88 Animals That Start with O

The world is filled with so many incredible creatures. Some are well-known while others are rarely talked about. Learning about the many animals we share a planet with is a great way to feel closer to nature.

Since there are so many animals in the world, it’s easiest to learn about them if we divide them up by letters of the alphabet. So, this article will discuss some incredible species starting with O.

List of Animals That Start with O

Here are 88 animal species that start with the letter O.

1. Oak Toad

• Scientific Name: Anaxyrus quercicus
• Habitat: Forests and savannas of the southeastern United States
• Size: About 1.3 inches long
• Diet: Ants, beetles, spiders

Oak toads are North America’s smallest toad species. Unlike similar species, these amphibians are usually active during daylight, but they’re hard to spot because of their small size and neutral-colored skin. They usually hide under logs and leaf litter. In the winter, they burrow in the soil to hibernate. These toads usually crawl along the ground instead of hopping. If a predator catches them, they can release a poisonous fluid with a foul taste.

2. Oak Treehopper

• Scientific Name: Platycotis vittata
• Habitat: Near oak trees in the United States and Mexico
• Size: About 0.3 inches long
• Diet: Woody plants

Oak treehoppers are most commonly found in groups on oak trees, both as nymphs and adults. The adults have light green bodies with red stripes while the nymphs have black, red, and yellow coloring. Once a group of eggs hatch, the mother usually stands guard over the newborn nymphs. Mothers stand so still that they can be picked up by humans before they’ll try to fly away.

3. Oasis Hummingbird

• Scientific Name: Rhodopis vesper
• Habitat: Coastal landscapes of Peru
• Size: 4.3 to 5.3 inches long
• Diet: Nectar, small insects

Most oasis hummingbirds have dull feathers in comparison to other hummingbird species, however, the males have violet throats when they’re ready to breed. Males are highly aggressive toward other males, so there’s a lot of competition during the mating season. The males will present the females with songs and unique flight patterns to impress them. They may also show off their purple feathers. These birds rarely travel long distances because the weather in their region is fairly consistent.

4. Oaxaca Cichlid

• Scientific Name: Vieja zonata
• Habitat: Slow-moving waters from southern Mexico to El Salvador
• Size: 7 to 13 inches long
• Diet: Algae, aquatic plants

Oaxaca cichlids are rarely mistaken for other species because of their distinct elongated shapes and their shimmering scales. However, hybrids can occur of this species mixed with another species in the genus Vieja. Oaxaca cichlids are sometimes kept in aquariums, but they need lots of space to prevent aggression toward other fish in the tank. However, researchers said that the behavior of this fish can vary greatly, so some may be more peaceful than others.

5. Oceanic Whitetip Shark

• Scientific Name: Carcharhinus longimanus
• Habitat: Worldwide in tropical and sub-tropical waters
• Size: 200 to 350 pounds
• Diet: Bony fish, cephalopods

These sharks can be distinguished from other shark species because of the white tips on their fins. They’re aggressive opportunistic hunters, so they pose a higher risk for humans than most shark species do. They prefer bony fish for their meals, but they will eat almost anything they can catch. They will often swim through schools of fish with their mouths open. Sadly, these sharks are critically endangered because humans hunt and use their fins for shark fin soup.

6. Ocellaris Clownfish

• Scientific Name: Amphiprion ocellaris
• Habitat: Coral reefs of the eastern Indian Ocean and western Pacific Ocean
• Size: 1.5 to 4 inches long
• Diet: Crustaceans, algae, polychaete worms

The coloring of the Ocellaris clownfish varies based on where it lives. These fish are most well-known for their orange bodies with white and black stripes, but some groups near Australia appear almost all black. These clownfish live in sea anemones because they have a slimy exterior that protects them from the stings. The clownfish eat harmful parasites off the anemone, and in return, the anemone protects them from predators. All Ocellaris clownfish are born male, but the dominant ones may become female as they age.

7. Ocellated Antbird

• Scientific Name: Phaenostictus mcleannani
• Habitat: Rainforests from Honduras to Ecuador
• Size: 7.5 to 7.7 inches long
• Diet: Insects, arthropods, small lizards

Despite having a bright blue face, these birds can be difficult to spot because they often stay close to the ground when foraging. Both males and females have the same unique colors. They usually travel in pairs or small flocks, following swarms of insects like ants. Groups of these birds usually include a breeding pair, their male offspring, and the offspring’s mates. These birds only lay clutches of two eggs.

8. Ocellated Dragonet

• Scientific Name: Synchiropus ocellatus
• Habitat: Reefs of the southwest Pacific Ocean
• Size: About 2.5 inches long
• Diet: Small crustaceans

Ocellated dragonets are also known as scooter blennies, but they’re not a type of blenny. They have a similar body shape to a blenny, which is what causes confusion. Males of this species are more colorful than females, and they have large sail-like fins. They stay in shallow water, primarily seeking out copepods to eat, but in captivity, they can get used to eating a wide variety of foods. However, they prefer to eat live food if available.

9. Ocellated Frogfish

• Scientific Name: Fowlerichthys ocellatus
• Habitat: Reefs and muddy areas of the western Atlantic Ocean
• Size: 15 to 16.5 inches long
• Diet: Small fish, crustaeans

Ocellated frogfish have unusual bumpy body shapes. Their skin is dark brown/purple as juveniles, and their skin lightens to a purple/pink color as they grow. They always stay close to the ocean floor, either in muddy and sandy substrates or on pieces of coral. These creatures are called frogfish because some of their fins resemble the legs of frogs.

10. Ocellated Tapaculo

• Scientific Name: Acropternis orthonyx
• Habitat: Humid, moist montane forests of Ecuador and Peru
• Size: 8.3 to 8.7 inches long
• Diet: Insects, spiders, plant materials

These beautifully colored birds usually forage on the ground in areas of dense vegetation. They dig using their feet to uncover food. They’re typically found at elevations between 7,500 and 9,800 feet in the northern Andes Mountains. These birds will let out a loud whistle whenever they want other creatures to be aware of their presence. They’re usually found alone or in pairs.

11. Ocellated Turkey

• Scientific Name: Meleagris ocellata
• Habitat: Forests of Guatemala, Belize, and Mexico’s Yucatan Peninsula
• Size: 6.6 to 11 pounds
• Diet: Seeds, berries, leaves, insects

These beautiful birds are near threatened because they’re often hunted for food and sport. However, you should not hunt and eat this turkey for a fancy meal because they are not domesticated and kept for food like other turkey species are. These turkeys usually roost in trees to avoid predators. Even though they’re timid, they regularly make gobble sounds that you can’t miss. They’re powerful fliers, but only for short distances.

