Feathers, flyways and fast food
Original by Dr Margaret Rowe, 2002
Last revised by the Department of the Environment and Heritage, December 2004
ISBN 0 6425 4820 X
Whatever the weather, birds keep their body temperature steady at about 40°C. The warm body temperature allows messages to be carried rapidly in the nerves, giving birds a quick reaction time. It also allows strong, rapid movement of muscles, enabling birds to be fast, active creatures at all times of day, in all seasons, and in extremes of climate. The constant, warm body temperature also makes endurance in flight possible; some birds can fly for hours, days, or even weeks without becoming exhausted.
How do birds create warmth?
From their food birds obtain substances such as sugars and fats that contain stored energy. Chemical processes in birds' body tissues release this energy, providing heat energy and energy for growth and movement. Birds can gain or lose heat to their surroundings. Dark plumage absorbs more heat than pale plumage.The wind has a dramatic cooling effect.
There are a number of ways birds can adjust their body temperature if they are too hot or too cold by:
- changing feather positions.When cold, a bird can fluff its feathers, creating more air pockets and increasing the insulation.When hot, raising feathers allows heat to escape from the body, cooling the bird.
- adjusting the amount of blood that flows into blood vessels near the surface of their skin. More blood near the surface of the skin has a cooling effect as heat passes into the surroundings.
A bird that is too hot can lose heat by:
- panting—rapid breathing with bill open increases the evaporation rate of water from the mouth and throat. The process of evaporation uses heat. In this way heat is removed from the mouth and throat tissues, cooling the bird.
- birds do not have sweat glands, but may lose some water from their skin by evaporation, providing a cooling effect.
- birds can behave in ways that keep them cool. For example, they can live in a burrow, or they may be nocturnal, resting during the day and becoming active at dusk or during the night.
A bird that is too cold can warm up by:
- shivering which produces additional heat. The movement of shivering muscles requires energy, increasing respiration which generates heat.
- birds can behave in ways that keep them warm. For example, they can roost in holes, cluster together, or take shelter from the wind among vegetation. Nests provide insulation that helps keep the eggs warm.
Some birds, such as petrels, herons, penguins and gulls that live in cold places, have a special system which cuts down on heat lost from their feet. Blood vessels carrying blood down each leg pass very close to the blood vessels carrying the blood back up the leg. In cold conditions, heat is transferred from the warmer blood moving down the leg to the cooler blood moving up the leg. In addition to this, some birds can reduce the amount of blood that passes through their feet. This also cuts down on heat lost when the bird' s feet are touching cold surfaces. Penguins do this when standing on snow.
Energy is needed to keep warm
Keeping warm uses up a lot of energy. Birds get energy from their food.When comparing birds with reptiles (snakes and lizards), we find that birds use 20 or 30 times more energy than reptiles of similar size. Reptiles do not maintain a constant body temperature and rely on absorbing heat from their environment to help warm their bodies. They do not need as much food as birds. When comparing birds with mammals, we find that flight usually needs a lot less energy than running. For example, a 20 gram bird, in flight, uses less than one percent of the energy it takes a 20 gram mouse to run the same distance.
Some people use doonas that contain feathers and down— usually from ducks.
- Why do the makers recommend that you shake the doona and "fluff" up the feathers when it is first removed from its bag?