# Explain how the adaptations of migratory birds allow them to store and utilise energy efficiently during long-distance migration.

> IB DP Biology Standard Level (2023 syllabus) — B4.1 Adaptation to environment · Explain · 4 marks

> 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.

## Mark scheme (4 marks)

1. Fat (lipid/triglyceride) is stored as the primary energy reserve because it releases more energy per gram than carbohydrate or protein.
2. 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.
3. 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.
4. 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

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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