12. Ocellated Wrasse

• Scientific Name: Symphodus ocellatus
• Habitat: Rocky areas of the eastern Atlantic Ocean
• Size: About 4.7 inches long
• Diet: Polychetes, bryozoa, mollusks, crustaceans

There are three different types of males of this species, and each one has a different appearance. Nesting males have the brightest colors and the largest bodies, and they court females and build nests. Sneaker males are the smallest with the dullest colors, and they try to fertilize eggs before nesting males can. Then, satellite males are medium-sized with average colors, and they help chase away sneaker males, but they never care for offspring like nesting males. The male’s type will be determined based on how fast or slow the fish grows.

13. Ocelot

• Scientific Name: Leopardus pardalis
• Habitat: Tropical and subtropical rainforests from Mexico to central South America
• Size: 20 to 35 pounds
• Diet: Small mammals, birds, reptiles, young deer

Despite being on the small side, ocelots are skilled hunters. Their sharp teeth allow them to deliver a killing bite when pouncing on their prey. Their teeth aren’t equipped for chewing, so they need to tear pieces off the meat and swallow the pieces whole. They’re usually solitary, but they can communicate with each other using scents, vocalizations, and body gestures. Every ocelot has unique markings on their fur, so no two ocelots look exactly alike.

14. Ochraceous Bulbul

• Scientific Name: Alophoixus ochraceus
• Habitat: Rainforests and evergreen forests from southeast Asia to Sumatra
• Size: 7.4 to 8.6 inches long
• Diet: Fruits, insects

Ochraceous bulbuls usually forage in small, loud flocks on low tree branches. Their sounds vary between short, dry notes and pleasant warbling songs. They can be distinguished from birds of similar species because they have fluffy, white beard-like feathers under their beaks, which stand out against their brown and yellow feathers. When picking fruits from trees, these birds often swallow them whole.

15. Ochre-Bellied Boobook

• Scientific Name: Ninox ochracea
• Habitat: Tropical and subtropical forests of Sulawesi, Indonesia
• Size: 9.8 to 11.4 inches long
• Diet: Insects

These medium-sized owls roost in small groups, making growling, frog-like calls. They’re active both during the day and night, but they’re difficult to spot because they live among dense vegetation. Their big yellow eyes and ochre-colored bellies are hard to miss. Not much is known about this species’ population, but these birds seem to be near threatened due to forest loss.

16. Ochre-Bellied Flycatcher

• Scientific Name: Mionectes oleagineus
• Habitat: Humid-forests from southern Mexico to central South America
• Size: About 5 inches long
• Diet: Seeds, berries, insects, spiders

At first glance, these birds don’t stand out much, but their olive and ochre feathers help separate them from similar species. They’re often seen lifting one wing at a time. When the males are looking for mates, they will let out high-pitched calls while jumping and hovering around the females. However, once a female lays eggs, the male has no part in caring for the young birds. The hatchlings are covered in soft gray feathers, so they don’t develop the species’ significant colors until they’re full-grown.

17. Ochre-Marked Parakeet

• Scientific Name: Pyrrhura cruentata
• Habitat: Humid lowland forests of Brazil
• Size: About 11.8 inches long
• Diet: Seeds, fruits

These parakeets are colorful with a mix of green, red, yellow, blue, and ochre feathers. They’ve been spotted in many forests, clearings, and agricultural areas of Brazil, but they never seem to feed on agricultural crops. During the breeding season, which is in the spring, the females lay their eggs in tree crevices. Their population is vulnerable because of habitat loss and illegal capturing.

18. Ochre-Striped Cardinalfish

• Scientific Name: Ostorhinchus compressus
• Habitat: Reefs of the Indo-West Pacific
• Size: Up to 4.7 inches long
• Diet: Zoobenthos, crustaceans, small fish

Ochre-striped cardinalfish, also known as blue-eyed cardinalfish, are typically found near coral reefs. Their shimmering eyes suggest that they have excellent vision, allowing them to avoid predators and locate food easier. They’re not picky, so they’ll eat most small invertebrates they find. They’re usually found close to the surface, but they seem to be able to tolerate low oxygen levels. These fish are often kept in aquariums due to their striking eyes and stripes.

19. Ocoee Salamander

• Scientific Name: Desmognathus ocoee
• Habitat: Near streams along the Blue Ridge Mountains and Cumberland Plateau
• Size: 2.5 to 4.5 inches long
• Diet: Insects, worms, spiders

Ocoee salamanders are one of several mountain dusky salamander species. Their coloring can vary greatly. They’re typically some shade of brown either with a large stripe down their backs or speckles. They spend most of their time on rocks and plants near water, but when it’s time to breed, they enter the water to lay their eggs under moss or floating logs. Females stay near their eggs until they hatch.

20. Odaigahara Salamander

• Scientific Name: Hynobius boulengeri
• Habitat: Temperate, moist forests of Japan
• Size: 5.6 to 7.9 inches long
• Diet: Insects, spiders, worms

“Odaigahara” is the name of the mountain where these salamanders were first discovered. Now, they’re present in most forests across Japan. They live near streams so it’s easy for them to enter the water during the breeding season. After breeding, the females lay two long egg sacs, and they attach one end to rocks submerged in water. In the winter, the salamanders sometimes feed on large earthworms that are close to their own body length.

21. Odorous House Ant

• Scientific Name: Tapinoma sessile
• Habitat: Near moist sources across North America
• Size: 0.06 to 0.12 inches long
• Diet: Honeydew secretion, human foods

As the name implies, odorous house ants usually live in houses, invading food stored by humans. They prefer sugary foods, but they will eat almost anything available. They forage for food both day and night, and they usually travel along the edge of rooms. When crushed, these ants emit a foul odor that’s described as rotten coconut or blue cheese. They build their nest in moist areas and create a series of tunnels so thousands of workers can come and go.

22. Oilbird

• Scientific Name: Steatornis caripensis
• Habitat: Evergreen forests of Central America and northern South America
• Size: 16 to 19 inches long
• Diet: Fruits

Oilbirds are nocturnal and use echolocation to navigate at night. However, unlike bats, oilbirds make sounds that are audible to humans. They make a variety of clicking and screeching sounds as they search for food. Most of the year, they rest in trees, but during the breeding season, they build nests in caves. They have flat postures, allowing them to blend in better and fly faster.

