Born in Estonia and educated in Berlin, Wolfgang Kohler is best known for his insight experiments with apes. During WWI, Kohler was director of an anthropoid station on Tenerife (in the Cannery Islands). He was either there to study chimpanzees or as a spy to study Allied shipping; both interpretations are possible.
Although his children report he had a secret radio they were not to talk about, Kohler preferred to discuss his observations of Sultan (an ape). According to Kohler’s observations, many animals are able to solve problems by insight. Chimpanzees could solve a string problem (how to get a banana tied to the end of a string), and Sultan was able to join two sticks together to get his food.
In Kohler’s later work, he trained chickens to peck at the darker of two discs. After acquiring the skill, they were able to select the darker disk even when the amount of grayness changed. When the original dark disc was paired with an even darker disc, the chickens were still able to choose the darker one.