Flying out of
the Australian twilight
is one of the most successful
mammals on the planet...
..the bat.
They're the second largest
order of mammals
after the rodents,
and the only ones capable of
sustained flight.
One group of bats,
the flying foxes,
are among the most gregarious
of their kind,
living communally in noisy
tens of thousands.
Spending their time feeding,
fighting for dominance...
..and indulging in a rather
torrid love-life.
They're found roosting in
the trees across Australia,
a vast island continent,
home to some of the most
unusual and fascinating
animals on the planet.
(Screeching)
These are the secrets
of the flying fox.
Cutting a lush green swathe
through the bustling
metropolis of Sydney,
Australia,
is Centennial Park.
In among its lofty treetops
live around 20,000
flying foxes.
They got this name because
their long muzzles give them
a foxy appearance.
They're members of
an ancient species.
Fossils of their ancestors
date back
around 58 million years.
There are four kinds of
flying fox in Australia,
but these grey-headed flying
foxes are the most numerous.
They have a distinctive
gingery collar,
and, unlike other fruit bats,
fur that goes all the way
down to their feet.
With a wingspan
of over three feet,
they're the largest
fruit-eating bat
in Australia.
These highly sociable mammals
like to live tightly packed,
wingtip to wingtip,
in extremely large groups
all along the eastern coastal
belt of Australia...
..from the cool climes of
Victoria in the south...
..right up into the tropics
of Queensland in the north.
(Screeching cacophony)
Wherever they go, the bats
are incredibly noisy.
(Screeching)
The sounds they make
are a complex form
of communication.
Grey-headed flying foxes
have been recorded making
over 30 different calls.
(Trilling and squeaking)
Moving from place to place
as their food trees come
into flower and fruit,
they're extremely adaptable,
and can live in the depths
of the rainforest,
on farmland...
and right next to humans.
(Blast of horn)
This colony lives in a park
right in the middle of a town
in New South Wales.
The flying foxes are
so flexible,
they've got used to cars
passing by right next to
where they rest and sleep,
and are tolerant of humans.
For flying foxes,
the coming of darkness
means feeding time.
Every dusk they take to the
skies en masse to find food.
Their flying height will vary
according to the topography
of the ground below them.
But their cruising altitude
is around 100 to 260 feet...
at speeds between
15 and 25 miles per hour.
Many bats use a kind of
organic sonar,
called echolocation,
to zero in on insects
and eat them.
But flying foxes don't hunt
live prey.
They eat fruit, so they
don't use echolocation.
They use their eyesight.
They have large eyes,
particularly well adapted to
recognizing colors at night,
which, with an excellent
sense of smell,
helps to identify
edible fruits and blossoms.
(Trilling)
The bats have found one of
their favorite foods -
the blossom of
the eucalyptus tree.
It's one of
Australia's most important
and distinctive trees,
with many hundreds of
different species,
many of them known as
gumtrees by the locals.
The flowers are rich
in nectar.
And the flying foxes
love them.
They aren't the only
creatures to come out
and feed
after the sun's gone down.
In fact, Australia's wild
animals have a thriving
nightlife.
Wombats and brush-tailed
possums are nocturnal,
as are quokkas -
small marsupials.
They all do most of
their feeding at night.
Little penguins go fishing
all day,
and for them, night-time
is for socializing.
(Trilling)
For the flying foxes, though,
night-time is all about
getting down enough food.
They have an extremely fast
digestive system,
and in a single night can
eat two and a half times
their own body weight.
It's the only way they can
acquire sufficient protein
from the fruit they eat.
They're well adapted to eat
soft blossoms and fruit.
The roof of their mouth,
or palate, is deeply ridged,
and their tongue crushes
the food up against it.
They can process large
amounts of food rapidly
by sucking the nectar out of
blossoms or chewing fruit.
Flying foxes help spread
tree and plant species.
Most tree species propagate
themselves by producing
pollen and seeds
that contain
their genetic information.
They rely on the wind,
insects or other animals
to spread this around
and ensure their survival.
It takes between
12 and 24 minutes
for food to pass through
flying foxes' digestive
tracts.
By the time they excrete
seeds or pollen,
they've often flown on
to a new area,
giving the plant species a
chance to grow somewhere new.
It's early morning
in Sydney's Centennial Park
and the foxes are returning
from foraging
back to their daytime
roosting area or camp.
Camps are the focal point
of flying fox life.
This is the place to rest up
after feeding, find a mate,
have babies,
safely bring up offspring...
..and argue with
the neighbors.
(Squeaking)
Within each geographical
area,
they generally stay faithful
to the same campsites -
one camp for the summer and
another for the winter.
Foxes are generally pregnant
during the winter
and raise their young
at summer camps,
before mating again.
