Photograph: Photograph and text by William Lamar. Amazon Milk Frog (Trachycephalus cunauaru) from Santa Cruz Reserve on the Río Mazán in Loreto, Peru, South America. The Amazon Milk Frog completes its entire life cycle in water-filled cavities of trees. The two-note sound of calling males can be heard over a long distance in the rainforest by night and the tree cavities may serve as call resonators.