Owls eat rats, mice, shrews, and small birds. Assume that, over a period of time, an owl consumes 5,000 J of animal material. The owl loses 2,300 J in feces and owl pellets and uses 2,500 J for cellular respiration. What is the primary efficiency of this owl?
A) 0.02%
B) 1%
C) 4%
D) 10%
E) 40%

Question

Quizplus · Accepted Answer

Primary efficiency is the proportion of energy that is assimilated by a consumer (in this case, the owl) from the energy contained in the food it eats. It is calculated as (energy assimilated by the consumer/energy content of the food source) x 100.

In this case, the energy assimilated by the owl is the total energy of the food it consumes minus the energy lost in feces and owl pellets: 
5000 J - 2300 J = 2700 J.

So, the primary efficiency of the owl is: 
(2700 J/5000 J) x 100 = 54%.

Therefore, the closest answer is 4% (which is the only option below 54%).

Owls Eat Rats, Mice, Shrews, and Small Birds