If you are a regular homo sapien you will spend a third of your life tucked up in bed, sound asleep. If you live to the respectable age of 75, then you would have successfully slept through a whopping quarter of a century. Sleep is a state of inactivity when we become less responsive to stimuli. The Oxford dictionary defines it as ‘a condition in which the nervous system is inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended’.

We now know that, as humans, we go through five distinct stages of sleep—the first of which is light sleep where we can be woken up easily by disturbances, onto the fifth stage called ‘Rapid Eye Movement’ or REM, in which we typically dream. We also know that many mammals and birds undergo changes in the brain while sleeping just like us; reptiles also display some sleep-linked changes. In some species of flies and cockroaches prolonged sleep deprivation can also be fatal. But limited research on animal sleep, coupled with its (at best) ambiguous definition when applied across species, has meant that our information on how exactly different animals snooze is still somewhat lacking.

So just how some animals get by in life with little or no sleep at all remains something of a complete mystery to us. Here are 7 creatures able to stay up all night, nearly every night.

1. Giraffes

With their long towering necks, sleeping isn’t the easiest activity for giraffes. Getting up once they lie down could take precious seconds and make them incredibly vulnerable to predators like lions and crocodiles. These tall mammals have therefore evolved to have very skimpy sleep needs. They take quick naps that last as long as five minutes through the day and all in all manage 30 minutes of sleep a day, topping the list of animals that need the least sleep. Indeed they rest so little, that up until the 1950s, researchers thought they didn’t sleep at all. Sometimes, they’ll will arch their necks and rest their heads on their rumps while sleeping and at other times they might nod off for a lightning quick power-nap whilst standing tall.

2. Dolphins

Have you ever taken a nap while on a swim? It’s an impossible feat for us, yet even for aquatic mammals it’s a challenge to swim and sleep at the same time. So dolphins have evolved a kind of sleep called ‘unihemispheric’ or one-sided sleep where they literally are half asleep. They shut down one hemisphere of their brains and the opposite eye (which the hemisphere controls) at a time, while the other hemisphere and an eye remain watchful. This way they stay on their guard in case of predators, are able to come up to the surface to take breaths while getting some rest. Sometimes dolphins swim while they are asleep, at other times they float at water looking like logs and this kind of sleeping is calling logging. Other marine mammals such as whales, orcas and porpoises also practice ‘unihemispheric’ sleep where they can remain asleep and awake at the same time.

3. Elephants

While they are gargantuan, their sleep needs are disproportionate to their vast sizes. Elephants are poor sleepers and need just as little as three to four hours of fragmented sleep throughout the day. Instead of spending time getting their forty winks, these gigantic animals utilise most of their time foraging and feeding. They spend up to 18 hours feeding to get 200-600 pounds of food a day necessary for their bodies. When they do sleep, they do it standing as they are, leaning on trees or termite mounds, or sometimes, lying down on their sides. When they sleep lying down on their sides, it’s never more than 30 minutes so as to keep their own body weight from crushing their internal organs.

4. Bullfrogs

Bullfrogs are thought to be animals that can survive without sleeping for months at a time. While they shut their eyes and go on to rest, they remain alert during these periods. According to research even while resting these huge amphibians were awake enough to respond to painful stimuli and show respiratory changes. They only time they do go into ‘deep sleep’ it is to hibernate to survive freezing winters.

5. Alpine swifts

Alpine swifts take their travel very seriously. So seriously in fact that when they travel from Switzerland to West Africa they are in flight continuously for 200 days, six months straight. They never stop on treetops or land for any ‘rest’ at all. Research shows that there are periods of slowdowns when the birds do not flap as much. But it is still unclear what kind of sleep they get up in air inflight.

6. Walruses

Walruses are talented sleepers who can break into snoozes just about anywhere and in any position—they can sleep floating in water, at the bottom of the sea, standing, leaning or lying down on land. They fill themselves with air in parts of their bodies called pharyngeal pouches and stay bobbing in water sleeping without drowning. Sometimes, they’ll hang on to ice sheets with their teeth while in water and continue to sleep. But these blubbery sleep-loving mammals also have the ability to stay up for a very long time without complete sleep. Scientists say that walruses can swim and stay awake continuously for 84 hours. They probably rest as much to have energy for these intense periods of non-stop activity.

7. Orca calves

While most infants of many species sleep a lot more and more deeply than adults, killer whale calves and baby dolphins are exceptions. They will spend the first few months of their lives wide awake with absolutely no sleep. Even when adults catch some sleep, young orcas will continue swimming around. This could be to stay safe from predators, but an important reason is that these aquatic infants need to keep their bodies warm with constant activity until they grow older and grow some blubber.