Out in the rural farmlands
of central New South Wales,
150 miles north of Sydney
and near to the small town
of Muswellbrook,
there's an even bigger colony
of around 40,000 bats.
Flying foxes like their camps
to be absolutely jam-packed,
and Muswellbrook is
no exception.
The colony occupies
every tree,
vine...
..and shrub available.
(Screeching)
With space at such a premium
in the camp,
each flying fox returning
home from feeding
must come in to land
in a tiny spot.
But a large wingspan
and a tight space
to maneuver into
makes landing a tricky task.
They must visually select
their spot
and slow their speed
right down
using all their wing surfaces
at different angles,
like the flaps
on an aircraft...
..then hover...
and slot into place.
The foxes need to develop
their aerial skills.
Often the younger,
less experienced fliers
will crash into branches
or vegetation
and rip through their wings.
Bat wings are living tissue,
so small rips and tears
will heal.
But large holes can
compromise their ability
to fly and to feed.
Their maneuverability is all
down to the physical make-up
of their wings.
Semi-transparent, the wings
are made up of two layers
of almost hairless skin
stretched over
the five-digit forelimb.
Sandwiched between
the two sheets of skin
is a thin layer of
connective tissue
containing blood vessels,
nerves
and elastin fibers.
To be aerodynamically
efficient,
the foxes need their wings
to be tough enough
not to tear in flight,
whilst having the flexibility
to fold around their bodies
when resting.
It's the elastin reinforcing
the wing membranes
that makes
all of this possible.
The wings are crucial to
getting airborne,
flying and feeding,
so the foxes' very
survival depends on keeping
them in tiptop shape.
They spend a part of each day
performing essential wing
maintenance,
cleaning every inch of
the leathery membrane.
Flying foxes' wings are
useful for far more than
just flying.
The membranes are spread out
over a skeleton
resembling
an elongated human hand,
equipped with a thumb.
And, just like human thumbs,
they're immensely useful.
They work as handy hooks...
..and climbing gear.
They help the flying foxes
scale their way up trees
and maneuver themselves into
positions it would be hard
to fly into.
Their thumbs also make
very serviceable weapons.
Tipped with
a razor-sharp claw,
these bat digits are top
tools for defending
their spot.
Jostling for position is
a major fox pastime.
And the daytime roosts
are where flying fox politics
play out.
Although to human eyes the
trees look pretty similar,
to a flying fox,
every inch of every branch
has social significance.
There's a hierarchy
within the bat camp.
Males will show
their dominance
by claiming and defending
the best spots in the trees.
The highest, coolest spots
in trees at the center of
the camp
are deemed the most desirable
pieces of real estate.
If a male can establish one
of these as his territory,
he'll have higher status...
and be more attractive
to females.
Once a male has staked out
his claim to one of
the top spots,
it's his job to defend it...
..vigorously.
Fall is the time of year
when all the pushing and
shoving could pay off.
It's mating season.
And the most successful
males will be those
who've put in the hard work
beforehand
to consistently win
the high-status spots.
This adult male has claimed
one of the most prized
perches,
high up in one of
the best trees.
It's his way of clearly
signaling his dominance
and superiority
to the females.
The mating system of
the gray-headed flying fox
is described as a lek,
where the female decides
which male to mate with,
based on his location
within the camp.
The better the location,
the greater the genetic
fitness of the male,
or so the theory goes.
This female has selected
one of the dominant males
as her breeding partner,
and moves from her own spot
to be with him on his branch.
But she's not alone.
She's joined by other females
who've also chosen this male.
Up to five females will form
his harem for this breeding
season.
They start the mating ritual
with some exploratory
sniffing on the male's part.
The female tolerates
his attention,
so mutual grooming is next,
which can last half an hour.
After a relatively long
wooing,
the act itself is over
fairly quickly.
And once again,
those thumbs come in handy.
The female may not look
that keen,
but she's actively moved
from her own roosting spot
to be with this
dominant male.
And they'll copulate
up to four times an hour
over several days.
For the other
non-dominant males,
mating is less of
a sure-fire certainty.
They haven't been strong enough
or dominant enough
to fight their way to
the center of the colony
and up to the top spots
in the highest trees.
Being on the outer fringes
of the camp in the less
desirable spots
means they have little chance
of attracting a harem.
So they need to work hard
to find a partner
amongst the remaining females
who have chosen not to join
a dominant male.
It's not known why
some females opt out of
the hierarchical system.
This lower ranking male
has been successful
and found a single female.
Bats operating outside
the harem system
are often monogamous,
and these two may stay
together for the entire
mating season.
But this young
non-dominant male
hasn't established
a pair bond.
He doesn't have the benefit
of sitting back
and letting the ladies
flock to him.
