Abstract: The aim of this study is to establish and calculate the allometric relationship between the total metabolic energy per life span and the body mass in Passerine and Nonpasserine birds for maximum and life span in captivity. The study shows that it exists near to linear relationship between the total metabolic energy per life span PTls (kJ) and the body mass M (kg) of birds from the type: PT_ls= A⁰_lsM^k, where P (kJ day ¹) is the basal metabolic rate, Tls (day) is the life span (maximum or life span in captivity) and A⁰_ls (kJ kg ¹) is the total metabolic energy, exhausted during the life span per 1 kg body mass of birds. The received results show that for all birds, the power coefficient (k) in the `lifespan metabolism-mass` relationship fall in the interval 0.8776-0.934 (for maximum and life span in captivity). For maximum life span the power coefficient k for all birds is 0.904 (R² = 0.976) and separately for Passerine it is 0.935 (R² = 0.987), for Nonpasserine it is 0.926 (R² = 0.98). The linear coefficient A⁰_ls for all birds is 26.866�10⁵ kJ kg ¹ and separately for Passerine it is 36,728�10⁵ kJ kg ¹, for Nonpasserine it is 25.199�10⁵ kJ kg ¹ . Possibly, the linearity between lifespan metabolic energy and body mass expresses a general allometric law in animal energetics, since it is valid for Poikilothetms, Mammals and approximately for Aves.