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Scaling of avian bipedal locomotion reveals independent effects of body mass and leg posture on gait

Daley, M A; Birn-Jeffery, A V


M A Daley

A V Birn-Jeffery


Birds provide an interesting opportunity to study the relationships between body size, limb morphology and bipedal locomotor function. Birds are ecologically diverse and span a large range of body size and limb proportions, yet all use their hindlimbs for bipedal terrestrial locomotion, for at least some part of their life history. Here, we review the scaling of avian striding bipedal gaits to explore how body mass and leg morphology influence walking and running. We collate literature data from 21 species, spanning a 2500× range in body mass from painted quail to ostriches. Using dynamic similarity theory to interpret scaling trends, we find evidence for independent effects of body mass, leg length and leg posture on gait. We find no evidence for scaling of duty factor with body size, suggesting that vertical forces scale with dynamic similarity. However, at dynamically similar speeds, large birds use relatively shorter stride lengths and higher stride frequencies compared with small birds. We also find that birds with long legs for their mass, such as the white stork and red-legged seriema, use longer strides and lower swing frequencies, consistent with the influence of high limb inertia on gait. We discuss the observed scaling of avian bipedal gait in relation to mechanical demands for force, work and power relative to muscle actuator capacity, muscle activation costs related to leg cycling frequency, and considerations of stability and agility. Many opportunities remain for future work to investigate how morphology influences gait dynamics among birds specialized for different habitats and locomotor behaviors.


Daley, M. A., & Birn-Jeffery, A. V. (2018). Scaling of avian bipedal locomotion reveals independent effects of body mass and leg posture on gait. Journal of Experimental Biology, 221,

Journal Article Type Review
Acceptance Date May 1, 2018
Publication Date May 22, 2018
Deposit Date May 26, 2018
Publicly Available Date May 30, 2018
Print ISSN 0022-0949
Publisher The Company of Biologists
Peer Reviewed Peer Reviewed
Volume 221
Public URL


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