Alcids ‘fly’ at efficient Strouhal numbers in both air and water but vary stroke velocity and angle
- Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, United States
- ZatzWorks Inc, United States
Figures
Figure 1
Measurements of stroke-plane angle (β) and chord angle (∝).
The wings drawn with the thin black line indicate the position at the start of downstroke in air (top) and water (bottom, with blue shading). The wings drawn with the dashed line indicate the position at the end of downstroke in air and water. β was measured using the wingtip in aerial flight and the wrist in aquatic flight. ∝ was measured at mid-upstroke and mid-downstroke (wing drawn with thick black line) during aquatic flight.
Figure 2
Strouhal numbers (St) of four species of alcid in aerial and aquatic flight.
Each hatch mark on the x-axis indicates a unique flight. The darker shaded section indicates 0.2 < St < 0.4, in which propulsive efficiency is predicted to peak, and the lighter shaded region indicates 0.12 < St < 0.47, which is the range of St exhibited during cruising flight of strictly aerial birds reported in Taylor et al., 2003. Points indicate St for horizontal aquatic flights (blue), descending aquatic flights (green), aerial flights based on ground speed (dark red), and aerial flights calculated using the range of cruising speeds of that species reported in the literature (light red). Each flight is represented by the mean St for that flight ± s.d., except for St calculated for aerial flights based on airspeed, for which we chose not to indicate a central tendency.
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Figure 2—source data 1
Strouhal numbers of four species of alcid in aerial and aquatic flight.
- https://cdn.elifesciences.org/articles/55774/elife-55774-fig2-data1-v2.xlsx
Figure 3
Stroke velocities of four species of alcid in aerial and aquatic flight.
Stroke velocity was significantly greater during aerial flights (red) than during aquatic flights (blue) for each of the four species for both downstroke (t-Value = 8.10, 11.5, 6.04, 25.9; df = 16.5, 19.0, 9.48, 16.5; p-values = 3.80e-07, 5.19e-10, 1.55e-04, 8.56e-15; for species in alphabetical order) and upstroke (t-Value = 10.5, 16.0, 6.83, 26.4; df = 15.0, 18.8, 9.18, 16.1; p-values = 2.67e-08, 2.13e-12, 6.97e-05, 1.09e-14; for species in alphabetical order). The central line in each box marks the median, while the upper and lower margins of the box indicate the quartile range. The entire range of values lie between the whiskers.
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Figure 3—source data 1
Stroke velocities of four species of alcid in aerial and aquatic flight.
- https://cdn.elifesciences.org/articles/55774/elife-55774-fig3-data1-v2.xlsx
Figure 4
Wingbeat amplitude and frequency of four species of alcid in aerial and aquatic flight.
Artwork by Emily Moore
Figure 5
Stroke-plane angle (β) of four species of alcid in aerial and aquatic flight.
β was significantly lower (the top of the stroke plane was rotated more caudally) during aerial flights relative to aquatic flights (F1,47 = 41.3, η2 = 0.422, p = 6.14e-08). Within aquatic flights, there was no consistent relationship between β and the angle of descent (F1,27 = 0.0755, η2 = 0.002, p = 0.786). Jitter was added to the points representing aerial flights and horizontal aquatic flights (descent angle = 0) to increase visibility.
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Figure 5—source data 1
Stroke-plane angle of four species of alcid in aerial and aquatic flight.
- https://cdn.elifesciences.org/articles/55774/elife-55774-fig5-data1-v2.xlsx
Figure 6
Chord angle (α) versus descent angle for aquatic flights of four species of alcids.
α increased with the angle of descent for upstroke (F1,30 = 55.7, η2 = 0.458, p = 2.55e-08) and downstroke (F1,27 = 8.17, η2 = 0.122, p = 8.11e-03). However, a significant crossed interaction between species and angle of descent for downstroke chord angle (F3,27 = 7.68, η2 = 0.343, p = 7.26e-4), indicates that the main effect of angle of descent on chord angle during downstroke is uninterpretable (i.e. the response depends on the species). Jitter was added to the points representing horizontal aquatic flights (descent angle = 0) to make all points visible.
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Figure 6—source data 1
Chord angle versus descent angle for aquatic flights of four species of alcids.
- https://cdn.elifesciences.org/articles/55774/elife-55774-fig6-data1-v2.xlsx
Videos
Video 1
Aerial and aquatic flight of the Common murre, Uria aalge.
Additional files
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Supplementary file 1
Average culmen length, asset numbers, and calculated body length during flight for each of four species of alcid.
Calculated body lengths were used to convert from units of species-specific body length to metric units. Average culmen length was calculated as the mean of all values present in the Birds of North America entry (Rodewald, 2015) for adult birds (males and females) of that species. Multiple birds were digitized in some photographs. See Materials and methods for details.
- https://cdn.elifesciences.org/articles/55774/elife-55774-supp1-v2.docx
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Transparent reporting form
- https://cdn.elifesciences.org/articles/55774/elife-55774-transrepform-v2.docx
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Alcids ‘fly’ at efficient Strouhal numbers in both air and water but vary stroke velocity and angle
eLife 9:e55774.
https://doi.org/10.7554/eLife.55774