23. Oita Salamander

• Scientific Name: Hynobius dunni
• Habitat: Temperate forests near rivers in Japan
• Size: 3.9 to 6.2 inches
• Diet: Insects, insect larvae, worms, spiders

Most of the year, male and female Oita salamanders appear identical. However, during the mating season, males have broader heads and lighter colors around their throats. Females gain weight as their egg sacs absorb water. When females release their egg sacs, males will compete to try to be the first to fertilize the eggs. These salamanders eat a wide variety of invertebrates, but they avoid slugs, which is unusual for a salamander species.

24. Okapi

• Scientific Name: Okapia johnstoni
• Habitat: Ituri Rainforest of Congo
• Size: 440 to 770 pounds
• Diet: Leaves, buds, twigs, shoots, fruits

Even though Okapis have black and white stripes on their legs, they’re related to giraffes, not zebras. Like giraffes, they have long tongues to help them grab leaves from trees. Their tongues are so long that they can also use them to clean their eyes and ears. Okapis live in dense vegetation, so their stripes help them camouflage with the light shining through the trees. Despite being beautiful creatures, they’re sadly endangered, and they’re only native to one rainforest in central Africa.

25. Oki Salamander

• Scientific Name: Hynobius okiensis
• Habitat: Temperate forests near rivers in Japan
• Size: 4.7 to 5.2 inches long
• Diet: Insects, worms, spiders

Oki salamanders are primarily found only on the Dōgo Island of Japan. Sadly, with such a small habitat range, the species is at risk of disappearing due to habitat loss. These amphibians are currently listed as critically endangered. They spend winters in the mountains near brooks so they can start breeding around February. Their clutches typically have less than 60 eggs, and some larvae mature within months while others take up to a year.

26. Old English Sheepdog

• Scientific Name: Canis familiaris
• Habitat: Domesticated
• Size: 60 to 100 pounds
• Diet: Domestic dog food

These shaggy canines originated in southwestern England, where they were used to drive sheep and cattle to the market rather than herding them. These dogs are friendly, cuddly, and intelligent, but they require experienced families. Their owners will need to spend hours each week brushing their fluffy coats. Even when trained properly, these dogs can have a loud, distinctive bark that’s sometimes compared to pots clanging together. They can make great guard dogs in homes today.

27. Old Wife

• Scientific Name: Enoplosus armatus
• Habitat: Temperate coastal waters of Australia
• Size: About 9.8 inches long
• Diet: Crustaceans, worms

The questionable name “old wife” was given to these fish because sailors compared the grunting sounds the fish made when caught to an old woman nagging. These fish have an elegant appearance, but they can also be dangerous. The spines on their dorsal fins contain venom that can cause severe pain if a person touches them. Researchers have located fossils of these fish that are about 50 million years old.

28. Oleander Aphid

• Scientific Name: Aphis nerii
• Habitat: Tropical and temperate regions worldwide
• Size: 0.05 to 0.1 inches long
• Diet: Dogbane, milkweed

All wild oleander aphids are female, and they can reproduce without fertilization. Instead of laying eggs, they deposit nymphs that look identical to the adults, only smaller. They are born wingless, but some can develop wings if their colony becomes too large, requiring some to fly to a different plant. These insects are a common pest to a variety of plants because they can stunt plant growth, cause plant deformations, and transmit diseases.

29. Oleander Hawk-Moth

• Scientific Name: Daphnis nerii
• Habitat: Hillsides and scrublands of Asia, northern Africa, and parts of Europe
• Size: 3.5 to 5.1 inch wingspan
• Diet: Nectar

Larvae of this species can be a pest since they feed on a variety of plants, however, the adults are essential for pollinating flowers. They prefer nectar from jasmine, honeysuckle, periwinkle, and petunia plants. The larvae feed on plants that are toxic to most humans and animals, such as oleander plants, but the larvae are immune to the toxins. These moths are most active at twilight, so bats often hunt them.

30. Olive Baboon

• Scientific Name: Papio anubis
• Habitat: Grasslands and forests across Africa
• Size: 25 to 80 pounds
• Diet: Plants, insects, birds, rodents

Olive baboons eat a wide variety of foods. They’re able to extract nutrients from almost any source, which is useful for surviving in dry climates. They also have cheek pouches that they can store extra food in. They’re highly intelligent and have sharp teeth, but they’re not usually dangerous unless provoked. These primates can successfully mate with baboons outside of their species, such as yellow baboons and Guinea baboons.

31. Olive Python

• Scientific Name: Liasis olivaceus
• Habitat: Rocky areas, woodlands, and savannas of northern Australia
• Size: Over 13 feet long
• Diet: Mammals, birds, reptiles

Despite being massive, these snakes are usually gentle toward humans. However, many people kill them because they look similar to king brown snakes, which are venomous. Olive pythons are nocturnal snakes that hide in caves and crevices during the day. They’re great swimmers, so they won’t hesitate to swim across a body of water to catch prey. They have more dorsal scale rows than other pythons, making their skin appear smoother.

32. Olive Ridley Sea Turtle

• Scientific Name: Lepidochelys olivacea
• Habitat: Tropical areas of the Atlantic, Pacific, and Indian oceans
• Size: 80 to 110 pounds
• Diet: Crabs, shrimp, algae, mollusks, tunicates

Olive Ridley sea turtles can be in tropical oceans worldwide up to 500 feet below the water’s surface. They often sleep while submerged, and they can sleep for up to two hours before needing to come back for air. These turtles usually live 50 to 60 years, and they don’t reach sexual maturity until they’re 13 years old. Females can lay over 100 eggs several times a year, but the chances of survival are low for the hatchlings since they need to crawl from the sandy shores to the water.

33. Olive Sea Snake

• Scientific Name: Aipysurus laevis
• Habitat: Shallow reef flats near Australia
• Size: Up to 6.5 feet long
• Diet: Fish, fish eggs, crustaceans, mollusks

Olive sea snakes don’t breathe underwater, but they can stay underwater for up to two hours before coming to the surface for a breath. They have valves in their noses to prevent them from inhaling water while swimming. They have venom that they use to paralyze their prey, which can also be dangerous for humans. These snakes are unlikely to attack unprovoked, but if you get bitten, you should seek medical attention immediately.

