The great dusky swift (Cypseloides senex) is the emblematic bird of the Iguazu falls, which mark in a majestic and thunderous way this border between Brazil and Argentina. These birds nest on the walls of the cliffs, often behind the water curtains which they pass through with brio and disconcerting ease, which allows them to shelter from predators, as well as their offspring. The contrast between their precise and tapered little silhouette, the elegance of their harmonious gregarious flight and the titanic bubbling of the falls that they are the only ones who can come so close, make this spectacle fantastic and bewitching. [+]