Animal Diets

Omnivore

Eats both plants and animals
1,038 Animals
1/44 Page
Overview

Understanding This Category

An omnivore is an organism whose habitual diet includes both plant-derived foods (e.g., fruits, leaves, seeds, roots) and animal-derived foods (e.g., insects, fish, meat, eggs, dairy). Omnivory is a flexible feeding strategy in which the proportion of plant versus animal foods can vary with ecology, season, life stage, and food availability.

An omnivorous diet includes meaningful food from both plants and animals. This gives access to macronutrients (carbohydrates, fats, proteins) and micronutrients (vitamins, minerals). Omnivory is common in animals that face changing food supplies because it lowers reliance on one food type and helps when food is scarce.

Omnivory does not mean an equal split between plants and animals. Some omnivores eat mostly plants with some animal food; others eat mostly animals with some plants. The balance can change with season, place, and individual need. Humans are often omnivores, eating grains, vegetables, fruits, nuts, plus meat, fish, eggs, and dairy.

Omnivores have flexible feeding and digestion that handle many food kinds. This gives dietary variety and helps them cope when foods are limited. But health depends on food choices: an omnivorous diet can be full of nutrients or high in processed foods and low in fiber and vitamins.

Etymology: From Latin roots meaning "all" and "to eat/devour," describing an organism that eats a wide variety of foods.

Key Characteristics

Regular consumption of both plant and animal foods (not exclusively one or the other)
Flexible plant-to-animal ratio that can change with season, availability, culture, or personal preference
Broad food repertoire (e.g., grains/legumes/produce plus meat/fish/eggs/dairy)
Often associated with generalist foraging behavior and dietary adaptability
Can meet nutrient needs through diverse sources, but overall healthfulness depends on food quality and balance

Common Misconceptions

Food Sources

What They Eat

Primary Foods

  • Fruits and berries
  • Leaves and shoots (greens)
  • Seeds, nuts, and grains
  • Insects and other invertebrates
  • Small vertebrates (fish, amphibians, reptiles, rodents)
  • Carrion/scavenged meat

Supplementary Foods

  • Roots, tubers, and bulbs
  • Fungi (mushrooms)
  • Eggs and nestlings
  • Crustaceans and mollusks
  • Human-associated foods (crops, refuse, pet food)
  • Nectar and plant exudates (sap/gum)

Nutritional Requirements

A mixed plant-and-animal diet supplies a broad nutrient profile: carbohydrates and fiber from plant foods for energy and gut health; protein and essential amino acids from meat/invertebrates for growth and tissue repair; fats (including essential fatty acids) for energy storage and hormone function; vitamins and minerals such as iron, zinc, B12 (more available from animal foods) and vitamin C, folate, potassium, magnesium (common in plant foods). This flexibility helps omnivores meet nutritional requirements across seasons and fluctuating food availability.

Foraging & Hunting Strategies

Opportunistic feeding: switching between plant and animal foods based on availability and season Generalist searching: wide-ranging movement and use of multiple habitats/strata (ground, vegetation, water edges) Active hunting/pursuit of small prey and invertebrates (stalking, chasing, pouncing) Gleaning and picking: harvesting fruits, seeds, and leaves directly from plants Digging and probing: extracting roots/tubers and soil/wood-dwelling invertebrates Scavenging and caching: using carrion or stored food to buffer periods of scarcity
Anatomy

Physical Adaptations

Teeth & Mouth

Omnivores typically have a mixed dentition suited for both tearing animal tissue and crushing/grinding plant material, allowing flexible processing of varied foods.

  • Moderately developed canines for gripping/tearing meat (often smaller than in strict carnivores)
  • Incisors for nipping, biting, and cutting plant matter and flesh
  • Broad premolars and molars with rounded cusps for crushing and grinding (intermediate between sharp carnivore shearing teeth and herbivore grinding surfaces)
  • Enamel and jaw strength adapted to handle a wide range of food textures (soft fruit to tougher meat or fibrous plant parts)
  • Jaw motion that can combine vertical biting with limited side-to-side grinding depending on species

Digestive System

Omnivore digestive systems are generally versatile, balancing the ability to digest animal proteins/fats with some capacity to process plant carbohydrates and modest fiber loads; the gut is intermediate in complexity and length compared to carnivores and herbivores.

Gut Length: Intermediate; commonly ~5-10× body length (species-dependent), longer than many carnivores but shorter than most specialized herbivores.

