Final answer:
In an ecological food chain, only about 10% of the energy is transferred from one trophic level to the next. Thus, if the grass has 100,000 kcal, a bird may obtain 1,000 kcal, from which a fox would get about 100 kcal.
Step-by-step explanation:
The question pertains to energy transfer within an ecological food chain. When energy is passed up from producers (like grass) to primary consumers (like rabbits), and then to secondary consumers (like birds), and finally to tertiary consumers (like foxes), there is a significant loss of energy at each level due to metabolic processes and heat loss. This concept is encapsulated by the 10% rule of energy transfer in ecology, which states that, on average, only about 10% of the energy from one trophic level is passed to the next. Therefore, if grass contains 100,000 kcal of energy, a primary consumer like a rabbit might only obtain about 10,000 kcal (10%), a secondary consumer like a bird would get around 1,000 kcal (10% of the rabbit's energy), and a tertiary consumer like a fox would receive approximately 100 kcal (10% of the bird's energy).