34. Olive Whistler

• Scientific Name: Pachycephala olivacea
• Habitat: Wet forests of southeastern Australia
• Size: 7 to 8 inches long
• Diet: Insects, seeds, leaves, fruit

These olive-brown birds make beautiful, smooth whistling sounds. They’re sometimes described as the whistler species with the most musical songs. These birds build their nests out of fragile twigs, and then they line the inside with softer items like plant materials and spiderwebs. They lay cream eggs that often have black or lavender spots.

35. Olive-Backed Euphonia

• Scientific Name: Euphonia gouldi
• Habitat: Humid forests of southern Mexico and Central America
• Size: 3.5 to 3.9 inches long
• Diet: Small fruits

Both males and females of this species have bronze/green feathers, which may appear lighter or darker depending on the lighting. However, the females’ feathers look less glossy. These birds usually travel in small groups, and they often feed in mixed-species flocks. They build spherical cup nests that they hide among moss on trees. They make a variety of sounds, but their most notable call is a nasally whistle.

36. Olive-Backed Oriole

• Scientific Name: Oriolus sagittatus
• Habitat: Woodlands across northern Australia
• Size: 9.8 to 11 inches long
• Diet: Insects, nectar, fruits

Olive-backed orioles have a distinct appearance because their red beaks and eyes greatly contrast with their olive-colored feathers. Like other oriole species, they make songs that sound like “orri-orri-orriole,” sometimes without even opening their beaks. They spend most of their time perched on trees alone, and even if they travel with a mate, they tend to keep their distance. They are rarely found near bodies of water.

37. Olive-Backed Sunbird

• Scientific Name: Cinnyris jugularis
• Habitat: Mangrove forests from southern Asia to northern Australia
• Size: About 4.7 inches long
• Diet: Nectar, insects

Both males and females of this species have olive backs and yellow bellies, but only the males have blue throats. Males use their colorful feathers to attract females, and then they work together to build a flask-shaped nest. They sometimes build their nests near human homes. Then, both of them abandon the nest until the female is ready to lay eggs. These sunbirds mostly eat nectar, so they will hover above a flower when feeding.

38. Olm

• Scientific Name: Proteus anguinus
• Habitat: Underwater caves of southern Europe
• Size: 8 to 12 inches long
• Diet: Insects, insect larvae, worms, mollusks

Olms are a species of aquatic salamander, similar to axolotls. However, they’re blind, due to their poorly developed eyes. They can breathe air using lungs, but they only do so if the water doesn’t have enough oxygen. They have pale skin because they spend most of their time in dark underwater caves. If exposed to light for a while, their skin can darken, but it will become pale again once they return to their dark habitats. These unique salamanders live over 58 years, and they can survive without food for up to 10 years.

39. Olrog’s Gull

• Scientific Name: Larus atlanticus
• Habitat: The Atlantic coast of Argentina, Uruguay, and Brazil
• Size: 20 to 24 inches long, 51 to 55 inch wingspan
• Diet: Crabs, barnacles, mollusks, worms

Young Olrog’s gulls have a mix of brown and white feathers, but they develop more white feathers as they age. When adults are ready to breed, they have pure white feathers everywhere except their wings and tails. Non-breeding adults still have some brown feathers on their heads. They’re usually found along the shore, searching for crabs, which take up the majority of their diets. They may also search in shallow water to find food.

40. Olympic Marmot

• Scientific Name: Marmota olympus
• Habitat: Alpine meadows of Olympic National Park in Washington
• Size: 14 to 18 pounds
• Diet: Flowers, grasses, roots

Olympic marmots are only native to the Olympic Mountains. They hibernate for seven to eight months of the year, and they survive by increasing their body fat and relying on their slow metabolism. They also have a thick double-layered coat to keep them warm in the winter months. Their coats change colors depending on the season, so their fur is tan after hibernation, but it turns almost black before the next winter. They’re social mammals, and males usually mate with several females each season.

41. Onagadori Chicken

• Scientific Name: Gallus gallus
• Habitat: Domesticated
• Size: 3 to 4 pounds
• Diet: Insects, worms, small frogs

This chicken breed originated in Kochi, Japan, and these birds are known for having long, flowing tails. They have the longest tails in the world, which grow up to 27 feet long. They rarely molt, and some don’t at all. Despite being a National Monument of Japan, these chickens are critically endangered with only about 1,000 remaining. They’re friendly, docile birds that require a high-protein diet to keep their tail feathers healthy.

42. Onager

• Scientific Name: Equus hemionus
• Habitat: Desert plains and mountain steppes across Asia
• Size: 440 to 575 pounds
• Diet: Grasses, herbs, leaves, fruits

Onagers have coats that change with the season. In the summer, their fur is thin and reddish-brown. However, in the winter, they grow curly coats that have a yellow or gray tint. Onagers are highly intelligent, but they’re more free-spirited than horses and donkeys. Thus, humans gave up trying to domesticate them and focused on easier animals instead. They can live to be about 40, and they can recognize the face of someone they met 25 years ago.

43. Oranda Goldfish

• Scientific Name: Carassius auratus auratus
• Habitat: Domesticated
• Size: 8 to 12 inches long
• Diet: Worms, crustaceans, vegetables

Oranda goldfish are recognized by their brain-like, overgrown head that’s called a “wen.” They originated in Japan and China, but they no longer exist in the wild. They were developed in the aquarium trade industry, and they’re one of the most popular fancy goldfish species today. They’re a much bigger commitment than most goldfish because they can live 15 to 20 years with proper care. They need a tank that’s at least 30 gallons.

44. Orange Baboon Tarantula

• Scientific Name: Pterinochilus murinus
• Habitat: Warm, humid areas of central and southern Africa
• Size: 3 to 4 inches long
• Diet: Insects, lizards, mice

These large spiders got their unique name because their faces resemble baboons with orange fur. Despite being kept as a pet in some areas, these tarantulas are dangerous. They have venomous bites that can harm humans, and the pain can last for up to 40 hours. They’ll lift their front legs if they feel threatened before biting. Their behaviors have earned them a silly nickname: “orange bitey thing.”

