Owls, oxen, octopuses, and orcas; how many animals with names starting with the letter O can you mention? We have so many different animals that start with O all over the world. Some of these fascinating creatures are common. Others are rare, and you may not have seen or heard of them before.
Below you'll find 30 animals beginning with O that are less common, and learn some fun facts about them.
The olive ridley sea turtle starts out with a grey shell and skin, slowly turning olive green as it becomes an adult. One of the smallest sea turtles, the olive ridley sea turtle, grows to 2 to 2.5 feet.
We can only find the olive ridley sea turtle in the tropical waters of the Pacific, Atlantic, and Indian oceans. Fun fact; It can stay underwater for about two hours before it comes up for air. Arribada mass nesting is a behavior unique to the olive ridley sea turtle and the kemp ridley turtle6.
An olive ridley sea turtle can live for 30 to 50 years. Climate change, marine debris, bycatching, poaching of eggs, and predation are threats to the population of olive ridley sea turtles.
The olive sea snake gets its name from its skin color and habitat. Although it breathes air like any other reptile, it spends all its life in the ocean. The olive sea snake lives in the coral reefs along the northern coast of Australia.
These animals grow to be more than 6 feet long. Thanks to its large lungs, the olive sea snake can remain deep underwater for about two hours before rising to the surface for air. The venomous night hunter targets small and medium-sized fishes3.
Olive sea snakes rarely bite people, but on the rare occasions they do, it could be fatal. Sharks and big birds are their predators. Trawlers may catch them unintentionally as well.
Related: Read our article on snake facts for more from the world of crawly reptiles.
This golden-eyed black, brown, and white eagle are quite striking. Perhaps its most fascinating feature is the large crest of long black feathers on its head. The bird keeps its large crest flattened but raises it when excited. The young ornate hawk-eagle looks a bit different; it's a black and white eagle with no brown feathers.
The ornate hawk-eagle is a bird of prey that can take prey twice its size12; now, that’s a fun fact. The bird has a wingspan of 3 to 4 feet and can weigh between 2 to 3 and a half pounds.
We find the ornate hawk-eagle in Central and South America. The IUCN lists the ornate hawk-eagle population as near threatened, with rapid deforestation as the main threat.
Otters are semi-aquatic members of the weasel family known for their playfulness2. There are 13 species of otters; two of them are marine otters, while the other two species are river otters. We can find otters on every continent except Antarctica and Australia.
They have flattened tails and webbed feet that enhance their swimming abilities. The smallest otter species, the Asian small-clawed otter, weighs about 6.6 pounds, but the sea otter species can weigh as much as 99 pounds.
Otters prey on fish, frogs, crayfish, mussels, and crabs, eating whichever prey is readily accessible. They rest in root system cavities, underground holes, or rock crevices. You'll find them playing and sliding on mud or snow while not hunting or resting.
Read more: Our otter facts further explore the world of these playful creatures and why most species of otter are endangered.
Other names for the Oscar fish include marble cichlid, velvet cichlid, and red oscar. It is a common choice for folks who want pet fish, perhaps due to the unique marble pattern and beautiful colors on its body. Many people who keep pet Oscars say that the fish has a great personality and can be taught tricks.
The fish is native to South America but has been artificially introduced to other parts of America, to Asia as sports fish. The average adult oscar fish weighs 3.4 pounds and is a little over 1 foot. The oscar fish has a jaw in its throat. It consumes mostly vegetation but will eat shrimps, snails, and clams.
Related: You might also like our fish quotes for more from the underwater world.
The olive baboon is the most widely distributed baboon species ranging throughout sub-Saharan Africa. Their fur is a dark olive-grey, and that's where their common name originated.
Male olive baboons are way bigger than their female counterparts. The male olive baboon weighs about 25 kg, and the females weigh around 14 kg. Males also have bigger canine teeth and a mane and can grow to a head-to-tail length of over 3 feet.
An olive baboon consumes a variety of foods9, including fruits, eggs, grass, insects, flowers, tubers, reptiles, etc. These animals can live for about 37 to 45 years.
An orb weaver is any of the spider species that construct circular webs. There are over 4,000 species of orb wear spiders, and they make up the third largest spider family. They shed their exoskeleton to grow. Most orb weaver spiders come out in the evenings to avoid predators like birds1.
