title: Rachis morphology cannot accurately predict the mechanical performance of primary feathers in extant (and therefore fossil) feathered flyers.
abstract: It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Central to the idea is the unvalidated assumption that the strength of a primary flight feather (i.e. its material and structural properties) may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils. Here, using three-point bending tests, the relationship between feather structural properties (maximum bending moment,Mmaxand Young's modulus,Ebend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from four species of bird of differing flight style was investigated. Intraspecifically, bothEbendandMmaxwere strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Without accounting for species, however, external morphology was a poor predictor of rachis structural properties, meaning that precise determination of aerial performance in extinct, feathered species from external rachis dimensions alone is not possible. Even if it were possible to calculate the second moment of area of the rachis, our data suggest that feather strength could still not be reliably estimated.
authors.affiliation: Faculty of Life Sciences , University of Manchester , Manchester M13 9PT , UK.
authors.forename: John
authors.identifier: 0000-0002-9627-1790
authors.initials: J
authors.lastname: Lees
authors.affiliation: Faculty of Life Sciences , University of Manchester , Manchester M13 9PT , UK.
authors.forename: Terence
authors.initials: T
authors.lastname: Garner
authors.affiliation: School of Mechanical, Aerospace and Civil Engineering , University of Manchester , Manchester M13 9PL , UK.
authors.forename: Glen
authors.initials: G
authors.lastname: Cooper
authors.affiliation: Faculty of Life Sciences , University of Manchester , Manchester M13 9PT , UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Nudds
keywords: birds; primary feathers; safety factors; structural properties