Ecology is the study of living things in their environment. More accurately, it is the interaction of organisms with their physical environment and each other. Birds do not live in their own little world, they have deal with the weather, finding food and nesting material, a place to nest, competitors, predators, and all manner of other things around them.This is the ecoological system or, more commonly, the ecosystem.

Ecosystems all work pretty much the same way, whether we're looking at a large tropical forest or a rotten log. The biological part of the system always has three components: producers, consumers, and decomposers. The producers are the green plants. They use sunlight and chlorophyll to turn carbon dioxide and water into energy-holding carbohydrates, the carbon-containing compounds. These are the plant parts - roots, stem, and leaves. The consumers typically have two or more levels. The first level consumer, a herbivore, eats the plants. The second level consumer is a carnivore and eats the first level consumer. The third level consumer, if there is one, eats the second level consumer. So lets say grass is the producer, a vole eating the grass is the first consumer, and a hawk eating the first consumer is a second level consumer. This is a food chain, going from bottom to top.

But it's not that simple. There are other producers in a ecological system; besides grass there are various other herbs and forbs and maybe shrubs and trees. They are eaten not just by mice but, for example, by moles, sparrows, turtles, insects, and snails. And these animals in turn are eaten by a variety of predators such as skunks, opossums, snakes, frogs, and owls. So the system in reality is not a food chain, but a food web, as the diagram on the top of the page shows. But the diagram is missing one important component: decomposers.

Plants and animals die or are killed by a consumer; their bodies or what is left of them fall to the ground. Their bodies are quickly invaded by decomposers - bacteria, protozoa, insects like beetles and other arthropods like millipedes break the bodies down until they return to the soil as organic compounds or inorganic elements. And not just bodies. The hawk, having eaten a mouse, moves the mouse through its digestive tract and, finally, the digested and undigested parts of the mouse leave the hawk and fall to the ground and are decomposed as well. This is natural recycling, as the elements and compounds used by plants, the producers, abd taken up by animal, the consumers, is returned to the soil for reuse. Matter is never lost, it just changes form. The proteins that form a giraffe's ear may one day become part of a tree trunk.

The whole system works because the sun provides the energy and all the animals and plants evolved together to interact to produce a stable system and every organism has its place in the system, both physically and functionally. These are the habitat and niche.