title: How do birds' tails work? Delta-wing theory fails to predict tail shape during flight.
abstract: Birds appear to use their tails during flight, but until recently the aerodynamic role that tails fulfil was largely unknown. In recent years delta-wing theory, devised to predict the aerodynamics of high-performance aircraft, has been applied to the tails of birds and has been successful in providing a model for the aerodynamics of a bird's tail. This theory now provides the conventional explanation for how birds' tails work. A delta-wing theory (slender-wing theory) has been used, as part of a variable-geometry model to predict how tail and wing shape should vary during flight at different airspeeds. We tested these predictions using barn swallows flying in a wind tunnel. We show that the predictions are not quantitatively well supported. This suggests that a new theory or a modified version of delta-wing theory is needed to adequately explain the way in which morphology varies during flight.
authors.affiliation: Department of Biological Sciences, University of Stirling, Stirling FK9 4LA, UK. mre2@stir.ac.uk
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Evans
authors.forename: Mikael
authors.initials: M
authors.lastname: Rosén
authors.forename: Kirsty J
authors.initials: KJ
authors.lastname: Park
authors.forename: Anders
authors.initials: A
authors.lastname: Hedenström
mesh_terms: D000818:Animals; D005426:Flight, Animal / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D020308:Songbirds / Q000033:anatomy & histology* / Q000502:physiology*; D013623:Tail / Q000502:physiology*; D014921:Wings, Animal / Q000502:physiology*