45. Orange Bullfinch

• Scientific Name: Pyrrhula aurantiaca
• Habitat: Temperate forests of India and Pakistan
• Size: About 5.5 inches long
• Diet: Seeds, buds, berries

All orange bullfinches have beautiful orange feathers, but females have duller plumage. They always have a black mask of feathers around their eyes and beaks. Their stubby beaks are used for picking up seeds and berries off the forest floor. Their foraging behaviors are even the same in snow-covered areas. These birds make soft whistling sounds when perched on tree branches.

46. Orange Clownfish

• Scientific Name: Amphiprion percula
• Habitat: Lagoons and reefs of the Indo-Pacific region
• Size: 3.1 to 4.3 inches long
• Diet: Algae, plankton, copepods

These clownfish travel in groups that include one breeding pair and about four individuals that don’t breed. The fish in each group are not related to each other. These groups locate a host anemone based on the chemical cues the anemones release. The anemone protects the clownfish from other fish, and in return, the clownfish eat parasites off the anemone. These fish stay in the same area year-round.

47. Orange Ground Thrush

• Scientific Name: Geokichla gurneyi
• Habitat: Montane forests of southeastern Africa
• Size: 8.3 to 9.1 inches long
• Diet: Insects, earthworms, fruit

These birds fly and rest in trees like other birds, but they’re called orange ground thrushes because of how they forage. They feed on the ground by picking up invertebrates and fallen fruits. They usually stay in the same areas their whole lives, only migrating short distances. They’re musical birds that regularly make a series of whistles and chatters. However, these birds are easily frightened when humans approach. They lay beautiful turquoise eggs.

48. Orange Nectar Bat

• Scientific Name: Lonchophylla robusta
• Habitat: Tropical habitats of Central America and northern South America
• Size: 2.2 to 2.9 inches long
• Diet: Insects, nectar, pollen, fruit

Orange nectar bats have a unique pumping mechanism on their tongues to help them obtain nectar faster. They have two grooves on their tongues that contain muscles to pull nectar toward them. This isn’t a behavior seen in other bat species. Since they feed on nectar, they will often eat from hummingbird feeders if they’re available. They have hovering flight patterns, so researchers have mistaken them for hummingbirds at first glance.

49. Orange River Francolin

• Scientific Name: Scleroptila levaillantoides
• Habitat: Grasslands and savannas across Africa
• Size: 12.5 to 13.7 inches long
• Diet: Weeds, corms, seeds, bulbs

Orange river francolins are shy birds that use their unique brown feathers to blend in with tall grass. Their timid nature is likely because they’re frequently hunted by humans. They let out fast repetitive calls when they feel threatened. During the breeding season, the females of this species dig shallow nests in the ground. Chicks are ready to leave the nest shortly after hatching, and they’re able to fly short distances at two weeks old.

50. Orange Sulphur Butterfly

• Scientific Name: Colias eurytheme
• Habitat: Open habitats from southern Canada to northern Mexico
• Size: About a 2-inch wingspan
• Diet: Nectar

Orange sulphurs are light orange with black markings on the outsides of their wings but yellow-orange on the insides. In rare cases, females could appear white instead of orange. As caterpillars, they’re always solid green with a yellow stripe. These butterflies take advantage of outside sources to regulate their body temperatures. They bask in the sun with their wings spread out to warm up or hang out near water to cool off. Sometimes, they rest on the moist ground to sip salt and minerals from the water.

51. Orange Weaver

• Scientific Name: Ploceus aurantius
• Habitat: Mangroves, thickets, swamps across Africa
• Size: About 5 inches long
• Diet: Fruits, insects, insect eggs, seeds

When these birds have bright orange feathers, it means they’re males ready to breed. The feathers of females and non-breeding males don’t stand out as much. These birds don’t form close bonds with other birds, even when breeding. One male will usually mate with about three other females each breeding season. Yet, large groups of these birds congregate together when it’s time to lay eggs, and they all build their woven nests near each other.

52. Orange-Bellied Flowerpecker

• Scientific Name: Dicaeum trigonostigma
• Habitat: Moist, tropical forests from Bangladesh to southern Indonesia
• Size: 3.1 to 3.6 inches long
• Diet: Berries, nectar, insects

These vibrant birds usually hang out near forest edges, hovering near flowers to collect food. They’re not afraid to live near humans, and they can be recognized by their sharp, buzzing notes. Both males and females have orange bellies, but males have gray-blue feathers on the rest of their bodies while females appear olive. Males also have a patch of orange feathers on their backs.

53. Orange-Bellied Himalayan Squirrel

• Scientific Name: Dremomys lokriah
• Habitat: Forests of Bangladesh, China, India, Myanmar, Nepal, and Bhutan
• Size: About 16 inches long
• Diet: Nuts, seeds, fruits, insects

As the name implies, these rodents look like typical squirrels, but they have bright orange fur on their bellies. Even though this species isn’t well-researched, its population is stable, and the squirrels can be frequently spotted in their region. These squirrels will forage both on the ground and in trees, and they can be skittish when humans are present.

54. Orange-Bellied Leafbird

• Scientific Name: Chloropsis hardwickii
• Habitat: Hilly woodlands of the central and eastern Himalayas
• Size: 5.9 to 7.8 inches long
• Diet: Insects, spiders, nectar

Orange-bellied leafbirds don’t migrate, so they stay high in the canopies of their regions year-round. They have curved bills and forked tongues to help them capture a variety of invertebrates and nectar. Their beak shape helps them pick insects from bark, and their tongue texture helps them grab nectar while hovering near flowers. These birds have small hair-like feathers at the base of their beaks so insect legs and wings won’t irritate their eyes.

55. Orange-Billed Sparrow

• Scientific Name: Arremon aurantiirostris
• Habitat: Subtropical and tropical forests from southern Mexico to northern South America
• Size: About 6.6 inches long
• Diet: Insects, spiders, seeds, fruits

The bright orange bills of these birds indicate their maturity. Juveniles have black beaks with hints of orange, and their bills gradually get more orange until they’re full-grown. At night, their vibrant beaks seem to glow in the dark. These birds spend most of their time perched in trees, but they will hop along the forest floor when foraging for plants and invertebrates.

56. Orange-Breasted Sunbird

• Scientific Name: Anthobaphes violacea
• Habitat: Fynbos biome of South Africa
• Size: 4.9 to 6.5 inches long
• Diet: Nectar, insects, spiders

Orange-breasted sunbirds are always on the move so they can find their favorite flowers. During the summer, they may migrate to higher altitudes to find nectar. Like hummingbirds, these birds will hover near their flower of choice and use their long, curved bills to reach the nectar. They often travel in flocks of up to 100 birds. However, males can act aggressive and territorial during the breeding season, so orange-breasted sunbirds are more spread out during that time.

