Animals ZZZZZZZZZZZZZZZZ

Groups - For warmth, some groups of animals will sleep huddled together. Many groups of animals or animals who travel in herds have guards to keep watch while the others sleep. Animals who often travel together will sleep together as well.

• Lions sleep near each other. Lion cubs sleep with their mothers.
• Walruses sleep on the rocks on the shore. They lie together on their sides or on their backs.
• Mallard Ducks sometimes sleep on the water in a row. A recent study shows that some of them may sleep just half a brain at a time in order to keep watch for their entire group. 
• Monkeys of many varieties sleep in "colonies."
• Some insects, including ants, ladybugs, and termites sleep in groups.
• Others, as diverse as buffalo and gazelles, giraffes and elephants, reindeer and penguins, wild horses and zebras, beavers and bats, sea lions and flocks of birds sleep in groups as well.

Families - Family groups often sleep together. Human homes vary in different cultures, from extended families sharing a house to a nuclear (parents and children only) family living in an apartment. Sometimes singles will by a condominium for a community environment. Children almost always live in their parents' homes, although most probably sleep separately from their parents. Young birds sleep in their parents' nests. Raccoons, and numerous mammals actually sleep together in family groups.
Alone - Solitary adults such as the bobcat, giant panda, iguana, koala, lynx, moose, and tiger, and many snakes prefer to sleep alone, coming together with others of their species for mating times. Some of these rear their young for a time before becoming solitary once more.

Location

Where an animal sleeps often relates to where it spends time awake. Sometimes this is the same location, but not always. Many animals sleep in areas that give them protection while they rest, such as caves, underground, or hollowed-out trees.
Humans are not the only ones to build their own sleeping quarters. An amazing variety of animals dig their own burrows, weave their own nests, and even create elaborate homes like the nests of paper wasps, bee hives, or beavers' lodges. African termites even create special tunnels in their mounds (which are up to 42 feet [12.8 meters] high!) to keep their dwelling cool, or "air-conditioned."
Caves

• Bats hang upside-down while they sleep. Long-eared bats tuck their ears under their wings. You can see bats live through a WebCam  at the National Zoo (Washington, D.C.)
• Bears
• Mountain lions

Trees - Many animals, both ground and tree dwellers, choose to sleep in trees. For some, it provides safety because of its high location and its many view-blocking branches. Those animals who hang from or perch in trees have special natural built-in body features in their claws, tails, etc.

• Birds that sleep on a perch or branch lock their legs in a bent position. Their toes curl to ensure a good grip. Many birds will make a nest to sleep in. 
• Some birds, such as woodpeckers, wood ducks, or barn owls, make their sleeping quarters inside the hollow of a dead tree.
• Elf owls will even sleep inside a cactus, once woodpeckers have left homes vacant. (4)
• Orangutans gather leaves to prepare a bed for themselves in the trees each night. While they sleep, their fingers and toes will wrap around the branches so that they don't fall.
• Many other primates including: chimpanzee, gibbon, baboon, the ring-tailed lemur, and the spider monkey. For those who have them, tails help to keep them in place while sleeping.
• Squirrels also make nests in trees, but like birds, these are for more than a one-night stay.
• Many others, including: sloths, koalas, red pandas, Native American porcupines , opossums, panthers, lynx, and raccoons.

Underground - Whether alone or in groups, some live in underground tunnels or under the mud, others in elaborate burrows.

• Frogs
• Prairie dogs, with live in elaborate underground communities
• Many more, including other insects, moles, shrews, rabbits, chipmunks, badgers, and African Crested porcupines.

Water

• Ducks will often sleep on the water.
• Fish cannot close their eyes at all. It is controversial as to whether or not all fish actually sleep. Parrot fish use a bubble for protection.
• Crabs live in a variety of places, but not all sleep in the water even if they spend much time there while awake. Some sleep in burrows in saltwater stream banks, in abandoned shells, in oyster shells, in fresh water, or even in burrows several miles inland! 
• Manatees (large water mammals) need to surface for air, but sleep upside down underwater.
• Seals can sleep both on land and on water. Body fat and air inside their bodies help keep them afloat, allowing their noses to be above water so that they can breathe.
• Sea Lions keep their head above water to breathe while sleeping. Sometimes, they also keep one flipper out, which gains warmth on a sunny day.
• Sea Otters float on their back in seaweed. The seaweed anchors them so that they don't drift away.
• Polar bearsmay sleep in temporary dens in snow banks, even hibernating there briefly in winter before giving birth. However, they occasionally end up sleeping on an iceberg or ice floes in cold northern water, in the middle of a long hunt or swim. (8)

Posture (Position) During Sleep

A sleeping animal's posture depends not only on the type of animal, but also the type of sleep and the air temperature.
Upside down - Some animals that sleep upside down are bats, manatees, and sloths.
Tucked In - Many animals sleep in a curled up position with their nose and tail touching. The fox, for example, will use its bushy tail as a pillow. Similarly, birds will tuck their beak into the feathers above the wing. These postures help to conserve body heat, keeping the animals warm while sleeping. At warmer temperatures, sometimes these animals will stretch out their bodies during sleep.
Standing vs. Lying - Animals who experience REM sleep usually will sleep in a different posture during REM sleep. Many large mammals can sleep standing up, but they must lie down for REM sleep!
Among animals who sleep standing up are adult herbivores. This might be in order to remain on partial alert in case of danger. Most young animals lie down to sleep. Baby penguins, for example sleep lying down whereas the adults will sleep standing with their heads tucked under their wings.
Standing on one leg is even harder to imagine. Flamingos and herons are only two of the many birds who can sleep with one leg tucked up and not lose their balance. etc. to allow them to sleep securely without falling.

Pets

Domestic animals learn different sleeping habits from the wild.

• Birds who sleep on a perch in a cage may need a cover over it to protect them from drafts.
• Cats may sleep in window sills, in a bed or on some other furniture, or outside on a sunny driveway.
• Rabbits should be kept indoors or in a large and very secure hutch outdoors, where they can hide from predators. They need padding or nesting material if their cage is made of metal or wire.
• Pet fish, lizards, and amphibians will probably sleep better with adequate cover or hiding places to feel protected.
• Pet gerbils and hamsters may run on squeaky exercise wheels or chew loudly during the night while you are trying to sleep, so you may wish to keep them separate from your bedroom so their nocturnal noise level will not prevent you from getting deep sleep.
• Dogs may sleep in a special dog bed with padding, outdoors in a doghouse, indoors in a kennel or crate, in a bed, on a couch or on a rug.
• If you are allergic to your pet, you will probably want to consider having it sleep on a different level of your home than you are, but certainly out of your bedroom for your own health and breathing ease.