Individuality in Problem Solving: String Pulling in Two Carduelis Species (Aves: Passeriformes)

A famous example of problem solving in birds is the string-pulling tactic. In an experimental setup a bird can obtain food by lifting a small food container suspended from a perch by a string. This behaviour is known as a popular entertainment since ancient times, in particular from goldfinches. It was mentioned by Plinius (1554), by Albertus Magnus in 1250, by the Italian historian Bartolomeo de Sacchi (1421–1481) as well as by Gesner (1669). In modern times string pulling has caught the scientists’ interest as being a special problem-solving ability. Various reports dealt with casual and systematic observations of string pulling in different birds: in corvids (Hertz 1926; Heinrich 1995, 2000), a garden warbler (Teyrovský 1930), in siskins (Thienemann 1933), larger parrots (Fischel 1936) and in parids and finches (Herter 1940; Vince 1956, 1958, 1961). Erhardt (1933) thought that string pulling derives from normal instinctive feeding behaviour and does not require intelligence. Likewise, Vince (1958, 1961) and Altevogt (1954) saw no need to apply terms like ‘insight’ and ‘understanding’ to this behaviour. Bierens de Haan (1933) suggested that string-pulling behaviour is not purely genetically determined but will need some intelligence, i.e. a capacity to have the behaviour influenced by individual experiences. Heinrich (1995, 2000) concluded from his experimental study that insight into the Correspondence Prof Dr Wolfgang Wickler, Max-Planck-Institut für Verhaltensphysiologie Seewiesen, D-82319 Starnberg, Germany. E-mail: [email protected]