JEB desktop wallpaper calendar 2016

JEB desktop wallpaper calendar 2016

Ontogeny of lift and drag production in ground birds
Ashley M. Heers, Bret W. Tobalske, Kenneth P. Dial

SUMMARY

The juvenile period is often a crucial interval for selective pressure on locomotor ability. Although flight is central to avian biology, little is known about factors that limit flight performance during development. To improve understanding of flight ontogeny, we used a propeller (revolving wing) model to test how wing shape and feather structure influence aerodynamic performance during development in the precocial chukar partridge (Alectoris chukar, 4 to >100 days post hatching). We spun wings in mid-downstroke posture and measured lift (L) and drag (D) using a force plate upon which the propeller assembly was mounted. Our findings demonstrate a clear relationship between feather morphology and aerodynamic performance. Independent of size and velocity, older wings with stiffer and more asymmetrical feathers, high numbers of barbicels and a high degree of overlap between barbules generate greater L and L:D ratios than younger wings with flexible, relatively symmetrical and less cohesive feathers. The gradual transition from immature feathers and drag-based performance to more mature feathers and lift-based performance appears to coincide with ontogenetic transitions in locomotor capacity. Younger birds engage in behaviors that require little aerodynamic force and that allow D to contribute to weight support, whereas older birds may expand their behavioral repertoire by flapping with higher tip velocities and generating greater L. Incipient wings are, therefore, uniquely but immediately functional and provide flight-incapable juveniles with access to three-dimensional environments and refugia. Such access may have conferred selective advantages to theropods with protowings during the evolution of avian flight.

FOOTNOTES

  • Supplementary material available online at http://jeb.biologists.org/cgi/content/full/214/5/717/DC1

  • We would like to thank Terry Dial, Brandon Jackson and Kristen Crandell for their assistance and suggestions. Images, electron microscopy services and resources were provided by the Electron Microscopy Facility, Division of Biological Sciences, University of Montana, Missoula, MT, USA. The EM Facility is supported, in part, by grant no. RR-16455-04 from the National Center for Research Resources (Biomedical Research Infrastructure Network program), National Institutes of Health. Supported by NSF grants GRFP-2007057068, IOS-0923606 and IOS-0919799. Deposited in PMC for release after 12 months.

  • LIST OF SYMBOLS AND ABBREVIATIONS

    A
    cross-sectional area of the wake
    CD
    coefficient of profile drag
    CH
    coefficient of horizontal force
    CL
    coefficient of lift
    CV
    coefficient of vertical force
    d.p.h.
    days post hatching
    D
    profile drag
    E
    Young's modulus
    EI
    flexural stiffness
    Fa
    applied force
    FH
    horizontal force
    FV
    vertical force
    I
    second moment of area
    l
    effective beam length
    L
    lift
    PIV
    particle image velocimetry
    Q
    torque
    Re
    Reynolds number
    S
    surface area
    S2
    second moment of area
    S3
    third moment of area
    v
    vertical velocity
    α
    active (aerodynamically loaded) angle of attack
    δ
    feather displacement at point of force application
    ϵ
    downwash angle
    ρ
    air density
    Ω
    angular velocity of wing
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