32 Animals That Start With O (Facts, Habitats & Photos)

Animals that start with O include the largest bird on earth, the only living relative of the giraffe, and an amphibian that can survive a decade without food. Otters, owls, ostriches, orangutans, orcas and octopuses are all here, alongside the okapi and the cave-dwelling olm.

This guide covers 32 animals beginning with O, with scientific names, animal group, where each lives and what makes it distinctive.

Animals Starting With O: Complete List

Mammals

Otter

Sea otters hold hands while sleeping so the group does not drift apart, and they tuck a favourite stone into a loose pouch of skin under the foreleg to crack shellfish — one of very few tool-using mammals. They have the densest fur of any animal, up to a million hairs per square inch, because they carry almost no blubber. River otters are separate species, lighter and far more terrestrial.

Orangutan

The only great apes that live mainly in trees, and the most solitary — adult males in particular range alone. Mature males develop broad cheek flanges, but only if they achieve dominance; subordinate males can remain flange-less for years and develop them within months if the dominant male disappears. They make a fresh sleeping nest of branches almost every night, and both Bornean and Sumatran species are critically endangered.

Orca

Not a whale in the strict sense but the largest member of the dolphin family, and one of very few animals with genuine culture — distinct populations have their own dialects, diets and hunting techniques passed down socially rather than genetically. Some hunt seals by generating waves to wash them off ice; others eat only fish and will not touch mammals. Females live decades past reproduction, and those matriarchs carry the knowledge of where to find food in lean years.

Okapi

The only living relative of the giraffe, sharing the long prehensile tongue — long enough to clean its own ears — and skin-covered horns on the male. The striped hindquarters break up its outline in dappled forest light. It was unknown to Western science until 1901, and it remains restricted to the rainforests of the Democratic Republic of the Congo.

Ocelot

A small spotted cat of Central and South America, roughly twice the size of a house cat, hunting mostly at night. Each coat pattern is unique. Ocelots were hunted heavily for fur through the twentieth century and were briefly fashionable as pets — Salvador Dalí famously kept one — which did the wild population no favours.

Opossum

North America’s only marsupial, and widely misunderstood. “Playing possum” is not a decision but an involuntary catatonic response to extreme threat, lasting minutes to hours. Their low body temperature makes them poor hosts for rabies, so they very rarely carry it, and they eat large numbers of ticks while grooming.

Oryx

Desert antelopes able to survive where almost nothing else can, tolerating a body temperature rise of several degrees rather than sweating away scarce water, and cooling the blood going to the brain through a network of vessels in the nasal passages. The Arabian oryx was hunted to extinction in the wild by 1972 and reintroduced from captive stock — the first animal to be downgraded from Extinct in the Wild back to Vulnerable.

Onager

An Asiatic wild ass, among the fastest members of the horse family, capable of sustaining high speed across open ground. Attempts to domesticate onagers in ancient Mesopotamia are documented but never took hold — they proved too difficult to manage, and horses and donkeys displaced them.

Olive Baboon

The most widely distributed baboon, living in troops that can exceed a hundred animals with intricate social alliances. Females stay in their birth troop for life while males disperse, so the social backbone is a network of related females. They are highly adaptable omnivores, which is why they thrive near human settlement and become a nuisance there.

Birds

Owl

Owls fly almost silently because the leading edge of the flight feather is combed into a fine fringe that breaks up the turbulence which would otherwise make noise. Many species have ear openings set at different heights on the skull, so a sound reaches each ear at a fractionally different moment, letting the bird locate prey in complete darkness by hearing alone. Their eyes are fixed tubes rather than spheres, which is why they must rotate the head instead of moving the eye.

Ostrich

The largest and heaviest living bird, too heavy to fly but able to run at 70 km/h with a stride up to five metres. Its eye is larger than its brain — the biggest of any land vertebrate. Ostriches do not bury their heads in sand; the impression comes from them lowering the head to the ground to turn eggs or to lie flat when threatened.