So he's got to take
his chances
and try his luck with
any female he can find.
He uses his claws to climb
around the tree,
encountering females
as he goes.
The young male is really
covering some ground,
checking out every female
in his path.
The choice of
whether to mate or not
lies with the females,
and they're signaling
their disinterest
by completely ignoring him,
moving away,
or using their own claws
to make their point.
But this bat Lothario
isn't giving up so easily.
Doggedly, he works his way
around the tree,
sniffing at females
to see if they'll reciprocate
and let him move on to
some grooming.
For a long time,
it's a fruitless task.
But it's vital for the
colony's long-term survival
that even his breeding season
is successful.
Although these colonies
may seem large,
flying foxes are listed
as vulnerable.
Thousands are shot by
fruit farmers
or die in fires or droughts
every year.
So the ardent young bat
needs to be persistent.
Eventually he gets a female
interested enough
to mate with him.
Breeding season is a very
active time for the foxes.
They're feeding every night
and returning to the camp
in the daytime to mate.
But breeding ends
with the arrival of winter,
and the pregnant females
will have a quieter camp life
for the next six months.
As the sun gets higher
in the sky,
it's time to prepare
for sleep.
The bat preference for living
in such tightly packed
quarters
makes for very eventful,
and noisy, bedtimes.
(Screeching and squawking)
This is also the time
when many of the bats
go for a poop.
For this job, they need
to turn right side up.
Their roost is around
ten miles from where
they fed last night,
and by carrying pollen on
their fur and excreting seeds
in this new location,
they're spreading
the tree species.
The flying foxes'
bedtime routine
involves a long checklist.
Not only must
they safely land,
tend to their wings,
defend their spot against
any newcomers
and empty their bowels,
they also have to get
themselves to the right
temperature.
Like humans,
they continuously regulate
their body temperature.
Their optimal levels are from
95 to 104 degrees Fahrenheit.
In Australia's often harsh
climate,
this isn't always easy,
and their wings are
a vital aid.
The blood vessels that run
throughout the wing membrane
help the bat with
thermoregulation.
Stretching their wings fully
can be both a display
and a way of getting warmth
from the sun.
On hot days, fanning their
wings can promote heat loss.
On cold days they wrap
their wings tightly around
themselves
to retain body heat.
With such a large wingspan,
there's plenty of membrane
to act as a blanket...
and even a raincoat
in bad weather.
Having made sure
they're comfortable,
it's finally time
to get some rest.
But for animals that sleep
upside down,
an absolutely critical
preparation for
a good long nap
is making sure they can't
fall off their perch.
The flying foxes have
a brilliant adaptation
for their topsy-turvy life...
..feet
with a locking mechanism.
When a bat hangs onto
a branch,
its leg muscles contract
to pull the toes tight.
It's a ratchet system, which
locks the toes in place
with an immensely
powerful grasp.
It means the foxes can rest
and sleep securely,
even in high winds.
Another adaptation allows
the legs to bend both ways,
forward and back,
so they can switch direction
without changing their grip.
This is possible because the
bat's femur, or thigh bone,
is twisted, and the kneecaps
are reduced or absent,
giving a greater degree of
movement at the knee joint.
Flying foxes have
another modification
that's essential to spending
so much time upside down...
..their cardiovascular
system.
A human wouldn't be able to
spend so much time suspended
like this
because blood would begin
to pool in places
that it shouldn't,
like the lungs and head.
Although bats have a typical
mammalian cardiovascular
system like us,
they've evolved
an unusually large heart.
Relative to body weight,
their hearts are at least
twice the size
of the hearts of other
similar-sized mammals.
This oversized heart can keep
enough blood circulating
to prevent it from flooding
the brain.
The flying foxes spend time
upside down to relax,
and, if not sleepy,
get some sunbathing in.
They'll rest and doze
for most of the day
in their spots in the trees.
But as prey animals
for eagles and pythons,
they remain ever-alert
and mindful
of what's happening
around them.
In the heart of Sydney,
the Centennial Park foxes
have their day's sleep
disturbed...
..by aerial visitors.
A group of black cockatoos
is circling the camp.
(Cockatoos screaming)
They're around the same size
as the flying foxes,
and just as noisy.
(Screaming and screeching)
The cockatoos appear to be
deliberately harassing
the bats.
They may want to intimidate
the bats out of their
roosting spots
so they can take over
the trees.
Eventually the noisy birds
move on,
and the flying foxes
can finally...
..with some squabbling,
get to sleep.
In the Muswellbrook camp,
the pastoral peace and quiet
is shattered
by the arrival of
a metal monster.
(Train horn)
(Horn)
Even though the foxes have
deliberately established
their camp here...
(Horn)
..the noise of the train's
horn unsettles them
and they take to the skies
in an unusual daytime
burst of activity.
