Five young scientists – participants of the Second Russian Expedition to South America – in their diaries described processes of development of territories in different parts of the continent. They started their work in Mato Grosso at the end of June 1914. Heinrich H. Manizer and Theodore A. Fjelstrup met Brasilians and various groups of Indios (Kadiwéu, Terena, Ofaié, Kainganges, Guaranies, Botocudos, etc.), recorded lexical and ethnographic materials. Naturalists Ivan D. Strelnikov and Nikolay P. Tanassiytchuk traveled from Corumbá to neighboring regions of Brazil, Paraguay, Bolivia: conducted systematic zoological studies, observed deforestation, clearing of fields, shallowing of water bodies, attacks of «Indios bravos» on «Indios mansos» (settled Chiquitos and Guaranies). Sergei V. Geyman in Spring 1915 observed Araucans at Misión Araucana (under Padre Carlos Sadleir, Temuco) and at Misión Panguipulli (under Padre Siegfrid von Frauenhäusl); Alacalufes in the Straits of Magellan; Onas at Estancia Viamonte (under E. Lucas Bridges) and at Misión Salesiana (under Padre Alberto M. De Agostini), Tierra del Fuego; Indios Chorotes, Toba, Mataco, Chiriguanos in Ledesma (Argentina). Everywhere researchers gathered collections for Russian, Brazilian and Argentinean Ethnographic museums. Their papers preserved in the Peter the Great Museum of Anthropology and Ethnography (Kunstkamera) RAS contain detailed observations on the difficulties in adaptation experienced by emigrants in South America (Croats, Jews, Russians, etc.), on the thoughtless destruction by the Corporations of the region’s fragile ecosystem. The report is written as part of the RFBR grant 19-09-00233 “Study of the materials of the Second Russian Expedition to South America (1914-1915)”.