Tools and Brains in Birds

Abstract

Tools are traditionally de ned as objects that are used as an extension of the body and held directly in the hand or mouth. By these standards, a vulture breaking an egg by hitting it with a stone uses a tool, but a gull dropping an egg on a rock does not. This distinction between true and borderline (or proto-tool) cases has been criticized for its arbitrariness and anthropocentrism. We show here that relative size of the neostriatum and whole brain distinguish the true and borderline categories in birds using tools to obtain food or water. From two sources, the specialized literature on tools and an innovation data base gathered in the short note sections of 68 journals in 7 areas of the world, we collected 39 true (e.g. use of probes, hammers, sponges, scoops) and 86 borderline (e.g. bait shing, battering and dropping on anvils, holding with wedges and skewers) cases of tool use in 104 species from 15 parvorders. True tool users have a larger mean residual brain size (regressed against body weight) than do users of borderline tools, con rming the distinction in the literature. In multiple regressions, residual brain size and residual size of the neostriatum (one of the areas in the avian telencephalon thought to be equivalent to the mammalian neocortex) are the best predictors of true tool use reports per taxon. Innovation rate is the best predictor of borderline tool use distribution. Despite the strong concentration of true tool use cases in Corvida and Passerida, independent constrasts suggest that common ancestry is not responsible for the association between tool use and size of the neostriatum and whole brain. Our results demonstrate that birds are more frequent tool users than usually thought and that the complex 1) Corresponding authors's e-mail address: louis.lefebvre@mcgill.ca 3) Current address: Ecole d'Optométrie, Université de Montréal. 4) We are grateful to Simon Reader for comments on earlier versions and to Sarah Timmermans for alerting us to the existence of Mlikovsky's data. We also thank Simran Kurir, Yutaka Nishioka and Johan Bolhuis for help with the German, Japanese and Dutchlanguage papers. This work was funded by an NSERC grant to LL and an FCAR fellowship to NN. © Koninklijke Brill NV, Leiden, 2002 Behaviour 139, 939-973 Also available online -940 LEFEBVRE, NICOLAKAKIS & BOIREcognitive processes involved in tool use may have repeatedly co-evolved with large brains in several orders of birds.

The evolution of primate general and cultural intelligence

“…Species differences in general intelligence are likely to extend beyond primates. For example, rooks Corvus frugilegus, members of the large-brained and behaviourally flexible corvid parvorder [37], use tools in captivity but apparently not in the wild [62,63], a finding consistent with the idea that such tool use can result from a generalized cognitive ability.…”

Sperm competition and sexually size dimorphic brains in birds

“…Previous studies have shown that the frequency of feeding innovations is correlated with forebrain size in birds (Lefebvre et al 1997). This result has been extended to include the anatomical correlates of tool use and nesting innovation (Nicolakakis & Lefebvre 2000;Lefebvre et al 2002). Feeding innovations may have ecological implications because introduction success of birds to New Zealand can be predicted by their frequency (Sol & Lefebvre 2000).…”

Diversification and cumulative evolution in New Caledonian crow tool manufacture

“…In both birds and primates there has been progressive encephalization of the brain in areas that seem to deal with so-called 'intelligent' behaviour . This brain specialization is associated with innovation, social intelligence and tool use (Lefebvre et al 2002;Reader & Laland 2002). Corvus species in particular have relatively large avian brains (Portmann 1947;Lefebvre et al 2002) and are renowned for their considerable social learning abilities (Fritz & Kotrschal 1999;Heinrich 1999) and innovative behaviour (Lefebvre et al 1997(Lefebvre et al , 2002.…”