It takes them a while to
regain some equilibrium.
As twilight falls, the flying
foxes are awake and restless.
Once again, it's almost time
for them to leave the camp
and fly out for their
evening's feeding.
The locking system in their
legs has kept them safely
hanging upside down
without falling all day.
Now it's time to release
this powerful grip.
To unlock the tightly
fastened feet,
they must flap their wings
until they become horizontal.
Taking the body weight
away from their legs
releases their feet
from the branch.
There's a definite
technique to it,
and inexperienced flyers
can struggle
with unlocking their feet.
Moving out from the camp in
the evening to find food
is called emergence,
and it's a waiting contest.
Depending on what's
flowering or fruiting,
the bats may have to travel
25 miles to find food.
So those who leave earliest
theoretically get the first
chance at the nearest fruit,
but they also have a higher
chance of being caught
by predatory birds
like kites and eagles.
In the end, it's usually
adults like this -
females with a poorer
body condition -
that leave first.
They're the hungriest, so
more likely to take the risk.
Like mating rights,
the emergence time of
the male adults
is related to their
social standing.
In the mating season,
a flying fox with a harem
will only leave his spot
once his last female
has flown out,
so as to avoid having her
stolen by a later-leaving
lower-ranked male.
(Screeching)
If they're not waiting to
steal the top bat's harem
member,
the non-dominant males will
leave with the adult females.
But eventually,
they all take flight.
As the days lengthen and
winter turns to spring,
the females are now
six months pregnant
and get ready to give birth.
When their time is close,
they segregate themselves
away from the males.
Birthing season is in
the Australian spring -
September through
to November.
Flying foxes give birth
in daylight hours
while hanging upside down.
The baby emerges head-first
and is caught in
the mother's wings.
The baby suckles from a teat
in her wing pit.
She'll give him milk for at
least six weeks after birth.
Baby bats, or pups,
can't regulate
their body temperatures,
so it's very important
that he stays
as close to mom as possible.
If it's too cold,
she can wrap her wings
tightly around the pup.
On the days
when it's too hot,
she can gently fan him
with her wing.
The pup will be very closely
attached like this
for the first two or three
weeks of his life.
He has a hook-like growth on
the inside of his thumb claw
that gives him a tight grip
on his mom's fur.
And it needs to be
an extremely strong grip.
For the first few weeks
of his life,
his mom takes him everywhere,
even going on foraging trips
with baby clinging on
underneath her
as she flies along.
After three weeks or so,
he'll get too heavy
for mom to carry,
so she'll leave him in a nursery
in the middle of the camp
with the other babies,
while she goes feeding
at night.
He'll wean at around
12 weeks old,
and learn to fly
at about the same age.
But he'll still stay close to
mom for five or six months.
Flying foxes usually only
have one pup a year.
This slow population growth
leaves the entire species
vulnerable to environmental
stresses like fires,
heatwaves and drought.
Entire colonies
have been wiped out.
There's also a high mortality
rate in young bats
over the winter, when they're
less than a year old,
especially if they have to
cover long distances
to find food.
Learning how to find
reliable food sources
is vital for young bats,
and getting it wrong
can be fatal.
The Muswellbrook pups are
around nine months old now,
and have left mom.
They've set up their own
little area on the edges
of the colony.
It functions as
a baby-training camp.
(Squeaks)
Here they learn the finer
points of bickering
amongst themselves,
and the harsh realities
of life
in a dominance-based
social hierarchy.
(Squeaking and trilling)
They get the knack of branch
negotiation and climbing.
They also practice
their flying skills...
..and the best way to land...
..and how to negotiate some
of the more tricky terrain,
like the reed beds
below the trees.
Flying foxes often make
their camps
by large bodies of water,
like lakes or rivers.
It's thought that the
proximity of a geographical
feature like this
may make navigation
back home easier.
But it also means that
in the more northern parts
of Australia,
water predators are a danger,
especially to young,
inexpert climbers.
Crocodiles will make a meal
of any flying fox
that ventures too close.
So the young bats
must stay vigilant.
The youngsters master the
basics over spring and summer,
then the weather
turns cooler.
As autumn and winter approach
in March and April,
they're still not
expert aviators yet,
but they're fit to fly.
(Screeching)
It's time for the entire
colony to move north
to its winter camp.
Fruit bats like these flying
foxes are critical species,
playing a key role in the
ecology of any system
they inhabit
throughout the world.
Without these furry flyers,
the pollination
and seed dispersal
of important tree species
would be endangered.
Whether in the heart
of a city park
or far out in the bush,
these winged mammals
are vital to the continuing
beauty and diversity
of the Australian
landscape...
..no matter how much noise
they make.
♪♪
