How do fish sleep? Do they keep swimming or do they sleep somewhere? – Anna, age 5, Thornleigh, NSW, Australia.

Nearly all animals sleep. Sleep is very important for refreshing the mind and body. When people sleep we close our eyes and lie motionless for a long time. We may be less aware of what is going on around us and our breathing slows down. Some people are very heavy sleepers and it takes a LOT to wake them up!

Fish don’t have eyelids — they don’t need them underwater because dust can’t get in their eyes. But fish still sleep. Some sleep during the day and only wake up at night, while others sleep at night and are awake through the day (just like you and I).

How do fish know when it’s bedtime?

It’s pretty easy to tell when fish are sleeping: they lie motionless, often at the bottom or near the surface of the water. They are slow to respond to things going on around them, or may not respond at all (see some sleeping catfish here). If you watch their gills, you’ll notice they’re breathing very slowly.

People with fish tanks at home will know that when the lights go off at night, the fish become far less active. If you turn a light on in the middle of the night you’ll see how still they are.

Like people, fish have an internal clock that tells them when to do things like sleep and eat. So even if you accidentally leave the lights on at night, the fish may settle down and go to sleep anyway.

Some scientists have studied sleep in fish that live in caves where it is always dark. Even in some of these species there are times of low activity that look just like sleep. Of course there is no sunrise or sunset in caves so their rhythm is often different to fish that live at the surface in bright sunshine.

Some fish, like tuna and some sharks, have to swim all the time so that they can breathe. Its likely that these fish sleep with half their brain at a time, just like dolphins.

Parrot fish make a mucus cocoon around themselves at night — a gross, sticky sleeping bag which might protect them from parasites attacking them while they sleep.

Fish may dream like people do!

One wonders if fish dream while they are sleeping. So far we don’t have the answer to that question but recent video footage of a sleeping octopus showed it changing colours, which suggests it may have been dreaming about hiding from a predator or sneaking up on its own prey (which is why octopuses change colour when they’re awake).

Believe it or not, fish sleep is being studied to help us better understand sleep in people. Most of these studies use zebrafish and try to understand things like the effects of sleep deprivation (lack of sleep), insomnia (trouble getting to sleep) and circadian rhythm (sleep cycles).

Here is a cool video about sleep in animals, including fish.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au — —

Culum Brown, Professor, Macquarie University

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What is the largest penguin that ever lived? – Casey, age 6, Perth

Hi Casey, thanks for this great question!

Today the largest living penguin is the emperor penguin, which lives in Antarctica and is about one metre tall. The appropriately named little penguin is the smallest, standing only about as high as a ruler.

But penguins have swum in Earth’s oceans for more than 62 million years – and they were not always these sizes. Long before humans walked the Earth, some penguins would have stood as tall as a grown-up person.

Diving in

To understand how penguins once got so big, we need to go back to the very first ones.

The closest relatives of penguins today can actually fly through the air. These include petrels and the soaring albatrosses.

While waddling penguins might seem quite different to these seabirds, they’re quite alike in a number of ways. They share similarities in their skeletons, and both share distant relatives (great, great grandparents going back millions of years) that flew in the air.

Penguins can’t fly in the air anymore. Instead, they “fly” through the water — and doing both well isn’t an option.

For birds, water is a lot harder to fly through than air. But penguins have certain qualities that allow them to do this.

The wings of penguins are flippers. These are great for moving underwater, but not very helpful for flying above it. Their heavy bodies help them dive further and deeper so they can hunt for food. But being heavier makes flying in the air difficult.

While penguins’ distant relatives were small seabirds, over many years they gave up flight to become professional swimmers. The bigger they were, and the stronger their bones, the better they could dive.

Because penguins have heavier and stronger bones than air-flying birds, this means their bones are less likely to break. It also means we are more likely to find them as fossils (what’s left behind from ancient life) long after they die.

In fact, the bones of one kind of giant penguin (Kairuku waewaeroa) were discovered by school children.

Room to grow

The asteroid that wiped out the dinosaurs (except birds!) 66 million years ago gave the distant relatives of penguins the perfect chance to go swimming.