Orb weaver spiders prey on insects and serve as biological insect repellents. They coat the strands of their circular webs with a sticky substance that traps insects that happen to enter the web. Fun spider fact; they use their web to communicate through vibrations
Orb weaver spiders will live almost anywhere as long as there are insects to prey on. You'll find the third largest spider family members in humid habitats than dry places. Some species of orb spiders can also sometimes take flight, using their webs to catch the air, which has led them to occasionally be known as flying spiders!
These beautiful birds have iridescent bronze-green plumage with gold-tipped blue-bronze eye spots at the tail. Their head and neck have no feathers, and the exposed skin is blue with a red ring around the eyes. Male ocellated turkeys have a brighter appearance compared to females. Only males have a blue fleshy crown on their heads.
These birds are impressive runners and flyers, which is great as they are heavily predated. They are also quieter than North American turkeys, most likely in an attempt to be more stealthy.
The ocellated turkey is native to the Yucatan Peninsula in Mexico, north of Guatemala, and some parts of Belize. They are protected birds, as hunting them for food and sport significantly reduced their population.
Opossums look like giant rats and have pouches like kangaroos. There are over a dozen different species of opossums. Baby opossums are as tiny as bees; as adults, they grow to an average nose-to-tail length of 2.5 feet. In North America, they call opossums possums.
Their prehensile claws make opossums nimble tree climbers. You may have heard of the term “playing possum”; it comes from an escape tactic of opossums. When confronted with predators, they flop onto their sides, stick out their tongues, and pretend to be dead.
Opossums are scavengers; they like to raid the garbage for food. They'll eat fruits, birds, mice, grass, insects, chickens, and even carrion. Some people hunt opossums as food.
Read more: Opossum Facts.
The old English sheepdog is a large fluffy dog breed developed for driving sheep and cattle in the 18th century15. Today these friendly, gentle, and clever dogs make great service and family dogs. The old English sheepdog is bred for work and is naturally energetic but not aggressive.
Other names for the old English sheepdog are Sussex sheepdogs or Smithfield’s. They are also called bobtails because their tails are cut off soon after birth. The old English sheepdog originated in London and was introduced to America by wealthy folks as pets.
An old English sheepdog can grow to be 26 inches tall and weigh 55 pounds. These dogs require a lot of grooming and exercise.
You may have often wondered what kind of animal an ox is exactly. Are there baby oxen? What are female oxen called? Why do oxen look like cattle? Well, to start with, oxen are actually cattle. An ox is a castrated and domesticated bull (male cattle).
People use oxen as farm animals, plowing, transporting people, and hauling heavy objects. Oxen are strong and can work for a long time with just a few hours of rest. Being castrated inhibits certain hormones that would have made them aggressive and difficult to work with otherwise.
Oxen can live up to 15 years, but some people overwork and abuse them, which could shorten their lifespan.
Oysters are highly valued for food and pearls. There are two types of oysters; true oysters cultivated for food and pearl oysters which produce pearls. Some species are as small as 3 inches, while others grow to about 14 inches.
Usually, an oyster is either male or female, but some species can change their sex according to season or water temperature changes14. An oyster can live for up to 20 years. They eat algae and other food particles extracted from water, constantly flowing through their gills.
The population of oysters is not listed as threatened by ecological authorities, and commercial harvesting of oysters is mostly regulated. However, pollution has reduced the oyster population in many places where they were once abundant.
Read more: Oyster Facts.
Ostriches are large flightless birds popular and the largest living bird. An adult male ostrich can grow to be about 9 feet tall and weigh over 300 pounds. The ostrich’s egg is also bigger than other birds; an average ostrich egg is 6 inches long and 5 inches wide.
Male ostriches are not just larger than other birds; they are bigger than female ostriches too. The two species of ostrich are the Somali ostrich and the common ostrich.
An ostrich can run at 72.5 km per hour5, and a not-so-fun fact; can deliver a kick strong enough to kill a human. Contrary to popular belief, ostriches don't bury their heads in the sand when they sense danger. These birds lie down on the ground with their necks stretched forward instead.
Read more: Ostrich Facts.
Also known as killer whales, orcas are the largest member of the oceanic dolphin family. They are called killer whales for something, orcas are powerful apex predators, and they are at the top of the food chain. They eat fish, seals, penguins, sea lions, squid whales, and even seabirds.
These apex predators owe much of their hunting success to their habit of hunting in groups called pods10. Killer whale pods typically have about 40 members and use echolocation for hunting and communicating.
