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Boye K. Ahlborn

Thermodynamic Limits of Body Dimension of Warm Blooded Animals

The metabolic rates ?_o = a_oM^0.73 [W], a₀ = 3.6, of animals of different body masses M [kg] determines their heat production Q? and their mechanical power output P. The metabolic heat production of small warm blooded animals living in a cold environment sets lower size limits for the body mass of birds and terrestrial mammals of M_t,b ? 0.01 kg and M_aq ? 10 kg for fast aquatic mammals. Birds must travel at the speed ?_fl = 15M^1/6 [m/s] in order to stay aloft, but their muscles only generate the metabolic velocity ?_? ?? 50M^?0.25 [m/s]. These conditions yield an upper body size limit for flying birds: M_b,max ? 15 kg. Walking speeds scale with body mass as ?_walk ? M^1/6, while propagation speeds for endurance running are nearly independent of body mass. This makes walking faster than endurance running for animals with body masses M ? 600 kg.

Journal of Non-Equilibrium Thermodynamics, Walter de Gruyter

Print ISSN: 0340-0204
Volume: 25, 05/2000
Pages: 87 - 102

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