Omnivores (from Latin: omni, meaning "all, everything"; vorare, "to devour") are species that eat both plants and animal material as their primary food source. They often are opportunistic, general feeders not specifically adapted to eating and digesting either meat or plant material primarily. Many depend on a suitable mix of animal and plant food for long-term good health and reproduction.
Although the term omnivore literally means "eater of everything," omnivores really cannot eat everything that other animals eat; they can eat only things that are moderately easy to acquire while being moderately nutritious. For example, most omnivores cannot live by grazing (not nutritious enough), nor are they able to eat some hard-shelled animals or successfully hunt large or fast prey (difficult to acquire).
Although there are cases of carnivores eating plant matter, as well as examples of herbivores eating meat, the classification "omnivore" refers to the adaptations and main food source of the species in general, so these exceptions do not make either individual animals nor the species as a whole omnivorous.
Pigs are a well-known example of omnivores.[1] The crow is another example of an omnivore.[2]
Humans are different from other omnivorous species. While they share virtually none of the characteristics of most other omnivores or carnivores,[3] such as claws, fangs, or short digestive tracts, the majority of humans eat as omnivores, consuming on a daily basis both plants and animal flesh.[4][5] Humans have the salivary enzymes, rounded molars, and long intestines of herbivores, but the canine teeth and cooperative behavior of a group-hunting species.
Most bear species are considered omnivores, but individual diets can range from almost exclusively herbivorous to almost exclusively carnivorous, depending on what food sources are available locally and seasonally. Polar bears are classified as carnivores while pandas are classified as herbivores, although giant pandas will eat some meat (e.g., insects) from time to time, and polar bears will sometimes eat plants (such as kelp), but for neither is the exception a significant part of its diet. Wolf subspecies (including wolves, dogs, dingoes, and coyotes) can live on such vegetable material as grain and fruit products indefinitely but clearly prefer meat; given a choice, dogs are much more carnivorous than humans.
Various mammals are omnivorous by nature, such as pigs, badgers, bears, coatis, hedgehogs, opossums, skunks, sloths, squirrels,[6] raccoons, chipmunks,[7] mice,[8] and rats.[9] Also, some primates are omnivorous, including chimpanzees and baboons.[10][11] Various birds are omnivorous, whose diet varies from berries and nectar to insects, worms, fish, and small rodents; examples include cassowarys, chickens, crows and related corvids, keas, rallidae, and rheas. In addition, some lizards, turtles, fish, such as piranhas, and invertebrates are also omnivorous.
While virtually all mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, etc., mammals will generally prefer one class of food or another, with optimized digestive processes. Like most arboreal species, most squirrels are primarily granivores, preferring nuts and seeds.[12] But as with virtually all mammals, squirrels can resort to consuming some meat as fallback food if starving or facultatively, e.g., when nests are in danger of being raided by predators, etc.
Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently.
While scientific classification aims to promote communication and analysis of various differences and similarities between species, the concept of an "omnivore" is broad and could be applied to virtually any mammal since disease risks and the quality of digestion are often not considered. There are social, psychological and non-nutritive factors that influence diet behavior.
In order for the concept of "omnivore" to be regarded as a scientific classification, some clear set of measurable and relevant criteria would need to be considered to differentiate between an "omnivore" and the other vague but less ambiguous diet categories e.g., faunivore, folivore, scavenger, etc.[13]
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