The social structure of New Caledonian crows

New Caledonian (NC) crows, Corvus moneduloides, have impressive tool-manufacturing and tool-using skills in the wild, and captive birds have displayed exceptional cognitive abilities in experimental situations. However, their social system is largely unknown. In this study we investigated whether the social structure of NC crows might have had a role in the development of their cognitive skills. We observed crows in their natural habitat on the island of Mare, New Caledonia, and estimated their social network size based on tolerance to family and nonfamily crows at feeding tables. Our findings suggest that NC crows are not a highly social corvid species. Their core unit was the immediate family consisting of a pair and juveniles from up to two consecutive breeding years. Pairs stayed together year round, and were closely accompanied by juveniles during their first year of life. Parents were highly tolerant of juveniles and sometimes continued to feed them well into their second year. NC crows predominantly shared feeding tables with immediate family. Of the nonfamily crows tolerated, juveniles were overrepresented. The main mechanism for any social transmission of foraging skills is likely to be vertical (from parents to offspring), with only limited opportunity for horizontal transmission. The social organization we found on Mare is consistent with the idea that NC crows' multiple pandanus tool designs on mainland Grande Terre are an example of cumulative technological evolution. (c) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.