Gradient limits and safety factor of Alpine ibex (Capra ibex) locomotion


Dam walls are like open laboratories useful to study the gradient limits of locomotion. Two dam walls, where Alpine ibex (Capra ibex) use to climb searching for the salty exuded, were filmed at 0.2 fps. The straight slope of the walls ranged from 123% to almost vertical. In total 54 animals were filmed and their body mass estimated as medium size, small size and kids. No large males were observed moving on the walls. The overall weighted average incline of their paths was 37% uphill and 46% downhill. They used to climb on zigzag routes and run down on more linear tracks. The gaits employed by the animals were walk and gallop. The steepest paths travelled by kids were 155% up and 157% down, the maximum height was 49 m, while their maximum estimated speeds were 2.6 ms-1 uphill and -4.2 ms-1 downhill. Medium: +143% and -157%; 49 m; +1.1 and -4.1 ms-1. Large: +102% and -123%; 32 m; +0.7 and –1.0 ms-1. The climbing performance of Alpine ibex, in term of speed and inclination, appeared to be negatively influenced by body mass, while the friction coefficient between their hooves and the dam walls was in a range higher than rubber on concrete surfaces. Protection against toppling depends on the slope and the ratio between the basal width and body centre of mass (bCOM) height. We propose a safety factor index (Fst),similar to that used in geology, defined as the ratio between the major distance from a downstream to an upstream leg and the centre of mass height, all divided by the tangent of the slope. An index value of “1” is the discriminant between unsafe and relative safe positions. Animals with shorter legs and lower bCOM, like females and kids, can negotiate steeper paths with a higher safety factor.


Alpine ibex; locomotion; steep slope; dam walls; safety factor

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Hystrix, the Italian Journal of Mammalogy ISSN 1825-5272 (electronic version) 0394-1914 (printed version) Impact Factor (2016) 1.479, CiteScore (2016) 3.51.
Published by Associazione Teriologica Italiana
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