57. Orange-Breasted Trogon

• Scientific Name: Harpactes oreskios
• Habitat: Forests from southern China to Indonesia
• Size: 9.8 to 12.2 inches long
• Diet: Insects, insect larvae, spiders, vegetable material

Orange-breasted trogons have distinct calls that sound like several “hoots.” They have a unique hunting style known as “sally-stall.” They wait on a perch, chase prey when they spot it, and then hover in front of the prey for a few moments before capturing it. Thus, the majority of their diet consists of flying insects. When it’s time to breed, these birds create nests by digging cavities in rotting parts of otherwise healthy trees.

58. Orange-Cheeked Waxbill

• Scientific Name: Estrilda melpoda
• Habitat: Grasslands and forest clearings of western and central Africa
• Size: About 4 inches long
• Diet: Grass seeds, small insects

Grass is important to orange-cheeked waxbills. They feed primarily on grass seeds, search for other food like insects in the grass, and use grass to build their nests. They travel in groups, which either consist of small family groups or flocks of up to 30 birds that may not be related. These birds spend more time climbing than flying. They climb up and down trees and may even hang upside down when picking up food. They communicate with each other by making high-pitched peeps.

59. Orange-Crowned Warbler

• Scientific Name: Leiothlypis celata
• Habitat: Woodlands and shrubby thickets across North America
• Size: 4.8 to 5.3 inches long
• Diet: Insects, berries, leaves, buds

The name of this bird is deceiving because its coloring is dull. These birds usually have a mix of olive, gray, and brown feathers. They have orange feathers on the top of their heads, but it’s rare to see that color unless the birds get excited and lift their crests. These birds have calls that can vary greatly, which helps them stand out when searching for a mate. Birds who live near each other may mimic the songs of their neighbors.

60. Orange-Headed Thrush

• Scientific Name: Geokichla citrina
• Habitat: Woodlands of southern Asia
• Size: 8.1 to 9.2 inches
• Diet: Insects, earthworms, fruit

Orange-headed thrushes are shy birds that usually travel alone or in pairs. If they sense danger, they can sit motionless until the threat passes. In flight, they’re completely silent. They’re most active at dawn and dusk, which is when they pick through leaf litter to find food. There are a few color variants of this species. Some have completely orange heads while others have white patches with brown stripes by their eyes. All of them have gray-blue wings.

61. Orbicular Batfish

• Scientific Name: Platax orbicularis
• Habitat: Reefs of the Indo-Pacific region
• Size: Up to 20 inches long
• Diet: Small fish, anemones, corals

Orbicular batfish can be found in both shallow and deep reefs. They often hang out near shipwrecks. These fish can travel alone, in small groups, or in large groups, depending on the area. Juveniles tend to stay in sheltered areas while adults are more drawn to open water. These fish have flat, disc-shaped bodies, but their bodies are much shorter in captivity than in the wild. They’re sometimes caught by fishermen because of their high-quality meat.

62. Orca

• Scientific Name: Orcinus orca
• Habitat: Cold waters across all oceans
• Size: 7,000 to 16,000 pounds
• Diet: Fish, squid, string rays, sharks

Orcas, also known as “killer whales,” are the largest species in the dolphin family. They earned their vicious nickname because they sometimes hunt small whales. Yet, these mammals rarely harm humans. They’re constantly on the move as they search for food. An orca can travel over 90 miles in a single day. They usually travel in family groups called pods, and each pod develops unique sounds to communicate with each other, similar to how humans develop different accents. Without counting humans, orcas are the most widespread species, existing in every ocean.

63. Orchard Oriole

• Scientific Name: Icterus spurius
• Habitat: Open woodlands from southern Canada through Mexico
• Size: 5.9 to 7.1 inches long
• Diet: Nectar, pollen, fruit, insects

Like other orioles, these birds don’t visit regular seed bird feeders. Instead, they’re attracted to feeders with nectar, orange slices, or fruit jelly. Since they eat pollen, they’re great at pollinating various flowers in the area. They get along well with most bird species, so they often nest near a variety of different birds. Each mating season, these orioles find one mate and stick by their side, but each year, they find a new mate.

64. Orchid Dottyback

• Scientific Name: Pseudochromis fridmani
• Habitat: Shallow reefs of the Red Sea
• Size: About 3 inches long
• Diet: Shrimp, krill, plankton

Despite being bright purple, these fish are great at blending into their surroundings. They can mimic the colors of the coral reef, making it easier for them to sneak up on prey. However, they’re unable to change their colors instantly. It sometimes takes days for them to alter their appearance. All orchid dottybacks are born with female organs, but dominant fish can develop male organs as they age. In an aquarium, they can be highly territorial if not given enough space.

65. Ord’s Kangaroo Rat

• Scientific Name: Dipodomys ordii
• Habitat: Sandy areas of western North America
• Size: 7.8 to 11 inches long
• Diet: Seeds, insects, grasses, fungi

Ord’s kangaroo rats survive in dry environments by rarely drinking water. They get enough moisture to sustain themselves through the food they eat. These rodents dig burrows in the sides of sand dunes for cover. They place their burrows beside trails leading to feeding areas. They will sometimes hide seeds in their cheek pouches and bring them back to the burrow before eating them. They may also bury hundreds of seeds in shallow holes.

66. Oregon Spotted Frog

• Scientific Name: Rana pretiosa
• Habitat: Wetlands across western Oregon and Washington
• Size: 2 to 4 inches long
• Diet: Flies, spiders, beetles, water striders

Oregon spotted frogs gain more spots the older they get. As tadpoles, they have brown, spotless skin, but as they become adults and continue to age, they keep getting more spots. Adult frogs have upturned eyes so they can see above the water when their bodies are submerged. When in the water, they make clicking sounds. These frogs are rare and endangered, so they no longer appear in 70% to 90% of their original range.

67. Oribi

• Scientific Name: Ourebia ourebi
• Habitat: Grasslands across Africa
• Size: 26 to 49 pounds
• Diet: Grasses, herbs, leaves, flowers

These mammals can be found alone, in pairs, or in groups, so they’re adaptable to all living situations. Males can be territorial, so they spend most of their time patrolling the edges of their territories. They may walk around the borders up to 16 times in one hour. When they’re not patrolling, these animals are almost always feeding on grass. If they sense a threat, they will let out a high-pitched whistle to warn others. Then, they can run up to 30 miles per hour to escape a predator.