Osprey

A fish-hunting raptor found on every continent except Antarctica, with a reversible outer toe and spiny scales on the feet that let it grip a slippery fish with two toes forward and two back. It carries prey head-first to cut drag. Ospreys collapsed across much of the northern hemisphere under DDT and recovered strongly after the ban.

Oystercatcher

A coastal wader with a heavy orange chisel of a bill, used either to hammer shellfish open or to stab between the shells and cut the muscle — individuals specialise in one technique or the other and teach it to their young, so the skill is culturally transmitted rather than instinctive.

Ovenbird

A ground-nesting North American warbler named for its domed nest, which looks like a small clay oven. It is far more often heard than seen; the ringing teacher-teacher-teacher call carries a long way through closed forest.

Oriole

Two entirely unrelated groups share the name. New World orioles belong to the blackbird family; Old World orioles are a separate family altogether. Early European settlers named the American birds after the familiar yellow-and-black ones back home, and the name stuck despite no relationship.

Marine Life

Octopus

An octopus has nine brains in effect — a central one plus a large cluster of neurons in each arm, so an arm can solve problems semi-independently. Its blood is blue because it uses copper-based haemocyanin, and it has three hearts, two serving the gills. It can change colour and texture in under a second despite being colourblind, and it can pour its entire body through any gap larger than its beak.

Oarfish

The longest bony fish in the world, reaching eleven metres, living in deep water and only rarely seen at the surface — usually when sick or dying. Its ribbon-like body and red dorsal crest are almost certainly the origin of many historical sea-serpent accounts. Japanese folklore links strandings to earthquakes, a connection that has been examined and not supported by the data.

Ocean Sunfish

The heaviest bony fish, reaching over two tonnes, with a body that looks abruptly truncated because it effectively has no tail — it steers with enormous dorsal and anal fins. It basks on its side at the surface, which is thought to help it rewarm after deep dives and lets seabirds pick parasites off its skin.

Oyster

A single oyster filters up to 200 litres of water a day, and dense reefs once clarified whole estuaries — which is why oyster restoration is now used as a water-quality measure rather than only as fisheries work. Most oysters change sex at least once in their lives, typically starting male.

Oceanic Whitetip Shark

Once described as the most abundant large animal on earth over about 45 kg, and now critically endangered after decades of finning and bycatch — among the steepest declines recorded for any shark. It is a slow, curious open-ocean hunter, and it is associated with several historical shipwreck accounts.

Olive Ridley Turtle

Best known for the arribada, a mass synchronised nesting in which tens of thousands of females come ashore on the same beach over a few nights. The strategy overwhelms predators through sheer numbers, though so many nests are dug that later arrivals destroy earlier clutches.

Reptiles, Amphibians and Invertebrates

Olm

A blind cave salamander of the Balkans, sometimes called the human fish for its pale pink skin. It lives around a century, can survive a decade without food by slowing its metabolism almost to a halt, and retains larval features including external gills for its entire life. It hunts by sensing electrical fields and water movement.

Oenpelli Python

One of the rarest pythons in the world, restricted to a small area of the Arnhem Land escarpment in Australia’s Northern Territory. It was unknown to Western science until 1977, and it is thought to have persisted as a relict population as the surrounding country dried out.

Oak Toad

The smallest toad in North America at around 3 cm, with a pale stripe down the back. Its call is a high, chirping whistle far more like a bird than a toad, and unusually for a toad it is active by day.

Orb Weaver Spider

Orb weavers take down and rebuild the sticky spiral of the web most nights, frequently eating the old silk to recycle the protein. Only the spiral is adhesive — the radial spokes are not, which is how the spider crosses its own web without sticking. Their venom poses no threat to people.

