Why ostriches DON'T bury their heads in the sand ... and the bizarre truth behind other great animal myths

This week, scientists from Germany's Max Planck Institute announced that sloths were far more active in the wild than had been previously thought. Here, DAVID THOMAS explains why sloths are not actually lazy  -  and dispels many more animal myths ...

MYTH: SLOTHS ARE SLOTHFUL

FACT: Whereas captive sloths sleep for up to 16 hours a day, wild sloths kip for fewer than ten hours, and are up and about  -  albeit very slowly  -  for the other 14 hours.

On the animal snooze-scale, sloths sleep far more than giraffes, which make do with a couple of hours a night, but far less than pythons, which are out for up to 18 hours in every 24.

If they sleep more in zoos, it's because they're safe, so they don't have to worry about being attacked by predators (it's no accident that the lion, whom no one attacks, is famously sleepy); they're fed, so they don't have to look for food; and they're bored, so they've nothing better to do. In the rainforest, however, that sloth is a real go-getter.

MYTH: GOLDFISH HAVE ONLY A THREE-SECOND MEMORY

FACT: That's what they say  -  particularly if 'they' are trying to justify keeping goldfish in a small glass bowl. The myth is that by the time they've circled the bowl, the fish have forgotten they ever did it, so they just keep going round and round.

Sadly, however, it's nonsense. Experiments at Plymouth University have shown that goldfish can be trained to collect food by bumping up against a lever. Further training taught them that the lever had to be pushed at a particular time of day to deliver food. They caught on to that, too.

Earlier this year, a 15-year-old Australian science prodigy called Rory Stokes trained fish how to negotiate mazes, and swim to a particular beacon to collect food. Then he took the beacon away for a week. When he put it back, the fish immediately swam towards it.

Whether female goldfish remember birthdays and anniversaries better than male fish, however, has yet to be determined.

MYTH: OSTRICHES BURY THEIR HEADS IN THE SAND

FACT: Here's another alleged animal habit that has given us a figure of speech. Since Roman times, ostriches have been said to be so dim that they react to danger by sticking their heads in the ground.

They've thus become a metaphor for humans who refuse to accept reality, preferring to ignore the truth, like children sticking their fingers in their ears and crying: 'Na-na, I can't hear you!'

In fact, however, ostriches react to danger in the most sensible, obvious way available to a flightless bird capable of running at 40mph. They skedaddle.

So where does the myth come from? Well, ostriches swallow sand and pebbles to help grind up food in their stomachs. This means they have to bend down and briefly stick their heads in the earth to collect the pebbles. Bingo! Another false myth is born.

MYTH: A CAMEL'S HUMP IS FILLED WITH WATER

FACT: As everyone knows, camels can cross deserts because their humps are filled with water. Well, 'everyone' is wrong. A camel's hump is actually filled with fat. Its main source of water is actually its bloodstream, where most of the 150 litres of water it can drink in a single go is stored.

Unlike other mammals, which have round blood cells, camels' blood cells are oval, so they can slip easily through veins and arteries even when they are dehydrated, and they can also absorb lots of water without rupturing.

Camels humps are filled with fat, not water

Camels also protect themselves against desert conditions by sweating far less than most animals; closing their elongated nostrils so that a large amount of water vapour in their exhalations is trapped and returned to their body fluids, reducing the amount of water lost through respiration; producing dry faeces and little urine, and reflecting sunlight from their coats.

Even that fatty hump comes in handy. As the fat is converted to energy, it produces water as a byproduct. So although the myth is false, it is half true in the long term.

MYTH: COWS LIE DOWN WHEN IT'S ABOUT TO RAIN

FACT: An old country myth claims that a field filled with cows lying on the ground is a sure sign of imminent rain.

But once again, there is no truth to this whatsoever.

Cows most often lie down when they are chewing their cud (regurgitated lumps of previously-eaten grass).

If they live in a place like Britain, where rain is frequent, there are bound to be times when their prone position coincides with precipitation. Next thing you know, there's an old wives' tale about their meteorological prowess.