  • Stomach acid and proteolytic enzymes effective for animal tissue digestion
  • Pancreatic enzymes (amylase, lipase, proteases) supporting digestion of starches, fats, and proteins
  • Moderate fermentation capacity in the large intestine/cecum for limited fiber breakdown (typically less developed than in hindgut fermenters)
  • Flexible bile production and fat digestion to accommodate variable dietary fat intake
  • Microbiome adaptable to seasonal or regional diet shifts

Sensory Adaptations

Generalist foraging perception: good vision for locating diverse foods (fruit, seeds, prey) and assessing ripeness/motion
Well-developed olfaction to detect both plant odors (ripening/volatile compounds) and animal cues (prey, carrion)
Taste receptors supporting evaluation of sweetness (carbohydrates), salt, and umami (amino acids/protein), aiding broad food selection
Tactile sensitivity (lips, whiskers, fingertips, tongue-species-dependent) for handling and assessing food items
Auditory acuity useful for detecting prey movement or social cues during opportunistic feeding (species-dependent)
Diet Spectrum

Strict vs Flexible

Obligate / Strict

Species that are consistently omnivorous across their normal ecology-regularly eating both plant material and animal matter as a core, year-round strategy (generalist feeders rather than primarily herbivores or carnivores).

  • Raccoon
  • Wild boar
  • Norway rat
  • American crow
  • Common carp

Facultative / Flexible

Facultative omnivores that can lean strongly toward herbivory or carnivory depending on season, habitat, life stage, or local food availability, but readily incorporate both plant and animal foods when accessible.

  • American black bear
  • Red fox
  • Coyote
  • Chimpanzee
  • Herring gull
Evolution

Evolutionary History

Omnivory evolved many times across life because animals that could eat plants and animals had more food. On land, early synapsids and many Mesozoic mammals ate plants and animals. In the Cenozoic, mammals like primates, bears, pigs, and many rodents grew more general teeth and flexible guts for mixed diets. Birds became omnivores many times, with beaks and guts letting them switch seasonally between seeds, fruit, insects, and small animals. Fish, amphibians, reptiles, and invertebrates often become omnivores in changing habitats, first by behavior and later by changes in teeth and gut function.

Selective Pressures

  • Seasonal and unpredictable food availability (e.g., winter scarcity of insects or summer pulses of fruit/seed production) favoring dietary flexibility
  • Habitat heterogeneity and ecotones (forest-grassland edges, riparian zones, coastal margins) providing mixed resource types in close proximity
  • High competition for specialized foods, making a generalized diet advantageous when preferred resources are contested
  • Resource pulses and boom-bust dynamics (mast years, insect outbreaks, carrion availability) rewarding opportunistic switching
  • Disturbance and environmental change (fire, drought, glaciations, human-altered landscapes) that restructure food webs and penalize strict specialists
  • Energetic and nutritional balancing pressures (need to combine protein, fats, micronutrients with carbohydrates/fiber) encouraging mixed feeding
  • Predation risk and foraging time constraints that make it beneficial to take locally available foods rather than search for a single specialized item
  • Ontogenetic shifts (different foods available or optimal at juvenile vs. adult sizes) promoting broad diet breadth across life stages

Convergent Evolution

Omnivory is a clear example of convergent evolution: many unrelated animal groups evolved mixed plant and animal diets on their own. Examples include bears (e.g., brown bear) and pigs (suids) that eat roots, fruit, insects, and meat; primates like humans and capuchins that added plants plus insects or small animals; canids such as foxes and corvid birds (crows and ravens) that eat fruit, seeds, insects, and carrion; freshwater fish like common carp and many cichlids that graze plants or algae and eat invertebrates; and some reptiles (skinks, box turtles) that evolved jaws for varied food and switch diets by season. These different lines share similar roles and flexible feeding.

Human Relevance

Human Connection

Comparison to Humans

An omnivorous diet closely mirrors many common human dietary patterns that include both plant and animal foods (e.g., "mixed" diets). Like human omnivory, it emphasizes flexibility-food choices can shift with season, culture, availability, and cost. It also highlights that nutritional needs can often be met through multiple food combinations, and that access to diverse food sources can buffer against shortages or single-crop failures.

Conservation Implications

Knowing a species is an omnivore helps conservation. Omnivores can switch foods when one resource drops, but they may also go into human areas (crops, garbage, livestock feed) and cause conflicts. Protect habitats that keep a mix of plants and prey through seasons. Reduce access to human food (lock bins, guard crops) to stop them relying on people and causing fights. Omnivores can help keep food webs stable, so watching their diet shifts can warn of ecosystem changes like prey collapse, vegetation shifts, or invasive species.

Agriculture Connection

Omnivores intersect strongly with agriculture because they may both help and harm farming systems. Many omnivores consume pest insects or rodents (natural biological control), while also eating fruits, grains, eggs, or young livestock, causing crop or poultry losses. Understanding their seasonal diet helps farmers time deterrents, habitat features (hedgerows, buffer strips), or integrated pest management to maximize pest-control benefits and reduce damage. Omnivores can also affect food production indirectly by scavenging waste, spreading seeds, or moving nutrients-services that can be beneficial or problematic depending on the context.

