Only a handful of bird species are known to use foraging tools in the wild. Amongst them, the New Caledonian crow (Corvus moneduloides) stands out with its sophisticated tool-making skills. 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. 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, 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, suggesting that their technical abilities arose convergently. This supports the idea that avian foraging tool use is facilitated by ecological conditions typical of islands, such as reduced competition for embedded prey and low predation risk. Our discovery creates exciting opportunities for comparative research on multiple tool-using and non-tool-using corvid species. Such work will in turn pave the way for replicated cross-taxonomic comparisons with the primate lineage, enabling valuable insights into the evolutionary origins of tool-using behaviour.

2For most avian species, social behaviour is critically important for survival and reproductive 21 success. Many social behaviours in birds are culturally transmitted, and as bird populations 22 decline across the globe, important elements of these behaviours may be lost. The Hawaiian 23 Crow or ´Alalā (Corvus hawaiiensis) is a socially complex avian species that is currently extinct 24 in the wild. As in other oscine passerines, vocalizations in the ´Alalā may be culturally 25 transmitted. We compared the vocal repertoire of three of the last four wild ´Alalā pairs from the 26 early 1990's to three current captive pairs on the Island of Hawaii to determine how acoustic 27 behaviour has been affected by changes in their social and physical environment. Over 18 hours 28 of recordings from wild breeding pairs were analysed and compared with 44 hours from captive 29 breeding pairs. Calls were placed into five putative behavioural categories: (1) Alarm, (2) 30 Territorial broadcast, (3) Aggression, (4) Submission, and (5) Courtship. There was little 31 difference in the overall number and diversity of call types among wild versus captive birds. 32 However, the repertoire was significantly different. Territorial broadcast calls, common 33 components of the wild repertoire, were absent from the captive repertoire. In addition, wild 34 birds had twice the number of alarm calls, and had a higher call rate than captive birds. Our 35 results show how socially learned behaviours may change over relatively short time periods for 36 an entire species. Understanding how the vocal repertoire and the functional context of 37 vocalizations change may provide useful information for ongoing efforts to reintroduce the 38 ´Alalā into the wild.39 40 41 42 43 3