There are several reasons why energy transfer between trophic levels (between consumers) is so low. Firstly, not all of the organism is consumed, or some parts are consumed but cannot be digested. These parts are released in faeces.
Some energy is lost between trophic levels due to excretory materials, such as urine. Also, some energy losses occur as heat from respiration and lost to the environment.
Energy losses due to respiration are high in mammals and birds because of their high bodytemperature, meaning a lot of energy is required to maintain this.
The net production of consumers can be calculated as N = I - (F + R), where N = net production, I = chemical energy store of ingested food, F = energy lost in faeces/urine, and R = energy lost in respiration.
