An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and from plant and animal matter, omnivores digest , protein, fat, and fiber, and metabolize the nutrients and energy of the sources absorbed. Often, they have the ability to incorporate food sources such as algae, Fungus, and bacteria into their diet.
Omnivores come from diverse backgrounds that often independently evolved sophisticated consumption capabilities. For instance, dogs evolved from primarily Carnivore organisms (Carnivora) while pigs evolved from primarily Herbivore organisms (Artiodactyla). Despite this, physical characteristics such as tooth morphology may be reliable indicators of diet in mammals, with such morphological adaptation having been observed in bears.
The variety of different animals that are classified as omnivores can be placed into further sub-categories depending on their feeding behaviors. include Maned wolf and ; include and pink fairy armadillos; Seed predation include Finch and mouse.
All of these animals are omnivores, yet still fall into special niches in terms of feeding behavior and preferred foods. Being omnivores gives these animals more food security in stressful times or makes possible living in less consistent environments.
Occasionally, it is found that animals historically classified as carnivorous may deliberately eat plant material. For example, in 2013, it was considered that American alligators ( Alligator mississippiensis) may be physiologically omnivorous once investigations had been conducted on why they occasionally eat fruits. It was suggested that alligators probably ate fruits both accidentally and deliberately.
"Life-history omnivores" is a specialized classification given to organisms that change their eating habits during their life cycle. Some species, such as grazing waterfowl like geese, are known to eat mainly animal tissue at one stage of their lives, but plant matter at another.Maclean, Gordon Lindsay (1993). Roberts' Birds of Southern Africa. Publisher: New Holland. . The same is true for many insects, such as beetles in the family Meloidae,Skaife, S. H. (1953). African Insect Life. Pub. Longmans, Green & Co., London. which begin by eating animal tissue as , but change to eating plant matter after they mature. Likewise, many mosquito species in early life eat plants or assorted detritus, but as they mature, males continue to eat plant matter and nectar whereas the females (such as those of Anopheles, Aedes and Culex) also eat blood to reproduce effectively.
Most bear species are omnivores, but individual diets can range from almost exclusively herbivorous (hypocarnivore) to almost exclusively carnivorous (hypercarnivore), depending on what food sources are available locally and seasonally. are classified as carnivores, both taxonomically (they are in the Taxonomic rank Carnivora), and behaviorally (they subsist on a largely carnivorous diet). Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently. Wolf subspecies (including wolves, , , and ) eat some plant matter, but they have a general preference and are evolutionarily geared towards meat. However, the maned wolf is a canid whose diet is naturally 50% plant matter.
While most mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, season and so on, they will generally prefer a particular class of food, to which their digestive processes are adapted. Like most arboreal species, most squirrels are primarily granivores, subsisting on nuts and seeds.Halle, S. & Stenseth, N. (2000). Activity patterns in small mammals: an ecological approach. Berlin; Heidelberg, Germany; New York: Springer-Verlag. p. 131. But like virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American eastern gray squirrel has been introduced by humans to parts of Britain, continental Europe and South Africa. Where it flourishes, its effect on populations of nesting birds is often serious, largely because of consumption of eggs and nestlings.Moller, H. (1983). "Food and foraging behaviour of red ( Scirus vulgaris) and grey ( Scirus carolinensis) squirrels". Mammal Review 13: 81-98.
Quite often, mainly herbivorous creatures will eagerly eat small quantities of animal food when it becomes available. Although this is trivial most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks insects while food is most needed for growth.Capinera, John (2010). Insects and Wildlife. Publisher: Wiley-Blackwell. . 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 cobalt/vitamin b12 that are absent from nectar. Similarly, monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit.Ewing, Jack (2005). Monkeys Are Made of Chocolate. Publisher: Pixyjack Press. . When to refer to such animals as omnivorous, or otherwise, is a question of context and emphasis, rather than of definition.