information:classification
Metabolism

Common ostriches are able to attain their necessary energetic requirements via the oxidation of absorbed nutrients. Much of the metabolic rate in animals is dependent upon their allometry, the relationship between body size to shape, anatomy, physiology, and behavior of an animal. Hence, it is plausible to state that metabolic rate in animals with larger masses is greater than animals with a smaller mass.

When a bird is inactive and unfed, and the ambient temperature (i.e. in the thermo-neutral zone) is high, the energy expended is at its minimum. This level of expenditure is better known as the basal metabolic rate (BMR), and can be calculated by measuring the amount of oxygen consumed during various activities. Therefore, in common ostriches we see use of more energy when compared to smaller birds in absolute terms, but less per unit mass.

A key point when looking at the common ostrich metabolism is to note that it is a non-passerine bird. Thus, BMR in ostriches is particularly low with a value of only 0.113 mL O g h. This value can further be described using Kleiber's law, which relates the BMR to the body mass of an animal.

where M is body mass, and metabolic rate is measured in kcal per day.

In common ostriches, a BMR (mL O g h) = 389 kg, describing a line parallel to the intercept with only about 60% in relation to other non-passerine birds.

Along with BMR, energy is also needed for a range of other activities. If the ambient temperature is lower than the thermo-neutral zone, heat is produced to maintain body temperature. So, the metabolic rate in a resting, unfed bird, that is producing heat is known as the standard metabolic rate (SMR) or resting metabolic rate (RMR). The common ostrich SMR has been seen to be approximately 0.26 mL O g h, almost 2.3 times the BMR. On another note, animals that engage in extensive physical activity employ substantial amounts of energy for power. This is known as the maximum metabolic scope. In an ostrich, it is seen to be at least 28 times greater than the BMR. Likewise, the daily energy turnover rate for an ostrich with access to free water is 12,700 kJ d, equivalent to 0.26 mL O g h.