Examples

Animal Examples

Iconic Examples

Human Eats a wide variety of plant foods (fruits, grains, vegetables) and animal foods (meat, fish, eggs, dairy), with diet shifting by culture and availability.
Brown bear Seasonally switches among berries/nuts/roots, insects, fish (e.g., salmon), and carrion or large prey when available.
Domestic pig / Wild boar Highly opportunistic feeder that consumes roots, tubers, fruits, grains, invertebrates, eggs, small vertebrates, and carrion.
Raccoon Flexible diet including fruits, nuts, corn, crayfish, frogs, insects, eggs, and human-associated foods-especially in urban areas.
American crow Eats seeds and fruit alongside insects, small animals, eggs, and carrion; often shifts diet with seasons and local resources.
Chicken Forages for grains and plant material but also readily eats insects, worms, and small animal matter when encountered.

Surprising Examples

White-tailed deer Primarily a browser, but documented eating animal matter (e.g., nestling birds, eggs, or bones) to obtain minerals/protein-an example of facultative omnivory.
Box turtle (Eastern box turtle) Often thought of as a plant eater, but commonly eats mushrooms, berries, insects, worms, snails, and carrion-mixing plant and animal foods.

Extreme Examples

Ostrich Largest living bird; an omnivorous diet that includes seeds/foliage plus insects and small animals when available.
Kodiak bear (brown bear subspecies) Often cited as the largest terrestrial omnivore, combining plant foods with fish and other animal matter.
Brown rat Among the most widely distributed omnivorous mammals globally, thriving on an extremely broad mix of plant and animal foods in human-dominated environments.

Found across: Mammals (e.g., bears, pigs, primates, many rodents), Birds (e.g., corvids, gulls, chickens, many waterfowl), Reptiles (especially many turtles/terrapins; some lizards), Fish (many species are opportunistic omnivores, shifting between algae/plant matter and invertebrates), Invertebrates (e.g., many crabs, cockroaches, ants, and other generalist scavengers)

Ecology

Ecological Role

Omnivores are flexible eaters that can be primary consumers when they eat plants and secondary (or higher) consumers when they eat animals. They link plant and animal energy paths, help steady food webs by switching foods, shape communities by grazing, eating seeds, hunting or scavenging, and aid seed spread and nutrient cycling.

Energy Efficiency

Energy transfer from plants to consumers and from prey to predators is about 10% on average (often 5–20%). Omnivores can improve energy intake by choosing higher energy foods like animal prey, fruits, and nuts, so they do not have to eat only hard to digest plants. But feeding at higher trophic levels gives less energy from the food-web base, so omnivores mix abundant low-trophic foods with richer high-trophic foods. This mix helps populations survive shortages but can increase competition across trophic levels.

Common Habitats

Forest
Deciduous Forest
Coniferous Forest
Rainforest
Woodland
Grassland
Savanna
Shrubland
Wetland
River/Stream
Lake
Estuary
Coastal
Urban
Suburban
Agricultural/Farmland
Desert
Tundra

Seasonal Variation: Omnivores follow seasonal food pulses. In spring and summer they eat protein-rich items like insects, young animals, amphibians and fresh plants to fuel growth and breeding. In late summer and autumn they shift to energy-rich fruits, nuts and seeds, building fat or caching food. In winter or dry times they use stored food, roots, plants, carrion, or human food.

Fun Facts

Did You Know?

"Omnivore" doesn't mean "eats everything"-many omnivores are still picky, with strong preferences and foods they can't digest or avoid for toxin reasons.

Omnivory can be seasonal: some omnivores shift diets dramatically across the year (more plants when they're abundant, more animal matter when plants are scarce), effectively "changing menus" with the weather.

A lot of omnivores rely on microbes to handle the plant side of the diet-gut bacteria help break down tough fibers and can even produce vitamins the animal can use.

Omnivory is a risk-management strategy: mixing foods can reduce dependence on any single resource and help animals survive droughts, harsh winters, or boom-and-bust prey cycles.

Some classic "predators" are actually omnivores in practice-many carnivore-looking animals regularly eat fruit, seeds, or roots when it's an efficient energy choice.

Omnivory is like a diversified investment portfolio: spreading calories across plants and animals can buffer against sudden "market crashes" in any one food source.

It's the dietary equivalent of having both a pantry and a freezer-plants can be abundant and easy to gather, while animal foods can be more intermittent but nutrient-dense.

An omnivore's gut is often a "middle-ground tool": not as specialized as a cow's fermentation chamber, but usually better at handling mixed meals than a strict carnivore's short, protein-focused system.

Omnivore Animals

Showing 1-24 of 1,038

All Animals A-Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z