Meeting Abstract

39.2  Jan. 6  Scaling theory and locomotor performance: the most speciose clade of birds fails to conform JACKSON, B.E.*; DIAL, K.P.; Univ. of Montana; Univ. of Montana brandon.jackson@mso.umt.edu

Allometric predictions of locomotor performance are often based on the scaling of a few morphological or physiological variables and rarely validated by actual measurements of performance. The prominent hypothesis for the negative scaling of avian burst-flight performance (e.g. peak acceleration) suggests that a single variable (wing length) explains size-dependent performance (mechanical power output) via decreasing wingbeat frequency (wbf). We provide the initial test of this hypothesis on the most speciose clade of birds (Passeriformes, containing >50% of all avian species) performing burst flight (vertical takeoff and acceleration). We measured the maximal escape-flight of a wide-range of passerines (N=29 species, 14 families, mass range 5.7-278 g) in a vertical chamber using four synchronized, high-speed cameras. During liftoff, the contribution from the legs was quantified using a force plate, and the aerodynamic power from the wings was estimated using 3-D kinematics in an aerodynamic model for accelerating flight. Mean peak jump force (6.04 +/- 1.26 x body weight; mean +/- s.d.) was independent of body mass (m). Contrary to the popular hypothesis, maximum mass-specific power (53.3 +/- 15.5 W kg^-1) was independent of m. Aerodynamic power is the product of wbf and aerodynamic work. The negative scaling of wbf (m^-0.24+/-0.05) was offset by positive scaling of mass-specific work (m^0.31+/-0.07). Work is dependent on numerous morphological and physiological variables. For example, work should vary inversely with wing loading, which scaled lower (m^0.20+/-0.05) than predicted for geometric similarity (m^1/3). Predicting performance in the most diverse clade of birds from traditional scaling appears inappropriate. As such, alternative multivariate approaches to predicting locomotor performance will be addressed.