What Do Mammals Eat?

Mammals are warm-blooded vertebrates whose bodies are covered in hair or fur. Female mammals have mammary glands that secrete milk for their young, and almost all give birth to live young. This class of animals includes about 5000 species, ranging from rhinos to wolves to sloths to humans to whales. Mammals are quite diverse in their feeding habits; as a whole they’ll eat practically anything. Protein fuels their energy, while fat insulates them from adverse weather and carbohydrates store energy and provide vitamins, minerals, and fiber. Mammals rarely adhere to a strict diet. Their environment often dictates what mammals will eat. If a certain food becomes scarce, they have to change their habits in order to survive.

What do carnivores mammals eat?

Carnivorous mammals eat a diet of mostly animal tissue, whether from vertebrates or invertebrates. Carnivores possess unique physical characteristics that enable them to kill and consume their prey, or in the case of scavengers, that enable them to locate and devour a carcass.

Obligate carnivores, such as lions, tigers and wolves, must feed on meat almost exclusively because they cannot easily eat and digest vegetable matter. These animals have limited facial muscles so that their jaws can open wide, which the latter do on a simple, stable hinge on the same plane as the teeth. Temporalis muscles cover a large area of the head and allow the upper jaw to separate from the lower. As for the teeth, short incisors are designed to grasp and shred; long, sharp canines to stab, tear, and kill; and flat, serrated molars to slice through flesh. When the mouth closes, the lower teeth slide back into place against the upper, like shears.  The mouth doesn’t secrete saliva for partial digestion, because carnivores don’t chew their food. They swallow whole chunks of flesh, which pass down into their large, single-chambered stomach. While the carnivore rests, its stomach maintains a consistent level of acidity to calmly break down protein and kill any bacteria in the food. Digestion of meat isn’t a difficult process, so the small intestine, where the nutrients are absorbed, doesn’t need to be extensive. The large intestine is also quite short, because it only needs to absorb salt and water.

It’s true that carnivorous mammals can consume vegetation, but they do so voluntarily, either to supplement a deficient diet or to use the plant matter as an emetic.

In marine environments, sea lions, walruses, and seals eat a diet of fish, octopi, crustaceans, mollusks, and other sea creatures. Dolphins prefer fish. Killer whales will eat fish, but they will also attack marine mammals, even other whales.

The term “meat” doesn’t merely include tissue from mammals and fish. It also refers to the soft inner bodies of insects and spiders. For instance, anteaters derive all their nutrients from ants, termites, and other insects. Most bats feed at night on hundreds of insects, such as mosquitoes. Shrews, hedgehogs, moles, and aardvarks also eat insects as their main source of food. All of these animals can be classified as insectivores.

Foxes and hyenas present probably the best examples of carnivorous scavengers. They exhibit opportunistic behavior, eating whatever they can find.

Herbivores

In contrast to carnivores, herbivorous mammals eat a diet of mostly plant matter. They possess an anatomy specially designed to consume and digest the cellulose contained in vegetation. These animals must forage for food and will sometimes cover great distances to find it, but they don’t have to hunt and kill their food as carnivores do.

To facilitate their feeding habits, herbivores have complex facial muscles. Their jaws generally do not open very wide, and these pivot on a hinge above the level of their teeth. This hinge allows for considerable movement when the animal is chewing. The lower jaw can move up and down and from side to side. The teeth vary depending on the animal’s diet, but in general the incisors are wide and flat for biting, and the molars are squat and flat on top for crushing and grinding. The canines can be large, small, or absent. (In sloths, the incisors are absent). Instead of working as shears, an herbivore’s teeth work as a mill, gradually breaking down the cellular structure of the food. Saliva actually starts digesting the carbohydrates before the food even enters the stomach.

Ruminants, such as cattle, llamas, goats, deer, sheep, antelope, giraffes, and camels, possess complex stomachs. They need a more extensive digestive system because they consume so much indigestible fiber. Bacterial enzymes in their stomachs work hard to draw out the nutrients from the food. One trip to the stomach isn’t always enough; sometimes the food must return to the mouth for further chewing and digestion and then pass down into the stomach again. After the matter leaves the last stomach chamber, the small intestine absorbs some of the nutrients and may digest the matter further. The large intestine then absorbs any water, electrolytes, and vitamins.

Non-ruminants, such as kangaroos, horses, elephants, and primates, eat more digestible plant matter and thus have a single-chambered stomach. In this case, the large intestine bears the burden of breaking down fibers and absorbing nutrients.

One interesting fact is, hippos, one of the most dangerous animals in the world, is not a carnivore but a herbivore. See my other post here: what do hippos eat.

Omnivores

An omnivorous mammal (e.g. pigs, hedgehogs, squirrels, badgers) has the anatomy of either a carnivore or an herbivore, but has developed physical adaptations that enable it to feed on another form of food.

Bears possess a carnivorous anatomy, yet they eat a diet of mostly plant matter. The structure of their facial muscles, jaws, and digestive tract enables them to consume fish, carrion, and other animal tissue they may find, but their molars facilitate the chewing of vegetation. When not hunting for prey, they generally eat berries, tubers, and legumes. (However the polar bears are mainly carnivores.)

Raccoons present another good example of omnivorous behavior, as they have the physical ability to feed on fish, bird eggs, amphibians, insects, and worms, but can also eat and digest fruits and nuts.

Contrary to what most people think, humans actually have the anatomy of herbivores. That is, our facial muscles, jaw, teeth, and digestive tract resemble that of a non-ruminant animal, but we have evolved the behavior of eating meat. Like our primate cousins, we are omnivores. Though primates consume a large amount of fruit and leaves, they also eat insects as their “meat.”

Specialized Eaters

Some mammals feed on a single kind of food. Whales eat only crustaceans, such as krill; koala bears only eucalyptus leaves; and giant pandas only bamboo. (Actually, giant pandas possess the anatomy of a carnivore, but rarely eat meat). In addition, some bats consume only fruit, or nectar and pollen from flowers.

In conclusion, it’s difficult to classify most mammals in a diet group, as seasonal and environmental changes influence variations in feeding behavior. However, the more we study the eating habits and anatomy of our fellow mammals, the better we will understand ourselves and what we must do to not only survive on this planet, but to live in health and harmony with nature.

References:

  1. http://www.enchantedlearning.com/subjects/mammals/classification/
  2. http://animaldiversity.ummz.umich.edu/accounts/Mammalia/
  3. http://www.afrc.uamont.edu/whited/WLF%203413%20pdf%20files/WLF%203413%20Feeding%20modes.pdf
  4. http://www.ecologos.org/anatomy.htm
  5. http://www.beyondveg.com/billings-t/comp-anat/comp-anat-1a.shtml
  6. http://www.bearsmart.com/resources/north-american-bears/food-and-diet
  7. http://blogs.scientificamerican.com/tetrapod-zoology/2012/08/30/the-anatomy-of-sloths/

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