These members of the oceanic dolphin family can live for about 50 to 80 years; being apex predators contributes to this long lifespan. Lack of opportunity to be as active as they naturally would be causes captive orcas to develop stereotypies which could range from swaying to self-mutilation.
Read More: 20 Wondrous Whale Facts
Oilbirds are nocturnal birds that live in caves. They also use echolocation to navigate in the dark; their eyes are also adapted for night vision. They share a lot of traits with another species of nocturnal birds; bats.
They eat fruit, especially oil palm fruits. A not-so-fun fact; the oilbird's name does not come from its love of oil palm fruits but from a practice of boiling the animal to produce oil. People used the oil for cooking and making fires in ancient times.
You can find the oilbird in the northern parts of South America. The locals call them guácharo. Their plumage is brown-black and spotted with white dots.
Other names for the osprey include sea hawk, fish hawk, and river hawk, thanks to their appetite for fish. This fish-eating bird only consumes fish and barely anything else. Ospreys will hover above the water surface at a distance of 30 to 100 feet. Once they spot prey, they dive to the surface and grab the fish with their spike-padded talons.
Ospreys bear some physical resemblance to bald eagles, and mixing them up is easy. But you can differentiate them from the bald eagle by the osprey’s white underparts. Eagles often steal food from ospreys, forcing them to drop their catch in midair.
We can find ospreys on all continents except Antarctica.
The octopus is one of the sea's most fascinating creatures and perhaps the cleverest of invertebrate animals. There are many different species of octopuses. The smallest is about 2 inches long, while the largest can grow to almost 18 feet.
When attacked by predators, octopuses release an inky substance to cloud the water so they can escape7. Some species of octopuses release toxic ink that paralyzes the predator.
On the food chain, some marine fishes eat octopuses; they, in turn, eat crabs, lobsters, and plankton. People eat octopuses in Asia and many other parts of the world as special delicacies. Read up on our octopus quotes for more about what people have to say about these eight-tentacled marine dwellers and fascinating and intelligent animals.
Orangutans are members of the great ape family and one of the largest primates in the world. There are three species of orangutans, all living in Southeast Asia and the Borneo area. All orangutans sport their famous red fur, but only adult male orangutans develop huge cheek pads.
These animals eat fruit primarily, but they consume meat on rare occasions when the opportunity arises. They spend most of their time hanging out in the trees and rarely come to the ground. Two species of orangutan, Bornean, and Sumatran orangutans are critically endangered due to poaching and habitat loss.
Read more: Orangutan Facts.
The Okinawa spiny rat is also called Muennik’s spiny rat. It is a reasonably large rodent.
Not much is known about this mystery animal, but studies suggest that it is diurnal in summer and becomes nocturnal in winter.
In 1994, the Okinawa spiny rat was considered extinct but rediscovered in 2008. This rodent is super rare; you can only find it in the northern areas of Okinawa, Japan. The animal restrictively occurs in less than 3 square km. It is thought to be a critically endangered species.
The ‘Ō'ū, pronounced 'oh,' is a bird you can only find in Hawaii. The bird has a musky scent that is so strong even museum specimens still retain them. An adult ‘Ō'ū has an olive green back and white underparts, while the males have a bright yellow head13.
Geometrid caterpillars, fruits, and flowers make up the diet of the ‘Ō'ū. The bird is a strong flier and flies far in search of food. This bird is presumed extinct but listed as a critically endangered species by authorities. An avian disease spread by mosquitoes, habitat degradation, natural disasters, and predation by rats contributed to the possible extinction of the ‘Ō'ū bird.
The oarfish is a ribbon-shaped fish; it is long and thin. The fish has a silvery body with a long red pelvic fin on one side of its body. The dorsal fin is a prominent crest on top of its head. Other names for the oarfish include King of Herrings and ribbonfish.
The giant oarfish holds the title of the world's longest-bony fish and even has an entry in the Guinness Book of World Records. Some sightings, which are very rare, claim oarfish as long as 50 feet long, but confirmed reports put oarfishes at 35 feet.
The longest bony fish lives in the ocean's very deep and dark parts and is rarely seen.
The orange fruit dove is next in our list of O animals, which may also be called a flame dove or orange dove. From the neck-down male adults are a bright orange color, hence their name. Their head is a golden olive in color. The females and young flame doves are less showy, with dark green feathers with some black and orange.
