From 1946 to 1948 he was research associate at the Biological Station Wilhelminenberg near Vienna and became a research associate of the Institute for Comparative Behavior Studies in Altenberg near Vienna with Konrad Lorenz in 1949.

Between 1951 and 1969 he worked at the Max Planck Institute for Behavioral Physiology (first in Westphalia, from 1957 at Seewiesen, Bavaria).

From 1975 he was the head of the Max Planck Institute for Behavioral Physiology, Department of Human Ethology in Andechs, Germany.

From 1992 he was Honorary Director of the Ludwig-Boltzmann-Institute for Urban Ethology in Vienna.

He was the author of many books such as Love and Hate: The Natural History of Behavior Patterns and Human Ethology.