narrator: THE TRACKING DATA REVEALS CAPTAIN BOGART ROAMED AROUND A PATCH OF BUSH NEXT TO A MAJOR INTERSECTION ON THE BRUCE HIGHWAY.

THEN HE WENT OVER A BUSY OVERPASS, GOING TO AND FRO, CROSSING IT NO LESS THAN FIVE TIMES.

BUT THE TRAVELING MALE'S JOURNEY DIDN'T END THERE.

HE WALKED ALONG THE HIGHWAY FOR A MILE, AND THEN DID SOMETHING NO ONE BELIEVED WAS POSSIBLE.

HE CROSSED THE HIGHWAY, ALL SIX LANES OF IT.

THIS IS A TRULY AMAZING FEAT FOR A TREE DWELLING ANIMAL.

Black: WHEN I FIRST SAW THIS, I COULDN'T BELIEVE WHAT WAS HAPPENING.

I WAS LIKE, THAT'S JUST INSANE, WE DIDN'T THINK THAT THEY WOULD TRY TO CROSS A SIX LANE HIGHWAY.

Dexter: I DON'T THINK ANYONE'S EVER SEEN THAT SORT OF INTERACTION WITH ROADS, AND MAJOR ROADS, AND HOW LUCKY HE'S BEEN TO ACTUALLY BE ABLE TO SURVIVE ALL OF THAT.

Narrator: TWO MONTHS AGO, CATHRYN AND DAVID INSTALLED SPY CAMERAS INSIDE A LOCAL UNDERPASS TO FIND OUT WHETHER KOALAS WERE USING IT.

TODAY THEY DISCOVER THE RESULTS.

SO, I'VE GOT THE IMAGES BACK FROM OUR TECH GUY, ROB.

UM, THIS IS, LIKE, ALL THE IMAGES OF THE UNDERPASS USING THE SCOUTGUARD CAMERAS.

FIRST ONE -- OH, YEAH.

IBIS -- VERY NICE.

GOANNA.

THE QUALITY IS ACTUALLY REALLY GOOD.

YEAH IT'S NOT BAD.

SOMETHING AT NIGHT.

OH, WALLABY.

IT'S A WALLABY.

YEAH, YOU CAN SEE HIS TAIL THERE.

HOLY... IT'S DEFINITELY A KOALA.

GO NEXT, GO NEXT.

OH, MY GOD... THIS IS AMAZING, YOU KNOW WHAT THIS MEANS?

I ACTUALLY THINK WE HAVE GOT THE FIRST EVER RECORDED PICTURES, I MEAN, OF A KOALA USING A RETROFITTED UNDERPASS.

Black: NOW THAT WE ACTUALLY HAVE CONFIRMATION, WE CAN START RETROFITTING OTHER AREAS WHERE WE KNOW KOALAS ARE CROSSING.

Dexter: THE WORK THAT WE'VE DONE IS GONNA HAVE SOME REALLY LONG TERM IMPLICATIONS FOR KOALAS, TO ALLOW THEM TO BE ABLE TO LIVE IN HARMONY WITH PEOPLE.

Narrator: TODAY IS A BIG DAY FOR ONE LITTLE KOALA.

BRUCE HAS REACHED THE FIRST STAGE OF ADULTHOOD AND IS NOW 13 MONTHS OLD.

MARY LETS HIM KNOW WITH A FRIENDLY BITE THAT THE TIME HAS COME FOR HIM TO STOP RELYING ON HER.

IT'S TIME TO EXPAND HIS HORIZONS AND FIND OUT WHAT THE WORLD IS LIKE ACROSS THE STREET.

HE'LL REMAIN WITHIN HIS MOTHER'S HOME RANGE AT LEAST FOR THE NEXT YEAR -- NOT TOO FAR AWAY, BUT STILL DAUNTING FOR A YOUNG ONE WHO IS FACING THE BIG WIDE WORLD ON HIS OWN FOR THE FIRST TIME.

BRUCE STUMBLES INTO A BACK YARD AND QUICKLY HEADS FOR HIGH GROUND.

[ DOG BARKING ] DEPENDING ON HOW STRONG HE GROWS OVER THE NEXT FEW YEARS, HE WILL EITHER BECOME A TRAVELER -- CONTINUALLY WANDERING THE STREETS -- OR AN ALPHA MALE THAT SETTLES DOWN IN ONE COLONY.

IT'S FEBRUARY, AND THE KOALA'S MATING SEASON IS DRAWING TO A CLOSE.

BUSTER GUARDS MARY JEALOUSLY, MATING WITH HER AS OFTEN AS SHE WILL ALLOW.

BUT THIS TIME SHE REJECTS HIM -- AND LET'S HIM KNOW WITH A SICKENING CRY.

[ MARY CRYING ] AGAINST ALL THE ODDS, JACK THE TRAVELING MALE HAS MADE IT BACK TO THE COLONY.

HE SENSES THE WEAKNESS IN BUSTER AND SEIZES THE OPPORTUNITY TO CHALLENGE HIM FOR CONTROL OF THE DOMAIN.

HE'S BEEN WAITING FOR THIS MOMENT ALL BREEDING SEASON, AND IS NOT HOLDING BACK.

BUSTER MUST RELINQUISH HIS DOMINANCE TO THE NEW CHAMPION.

JACK HAS TRIUMPHED AT LAST.

JACK'S RESILIENCE HAS KEPT HIM ALIVE AND ALLOWED HIM TO RISE TO THE TOP OF KOALA SOCIETY.

ONLY THE TOUGHEST SURVIVE LIFE IN THE SUBURBS.

BUT WITH FEWER WILD STRETCHES OF KOALA HABITAT LEFT IN QUEENSLAND, THIS IS BECOMING THE REALITY MORE AND MORE KOALAS WILL FACE.