The great dusky swifts rest and make their nests for breeding behind the waterfall as a strategy to keep safe from predators. They build their nests in caves or on rocky ledges by sticking mud and moss with saliva. I was very taken by how hundred of swifts appeared and disappeared behind the curtains of water in the bigger falls of Iguazú Falls National Park, flying vertiginously through clearings and gaps. This is something I knew before travelling there, and had a previous image in my mind to try to capture the essence of that moment.