Original by Dr Margaret Rowe, 2002
Last revised by the Department of the Environment and Heritage, December 2004
ISBN 0 6425 4820 X
Birds use a lot of energy and need to eat a lot and feed frequently to refuel themselves. When moulting, preparing for migration, or their eggs are developing, they need even more food. The bodies, legs and bills of different types of birds are suited to a variety of ways of getting food. They may sit, walk, hop, fly or dive in search of food. The size, shape and strength of a bird's bill suits it to a specialised type of feeding. Bills are designed to tear meat, spear fish, crack hard seeds, catch insects, gather water weeds, reach the nectar in flowers, probe into mud for tiny shellfish, or filter tiny creatures from mud. Many birds are able to gather food in more than one way, when necessary.
Look at the bill shapes shown in the illustration.
- Draw the bill shapes and write answers beside each one:
- (i) What type of food do you think the bird eats?
- (ii) Give a reason for your answer.
Figure 8 Bill shapes are adapted to the type of food the bird eats
Birds usually swallow their food whole. Fisheating birds often have hooks on their bill or tongue that help swallow slippery fish, headfirst. Most birds can store and soften food in their expandable oesophagus and crop before it is passed into the stomach. In the first of the two sections of the stomach, digestive juices begin dissolving the food. In the second section of the stomach, the muscular gizzard, food is ground to a pulp. Moisture and digested food passes through the walls of the intestines into the bird's blood. Parts of the food that cannot be digested are ejected from the mouth as pellets or pass out of the body through the cloaca.
- Why do fish-eating birds always swallow the fish head first?
- Suggest an advantage of having a large, expandable oesophagus and crop that stores food while it waits its turn to enter the stomach to be digested.
Look at the bills of the shorebirds shown in this illustration.
- Do they all eat the same food?
- What stops them from competing with each other for food?
Figure 9 Bill lengths and food of shorebirds
Shorebirds feed by walking on wet sand or mud, or wading in shallow water pecking small worms, insects, fish, and a variety of molluscs and crustaceans. Expansive intertidal flats provide good feeding areas for most shorebirds at the wintering grounds. Some shorebirds, like plovers, rely on their extra good eyesight to find their prey. Others, like sandpipers and curlew that probe in the sand or mud for their food, use their sensitive bills to feel for prey.
- Which of the shorebirds can feed best in dull light, plovers or curlew? Why?
- Terns dive for fish. Would good eyesight, or a sensitive bill be more useful?
- Turnstones are waders that winter on rocky seashores. Make a guess at what food they eat. (Hint: their name.)
- Some types of oystercatchers also feed on rocky shores. They rarely if ever eat oysters. What do they eat?
When food supplies are stable birds may defend territories and feed within these areas.When food is hard to find, and birds must be on the move, they often find safety in flocks.When a member of a flock sees a predator, it calls to warn the flock. Isolated individuals in exposed places are easy targets for predators.The flock can confuse an attacking predator.
Shorebirds, when resting (roosting) at high tide, usually form flocks. Their predators include and birds such as eagles, hawks and falcons.
- What advantages does a bird have if it is in a flock?