What is the energy source of a tigers muscle protein when he eats a deer and the deer eats a plant?

Their source of energy is the sun.

The producers (plants), absorb photons from the sun to make glucose and water, then when the primary consumers (deer) eats the plant, it absorbs 10% of that energy from the plant. The secondary consumer (tiger) eats the deer and only gets 10% of the energy it got from the plant (1% of the original energy).