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

Abstract
Data availability
Article and author information
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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.

Data availability

All data needed to evaluate the conclusions presented in the paper are available on Dryad, https://doi.org/10.5061/dryad.73n5tb2vs.

The following data sets were generated

1. Hightower BJ
2. Wijnings PWA
3. Scholte R
4. Ingersoll R
5. Chin DD
6. Nguyen J
7. Shorr D
8. Lentink D
(2020) Data from: How Oscillating Aerodynamic Forces Explain the Timbre of the Hummingbird's Hum and Other Animals in Flapping Flight
Dryad Digital Repository, 10.5061/dryad.73n5tb2vs.

http://dx.doi.org/10.5061/dryad.73n5tb2vs

Article and author information

Author details

Ben J Hightower

Mechanical Engineering, Stanford University, Stanford, United States

Competing interests
No competing interests declared.
Patrick W A Wijnings

Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands

Competing interests
No competing interests declared.
Rick Scholte

Engineering, Sorama, Eindhoven, Netherlands

Competing interests
No competing interests declared.
Rivers Ingersoll

Mechanical Engineering, Stanford University, Stanford, United States

Competing interests
No competing interests declared.

"This ORCID iD identifies the author of this article:" 0000-0001-7194-0911
Diana D Chin

Mechanical Engineering, Stanford University, Stanford, United States

Competing interests
No competing interests declared.
Jade Nguyen

Mechanical Engineering, Stanford University, Stanford, United States

Competing interests
No competing interests declared.
Daniel Shorr

Mechanical Engineering, Stanford University, Stanford, United States

Competing interests
No competing interests declared.
David Lentink

Mechanical Engineering, Stanford University, Stanford, United States

For correspondence
dlentink@stanford.edu

Competing interests
David Lentink, Reviewing editor, eLife.

"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).

Copyright

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.