80+ Animals That Start With O: List, Facts & Fun

Nature doesn’t disappoint when it comes to animals that start with O. From open-ocean octopuses to oak-dwelling owls, this list explores a variety of creatures across continents and ecosystems. To make things easier, we’ve grouped them by general type—mammals, birds, reptiles, amphibians, fish, and invertebrates.

Each one includes a photo-ready description, fascinating facts, and metric-first quick stats so you can dive deeper into the animal kingdom. Whether you’re a student, trivia fan, or animal lover, get ready to meet over 80 species that all have one thing in common—they begin with the letter O.

Animals That Start With O

Ostrich (Struthio camelus)

The ostrich is the largest and heaviest living bird, found across the savannas and deserts of Africa. This flightless bird uses its powerful legs to run at incredible speeds, often exceeding 70 km/h. Standing up to 2.7 meters tall, ostriches are known for their long necks, large eyes, and distinctive plumage. They feed mainly on seeds, plants, and insects. Males are territorial during breeding season and care for communal nests. Listed as “Least Concern,” ostriches thrive in open areas but face localized threats from hunting.
Fun Fact: An ostrich eye is larger than its brain.

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Osprey (Pandion haliaetus)

The osprey is a fish-eating bird of prey found on every continent except Antarctica. With a wingspan exceeding 1.5 meters, it’s easily recognized by its white underside, dark eye mask, and hooked beak. Ospreys build large stick nests near water and are excellent divers, using reversible outer toes to grip slippery fish. They migrate long distances and are often found near lakes, rivers, and coastlines. Thanks to conservation efforts, their numbers have rebounded.
Fun Fact: Ospreys have a reversible outer toe for catching fish.

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Oriental Magpie-Robin (Copsychus saularis)

Common across South and Southeast Asia, the Oriental magpie-robin is a small, melodious bird found in urban gardens, forests, and farmlands. Males are mostly black with white underparts and patches on their wings. These insectivores are territorial and sing loudly during the breeding season to attract mates. Though small, they have big personalities and are known to mimic sounds. They are currently listed as Least Concern due to their broad range.
Fun Fact: It was once the national bird of Bangladesh.

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Orange-bellied Parrot (Neophema chrysogaster)

Native to southern Australia, the orange-bellied parrot is critically endangered and known for its vibrant green body and distinct orange belly. These small parrots breed in Tasmania and migrate to mainland Australia during winter. They inhabit coastal saltmarshes and feed on seeds and fruits. Extensive conservation programs are underway to save the remaining wild population.
Fun Fact: Fewer than 100 individuals remain in the wild.

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Oilbird (Steatornis caripensis)

The oilbird is a nocturnal fruit-eating bird found in the caves of northern South America. It uses echolocation—rare among birds—to navigate in complete darkness. With its long wings and soft feathers, it glides silently through forests and rocky grottos. Oilbirds primarily eat oily fruits from palm trees and play a crucial role in seed dispersal.
Fun Fact: It’s one of the only birds that uses echolocation.

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Okapi (Okapia johnstoni)

Found only in the dense rainforests of the Democratic Republic of Congo, the okapi is a shy, forest-dwelling relative of the giraffe. With zebra-like striped legs and a long purple tongue, it is well-camouflaged in the undergrowth. Okapis feed on leaves, fruits, and fungi and are typically solitary animals. They are extremely elusive and were unknown to Western science until the early 1900s. Due to habitat destruction and poaching, they are currently endangered.
Fun Fact: The okapi’s tongue is long enough to clean its own ears.

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Orangutan (Pongo pygmaeus, Pongo abelii, Pongo tapanuliensis)

Orangutans are large, intelligent great apes native to the rainforests of Borneo and Sumatra. With long, reddish hair and extremely long arms, they are excellent climbers and spend most of their lives in trees. Their diet consists mainly of fruits, leaves, and insects. Orangutans are known for using tools and having high problem-solving skills. All three species are critically endangered due to deforestation and the illegal pet trade.
Fun Fact: Orangutans share about 97% of their DNA with humans.

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Ocelot (Leopardus pardalis)

Ocelots are sleek, medium-sized wild cats found in South and Central America, as well as parts of southern Texas. Their golden coats with black rosettes make them look like miniature leopards. Ocelots are nocturnal and hunt rodents, reptiles, and birds. They’re agile climbers and swimmers, often found in tropical forests, mangroves, and shrublands. Though once hunted for their fur, they are now protected in many regions.
Fun Fact: Ocelots sleep in trees during the day and hunt at night.

