For survival a hummingbird uses a considerable amount of energy . this energy most directly results from the life activity of ?

This energy most directly results from the life activity of  respiration.

The hummingbirds have very high energy expenditure (have the highest oxygen requirements of all vertebrae) with a fast heart rate, very fast wing beats and sustained hovering. So the hummingbird is nearly always on the edge of starvation, needing to take in more nectar than its body weight each day.

The respiratory system of these birds is highly adapted for the high oxygen needs. So, the muscles of the hummingbird cause pressure changes within the air sacs. As a result, more oxygen can enter the respiratory system. Also, they have the highest density of red blood cells which allows them to rise heart beat to around 500 breaths per minute during flight.