Many of the animals that would have eaten them in the sea were gone, which meant they could go underwater without worrying about being eaten.

The oldest penguin bones we have belonged to birds that lived only a few million years after the asteroid hit, and come from Aotearoa, or New Zealand. These are similar to the bones of today’s penguins, so we think penguins probably stopped flying in the air some time soon after the asteroid event.

Some of these first penguins were enormous. One was the gigantic Kumimanu biceae, which was probably 1.7 metres tall (the same size as many human adults).

Kumimanu may have been one of the largest penguins ever. It probably weighed 100kg, whereas the emperor penguin weighs less than half of that.

While many giant penguins lived in the millions of years after Kumimanu, the only penguin that may have been larger was the huge Palaeeudyptes klekowskii, which swam off the coast of Antarctica more than 34 million years ago. This penguin may have been two metres tall and weighed 115kg!.

As for what happened to giant penguins, they vanished about 15 million years ago and no one really knows why. There are still many questions, but with more fossil discoveries, we might find some answers!

Jacob C. Blokland, Vertebrate Palaeontology PhD Candidate and Casual Academic, Flinders University

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Why do sloths go slow? Nina, Sydney, aged 5

You’re right, sloths do move very slowly!

Sloths live in tropical forests in South and Central America, and they actually move so slowly that algae grows on their fur. This can give sloths a green colour that helps them hide in the forest from predators like nocturnal cats and harpy eagles.

This is very lucky, because some sloths often move less than 40 meters a day. They are much slower on the ground than in the trees, some travelling just four meters every minute on the ground — far too slow to outrun a jaguar!

The reason sloths go slow has a lot to do with what they eat. Let’s look at why.

Counting sloth toes

Sloths might all look the same to us, but there are actually two main types: sloths with two toes, and sloths with three toes.

Two-toed sloths are “omnivores”, which means they eat both plants and animals.

Three-toed sloths are “folivores”, which means they can only eat leaves and flower buds. Unlike most other plant-eating animals, they stay away from stems or roots.

This type of diet is extremely rare — only about 100 other types of animals that live in trees are folivores, and Australia’s cuddly koala is one of them.

Koalas and sloths have a lot in common

Koalas, like sloths, have claws that are good for climbing, are often more active at night and only munch on leaves.

There is a very good reason there are only very, very few folivores like the three-toed sloth and koala in the world.

Leaves are very low in nutrients, and contain very little energy. This means the koala and sloth have discovered a way to survive on very little energy at all.

Imagine how slow you’d move if you were only able to eat leaves instead of all your high energy fruit and vegetables!

One of the main ways sloths and koalas keep their energy low is by resting lots, and not moving very often. If you have ever seen a koala, you might have noticed they are often resting and sleeping — some say up to 20 hours a day.

Compared to sloths, koalas are much more active but often only with a short burst in energy. Koalas move about 190 metres every day, but some have been recorded moving as much as 2,500 meters in one day.

In fact, the three-toed sloth uses the least amount of energy of any animal that doesn’t hibernate. But when sloths need to travel longer distances, they can use their long legs to swim, which they are much faster at.

Koalas and sloths are losing their homes

Unfortunately, when trees in forests are chopped down, sloths and koalas must travel further away along the ground to find food and mates. This exposes these rare animals to dangers, like cats and jaguars, or busy roads where they could get hurt.

Losing their tree homes has led to a big drop in the number of sloths left in the world, particularly the pygmy three-toed sloth which is “critically endangered”. This means we don’t have long left to save it from going extinct.

Koalas are in similar danger. Because so many trees are getting chopped down in Australia, scientists think there might be no koalas left in the wild in New South Wales by the year 2050.

To look after sloths and koalas, scientists and the community need to work together to protect these incredible animals and their homes.

Shelby A. Ryan, PhD Candidate | School of Environmental and Life Sciences, University of Newcastle and Ryan R. Witt, Postdoctoral Researcher and Honorary Lecturer | School of Environmental and Life Sciences, University of Newcastle

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Spring in Australia has arrived like a celebration. Magpies are warbling in the morning, wildflowers are bursting open across bushland, and the air is humming with life as tiny creatures have stirred back into action after the winter: bees darting between flowers, dragonflies skimming across ponds, and swarms of flying ants mating.

