Abstract
Understanding causal regularities in the world is a key feature of human cognition. However, the extent to which non-human animals are capable of causal understanding is not well understood. Here, we used the Aesop's fable paradigm – in which subjects drop stones into water to raise the water level and obtain an out of reach reward – to assess New Caledonian crows' causal understanding of water displacement. We found that crows preferentially dropped stones into a water-filled tube instead of a sand-filled tube; they dropped sinking objects rather than floating objects; solid objects rather than hollow objects, and they dropped objects into a tube with a high water level rather than a low one. However, they failed two more challenging tasks which required them to attend to the width of the tube, and to counter-intuitive causal cues in a U-shaped apparatus. Our results indicate that New Caledonian crows possess a sophisticated, but incomplete, understanding of the causal properties of displacement, rivalling that of 5–7 year old children.
Highlights
As adult humans we are capable of recognising that objects in the world behave in predictable ways
The results presented here show that the NC crows we tested were successful on some, but not all, of the displacement experiments
NC crows attended to the water level of the tubes, dropping more objects into a tube with a high rather than low starting water level
Summary
As adult humans we are capable of recognising that objects in the world behave in predictable ways. We know that two objects cannot occupy the same space, round objects will roll down hills, and heavy objects sink in water. Many of these expectations are present very early in life [1,2], whilst others emerge and evolve over the course of development [3]. It is easy to imagine that an ability to attend to causal regularities in the world, and to understand the forces underlying them, would have adaptive significance for many animal species. Whether animals do attend to causal regularities has been studied using various methodologies in different species (for review see [4]). Finding comparative tasks to assess how causal information is processed by different species can be difficult. Existing tasks are often tied to specific ecologically relevant behaviours such as tool use (e.g. [5,6]), involve face-to-face interactions with humans [7], or are too cognitively challenging to be attempted by more than a select few animals [8]
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