As an actual weatherman, Bill Giles, notes: 'I used to ask a farmer friend, who swore by the saying, what happened if half were standing up, and half were lying down. He turned to me and said one word: "Showery!"'

MYTH: BATS ARE BLIND

FACT: People wouldn't be mocked as 'blind as a bat' if we didn't think bats were blind. But they aren't. True, bats have tiny eyes, and can operate effectively at night, or in dark caves, where vision is impossible. This does not, however, mean they cannot see.

They use their sight to navigate over long distances in open, daylight conditions, and some can even detect ultraviolet light beyond the limits of human vision. It's just that their bat-sight is not as finely-tuned as their other senses.

As their oversized ears suggest, bats have astonishing hearing. They can emit high-pitched squeaks and use the reflected sound waves to locate prey and navigate their immediate surroundings with incredible accuracy.

MYTH: LEMMINGS THROW THEMSELVES OFF CLIFFS

FACT: The lemming, a small arctic rodent, has become synonymous with self-destructive behaviour, due to its alleged propensity to throw itself off cliffs.

It's true that lemmings migrate in large numbers, and these migrations might, in theory, lead to riverbanks, from which lemmings would have to jump into water. But lemmings can swim, so it wouldn't hurt them.

The myth is believed to have arisen thanks to a 1958 Disney nature documentary called White Wilderness, which appeared to show suicidal lemmings leaping into a river. But the poor wee beasties were (allegedly) thrown into the river by an off-camera member of the production crew.

This could be a myth, too, of course. One would hate to lose faith in Disney. Next they'll be telling us mice can't talk, elephants can't fly, and little woodland creatures can't clean up a multi-dwarf household.

MYTH: PIRANHAS ARE DEADLY

FACT: As anyone who has ever seen You Only Live Twice will recall, James Bond's enemy Ernst Stavro Blofeld keeps a pool filled with Amazonian piranha fish.

'You will see that my piranha fish get very hungry,' says Blofeld, stroking his white cat. 'They can strip a man to the bone in 30 seconds.' The point is soon demonstrated, at an unfortunate flunkey's expense. What a pity it's nonsense.

Piranhas do have sharp little teeth, and can give you a nasty nip. And they do sometimes swim in large schools, but only to defend themselves against natural predators, such as river dolphins.

Piranhas are predators (of smaller fish and shrimp), and they do have to be kept in even-numbered groups in aquariums to stop them ganging up on an odd one out. But, whatever Blofeld says, they won't gang up on you.

MYTH: SHARKS HAVE TO KEEP MOVING, OR THEY DIE

FACT: 'A relationship is like a shark,' says Woody Allen in Annie Hall. 'It has to keep moving, or it dies.' Well, he's wrong. Not all sharks have to move.

Sharks do, admittedly, need to keep water moving over their gills, in order to breathe. But many species manage to do this while lying on the seabed and moving their gills to create a pumping effect.

Others, however  -  like the great white shark  -  possess no muscles in their gills, cannot pump and do have to keep moving. No wonder the great white is so darn hungry.

MYTH: ONE DOG YEAR EQUALS SEVEN HUMAN YEARS

FACT: This is a simple question of mathematics. The current, global human life-expectancy is around 67.5 years. The average life expectancy for a dog is 12.8 years.

So a dog year is actually a little over five human years. But not all humans, or dogs, have the same life-expectancy.

By and large, the smaller the dog, the longer it lives. An average Irish wolfhound will only last for about six years, whereas a toy poodle or miniature dachshund will breeze past 14 with no trouble.

Similarly, a citizen of Andorra can expect to reach the grand old age of 83, whereas an inhabitant of Swaziland has an average of only 39 years on the planet. So a wolfhound year is equivalent to almost 14 Andorran years, whereas a dachshund year is about two-and-a-half Swazi years.

And there's another, biological factor. A dog is fully developed by its first birthday, whereas we humans do not, traditionally, reach full adulthood until our 21st birthdays. So that first dog year equals two whole human decades.