But we are largely blind to Australia’s insects, and more specifically, what has happened to them over years and decades. That’s because Australia – despite having some of the richest insect biodiversity on the planet – doesn’t have long-term datasets about insects. And because of this, we don’t have a coordinated way to know whether our native bees, butterflies, or even pest species are stable, declining, or booming.

But we can all help address this knowledge gap, and now is the perfect time of the year to do so.

Huge changes in insect numbers

Depending on where we look, and which insects we look at, we are seeing huge changes in insect populations.

For example, Europe’s long-running insect monitoring programs, such as the Krefeld study in Germany, have revealed dramatic declines in flying insect biomass, with losses of up to 75% over three decades.

The lack of similar monitoring programs and long-term data about insect populations in Australia is already having consequences. Take the bogong moth.

Once so abundant its migrations darkened the skies of eastern Australia, its numbers have plummeted by more than 99% in some areas in recent years. The mountain pygmy possum, an endangered species that depends on these moths for spring feeding, is now struggling to survive without its main food source.

This cascading effect is a stark reminder that when insect populations collapse, everything that depends on them – plants, animals, even people – can feel the impact.

Yet, we only noticed the bogong moth crash after it happened. Without consistent monitoring, we simply don’t have a baseline to detect change early – let alone prevent it.

Why spring matters for data collection

Spring is when insect life explodes into action. It’s when pollinators emerge to feed and breed, when decomposers such as beetles and flies begin their crucial work recycling nutrients, and when countless species begin to build the food webs that sustain ecosystems through the year.

Miss the spring data collection window, and you miss the moment when insect activity is at its peak. It’s like trying to understand traffic flow in a city by observing it at 3am instead of during peak hour.

Without good insect data, we can’t track shifts in emergence times that are changing due to warming temperatures (aphids are emerging up to a month earlier in the United Kingdom), or notice if key species are missing altogether.

That makes it harder to support agriculture, manage ecosystems, or respond to biodiversity loss in a meaningful way.

The need for a national monitoring network

For years Australian entomologists have been calling for a national insect monitoring network, one that collects regular, standardised data across ecosystems and seasons.

Without better baseline data, we simply lack the capacity to detect or respond to significant declines.

While not a fully fledged national network, initiatives such as Butterflies Australia demonstrate the potential of citizen science to contribute to long-term monitoring through standardised protocols and broad public participation.

Beyond conservation and risk detection, a national monitoring network would also play a critical role in discovering new species. Many of Australia’s invertebrates remain undocumented, and ongoing monitoring can lead to significant scientific discoveries.

One recent discovery came from a citizen science project where students helped identify a previously unknown wasp species in suburban Perth. This highlights the potential of a national-scale approach to not only track what we know, but also uncover what we don’t know.

What you can do

While Australia still lacks a national insect monitoring network, you can help fill the data gaps right now. Whether you’re a budding naturalist, a student, or simply curious about the life around you, there are ways to get involved in building the baseline scientists urgently need.

The Christmas Beetle Count runs every summer and involves taking photos of Christmas beetles to help researchers understand if their populations have declined. From this initiative, we have been able to see Christmas beetles that have not been observed in decades.

The Great Southern Bioblitz is a big citizen science project, where users of iNaturalist are encouraged to upload photos of all kinds of nature to the website. Its goal is to increase our knowledge of southern hemisphere nature.

If you’ve got kids and want to observe nature, the app Seek provides a safer environment for children to take photos and contribute to citizen science.

On a more local scale, you can join a local initiative run by some councils and environmental groups, such as Moth Night and the Sutherland Shire Beetle Hunt.

Insects are the unsung heroes of our ecosystems, pollinating crops, recycling nutrients, feeding birds, and much more. By getting involved in citizen science, you’re not just collecting data, you’re laying the groundwork for a national monitoring system Australia urgently needs, and ensuring we notice what’s changing before it’s too late.

