1. Evolutionary Biology
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How oscillating aerodynamic forces explain the timbre of the hummingbird’s hum and other animals in flapping flight

  1. Ben J Hightower
  2. Patrick W A Wijnings
  3. Rick Scholte
  4. Rivers Ingersoll
  5. Diana D Chin
  6. Jade Nguyen
  7. Daniel Shorr
  8. David Lentink  Is a corresponding author
  1. Stanford University, United States
  2. Eindhoven University of Technology, Netherlands
  3. Sorama, Netherlands
Research Article
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Cite this article as: eLife 2021;10:e63107 doi: 10.7554/eLife.63107

Abstract

How hummingbirds hum is not fully understood, but its biophysical origin is encoded in the acoustic nearfield. Hence, we studied six freely hovering Anna's hummingbirds, performing acoustic nearfield holography using a 2176 microphone array in vivo, while also directly measuring the 3D aerodynamic forces using a new aerodynamic force platform. We corroborate the acoustic measurements by developing an idealized acoustic model that integrates the aerodynamic forces with wing kinematics, which shows how the timbre of the hummingbird's hum arises from the oscillating lift and drag forces on each wing. Comparing birds and insects, we find that the characteristic humming timbre and radiated power of their flapping wings originates from the higher harmonics in the aerodynamic forces that support their bodyweight. Our model analysis across insects and birds shows that allometric deviation makes larger birds quieter and elongated flies louder, while also clarifying complex bioacoustic behavior.

Article and author information

Author details

  1. Ben J Hightower

    Mechanical Engineering, Stanford University, Stanford, United States
    Competing interests
    No competing interests declared.
  2. Patrick W A Wijnings

    Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
    Competing interests
    No competing interests declared.
  3. Rick Scholte

    Engineering, Sorama, Eindhoven, Netherlands
    Competing interests
    No competing interests declared.
  4. Rivers Ingersoll

    Mechanical Engineering, Stanford University, Stanford, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7194-0911
  5. Diana D Chin

    Mechanical Engineering, Stanford University, Stanford, United States
    Competing interests
    No competing interests declared.
  6. Jade Nguyen

    Mechanical Engineering, Stanford University, Stanford, United States
    Competing interests
    No competing interests declared.
  7. Daniel Shorr

    Mechanical Engineering, Stanford University, Stanford, United States
    Competing interests
    No competing interests declared.
  8. David Lentink

    Mechanical Engineering, Stanford University, Stanford, United States
    For correspondence
    dlentink@stanford.edu
    Competing interests
    David Lentink, Reviewing editor, eLife.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4717-6815

Funding

National Science Foundation (Faculty Early Career Development (CAREER) Award,1552419)

  • David Lentink

National Science Foundation (Graduate Research Fellowship)

  • Ben J Hightower

Stanford University (Stanford Graduate Fellowship)

  • Ben J Hightower

Netherlands Organisation for Scientific Research (Research Program ZERO (P15-06))

  • Patrick W A Wijnings

Stanford University (Stanford Graduate Fellowship)

  • Diana D Chin

National Defense Science and Engineering Graduate (Graduate Fellowship)

  • Diana D Chin

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: All bird training and experimental procedures were approved by Stanford's Administrative Panel on Laboratory Animal Care (APLAC-31426).

Reviewing Editor

  1. Gordon J Berman, Emory University, United States

Publication history

  1. Received: September 15, 2020
  2. Accepted: February 28, 2021
  3. Accepted Manuscript published: March 16, 2021 (version 1)

Copyright

© 2021, Hightower et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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