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Friman SI, Elowe CR, Hao S, Mendez L, Ayala R, Brown I, Hagood C, Hedlund Y, Jackson D, Killi J, Orfanides G, Ozcan E, Ramirez J, Gerson AR, Breuer KS, Hedrick TL. It pays to follow the leader: Metabolic cost of flight is lower for trailing birds in small groups. Proc Natl Acad Sci U S A 2024; 121:e2319971121. [PMID: 38885375 PMCID: PMC11214060 DOI: 10.1073/pnas.2319971121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2023] [Accepted: 05/12/2024] [Indexed: 06/20/2024] Open
Abstract
Many bird species commonly aggregate in flocks for reasons ranging from predator defense to navigation. Available evidence suggests that certain types of flocks-the V and echelon formations of large birds-may provide a benefit that reduces the aerodynamic cost of flight, whereas cluster flocks typical of smaller birds may increase flight costs. However, metabolic flight costs have not been directly measured in any of these group flight contexts [Zhang and Lauder, J. Exp. Biol. 226, jeb245617 (2023)]. Here, we measured the energetic benefits of flight in small groups of two or three birds and the requirements for realizing those benefits, using metabolic energy expenditure and flight position measurements from European Starlings flying in a wind tunnel. The starlings continuously varied their relative position during flights but adopted a V formation motif on average, with a modal spanwise and streamwise spacing of [0.81, 0.91] wingspans. As measured via CO2 production, flight costs for follower birds were significantly reduced compared to their individual solo flight benchmarks. However, followers with more positional variability with respect to leaders did less well, even increasing their costs above solo flight. Thus, we directly demonstrate energetic costs and benefits for group flight followers in an experimental context amenable to further investigation of the underlying aerodynamics, wake interactions, and bird characteristics that produce these metabolic effects.
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Affiliation(s)
- Sonja I. Friman
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
| | - Cory R. Elowe
- Department of Biology, University of Massachusetts, Amherst, MA01003
| | - Siyang Hao
- Center for Fluid Mechanics, School of Engineering, Brown University, Providence, RI02912
| | - Laura Mendez
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
| | - Raul Ayala
- Center for Fluid Mechanics, School of Engineering, Brown University, Providence, RI02912
| | - Ian Brown
- Center for Fluid Mechanics, School of Engineering, Brown University, Providence, RI02912
| | - Caylan Hagood
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
| | - Yseult Hedlund
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
| | - Dayna Jackson
- Department of Physics, Howard University, Washington, DC20059
| | - Justin Killi
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
| | - Gabriella Orfanides
- Thomas H. Gosnell School of Life Sciences, Rochester Institute of Technology, Rochester, NY14623
| | - Evrim Ozcan
- Center for Fluid Mechanics, School of Engineering, Brown University, Providence, RI02912
| | - Jared Ramirez
- Department of Aerospace and Mechanical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA90089
| | | | - Kenneth S. Breuer
- Center for Fluid Mechanics, School of Engineering, Brown University, Providence, RI02912
| | - Tyson L. Hedrick
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC27599
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Zhang Y, Ko H, Calicchia MA, Ni R, Lauder GV. Collective movement of schooling fish reduces the costs of locomotion in turbulent conditions. PLoS Biol 2024; 22:e3002501. [PMID: 38843284 PMCID: PMC11156351 DOI: 10.1371/journal.pbio.3002501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Accepted: 04/18/2024] [Indexed: 06/09/2024] Open
Abstract
The ecological and evolutionary benefits of energy-saving in collective behaviors are rooted in the physical principles and physiological mechanisms underpinning animal locomotion. We propose a turbulence sheltering hypothesis that collective movements of fish schools in turbulent flow can reduce the total energetic cost of locomotion by shielding individuals from the perturbation of chaotic turbulent eddies. We test this hypothesis by quantifying energetics and kinematics in schools of giant danio (Devario aequipinnatus) and compared that to solitary individuals swimming under laminar and turbulent conditions over a wide speed range. We discovered that, when swimming at high speeds and high turbulence levels, fish schools reduced their total energy expenditure (TEE, both aerobic and anaerobic energy) by 63% to 79% compared to solitary fish (e.g., 228 versus 48 kj kg-1). Solitary individuals spend approximately 22% more kinematic effort (tail beat amplitude•frequency: 1.7 versus 1.4 BL s-1) to swim in turbulence at higher speeds than in laminar conditions. Fish schools swimming in turbulence reduced their three-dimensional group volume by 41% to 68% (at higher speeds, approximately 103 versus 33 cm3) and did not alter their kinematic effort compared to laminar conditions. This substantial energy saving highlights that schooling behaviors can mitigate turbulent disturbances by sheltering fish (within schools) from the eddies of sufficient kinetic energy that can disrupt locomotor gaits. Therefore, providing a more desirable internal hydrodynamic environment could be one of the ecological drivers underlying collective behaviors in a dense fluid environment.
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Affiliation(s)
- Yangfan Zhang
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Hungtang Ko
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States of America
| | - Michael A. Calicchia
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, United States of America
| | - Rui Ni
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, United States of America
| | - George V. Lauder
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
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Zhang Y, Lauder GV. Energy conservation by collective movement in schooling fish. eLife 2024; 12:RP90352. [PMID: 38375853 PMCID: PMC10942612 DOI: 10.7554/elife.90352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024] Open
Abstract
Many animals moving through fluids exhibit highly coordinated group movement that is thought to reduce the cost of locomotion. However, direct energetic measurements demonstrating the energy-saving benefits of fluid-mediated collective movements remain elusive. By characterizing both aerobic and anaerobic metabolic energy contributions in schools of giant danio (Devario aequipinnatus), we discovered that fish schools have a concave upward shaped metabolism-speed curve, with a minimum metabolic cost at ~1 body length s-1. We demonstrate that fish schools reduce total energy expenditure (TEE) per tail beat by up to 56% compared to solitary fish. When reaching their maximum sustained swimming speed, fish swimming in schools had a 44% higher maximum aerobic performance and used 65% less non-aerobic energy compared to solitary individuals, which lowered the TEE and total cost of transport by up to 53%, near the lowest recorded for any aquatic organism. Fish in schools also recovered from exercise 43% faster than solitary fish. The non-aerobic energetic savings that occur when fish in schools actively swim at high speed can considerably improve both peak and repeated performance which is likely to be beneficial for evading predators. These energetic savings may underlie the prevalence of coordinated group locomotion in fishes.
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Affiliation(s)
- Yangfan Zhang
- Department of Organismic and Evolutionary Biology, Harvard UniversityCambridgeUnited States
| | - George V Lauder
- Department of Organismic and Evolutionary Biology, Harvard UniversityCambridgeUnited States
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