68. Oriental Bay Owl

• Scientific Name: Phodilus badius
• Habitat: Tropical moist forests of southeastern Asia
• Size: 8.8 to 11.4 inches long
• Diet: Rodents, bats, lizards, large insects, small birds

During the day, oriental bay owls rest in hollow tree trunks or shady areas. They’re not very alert when it’s light out, so humans can get close to them without scaring them. Since they’re nocturnal, they hunt at night by sitting on a perch and searching for prey. They have short, round wings that make flying through trees to capture animals easier. These owls let out loud calls at night, starting in the early evening and sometimes lasting until after midnight.

69. Oriental Cockroach

• Scientific Name: Blatta orientalis
• Habitat: Cool, damp areas worldwide
• Size: About 1 inch long
• Diet: Garbage, sewage, decaying organic matter

Oriental cockroaches are considered one of the dirtiest cockroach species. They typically travel through drains and sewer pipes instead of invading homes, causing them to carry a foul smell. These insects are often called “water bugs” because they thrive in damp environments. They can survive up to a month without food, but they can’t survive more than two weeks without water.

70. Oriental Cuckoo

• Scientific Name: Cuculus optatus
• Habitat: Monsoon forests across Asia
• Size: 11.8 to 12.6 inches long
• Diet: Insects, insect larvae, worms

Oriental cuckoos are usually perched on tree branches, and they will swoop down to scoop up insects if they see them. They live among dense foliage, and their coloring helps them stay hidden. Male and female oriental cuckoos have unique calls. Males make low notes that sound like they’re saying “poo poo” while females make deep bubbling trills. These birds never build their own nests, but instead, they lay their eggs in the nests of other birds. Once the eggs hatch, the chicks push the host bird’s eggs out of the nest.

71. Oriental Dwarf Kingfisher

• Scientific Name: Ceyx erithaca
• Habitat: Forests and wetlands of southern Asia
• Size: 4.5 to 6 inches long
• Diet: Insects, spiders, worms, crabs, fish

Both males and females of this species are vibrantly colored. They perch low to the ground and wait for prey to pass by before they ambush it. They regularly clean their feathers in lakes and streams, and then they dry themselves off in the sunlight. These birds build their nests in underground tunnels so their eggs can be protected from predators. After the female lays the eggs, both parents take turns incubating them.

72. Oriental Fire-Bellied Toad

• Scientific Name: Bombina orientalis
• Habitat: Ponds and slow-moving streams of eastern Asia
• Size: Up to 2 inches long
• Diet: Insects, mollusks, worms

Oriental fire-bellied toads have brightly colored skin to warn predators that they’re poisonous. Their skin can release a substance that stings the eyes and mouth of any animal trying to eat them. Their poison can’t severely harm a human, but little to no handling is recommended, even if they’re kept as pets. Some snake species don’t seem bothered by the foul poison these amphibians produce. These toads don’t have long tongues, so they need to leap close to prey and grab it with their mouths instead.

73. Oriental Flying Gurnard

• Scientific Name: Dactyloptena orientalis
• Habitat: Tropical waters of the Indo-Pacific region
• Size: 8 to 16 inches long
• Diet: Small fish, crustaceans, bivalves

Oriental flying gurnards have massive pectoral fins that resemble wings. They do not jump out of the water and fly, but when they’re swimming with their fins outstretched, they look like they’re flying beneath the water. When they need to swim faster, they usually quickly retract their fins. These fish often stay close to the ocean floor and use their pelvic fins to “walk” along the substrate while picking up food.

74. Oriental Plover

• Scientific Name: Charadrius veredus
• Habitat: Dry areas of northern Australia
• Size: 8.2 to 9.8 inches long
• Diet: Insects, snails, seeds

Females and non-breeding males of this species have dull brown feathers, but during the breeding season, males have only white feathers on their heads. They forage in loose flocks on the ground. Even though they normally stay in dry areas, they will wade in shallow water to forage if the food on land is scarce. They’re always on the move, so they’re rarely seen in the same spot for more than a few days.

75. Oriental Turtle Dove

• Scientific Name: Streptopelia orientalis
• Habitat: Open woodlands in parts of Europe and eastern Asia
• Size: 12.9 to 13.7 inches long
• Diet: Seeds, grains, berries, snails

Oriental turtle doves spend a lot of their time on the ground so they can forage for fallen seeds. They most commonly travel alone or in pairs, but large groups have been spotted. During the mating season, males try to impress females by hopping around and bobbing their heads. Once paired up, these birds usually mate for life. Males and females work together to build a nest in a tree, and they take turns guarding the nest. The chicks leave the nest about two weeks after hatching.

76. Orinoco Crocodile

• Scientific Name: Crocodylus intermedius
• Habitat: Lagoons of Venezuela and Colombia
• Size: 500 to 880 pounds
• Diet: Fish, birds, small mammals

Orinoco crocodiles have existed on this planet for at least 240 million years. They’ve barely changed in the last 200 million years, making them a living fossil. Sadly, they’re currently endangered, with somewhere between 250 and 1,500 remaining. They’re at the top of the food chain, so their main threat is illegal hunting from humans. Despite having 68 teeth, these crocodiles cannot chew their food. Instead, they rip off chunks and swallow them whole. They’re sluggish animals with low metabolisms, so they can survive up to three years without food.

77. Orinoco Goose

• Scientific Name: Neochen jubata
• Habitat: Freshwater wetlands of Venezuela and Colombia
• Size: 24 to 30 inches long
• Diet: Grasses, algae

This species got its name because these birds are typically found along the Orinoco River in Venezuela. Even though “goose” is in their name, they’re technically shelducks instead of geese. However, their heavy flight style resembles a goose. They usually live and nest near water, but they don’t swim unless they need to. They like to stay in one place for most of their lives, so they rarely fly either. They’re highly social, living in pairs or family groups.

78. Ornate Box Turtle

• Scientific Name: Terrapene ornata ornata
• Habitat: Grasslands and plains of central United States
• Size: 0.5 to 1.5 pounds
• Diet: Insects, berries, carrion

Ornate box turtles are one of the few turtle species that live primarily on land instead of in the water. Even though they’re not built for an aquatic lifestyle, they can swim if they get stuck in the water. Fat deposits on the bottom of their shells help them float long enough to swim back to shore. They’re solitary for their entire lives, except for when it’s time to breed. If they feel threatened, they will hide in their shells to protect themselves from predators.

