Feathers for escape: the transition from juvenile to adult in red-legged partridges (Alectoris rufa)

Abstract

Almost all birds use their fight feathers as a means of escaping predators, and their specific design is adapted to their individual circumstances. For example, Galliform birds use a fast, explosive, noisy takeoff to startle a predator. Their legs, wings and feathers must work together to create a strong propulsive force and loud, rhythmic sound. Partridges in a group initiate escape simultaneously, even though individuals in the flock differ in size and experience, as well as in age and sex resulting in feathers that differ in length and shape. In a long-term study, we measured 13 814 wild red-legged partridges (Alectoris rufa) to understand how variation in feather proportions and morphometrics between the age-sex classes relate to their escape abilities. We devised two new indexes to quantify the aerodynamic differences between age-sex classes. Our approach synthesizes the understanding of bird take-flight mechanics, feather proportions and the aerodynamic properties of wing tips to show how differences in feather length and tip shape characterize age-sex classes. Our findings suggest that the density, stiffness, permeability, size and shape of the distal primary feathers and wing tips can explain aerodynamic differences between individuals and the efficiency of groups in escape situations. ADDITIONAL KEYWORDS: distal primary feathers-feather tip-flock coordination-predator escape-takeoff-wing tip.

Body proportions for the facilitation of walking, running and flying: the case of partridges

“…As a consequence, changes in species proportions [ 54 ] and increasing potential to escape predation [ 55 ] could condition survival. Wing models in age-sex classes of partridges were better linked to juvenile females than other age-classes, because juvenile females have less mass and a larger surface/mass index than the other age-sex classes [ 39 ]. Thus, females have a better conformation than males, and juveniles than adults, for flying but not for walking-running; for walking-running, males and adults have an advantage due to their larger size [ 47 ].…”

“…1 ). In previous studies we found scaling between mass and body length, wing length [ 38 ], 8th, 9th 10th feather length, and surface index (body length x wing length) [ 39 ], with bivariate approximations of multivariate phenomena. Scaling reflects physical constraints and natural selection based on a conflict between terrestrial and aerial locomotion due to multiobjective optimization [ 11 ] of body structure.…”

Age-Related Variation in Wing Shape Differs between Bird Orders: Implications for Interpretation of the Pointedness Index (C2 Axis) in a Size-Constrained Principal Component Analysis (SCCA)

“…Among the few studies that have assessed variation between age classes in wing shape in nonpasserine birds, one carried out on western Sandpipers Calidris mauri (Charadriiformes), a migratory species, found the same pattern as in passerines, with juveniles having more rounded wings than adults (Fernández & Lank, 2007). In turn, two other studies, of Red-Legged Partridges Alectoris rufa (Galliformes, sedentary) and European Turtle Doves Streptopelia turtur (Columbiformes, migratory) found the opposite pattern (nadal et al, 2017;Cabodevilla et al, 2018). This illustrates that the pattern of wing shape differences between juvenile and adult passerines cannot be generalised to all species and bird orders.…”

“…The most important variable that makes this heterogeneity possible is wing shape (Hickman et al, 2008). wing morphology is directly linked to bird activity and behaviour (del Hoyo et al, 1997;Lockwood et al, 1998;Burns & ydenberg, 2002;Swaddle & Lockwood, 2003) and thus provides information about the relative importance of different activities and behaviours in the life of birds (Pérez-Tris & Tellería, 2001;nadal et al, 2017;Cabodevilla et al, 2018).…”

“…These are, indeed, two ends of the spectrum of variation in wing shape design: high aspect ratio wings (pointed and concave), typical of long-distance migrants and elliptical wings (rounded and convex), typical of sedentary, terrestrial and forest birds. Differences in wing shape may occur not only between different species or populations of the same species with contrasting migratory regimes (Pérez-Tris & Tellería, 2001), but also between ages and sexes of the same species and populations (Alatalo et al, 1984;Fernández & Lank, 2007;Green et al, 2009;nadal et al, 2017). For instance, juvenile passerines usually have more rounded wings than adults (Alatalo et al, 1984;Milá et al, 2008, Green et al, 2009, de la Hera et al, 2014, which aids first flights, improving survival chances early in life (Alatalo et al, 1984;de la Hera et al, 2014).…”