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Great dusky swift (Cypseloides senex) are birds that nest behind the water curtain of the Iguazu falls.

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Title: Great dusky swift (Cypseloides senex) are birds that nest behind the water curtain of the Iguazu falls.

Great dusky swift (Cypseloides senex) are birds that nest behind the water curtain of the Iguazu falls.

Credit: gerhard Hüdepohl / atacamaphoto