An investigation into the cognition behind spontaneous string pulling in New Caledonian crows

Abstract

The ability of some bird species to pull up meat hung on a string is a famous example of spontaneous animal problem solving. The "insight" hypothesis claims that this complex behaviour is based on cognitive abilities such as mental scenario building and imagination. An operant conditioning account, in contrast, would claim that this spontaneity is due to each action in string pulling being reinforced by the meat moving closer and remaining closer to the bird on the perch. We presented experienced and naïve New Caledonian crows with a novel, visually restricted string-pulling problem that reduced the quality of visual feedback during string pulling. Experienced crows solved this problem with reduced efficiency and increased errors compared to their performance in standard string pulling. Naïve crows either failed or solved the problem by trial and error learning. However, when visual feedback was available via a mirror mounted next to the apparatus, two naïve crows were able to perform at the same level as the experienced group. Our results raise the possibility that spontaneous string pulling in New Caledonian crows may not be based on insight but on operant conditioning mediated by a perceptual-motor feedback cycle.

Figure 1. The visually-restricted apparatus.

(A) Without the mirror. (B) With the mirror.

Figure 2. Standard string-pulling problem and string discrimination tasks.

(A) Standard string-pulling problem. (B) Object discrimination test: circle  =  meat; rectangle  =  rock. (C) Overload test: small circle  =  meat; large circle  = 700 g chicken. (D) Slanted-string test. (E) Crossed-string test.

Figure 3. String-pulling efficiency across the three groups with the visually-restricted apparatus.

E: experienced group; SM: successful mirror crows; SN: successful naïve crows; FM: failed mirror crows; FN: failed naïve crows.

Figure 4. Error rates in successful trials with the visually-restricted task.

Red bars: experienced group; Blue bars: mirror group; Green bar: naïve group.

Figure 5. Pull-step ratios in the first five successful trials for the experienced, naïve and mirror groups with the visually-restricted task.

White circle: experienced group; Dark circle: mirror group; Triangle: naïve group.