Final answer:
Hummingbirds store triglycerides over glycogen because they provide a denser energy source, critical for their energetic demands during long periods of flight. Triglycerides are metabolized through glycolysis and the citric acid cycle to produce ATP, which powers muscle contractions for flight.
Step-by-step explanation:
Hummingbirds primarily store triglycerides to fuel the energy metabolism of their flight muscles instead of glucose stored as glycogen because triglycerides are a more dense form of energy storage. Since triglycerides contain more than twice as much energy as carbohydrates, they provide a more efficient way to store the vast amount of energy required for hummingbirds' prolonged periods of flight. Moreover, the flight muscles in birds are highly efficient in energy production and can utilize the energy released from the breakdown of triglycerides effectively.
The process of breaking down triglycerides involves hydrolyzing them into glycerol and fatty acids. The glycerol can be phosphorylated and proceed through glycolysis, while the fatty acids are broken into two-carbon units that enter the citric acid cycle. These catabolic pathways result in the production of ATP, which can be then used by cells for energy-intensive processes such as muscle contraction during flight.