In 1873, he was invited by Hermann Burmeister (1807–1892), director of the Museum of Buenos Aires, to join him in Argentina.

As early as 1874, Berg began an expedition to Patagonia to collect specimens for the museum.

Apart from a period of two years from 1890 to 1892, spent at the Museo Nacional in Montevideo, he was based in Buenos Aires.

His first specialty was entomology, but he was also dedicated to paleontology and the study of vertebrates.

Amongst his many other achievements, he described Cactoblastis cactorum, the cactus moth.