Is Beak Morphology in Darwin's Finches Tuned to Loading Demands?

PLoS One. 2015 Jun 12;10(6):e0129479. doi: 10.1371/journal.pone.0129479. eCollection 2015.


One of nature's premier illustrations of adaptive evolution concerns the tight correspondence in birds between beak morphology and feeding behavior. In seed-crushing birds, beaks have been suggested to evolve at least in part to avoid fracture. Yet, we know little about mechanical relationships between beak shape, stress dissipation, and fracture avoidance. This study tests these relationships for Darwin's finches, a clade of birds renowned for their diversity in beak form and function. We obtained anatomical data from micro-CT scans and dissections, which in turn informed the construction of finite element models of the bony beak and rhamphotheca. Our models offer two new insights. First, engineering safety factors are found to range between 1 and 2.5 under natural loading conditions, with the lowest safety factors being observed in species with the highest bite forces. Second, size-scaled finite element (FE) models reveal a correspondence between inferred beak loading profiles and observed feeding strategies (e.g. edge-crushing versus tip-biting), with safety factors decreasing for base-crushers biting at the beak tip. Additionally, we identify significant correlations between safety factors, keratin thickness at bite locations, and beak aspect ratio (depth versus length). These lines of evidence together suggest that beak shape indeed evolves to resist feeding forces.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adaptation, Physiological
  • Animals
  • Beak / anatomy & histology*
  • Beak / physiology
  • Biological Evolution*
  • Finches / anatomy & histology
  • Finches / genetics*

Grant support

This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS- 0335765. CNS is part of the Faculty of Arts and Sciences at Harvard University. Financial support to this project was provided by the Research Foundation - Flanders (FWO) to JS, an interdisciplinary research grant of the special research fund of the University of Antwerp to PA, JD, AH, a PHC Tournesol project to AH, AG and DA, and JP was supported by NSF grant IBN-0347291. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.