TY - JOUR

T1 - Repeated evolution of drag reduction at the air-water interface in diving kingfishers

AU - Crandell, K. E.

AU - Howe, R. O.

AU - Falkingham, P.L.

N1 - Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9. figshare.c.4486739.

PY - 2019/5/31

Y1 - 2019/5/31

N2 - Piscivorous birds have a unique suite of adaptations to forage under the water. One method aerial birds use to catch fish is the plunge dive, wherein birds dive from a height to overcome drag and buoyancy in the water. The kingfishers are a well-known clade that contains both terrestrially foraging and plunge-diving species, allowing us to test for morphological and performance differences between foraging guilds in an evolutionary context. Diving species have narrower bills in the dorsoventral and sagittal plane and longer bills (size-corrected data, n = 71 species, p < 0.01 for all). Although these differences are confounded by phylogeny (phylogenetically corrected ANOVA for dorsoventral p = 0.26 and length p = 0.14), beak width in the sagittal plane remains statistically different (p < 0.001). We examined the effects of beak morphology on plunge performance by physically simulating dives with three-dimensional printed models of beaks coupled with an accelerometer, and through computational fluid dynamics (CFD). From physically simulated dives of bill models, diving species have lower peak decelerations, and thus enter the water more quickly, than terrestrial and mixed-foraging species (ANOVA p = 0.002), and this result remains unaffected by phylogeny (phylogenetically corrected ANOVA p = 0.05). CFD analyses confirm these trends in three representative species and indicate that the morphology between the beak and head is a key site for reducing drag in aquatic species.

AB - Piscivorous birds have a unique suite of adaptations to forage under the water. One method aerial birds use to catch fish is the plunge dive, wherein birds dive from a height to overcome drag and buoyancy in the water. The kingfishers are a well-known clade that contains both terrestrially foraging and plunge-diving species, allowing us to test for morphological and performance differences between foraging guilds in an evolutionary context. Diving species have narrower bills in the dorsoventral and sagittal plane and longer bills (size-corrected data, n = 71 species, p < 0.01 for all). Although these differences are confounded by phylogeny (phylogenetically corrected ANOVA for dorsoventral p = 0.26 and length p = 0.14), beak width in the sagittal plane remains statistically different (p < 0.001). We examined the effects of beak morphology on plunge performance by physically simulating dives with three-dimensional printed models of beaks coupled with an accelerometer, and through computational fluid dynamics (CFD). From physically simulated dives of bill models, diving species have lower peak decelerations, and thus enter the water more quickly, than terrestrial and mixed-foraging species (ANOVA p = 0.002), and this result remains unaffected by phylogeny (phylogenetically corrected ANOVA p = 0.05). CFD analyses confirm these trends in three representative species and indicate that the morphology between the beak and head is a key site for reducing drag in aquatic species.

KW - Alcedinidae

KW - avian hydrodynamics

KW - beak

KW - bow wave

KW - plunge diving

UR - https://dx.doi.org/10.6084/m9.figshare.c.4486739

U2 - 10.1098/rsif.2019.0125

DO - 10.1098/rsif.2019.0125

M3 - Article

VL - 16

JO - Journal of the Royal Society: Interface

JF - Journal of the Royal Society: Interface

SN - 1742-5662

M1 - 20190125

ER -