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Onager (Equus hemionus)

Also known as the Asiatic wild ass, the onager roams arid regions in Iran, Turkmenistan, and Mongolia. It resembles a donkey but is faster and more slender. Onagers feed on grasses and shrubs and survive in harsh desert climates with minimal water. They live in small herds and are extremely wary of humans. Populations have declined due to habitat loss and competition with livestock.
Fun Fact: Onagers can run up to 70 km/h, outrunning most predators.

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Olive Baboon (Papio anubis)

The olive baboon is a highly adaptable primate found throughout sub-Saharan Africa. Named for its olive-colored fur, it lives in large troops that can include over 100 individuals. Olive baboons are omnivores, feeding on fruits, insects, small animals, and roots. They have complex social hierarchies and exhibit a range of vocalizations and facial expressions. Despite being common, they often clash with humans due to crop-raiding behavior.
Fun Fact: Olive baboons can recognize over 50 individuals by face and voice.

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Oceanic Dolphin (Delphinidae)

Oceanic dolphins include more than 30 species that inhabit open oceans around the world. Highly intelligent and social, dolphins use echolocation to communicate and hunt fish or squid. They travel in pods and often display acrobatic behavior like leaping and spinning. Species like the bottlenose dolphin are commonly seen, while others are more elusive. Many species face threats from fishing nets and pollution.
Fun Fact: Dolphins have been observed using tools like sea sponges for protection.

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Olive Ridley Sea Turtle (Lepidochelys olivacea)

This small sea turtle is best known for its mass nesting behavior, called arribadas, where thousands of females come ashore simultaneously to lay eggs. Found in warm oceans around the world, the olive ridley gets its name from its olive-colored shell. It spends most of its life in the open ocean, feeding on jellyfish, shrimp, crabs, and algae. Though once abundant, its numbers have declined due to bycatch, habitat loss, and egg poaching.
Fun Fact: Olive ridleys can dive over 150 meters deep in search of food.

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Oriental Garden Lizard (Calotes versicolor)

Widespread across South and Southeast Asia, the oriental garden lizard is a colorful reptile often seen in urban areas. Males develop bright red or orange heads during mating season, earning them the nickname “bloodsucker lizard.” It preys on insects and small invertebrates and uses camouflage to avoid predators. Though commonly found on fences and walls, it also thrives in forests and grasslands.
Fun Fact: Males puff their throats and nod to attract mates or warn rivals.

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Ornate Box Turtle (Terrapene ornata)

This North American turtle is easily recognized by its domed shell adorned with yellow lines and swirls. Ornate box turtles inhabit prairies and open grasslands and are most active during warm, humid weather. They are omnivorous, feeding on insects, plants, berries, and carrion. This species hibernates during cold months and can live for several decades. Habitat destruction and road mortality are major threats.
Fun Fact: They can completely close their shells to protect themselves.

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Orange-bellied Newt (Taricha torosa)

Native to California’s coastal forests, the orange-bellied newt is a brightly colored amphibian with a rough-textured skin. It is active during the rainy season and returns to water bodies to breed. This newt secretes a potent neurotoxin through its skin as a defense against predators. It feeds on small invertebrates like worms, insects, and slugs. Their populations are localized and face threats from urban development.
Fun Fact: Its skin toxin is potent enough to kill predators like birds and mammals.

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Ocean Sunfish (Mola mola)

The ocean sunfish is the heaviest bony fish in the world, known for its flattened, disc-like body and enormous dorsal fin. Found in temperate and tropical oceans, it basks near the surface to regulate its body temperature. Sunfish feed on jellyfish, small fish, and plankton. Despite their bulky appearance, they swim gracefully and can leap out of the water. Their main threats are fishing bycatch and plastic ingestion.
Fun Fact: Adult sunfish can weigh over 1,000 kilograms.

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Orange Roughy (Hoplostethus atlanticus)

A deep-sea fish found in cold waters around the world, the orange roughy is slow-growing and long-lived, with some individuals reaching over 150 years old. They have bright reddish-orange scales and large eyes adapted for low-light environments. These fish feed on small crustaceans and squid. Overfishing has severely depleted their populations, as they mature late and reproduce infrequently.
Fun Fact: They were once called “slimehead” before being renamed for marketing.

