South America’s Iguazu Falls is the world’s largest waterfall system. Yet, despite its imposing size, a devoted bird flies through its crashing cascades to raise its young.
When it comes to nest building, few animals on the planet are quite as bold as the great dusky swift.
Found across Brazil, in northeastern Argentina and eastern Paraguay, these large, grey-brown swifts roost around waterfalls, often choosing nest spots directly beside and even behind the gushing torrents.
A waterfall may seem like a treacherous place to lay eggs, but the steep walls combined with the tumbling water offer good protection against both climbing and flying predators.
Once a suitable site has been chosen, these daring birds build a disc-shaped nest using moss, pebbles and mud, typically laying just one egg within it.
One of the most famous places to see great dusky swifts is Iguazu Falls on the border of Brazil and Argentina. Standing around 80 metres tall, spanning 2.7 kilometres (1.7 miles) and made up of hundreds of cascades, this is the largest waterfall system in the world.
Iguazu Falls is so big it can be seen from space – images of the cascades have been captured from the International Space Station.
Yet despite the impressive size of Iguazu, many swift adults choose the damp cliffs behind the raging falls as a place to rear their young.
Because of this, fledglings are faced with the formidable challenge of not only taking to the wing off the sheer cliffs, but doing so through a deluge of water.
“The chicks have never seen the world beyond the falling waters,” said David Attenborough of the great dusky swift fledglings in the 2019 BBC documentary, Seven Worlds, One Planet. “Unless they can find a way through, they will not survive.
“Amazingly, driven by blind instinct, chicks do manage to power their way through,” adds Attenborough. “These remarkable birds have colonised a niche in which few can survive.”
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