String-pulling in the Goffin's cockatoo (Cacatua goffiniana)

Abstract

Goffin's cockatoos, a parrot species endemic to the Tanimbar Islands in Indonesia, demonstrate remarkable cognitive skills across various technical tasks. These neophilic extractive foragers explore objects with their beak and feet, and are skilled in several modes of tool use. In this study, we confronted the animals for the first time with a vertical string-pulling setup, including a set of classic and novel controls. Nine of the 12 subjects, two of which were subadults, immediately interacted with the single-string task, with seven individuals successfully obtaining the reward on their very first attempt. Four different double string discrimination tests with varying spatial relations were used to assess the Goffin's cockatoos' apprehension of basic physical task properties. We found significant differences in performance between the respective experimental conditions, as well as the development of side biases. The results suggest that while the birds seem to consider simple cause-effect relationships, there is no evidence for a mental representation of the causal mechanisms underlying the string-pulling tasks, as subjects failed the crossed strings condition out of immediate sight. Finally, we provide suggestions on improving the methodology, and discuss our findings in regard to the Goffin's cockatoo's ecology.

Keywords: Mental representation; Perception; Physical cognition; Problem solving; Sensorimotor skills.

Fig. 1

Illustration of the apparatus used with measurements (left). Arrangement of strings in different conditions (right) with the blue cube representing rewarded containers and the white cube containers without a reward. Arrows show the insertion direction of the string. a Perpendicular (baseline) condition: two strings both 70 cm in length. b Proximity condition: two strings, 70-cm and 35-cm long, both baited. c Coiled condition: two strings 70-cm and 100-cm long, the longer one baited and being coiled on the bottom of the box. d Crossed condition: two strings, both 85 cm in length, held in a crossed position by ring-shaped pieces of plastic; note that visual access to the crossing of the strings from above is prevented by the board

Fig. 2

The observed proportion of correct choices per individual shown by condition; solid black line and grey bounding box indicate performance at chance level; dashed lines demark borders of significantly less (red; probability of success = 0.36, p = .066) and more (green; probability of success = 0.6, p = .066) correct choices than predicted by chance. (Color figure online)

Fig. 3

The observed proportion of sides chosen by each individual shown within each condition. Solid black lines and grey bounding boxes indicate a nonsignificant choice of one side over another; dashed lines demarcate strings significantly chosen more often on the right side (red) or on the left side (turquoise). (Color figure online)

Fig. 4

String-pulling sequence as performed by subject Irene (Illustration by Mark O’Hara)