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Octopus (Octopoda)

Octopuses are soft-bodied, eight-armed cephalopods found in oceans worldwide—from shallow coral reefs to deep-sea trenches. Highly intelligent, they exhibit problem-solving abilities, use camouflage, and escape predators by releasing ink. Octopuses feed on crabs, mollusks, and small fish using their beak-like mouths. Most are solitary and short-lived, with lifespans ranging from 1 to 3 years. They reproduce once and then die shortly after spawning.
Fun Fact: Octopuses have three hearts and blue blood.

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Orb-Weaver Spider (Araneidae)

Orb-weaver spiders are a widespread family known for their iconic wheel-shaped webs. Found in gardens, forests, and grasslands around the world, they use silk to catch flying insects. Their colors range from dull browns to striking patterns, often acting as camouflage. Females are typically larger than males and rebuild their webs daily. They are harmless to humans and contribute to natural pest control.
Fun Fact: Some orb-weavers create zigzag patterns called stabilimenta in their webs.

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Olive Snail (Oliva spp.)

Olive snails are marine gastropods known for their smooth, glossy, olive-shaped shells. Found in tropical and subtropical sandy seafloors, they are active predators that burrow into the sand to catch small invertebrates. They use a siphon to detect prey and produce mucous to glide quickly along the ocean bottom. These snails are often collected for their attractive shells.
Fun Fact: Olive snails can move faster than most other sea snails.

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Osedax Worm (Osedax spp.)

Also called “bone-eating worms,” Osedax live on whale carcasses that have sunk to the ocean floor. These bizarre, tube-dwelling worms feed on bone marrow using root-like structures that release acids. Females dominate the colonies, while tiny males live inside their bodies. Discovered only in 2002, Osedax worms play a critical role in recycling nutrients in deep-sea ecosystems.
Fun Fact: Osedax worms dissolve bones with acid to extract nutrients.

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Olive Sea Snake (Aipysurus laevis)

Although technically a reptile, the olive sea snake is often grouped with marine invertebrates due to its oceanic lifestyle. It inhabits coral reefs of the Indo-Pacific and has a paddle-like tail for swimming. Its scales are smooth and olive-colored, and it breathes air but can stay submerged for up to two hours. The snake feeds on small fish and crustaceans and delivers venomous bites if provoked.
Fun Fact: It gives live birth underwater, unlike most snakes that lay eggs.

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Ornate Tailed Mite (Ornithonyssus bacoti)

This tiny parasitic mite primarily affects rodents but can also bite humans. Common in urban settings, it hides in bedding and walls, emerging at night to feed. The ornate tailed mite causes skin irritation and can spread bacterial infections. Though not deadly, infestations can become problematic in unsanitary environments.
Fun Fact: It can survive over a week without a host.

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Read: Animals That Start With F
Read: Animals That Start With M
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Read: Animals That Start With T
Read: Animals That Start With V

FAQs About O-Letter Wildlife

What kinds of animals begin with O?

Animals that start with O span all categories—birds like owls and ostriches, mammals like orangutans and ocelots, and sea creatures like octopuses and ocean sunfish.

Are octopuses considered fish or invertebrates?

Octopuses are invertebrates. They belong to the class Cephalopoda, which also includes squids and cuttlefish.

Which O animals are endangered?

Several animals that start with O are endangered, including the okapi, orangutan, orange-bellied parrot, and orange roughy.

Where can I see animals that start with O in the wild?

It depends on the species—oceans, rainforests, savannahs, and even urban parks host animals that start with O. From the Okavango to the open ocean, they’re widespread.

How many animals really start with the letter O?

This list includes over 80 animals that start with O, covering a wide range of taxonomic groups.

Conclusion: Observing the Wonders of O-Wildlife

From open-ocean dwellers like the octopus to iconic land animals like the ostrich and orangutan, the animal kingdom offers incredible diversity among animals that start with O. This list proves how one letter can unlock an entire alphabet of natural wonders.

Whether you’re a wildlife enthusiast or a trivia buff, learning about these species expands your understanding of Earth’s biodiversity and encourages a deeper respect for nature. Keep exploring—you never know what odd and outstanding O-animal you’ll discover next.