- Flight is the most energy-consuming activity that birds do, accounting for 80% of their daily energy expenditure. Powering the wings during flight requires extremely high metabolic rates.
- Basal Metabolic Rate (BMR) is a measure of the energy required to sustain basic life functions, such as breathing, digestion, and circulation.
- Maximum Metabolic Rate (MMR) is the maximum rate of energy expenditure that an organism can achieve.
- Birds often have a high BMR and MMR relative to other animals: they may have a BMR that is 10 times that of mammals of the same mass.
- Flying birds generally have a higher MMR than non-flying birds. For example, the MMR of a sparrow is 19.6 ml O₂ g-¹ h-¹, while the MMR of a penguin is only 4.9 ml O₂ g-¹ h-¹.
Energy Sources
- Carbohydrates are the primary fuel for flight.
- Fats are the preferred fuel for long distance migration and other low intensity activities, such as standing or perched.
- Proteins are rarely used for energy production.
Energy Storage
- Body fat is the main energy store in birds.
- Fat is lighter and more compact than other energy sources, making it ideal for long distance flights.
- The amount of body fat that a bird carries varies depending on the time of year and its activity level. Birds typically deposit fat prior to migration and during the winter months.
- Some birds, such as the ruby-throated hummingbird, can store up to half of their body weight in fat.
Energy Conservation
- Birds have a number of adaptations that help them to conserve energy. These include;
- A high density of mitochondria in flight muscles: mitochondria are the organelles responsible for cellular respiration and energy production.
- Efficient respiration: birds have a high lung volume and a rapid respiratory rate, which allows them to extract more oxygen from the air.
- Feathers: feathers provide insulation, which helps to maintain body heat and reduce energy loss.
- Huddling: some birds huddle together in groups to reduce energy loss.