Owl Butterfly

Large tropical butterflies whose underwings carry an enormous eyespot resembling the eye of an owl. Whether this deters predators by mimicking a predator or simply by being conspicuous enough to startle is still debated, with recent evidence favouring startle. They fly mostly at dusk.

Specialist and Regional Species

Ocean Whitefish

The Malacanthidae family of brickfish includes the whitefish, which has a long history in Southern California. Despite being a frequent bycatch in commercial fisheries in the United States, whitefish are not typically actively targeted. Outside of the breeding and mating season, they are quite busy and spend most of their time alone. They surface during the day to hunt or gather food on sand or rock beds, then retreat behind reefs and kelp at night for cover.

These fish have a small mouth located just in front of the eye and a deep, spherical head with a sharp, sloping contour. The square, robust-looking elongated body has a fleshy channel right in front of the dorsal fin. The dorsal fin typically has 2–27 soft rays and 7–10 spines. The caudal fin also comprises 22–26 soft rays and one to three spines. The belly looks to be white, while the majority of the body is covered with light brown scales. The dorsal fin is yellow, while the pectoral fin bears blue and yellow stripes. The majority of saltwater whitefish measure 12 to 15 inches in length and weigh around 8 pounds.

Ocellated Turkey

The Yucatan, along with some of Belize and Guatemala, is home to the endemic ocellar turkey (Meleagris ocellata). Although a little secretive and challenging to capture, these birds are loud and raucous. They spend their days scavenging for bugs and vegetables on the ground or taking naps in trees in tiny family groups where they reside in tropical and evergreen forests. Learn everything there is to know about this bird, including its habitat, diet, and social habits.

The ocellar turkey is a close relative of the wild turkey found in North America and is a rather sizable bird. In contrast to other wild turkey subspecies in North America, it is considerably smaller. This turkey has a wingspan of 67 inches, is 28 to 8 inches long, and weighs 6 to 11 pounds. Their tails include dots called ocelli that resemble the spots on peacocks, and their feathers are golden and iridescent green. Both sexes have blue heads with orange and red pimples, however, females are colorless and greener. Male corollas enlarge and turn bright yellow or orange during reproduction.

Frequently Asked Questions

What animals start with the letter O?

Thirty-two are covered here, including otter, owl, ostrich, orangutan, orca, octopus, oyster, okapi, opossum, oryx, osprey, ocelot, ox, olm, onager, oribi, olive baboon, oarfish, ocean sunfish, olive ridley turtle, oystercatcher, ovenbird, oriole, orb weaver spider, owl butterfly, oak toad and the Oenpelli python.

Do ostriches bury their heads in the sand?

No. The myth comes from ostriches lowering their heads to the ground to turn their eggs in the nest, and from their habit of lying flat with the neck extended when threatened, which from a distance looks like the head has disappeared.

Is an orca a whale or a dolphin?

A dolphin — the largest member of the dolphin family. The name killer whale is a reversal of the older Spanish description of them as whale killers, since they hunt large whales.

Why does an octopus have blue blood?

Because it carries oxygen using copper-based haemocyanin rather than iron-based haemoglobin. Haemocyanin works better in cold, low-oxygen water, which suits deep and cold ocean habitats.

Are opossums dangerous or disease-ridden?

Largely the opposite. Their low body temperature makes them poor hosts for rabies, so they very rarely carry it, and they consume large numbers of ticks. Playing dead is an involuntary shock response, not aggression.

What is the closest relative of the giraffe?

The okapi, and it is the only one. Despite looking like a cross between a horse and a zebra, it shares the giraffe’s long prehensile tongue and skin-covered horns, and the two are the sole surviving members of their family.

Sources

Classifications, distributions and conservation statuses follow current taxonomic and IUCN references. Orca cultural transmission and dialects: cetacean behaviour research. Oystercatcher feeding-technique inheritance: ornithological literature. Oarfish stranding and earthquake correlation studies: seismology and marine biology literature.

This article is for general information. Do not handle wild animals.

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