Eliza Middleton, Senior Ecologist, University of Sydney and Caitlyn Forster, Associate Lecturer, School of Life and Environmental Sciences, University of Sydney

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Why do we dream? Vishnu, aged nine, Kerala

That’s a really interesting question, and people have been asking it for thousands of years. But it’s difficult to answer because dreams are difficult to study scientifically.

Think about it: how easy do you find it to remember your dreams every night? Not everyone can do this. If we can’t remember our dreams, we can’t study them.

Curious Kids is a series by The Conversation that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.com and make sure you include the asker’s first name, age and town or city. We won’t be able to answer every question, but we’ll do our very best.

Some ancient cultures like the Egyptians, the Greeks and the Romans believed that dreams were important messages from the gods. But even they could not agree about exactly where dreams come from, why they happen or what they might mean.

In the last 100 years, many scientists across the world have learned a lot about the science of dreaming. But even still, there is disagreement.

Some scientists think dreams have an important job, others do not. I’ll explain some of the most well-known ideas.

Around the year 1900, an Austrian psychologist (someone who studies how we think) called Sigmund Freud published an influential book called The Interpretation of Dreams. In it, Freud wrote about his experiences of talking to other people about their dreams (and his own dreams too).

He believed that dreams came from wishes or desires buried deep in the mind. He thought these wishes were usually transformed in some way to disguise them in the dream, as they could be quite scary or rude.

Freud would help people to work out what these hidden wishes and desires might be, so they could address them in waking life. He also wrote that dreams are a part of the process that helps keep us asleep, that dreams protect sleep from disturbances. And there is some evidence to support that idea.

Freud’s ideas had a great influence on thinking about dreams for many decades. But since Freud’s time, we have learned much more about how sleep works. And that has inspired new ideas about what dreams might (or might not) be doing.

In the 1970s, scientists like Allan Hobson started to reject Freud’s ideas about dreams, and suggested that perhaps dreams don’t do anything important. In Hobson’s view, dreams had no hidden meaning or function to them.

He thought they might just be random side-effects of chemical processes going on in the brain during sleep. It is one good explanation for why dreams often seem so strange. Hobson thought little bits and pieces of knowledge and imagination get activated and merge together meaninglessly.

But other scientists since then have noticed that not all dreams are strange. Many of them are in fact quite ordinary, and some have content that is important to the dreamer.

Perhaps you have dreamed about something that happened in your life recently, like a fun day out with your school friends or family, or maybe you dreamed you were in a film you watched the day before.

We often dream about things that had a significant effect on us in waking life, or are related to worries we carry with us. And this I think is the most important thing we need to realise: our dreams are connected with our waking lives.

Some scientists now believe that dreaming about these things might help us to process them, or give us new ideas about what to do in our waking life. This is still difficult to test though. Whether or not this is what dreams are really doing by themselves, you have the choice to look at your dreams and decide what new ideas you can draw from them.

Another interesting idea is that dreams evolved long ago to help us survive threats. A lot of people seem to report dreaming about being chased by monsters or dangerous animals. Maybe you have too.

Some scientists see this as evidence for a threat simulation system that emerged back when we were living in caves and had to hunt for our food while trying not to be hunted ourselves.

If we survive a threatening encounter in a dream, that could better prepare us for surviving real threats when we are awake. The problem with this idea though is that it is too dangerous to test properly.

Even if someone dreams about fighting a tiger, for example, scientists cannot then lock people in a cage with a real tiger and see how well they survive!

That’s one of the exciting things about being a scientist. There are still lots of questions to answer and we’re learning new things all the time.

Anthony Bloxham, Lecturer in Psychology, Nottingham Trent University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

Why can’t we feel the Earth moving? – Dave H., age 12, Atlanta

Right now, you’re zooming through space at incredible speeds. As just one of all the living creatures on Earth, you’re along for the ride as our planet constantly moves in two major ways.

First, consider that the Earth spins around like a top. It’s rotating around the imaginary line that runs from the North Pole to the South Pole through the center of our planet. Earth completes one full rotation every 24 hours, with a speed of about 1,000 miles per hour at the equator (1,670 km/h).