79. Ornate Butterflyfish

• Scientific Name: Chaetodon ornatissimus
• Habitat: Tropical waters of the Indo-Pacific region
• Size: 5.1 to 7 inches long
• Diet: Coral polyp tissue

Each pair of ornate butterflyfish usually occupy their own territory, which has plenty of corals. Juveniles are solitary until they find a partner, and they will spend a lot of time hiding in coral crevices until then. Breeding pairs of these butterflyfish rarely leave their home range. They mate for life, and they reproduce at different times depending on where they live. If the water is tropical, they will breed in the winter or early spring, but if the water is temperate, they will breed in the middle of summer.

80. Ornate Flycatcher

• Scientific Name: Myiotriccus ornatus
• Habitat: Tropical moist montane forests in Colombia, Ecuador, and Peru
• Size: About 4.7 inches long
• Diet: Insects

These colorful little birds sit on perches as they wait for insects to fly past. When they spot their prey, they will chase it down, sometimes catching it in mid-air. They’re most commonly found in forests, but they can also be found perched along roadsides. These birds are distinguished by their yellow rumps and the white spots on their faces that resemble headlights.

81. Ornate Hawk-Eagle

• Scientific Name: Spizaetus ornatus
• Habitat: Neotropical rainforests of Mexico and Belize
• Size: 22 to 27 inches long, 3.8 to 4.6 foot wingspan
• Diet: Other birds, small and medium mammals, reptiles

Ornate hawk-eagles are strong predators, sometimes hunting animals that are twice their weight. They have a large black crest on the top of their heads that they will raise if they’re excited, alert, or curious. They like to perch in heavily vegetated areas so they can remain hidden before targeting their prey. Female hawk-eagles usually only lay one egg at a time, and the females look after the egg while the males do the hunting.

82. Ortolan Bunting

• Scientific Name: Emberiza hortulana
• Habitat: Open landscapes of Europe, Africa, and western Asia
• Size: 6.3 to 6.7 inches long
• Diet: Insects, seeds

These little birds might look like any other birds you’d come across, but they’re known as a forbidden delicacy. These birds have been roasted and eaten whole since Ancient Rome, but hunting and eating them is now illegal. In history, the correct way to eat these birds was with a napkin over your head, but there are several reasons behind it. Some believe it’s so no one sees you spitting out the bones while others believe it helps hold in the aroma of the food. Some even believe that eating the bird is shameful, so the napkin is a way to prevent God from seeing you do it.

83. Oscar Fish

• Scientific Name: Astronotus ocellatus
• Habitat: Shallow rivers of South America
• Size: 12 to 15 inches long
• Diet: Fish, insects, insect larvae

Oscars are common pets because of their friendly personalities. Oscars seem to recognize their humans when they see them, and they’ll often eat food out of their hands. If they don’t like the layout of their tank, they make pick up rocks and move them around. These fish can alter their colors based on how they’re feeling, but they usually have patterns of gray, black, and orange. They have teeth in their throats to help process prey as they swallow it.

84. Osprey

• Scientific Name: Pandion haliaetus
• Habitat: Near water across all continents except Antarctica
• Size: 2 to 4.6 pounds, 4.1 to 5.9 foot wingspan
• Diet: Fish, small mammals, birds, reptiles, amphibians

These powerful birds are capable of catching a wide variety of animals, but their diets consist of 99% fish. They have sharp claws and reversible outer toes, allowing them to easily scoop up slippery fish. They can fly up to 50 miles per hour before diving toward the water to catch their prey. These birds may dive feet-first into the water to grab a fish, but they can still fly away even after getting drenched. They often reuse nests from other ospreys, and the same nesting sites could be used for up to 70 years.

85. Otago Skink

• Scientific Name: Oligosoma otagense
• Habitat: Rocky canyons of Otago, New Zealand
• Size: Up to 12 inches long
• Diet: Insects, fruits, flowers, small reptiles

Otago skinks are one of New Zealand’s biggest lizard species. They eat a wide variety of food, and they hunt live prey by pouncing on it and killing it with their strong jaws. When eating plants, they help distribute the seeds. They’re social with their own species, but they act aggressively toward other lizards, so they won’t even share a rock with a different species. These lizards can live for over 40 years in the right environment.

86. Ouvea Parakeet

• Scientific Name: Eunymphicus uvaeensis
• Habitat: Forests on Ouvea Island in New Caledonia
• Size: About 12.5 inches long
• Diet: Fruits, other plants

Ouvea parakeets look like they have horns, but those are just a crest of black feathers. They used to be considered the same species as the horned parakeet, but the two are now separate species due to slight differences in appearances and behaviors. These birds don’t like to be active during extreme heat, so they’re more likely to forage in the early morning and late afternoon. Females lay two to three eggs, but only one chick usually survives because of predators and illegal capturing by humans.

87. Ovenbird

• Scientific Name: Seiurus aurocapilla
• Habitat: Dense forests across eastern North America
• Size: 4.3 to 6.3 inches long
• Diet: Insects, spiders, worms

Ovenbirds got their unique name because they build nests that are shaped like ovens. The nests are spherical with one opening in the front. A lot of animals will try to steal eggs and chicks from the nests, which is why the nest is covered on all sides except one. If predators approach the nest, the mother will fake an injury to lure the threat away from her offspring. Males of this species sing frequently, but females are typically silent.

88. Owl-Faced Monkey

• Scientific Name: Cercopithecus hamlyni
• Habitat: Bamboo forests of the Democratic Republic of Congo
• Size: 15 to 22 pounds
• Diet: Bamboo shoots, leaves, shrubs, fungi, insects

Owl-faced monkeys, also known as Hamlyn’s monkeys, have olive-gray fur surrounding their distinct faces. Their unique coloring helps them hide from predators in dense vegetation. They have longer fingers than most monkeys, allowing them to grip onto branches even when they’re wet. They usually live in small groups of 10 monkeys or less, and each group has one dominant male. They use scents to mark their territory to keep other animals out.

A Beautiful World of Animals

O is only one letter of the alphabet, so there are many animals that start with the other letters. There are more animals in this world than we can even imagine, and many of them have unique behaviors and lifestyles. If you’re interested in learning about more species, check out animals starting with other letters.