Study of the cognition and its neural substrate in New Caledonian crows

Abstract

New Caledonian crows are renowned for their impressive tool culture in the wild and their advanced problem-solving skills in captivity. In toto, this suggests that their complex behaviour is based on flexible cognition. In this thesis, I combine research methods and tools from the fields of experimental and evolutionary psychology and neuroscience to investigate the cognitive abilities and neuroanatomy of the NC crow. In the first part of this work, I carried out two experiments to show that NC crows’ cognition is indeed flexible, as had been inferred. In the first such study on wild-caught NC crows, I presented birds with a vertical mirror to investigate their mirror-induced responses. I also gave the NC crows a mirror-mediated spatial location task with a horizontal mirror to assess whether they could learn to use the mirror to locate visually displaced objects. The NC crows were able to exploit the correlation between an object’s image in the mirror and its location in the real world, in spite of their continuing agonistic social behaviour in front of vertical mirrors. In the second experiment, I gave NC crows a novel visually-restricted string pulling task to test between two alternative mechanisms behind avian spontaneous string pulling: visual reinforcement-independent insight and visual reinforcement-dependent operant conditioning. This study demonstrated the limitations of using visually-restricted string-pulling tasks to distinguish between insight and operant conditioning. The findings of these experiments support the view that the NC crow’s impressive cognitive abilities extend beyond their tool use. The second part of this thesis presents the first detailed gross neuroanatomical and cytoarchitectural study of the NC crow’s telencephalon, along with the first brain atlas for this species. This research challenged previous claims that NC crows are a highly encephalised species and that their complex cognition is linked to enlargement of associative regions such as the mesopallium or increased foliation of the cerebellum. I also found no relationship between gross neuroanatomical interhemispheric asymmetries and eye dominance associated with lateralized tool holding. Last but not least, I describe the potentially important discovery of clusters of perineuronal satellite oligodendroglia in the telencephala of healthy NC crows and other passerine birds. In humans, reduced numbers of these clusters is linked to psychiatric disorders and schizophrenia. I conclude by proposing that the slow development and prolonged parental care observed in NC crows, and the general evolutionary cephalisation process in corvids, have combined to forge a brain-mind capable of extraordinary feats.