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the iguazu falls
where more than a thousand tons of water
plummet over the cliffs
every second the power of this roaring
mass of water is
pretty daunting but not for these little
birds
great dusky swifts happily fly straight
through the curtains of water
18 centimeters of bird taking on 80
meters of waterfall
just like that but what could possibly
bring them to do it
in the heart of south america between
brazil and argentina
the nearly three kilometer long canyon
of the iguazu falls
shapes the landscape an average of 1.5
million liters of water drops down the
series of waterfalls
every second
the highest waterfall is an impressive
80 meters deep
and bears the promising name devil's
throat
spray from the falls reaches so high
it's visible from space
these large clouds of spray permanently
soak the surrounding rainforest
creating thick lush subtropical
vegetation
animal life is equally varied and
abundant
and one of the biggest daredevils out
there is the great dusky swift
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it's not just for the fun of it that
these birds go up against the thundering
waterfalls
really it's a survival strategy
great dusky swifts spend their days on
the wing
snatching insects flying out of the
forest
but when the sun goes down the forest
stops being a safe place for them
a long time ago the birds spotted a
perfect roost behind the massive
curtains of water
far away from predators they even build
their nests on the rocky outcrops
lining the falls to protect their eggs
and chicks
but getting hold of a good spot isn't so
easy
even with kilometers of cliff available
the birds still fight over prime
roosting sites they seem to be naturally
aggressive
which is probably a useful evolutionary
gift for a bird that weighs
approximately
60 grams but wants to fly through
tons of water
one theory put forward by an
evolutionary biologist suggests
that the unusual behavior of great dusky
swifts
might go back to a time before records
began
when the dry season was more intense and
there was much less water in the rivers
this would have meant the water curtain
was thinner and easier for the birds to
fly through
the theory concludes that as the water
flow increased
the great dusky swifts simply evolved to
withstand the growing power of the
waterfall
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nesting here certainly has its
challenges
rocky ledges that never flood are always
in demand
more experienced pairs know exactly
where they can find them
and will reuse these ledges season after
season
in such a cramped space the female
usually lays just
one egg but for the younger birds
all this is new some of them seem to
struggle with the basics of breeding
every year the rivers fill up before
long
seven times as much water will be
thundering over the falls
that's 10 000 tons per second
now the location of the nest ledge
becomes critical
the young pair are in trouble
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the rising waters have flooded their
nest
all is lost
the more experienced pair is still safe
together they take care of their chick
and after six weeks it's time to learn
to fly
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the fledgling ventures out of the nest
it's never seen what lies beyond the
wall of water
the young great dusky swift spreads its
wings for the first time
and masters the air and
the water
these small birds have harnessed the
ferocious power of the iguazu falls
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along with the thousands of other animal
species
and tens of thousands of plant species
great dusky swifts have contributed to
brazil and argentina's
iguazu national parks being listed as a
unesco world heritage site
but outside the borders of the national
parks the landscape is being altered
beyond recognition
by logging intensified agriculture
forestry plantations
and rural settlement
so let's keep a lookout for sustainable
products that don't harm rainforests
and if you want to know more about the
vital role forests play in the
environment
go ahead and click on our video about
worldwide deforestation