Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows.

Hiroshi Matsui,Kevin J Mcgowan,Naomichi Ogihara,Gavin R Hunt,Takeshi Yamasaki,Kumar Mithraratne,Ei-Ichi Izawa,Russell D Gray,Katja Oberhofer

doi:10.1038/srep22776

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.

Highlights

Human tool behaviour is underpinned by adaptations associated with enhanced manipulation of tools and tool material
A potential morphological adaptation associated with the NCC’s tool behaviour is the shape of its bill, which is noticeably straight for a Corvus species[15,16]
There has been no in-depth study of the shape and internal structure of its bill to examine if it has been adapted for tool manipulation

Summary

Introduction

Human tool behaviour is underpinned by adaptations associated with enhanced manipulation of tools and tool material. The species-level tool lifestyle[5], the genetic disposition for basic tool skills[13,14], the dexterity of tool making and use and the complexity of tool designs together suggest that the NCC’s tool behaviour has evolved over a very long period of time. A potential morphological adaptation associated with the NCC’s tool behaviour is the shape of its bill, which is noticeably straight for a Corvus species[15,16]. In the second part of the study we compared the internal structure and cross-sectional shape of the NCC’s bill and two other Corvus species with different foraging behaviour (the rook C. frugilegus and the large-billed crow C. macrorhynchos) based on Computed Tomography images

Methods

Results

Conclusion