1. Ecology
  2. Evolutionary Biology
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Alcids 'fly' at efficient Strouhal numbers in both air and water but vary stroke velocity and angle

  1. Anthony Lapsansky  Is a corresponding author
  2. Daniel Zatz
  3. Bret W Tobalske
  1. University of Montana, United States
  2. ZatzWorks Inc, United States
Research Article
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Cite this article as: eLife 2020;9:e55774 doi: 10.7554/eLife.55774


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.

Article and author information

Author details

  1. Anthony Lapsansky

    Department of Biological Sciences, University of Montana, Missoula, United States
    For correspondence
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7530-7830
  2. Daniel Zatz

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

    Department of Biological Sciences, University of Montana, Missoula, United States
    Competing interests
    No competing interests declared.


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.


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.

Reviewing Editor

  1. Richard Bomphrey, Royal Veterinary College University of London, United Kingdom

Publication history

  1. Received: February 5, 2020
  2. Accepted: June 20, 2020
  3. Accepted Manuscript published: June 30, 2020 (version 1)
  4. Version of Record published: July 2, 2020 (version 2)


© 2020, Lapsansky 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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