title: Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows.
abstract: Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow's bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii) a strong precision grip to hold tools securely, and (iii) enhanced visually-guided tool use. Our findings indicate that the New Caledonian crow's innovative bill has been adapted for tool manipulation to at least some degree. Early increased sophistication of tools may require the co-evolution of morphology that provides improved manipulatory skills.
authors.affiliation: Department of Psychology, Keio University, Tokyo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsui
authors.affiliation: School of Psychology, University of Auckland, Auckland, New Zealand.
authors.forename: Gavin R
authors.initials: GR
authors.lastname: Hunt
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Katja
authors.initials: K
authors.lastname: Oberhofer
authors.affiliation: Department of Mechanical Engineering, Keio University, Yokohama, Japan.
authors.forename: Naomichi
authors.initials: N
authors.lastname: Ogihara
authors.affiliation: Cornell Lab of Ornithology, Ithaca, New York, USA.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: McGowan
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Kumar
authors.initials: K
authors.lastname: Mithraratne
authors.affiliation: Yamashina Institute for Ornithology, Abiko, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamasaki
authors.affiliation: School of Psychology, University of Auckland, Auckland, New Zealand.|Max Planck Institute for the Science of Human History, Jena, Germany.
authors.forename: Russell D
authors.initials: RD
authors.lastname: Gray
authors.affiliation: Department of Psychology, Keio University, Tokyo, Japan.
authors.forename: Ei-Ichi
authors.initials: E
authors.lastname: Izawa
mesh_terms: D000818:Animals; D001502:Beak / Q000033:anatomy & histology*; D001522:Behavior, Animal; D005075:Biological Evolution; D046368:Crows / Q000033:anatomy & histology* / Q000502:physiology*; D025341:Principal Component Analysis; D014057:Tomography, X-Ray Computed; D053001:Tool Use Behavior