Discovery of species-wide tool use in the Hawaiian crow

A species-wide study shows that the Hawaiian crow Corvus hawaiiensis is a highly proficient tool user, creating opportunities for comparative studies with tool-using New Caledonian crows and other corvids. Tool use in a second tropical crow species Birds in the crow family are renowned for their cognitive abilities. The New Caledonian crow Corvus moneduloides is well known for its ability to make and use foraging tools. Christian Rutz et al . show that it is not some lone outlier—it is now joined by another species from the Pacific, the Hawaiian crow Corvus hawaiiensis , better known by its indigenous Hawaiian name 'Alalā. These birds naturally develop tool-using skills when young, and proficient tool use is a species-wide capacity. The authors can say this with confidence as the 'Alalā is extinct in the wild, and they were able to test 104 of the 109 surviving members of the species at the time, all in captivity. The research suggests that the technological skills of tropical crows might be fostered by rather unusual ecological circumstances found on remote islands, such as reduced competition for embedded prey and low predation risk. The discovery of a second tool-using crow species opens up exciting opportunities for comparative studies on animal tool use. Only a handful of bird species are known to use foraging tools in the wild 1 . Amongst them, the New Caledonian crow ( Corvus moneduloides ) stands out with its sophisticated tool-making skills 2 , 3 . Despite considerable speculation, the evolutionary origins of this species’ remarkable tool behaviour remain largely unknown, not least because no naturally tool-using congeners have yet been identified that would enable informative comparisons 4 . Here we show that another tropical corvid, the ‘Alalā ( C. hawaiiensis ; Hawaiian crow), is a highly dexterous tool user. Although the ‘Alalā became extinct in the wild in the early 2000s, and currently survives only in captivity 5 , at least two lines of evidence suggest that tool use is part of the species’ natural behavioural repertoire: juveniles develop functional tool use without training, or social input from adults; and proficient tool use is a species-wide capacity. ‘Alalā and New Caledonian crows evolved in similar environments on remote tropical islands, yet are only distantly related 6 , suggesting that their technical abilities arose convergently. This supports the idea that avian foraging tool use is facilitated by ecological conditions typical