These brightly colored birds are small, just about 20 cm long. They eat fruits, insects, berries, and caterpillars. Orange fruit doves have a stable population but thrive in a limited area on the island of Fiji.
The okapi looks like what you'd get if a zebra and deer had offspring. But really, it is the only living relative the giraffe family has in the animal kingdom. Another name for the okapi is the forest giraffe. It has brown thick oily fur, and its legs have stripes. The okapi's plant diet is supplemented with riverbed clay and bat poop.
This animal is native to the Ituri Rainforest in the Democratic Republic of Congo, Central Africa. The okapi is an endangered species, and conservation efforts in Congo are difficult due to civil unrest8.
Read more: Okapi Facts.
The oystercatcher is a large wading bird found along the coasts of North Africa, Asia, and Europe. All seven oystercatcher species are identifiable by their long wedge-shaped red-orange bills. Their plumage could be black or black with white patches. They are usually about 16 to 20 inches long with thick pink legs.
This large wading bird found on beaches and inland tidal flats feeds on oysters, clams, and mussels. You can find this bird catching prey as the tide ebbs when its shells are partially open.
Otterhounds are a type of dog breed that breeders developed to hunt otters. These dogs can hunt otters on land and in water. Otterhounds have been around since the 1700s or 1800s. They have thick shaggy fur that is water resistant.
Fun fact about otterhounds; they have webbed feet; no wonder they are such great swimmers. Otterhounds are friendly and make great family and therapy dogs. According to The Otterhound Club of America, there are just about 800 otterhounds worldwide.
Fun fact about the ocellaris clownfish; it is the hero in the popular kids' movie, Finding Nemo. People sometimes call it the Nemo fish. Other common names for the animal are common clownfish and false clown anemonefish.
The natural habitat of the ocellaris clownfish is coral reefs, around sea anemones in particular. They are immune to the anemone’s sting. The ocellaris clownfish ranges through Southeast Asia, northwest Australia and the Ryukyu Islands of Japan.
Another fun fact is that although most common clownfish fish species are orange to brown-red with white bands outlined with black, you can find a type with only black and white colors in Australia.
This bird species is endemic to the northern parts of Southeast Asia and central and eastern Himalayas and Yunnan. It is a non-migratory bird. Like Christmas ornaments, orange-bellied leafbirds hang their nests on the edges of tree branches. They feed on nectar and insects.
True to its name, this bird has orange feathers on its belly area. The feathers on its back are green, and those on its chest and throat are a mix of bright blue and blue-black patches. Its tail and part of its wing have blue feathers too.
The ornate chorus frog is a small frog native to the southeast United States. You'll find them in pine woodlands or upland fields. These frogs come in three colors; red-brow, grey, and green. The coloring and markings of ornate chorus frogs depend on their particular habitat in the range in the southeast United States11.
A very small frog, the ornate chorus frog, does not grow longer than 1.5 inches. A fun fact about this frog, it cannot stand the heat. Ornate chorus frogs can be found hiding under a layer of sand and vegetation in the warmer seasons in their upland and pine woodlands habitats.
The owl butterfly is remarkable because of the distinct owl-like eye markings on its wings. The marking, called eye spots, can scare away natural predators who might mistake the butterfly for a bigger animal. There are several species of the owl butterfly with these owl-like eye markings.
Owl butterflies are native to Central and South American rainforests. Fun butterfly fact; owl butterflies do not fly during the day, only at dawn or dusk. That sure helps the illusion they create with their eye spots. An owl butterfly feeds on nectar and juices from fermenting fruits.
Related: Whereas not an owl, you might like our rundown on the different types of owls for the real deal.
The ocelot is a wildcat; it is bigger than a housecat but smaller than a jaguar. Its gorgeous grey or tan fur has black stripes and spots, and its underparts are white. Ocelots are native to southern North America and South American rainforests. These amazing animals adapt favorably to disturbed habitats and can live near villages.
Ocelots are great climbers and swimmers. They hunt diverse prey, from rodents and reptiles to primates, birds, and fish. They are nocturnal and rarely move around in the daytime. Hunted for their skin, the Ocelots are now rare in some areas4.
Read more: Ocelot Facts.
This list exposes you to fascinating animals starting with O, like the orca, which we also know as the killer whale, orangutans, one of the world's largest primates, and so many more. If you ever need to make a list or talk about animals beginning with the letter O.
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Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.
Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.