Kinematics of turning maneuvers in the southern flying squirrel,Glaucomys volans

Abstract

The ability to change direction is essential to any animal that moves around in a complex, 3D environment. In this study we present the first 3D description of body positions during gliding turns in a mammalian gliding specialist, the southern flying squirrel, Glaucomys volans. In addition, we used these kinematic data to estimate the aerodynamic forces generated by the animals and rotational velocities and accelerations of the body while turning. These results were compared with similar measurements of flying squirrels during straight glides. The two individuals used in this study differed significantly in limb position asymmetries between the two sides of their bodies and also were significantly different in measures of turning performance. The individual with better performance used limb positions consistent with a primarily lift-based turning mechanism (banked turn), whereas the individual with poorer performance used limb positions consistent with a primarily drag-based turning mechanism (crabbed turn). Both individuals employed limb movements continuously through the gliding turn, but these movements did not have any consistent relationships with body rotations or lateral acceleration. As compared with straight glides, squirrels used significantly higher angles of attack and had lower lift-to-drag ratios, but did not differ in glide angle. Contrary to the typical view of maneuvering during gliding as a simple, static form of locomotion, the results presented here indicate that mammalian gliding is a complex behavior comprising the interplay of many components of limb position and wing shape that affect the balance of forces that control the turn.

How animals glide: from trajectory to morphology

“…This framework is often considered when discussing animal gliders, but the picture that is emerging from recent studies is that gliders are often not in equilibrium during flight , Bishop 2006, 2007, Bishop and Brim-DeForest 2008, Byrnes et al 2008, McGuire and Dudley 2005, Socha 2002; in fact, unsteady gliding may be advantageous for shorter glides (Willis et al 2011). There are at least two reasons why gliders are rarely observed in equilibrium.…”

“…For example, lowering or raising the limbs with respect to the body alters the dihedral/anhedral angle and thereby affects roll stability. Such postural adjustments allow for a stable configuration in straight glides, but a more unstable and thus maneuverable configuration to produce turns (Bishop and Brim-DeForest 2008). Altering limb position can also be used to change the angle of attack of the wing (Bishop 2006(Bishop , 2007.…”

“…These studies have tracked the two-or three-dimensional position of the glider (e.g., Fig. 4) throughout the entire trajectory (McGuire and , Socha 2002 or part of the trajectory , Bishop 2006, 2007, Bishop and Brim-DeForest 2008). In some of these studies, multiple parts of the anatomy were tracked, enabling further analysis of body posture and orientation (Bishop 2006, 2007, Bishop and Brim-DeForest 2008.…”

“…By abducting or adducting the forelimbs, the center of pressure of the wing can be shifted anteriorly or posteriorly with respect to the center of mass of the animal as a means of controlling pitch angle during flight (Bishop 2006(Bishop , 2007 or landing (Byrnes, unpublished data). In addition, any left-right asymmetries in the position of the limbs can result in turning moments about the roll or yaw axes that can be useful for flight maneuvers (Bishop and Brim-DeForest 2008).…”

Kinematics of slow turn maneuvering in the fruit batCynopterus brachyotis

“…They have been described for organisms as diverse as fruit flies (Fry et al, 2003), locusts (Berger and Kutsch, 2003), dragonflies (Alexander, 1986), gliding frogs (McCay, 2001) gliding mammals (Bishop and Turning kinematics of fruit bats Brim-DeForest, 2008) and birds . However, crabbed turns are also phylogenetically widespread having been described in some dipterans (see Dudley, 2002), dragonflies (Alexander, 1986), gliding frogs (McCay, 2001) and gliding mammals (Bishop and BrimDeForest, 2008).…”