What an animal eats shows in its body. Plant-eaters usually have big, wide molars that grind leaves and grasses. Meat-eaters' teeth are built differently, and the two groups' guts differ as well. An herbivore is an animal that eats plants, a carnivore eats other animals, and an omnivore eats both. Brown bears eat almost anything nutritious, and what they eat changes with the season.
A cow can eat about 70 kg (150 pounds) of grass in an 8-hour day, and its food takes 70 to 100 hours to pass through. You may have heard that a cow has four stomachs. Ruminants such as cattle have four stomach compartments, and the rumen is the biggest, but the four compartments are part of one stomach. Cows cannot digest grass on their own. Microbes in the rumen ferment the feed in a place with almost no oxygen, and without them a ruminant could not use forages such as hay for energy as efficiently.
Sloths eat leaves, and food stays in their gut for about a month. Hippos can store two days' worth of grass in their stomachs. A koala sleeps so much because eucalyptus leaves give it very little energy.
Vultures are scavengers that mostly eat animals that are already dead. A turkey vulture can smell its food, which is unusual for a bird. Vultures eat as much as they can when they find food, because the next meal may be up to two weeks away.
Wolves usually take the weak, old and young among their prey. A cheetah gets within about 100 yards of its prey and then sprints, and a full sprint lasts about 20 seconds. An owl can hear a mouse stepping on a twig from 75 feet (23 meters) away.
Snail kites are specialists. They eat apple snails, pluck them off plants, and use a sharp, curved beak to extract the snail from its shell, so their food supply is tied to the wetlands where snails live.
Some animals feed in the sea. Emperor penguins eat mostly fish and krill, the most abundant food in the ocean around Antarctica. Baleen whales feed by filtering: baleen plates are made of keratin and work as a sieve, and baleen grows continuously, like hair and nails.
A food chain shows who eats whom, and plants are producers that make their own food from sunlight. Primary consumers are herbivores, and secondary consumers eat the herbivores. Carnivores that eat other carnivores are called tertiary consumers. On average only about 10 percent of the energy at one level of a food chain passes to the next level. Because so much energy is lost at each step, a food chain can have only a limited number of levels. Detritivores eat dead plant and animal remains and turn waste into nutrient-rich soil.
Words to know
- molars: wide grinding teeth
- ruminants: cud-chewing animals
- scavengers: eat dead animals
- detritivores: eat dead remains
- specialists: narrow-diet eaters
