Omnivore - Omnivorous Species

Omnivorous Species

Although cases exist of carnivores eating plant matter, as well as 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. 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. Some researchers argue that evolution of any species from herbivory to carnivory or carnivory to herbivory would be rare except via an intermediate stage of omnivory.

Various mammals are omnivorous in the wild, such as the Hominidae, pigs, badgers, bears, coatis, hedgehogs, opossums, skunks, sloths, squirrels, raccoons, chipmunks, mice, and rats. Various birds are omnivorous, with diets varying 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 catfish, and invertebrates are also omnivorous.

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, both taxonomically (they are in the order Carnivora), and behaviorally (they subsist on a largely carnivorous 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. Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently.

While most mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, season and so on, they will generally prefer one class of food or another, and when their digestive processes are adapted to a particular class, their long-term preferences will reflect such adaptations. Like most arboreal species, most squirrels are primarily granivores, subsisting on nuts and seeds. But as with virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American Eastern gray squirrel has spread to parts of Europe, Britain and South Africa. Where it flourishes, its effect on populations of nesting birds is often serious, largely because of consumption of eggs and nestlings.

Quite commonly, predominantly herbivorous organisms will eagerly eat small quantities of animal food when it happens to become available. Although this is a trivial matter most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks animal food (largely insects) as far as possible while the need for growth is most urgent. On close inspection it appears that nectar-feeding birds such as sunbirds rely on the ants and other insects that they find in flowers, not for a richer supply of protein, but for essential nutrients such as Cyanocobalamin that are essentially absent from nectar. Similarly monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit. When to refer to such animals as omnivorous or otherwise becomes a question of context and emphasis rather than of definition.