Alcids 'fly' at efficient Strouhal numbers in both air and water but vary stroke velocity and angle

Abstract
Data availability
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Abstract

Birds that use their wings for 'flight' in both air and water are expected to fly poorly in each fluid relative to single-fluid specialists; i.e., these jacks-of-all-trades should be the masters of none. Alcids exhibit exceptional dive performance while retaining aerial flight. We hypothesized that alcids maintain efficient Strouhal numbers and stroke velocities across air and water, allowing them to mitigate the costs of their 'fluid generalism'. We show that alcids cruise at Strouhal numbers between 0.10 and 0.40 – on par with single-fluid specialists – in both air and water but flap their wings ~50% slower in water. Thus, these species either contract their muscles at inefficient velocities or maintain a two-geared muscle system, highlighting a clear cost to using the same morphology for locomotion in two fluids. Additionally, alcids varied stroke-plane angle between air and water and chord angle during aquatic flight, expanding their performance envelope.

Data availability

All data are available at the following link: https://github.com/alapsansky/Lapsansky_Zatz_Tobalske_eLife_2020

The following previously published data sets were used

1. Taylor
2. Nudds
3. Thomas
(2003) Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency
www.nature.com.

https://www.nature.com/articles/nature02000

Article and author information

Author details

Anthony Lapsansky

Department of Biological Sciences, University of Montana, Missoula, United States

For correspondence
anthony.lapsansky@umontana.edu

Competing interests
No competing interests declared.

"This ORCID iD identifies the author of this article:" 0000-0001-7530-7830
Daniel Zatz

ZatzWorks Inc, Homer, United States

Competing interests
Daniel Zatz, is affiliated with ZatzWorks Inc. The author has no financial interests to declare.
Bret W Tobalske

Department of Biological Sciences, University of Montana, Missoula, United States

Competing interests
No competing interests declared.

Funding

National Science Foundation (EFRI 1935216)

Bret W Tobalske

National Science Foundation (CMMI 1234737)

Bret W Tobalske

Drollinger-Dial Family Charitable Foundation (NA)

Anthony Lapsansky

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 work was approved by the University of Montana's Institutional Animal Care and Use Committee (AUP 004-19BTDBS-020419). Work at the Alaska SeaLife Center was performed with approval from the animal husbandry and research staff.

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.