Explain how the adaptations of migratory birds allow them to store and utilise energy efficiently during long-distance migration.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Many migratory bird species travel thousands of kilometres without stopping, relying almost entirely on stored energy reserves. Prior to migration, birds undergo a period of hyperphagia, during which they accumulate large fat deposits.
Model answer (4 marks)
Fat (lipid/triglyceride) is the main energy store because it releases more energy per gram than carbohydrate or protein. During hyperphagia birds build large fat deposits beneath the skin and around organs; the hydrophobic nature of fat means it can be stored without extra water, keeping the mass light for the energy it contains.
The high metabolic rate of migratory birds is supported by a four‑chambered heart and efficient double circulation, which quickly delivers oxygen and fatty acids to the flight muscles.
Air sacs linked to the lungs create a unidirectional flow of air, maintaining a high oxygen gradient and allowing sustained aerobic respiration during long flights.
The high metabolic rate of migratory birds is supported by a four‑chambered heart and efficient double circulation, which quickly delivers oxygen and fatty acids to the flight muscles.
Air sacs linked to the lungs create a unidirectional flow of air, maintaining a high oxygen gradient and allowing sustained aerobic respiration during long flights.
Examiner tips
- Mention the higher energy density of fat, the location of fat stores, the lightweight nature of fat, the four‑chambered heart and double circulation, and the unidirectional air flow in air sacs.
Common mistakes
- Confusing carbohydrate with fat as the main energy store; forgetting the lightweight aspect of fat; omitting the role of the air sacs in oxygen delivery.
Mark scheme (4 marks)
- Fat (lipid/triglyceride) is stored as the primary energy reserve because it releases more energy per gram than carbohydrate or protein.
- Fat deposits are accumulated (during hyperphagia) beneath the skin / around organs, and fat is hydrophobic so it is stored without the additional mass of associated water, making it lightweight relative to its energy content.
- Birds have a high metabolic rate supported by a four-chambered heart and efficient double circulation, ensuring rapid delivery of oxygen and glucose/fatty acids to flight muscles.
- Birds have air sacs connected to the lungs that allow a unidirectional / continuous flow of air over gas exchange surfaces, maintaining a high concentration gradient for oxygen uptake and sustaining aerobic respiration during prolonged flight.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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