We described in the previous sections how energy and organic compounds are passed from one trophic level to the next. What was not mentioned is the efficiency of the transfer. In a typical food chain, not all animals or plants are eaten by the next trophic level. That is why the transfer of matter and energy from one trophic level to the next is not an efficient one. One way to calculate the energy transfer is by measuring or sizing the energy at one trophic level and then at the next.
Calorie is a unit of measure used for energy.
For example, if there are 10,000 calories at one level, only 1,000 are transferred to the next. Take a guess. It might not look like it but they are close to 10 times larger. The greatest food value comes from the acorn, especially during the winter season when other foods are scarce. Squirrels, which are omnivores , are neither at the bottom or the top of the food chain.