While Earth is spinning on its axis, it’s also traveling around the Sun. It takes a year to finish the journey – that is, to make one full revolution and wind up back where we started. Earth hurtles along its path with a whopping average speed of 67,000 miles per hour (107,000 kmh).

These speeds are way faster than any vehicle you’ve ever traveled in. So why aren’t you dizzy or flying off into space? Why don’t you even feel the Earth moving?

It’s this kind of question that lit a desire in me as a child to understand the universe and our place in it. Now I have a Ph.D. in astronomy and teach college students some of the same physics principles that explain why you can’t feel Earth’s motion as it zips through space.

No jerks or bumps

Think about a time when you do feel motion, such as on a carousel ride at an amusement park. When it speeds up, slows down or turns quickly, your body notices because the motion isn’t smooth.

In contrast, the Earth’s motion is remarkably steady. It has been spinning on its axis and orbiting the Sun at nearly the same speeds for billions of years, with no sudden jolts or stops. As Earth travels its slightly oval-shaped path around the Sun, its speed does change to be a bit faster when it’s closer to the Sun and a bit slower when it’s farther away. But the changes happen so gradually and smoothly that you don’t feel them at all.

Imagine you’re flying on an airplane that has reached cruising altitude. The engines are humming, you’re soaring through the sky at hundreds of miles per hour – but everything inside feels calm and still. You can walk around, relax and forget you’re traveling at all. That’s because the plane, you and everything else inside it are moving at the same speed, in the same direction.

Just as passengers don’t feel the plane’s speed while smoothly cruising, we don’t feel Earth’s movement because we’re traveling at the same speed as our planet. You, your chair, the trees, buildings, oceans – everything is moving together with the Earth.

There’s no difference in motion for your body to detect unless Earth were to suddenly speed up, slow down or change direction – and, thankfully, that doesn’t happen.

Very small ants on a very big ball

Imagine holding a huge beach ball in your hands. Picture a tiny ant crawling on the surface of that ball.

Now, think about us on Earth. We are like that ant, but the ball we’re crawling on is almost 8,000 miles (almost 13,000 kilometers) wide at the equator. That’s about the distance you’d travel driving from New York to Los Angeles and back to New York.

Because the Earth is so humongous, any movement feels very slow and gentle to our comparatively minuscule bodies as we stand on its surface.

Another reason you don’t notice Earth’s motion is that there are no nearby “landmarks” in space to act as reference points. When you’re in a car on the highway, you see trees, signs or telephone poles rushing by. Those fixed points help your brain register motion. But in space, the stars are so far away that they appear completely still, even though we’re moving relative to them at thousands of miles per hour.

Luckily, these high speeds don’t fling us off into space thanks to gravity. Gravity is an invisible force of attraction. It pulls everything on the surface of the planet toward the Earth’s center. It’s like the Earth is giving us a giant, constant hug, keeping us safely grounded.

How do we know the Earth is actually moving?

Even though we don’t feel the Earth moving, people long ago figured out that it really is by watching the sky carefully.

Start with day and night. The Sun appears to rise and set because Earth makes one full rotation on its axis every 24 hours. If Earth weren’t spinning, one side would always face the Sun, and the other would be in darkness.

Then there are the seasons. Earth is tilted on the axis it spins around. Over the course of its orbit of the Sun, Earth’s tilt causes different parts of the planet to get more or less sunlight. That’s why we have summer, winter and everything in between.

At night, stars and constellations seem to move across the sky as Earth rotates. And their positions in the sky change with the seasons. Our view of the stars changes as we move along our yearly path around the Sun. If everything stayed still, the night sky would never change.

By seeing Earth spinning and orbiting, satellites and space telescopes have confirmed what astronomers have long deduced. We may not feel it, and we can’t see any obvious landmarks rushing by, but the clues are everywhere. Earth is on the move.

And it’s not just Earth – the Sun itself rotates and moves around the center of our Milky Way galaxy at hundreds of thousands of miles per hour. Nothing in the universe is truly standing still. Everything is in motion, from planets and stars to galaxies themselves.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Nilakshi Veerabathina, Professor of Physics Instruction, University of Texas at Arlington

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