Carrying a cargo of comet grains and stardust, the Stardust capsule landed in the Utah desert on Jan. 15, 2006.

NASA/JPL

Scientists are now teasing out tiny comet fragments from a protective gel inside the Stardust capsule. In addition, they’re asking for your help to spot the grains of stardust that the capsule also captured and brought back to Earth.

By studying these bits of space material, the investigators hope to learn more about comets, stars, and the origin of the solar system.

Long voyage

The Stardust spacecraft was launched from Earth in February 1999. Since then, it’s traveled 2.88 billion miles. In January 2004, on its second loop around the sun, Stardust brushed past the comet Wild 2.

This image of Wild 2 shows the comet’s rough surface and gas streaming into space, leaving long trails.

NASA/JPL

The spacecraft came within 149 miles of the comet, snapped its picture, and captured bits of comet dust in a special sample-collection tray.

Catching comet dust isn’t an easy task. Even though they’re small, the particles fly toward a spacecraft at a rate up to seven times as fast as that of a speeding bullet.

To slow down, trap, and cushion the dust, scientists filled the grids in the sample tray with a material known as aerogel, sometimes called “blue smoke.” Aerogel is a strong but extremely light substance that is 99.8 percent air.

Although aerogel has a ghostly appearance, it feels as solid and hard as a piece of Styrofoam.

NASA/JPL

Scientists didn’t know what to expect when they opened the Stardust capsule on Jan. 17. They were excited to see thousands of tracks left by fragments of Wild 2.

“We were relieved that anything survived at all,” says Don Brownlee. He’s the lead scientist with the Stardust project and a professor at the University of Washington in Seattle. “We didn’t know how the particles would survive during capture.”

Carrot and hedgehog tracks

When Brownlee and his colleagues looked at the gel, they saw that the particles had left a variety of tracks when they careened into the sample tray.

Some particles went straight into the gel, leaving a carrot-shaped track as they slowed and eventually came to rest, Brownlee says. Other comet grains came apart when they hit the gel, creating a bulbous hole at the surface before narrowing to a turnip shape.

In an experiment on Earth, researchers used a special gun to fire particles into an aerogel. As the particles slowed to a stop, they left carrot-shaped tracks.

NASA/JPL

Sometimes, little pieces broke off from the main comet grain, changing a turnip-shaped track into one that resembled a hairy, heavily branched root.

But when some big particles slammed into the gel, the tracks looked less like a vegetable and more like a prickly animal.

“The biggest ones made . . . cavities that people describe as hedgehogs,” Brownlee says. These particles, barely visible to the naked eye, left tracks half-a-centimeter wide. Smaller pieces broke off to form the hedgehog’s spikes.

Dust removal

The researchers have a variety of special tools to get the comet dust out of the gel. Working in a superclean room, they use tiny, computer-controlled needles that jab the material over and over again, eventually cutting out a wedge containing a dust particle. They use knives made of steel or diamond to slice along a dust track. In addition, the scientists can use microtweezers and miniature forks to snag comet grains.

The yellow circles mark spots where large particles entered this aerogel tile, which is 4 centimeters long and 2 centimeters wide.

NASA/JPL

The scientists now plan to analyze the dust to see what chemical compounds it contains.

The particles that Stardust collected date to the time when Wild 2 was created—4.5 to 4.6 billion years ago. “We believe that [these particles are] the original building blocks of the solar system,” Brownlee says.

The particles could provide answers to questions not only about comets but also about the origins of our sun, Earth, and the other planets.

A search for stardust

Scientists with the Stardust mission will also investigate interstellar dust—stardust, for short. These particles are created when a star is dying or explodes. The Stardust capsule collected samples of interstellar dust using the back of the comet-dust collector.

We can get a sense of what stardust is like from faraway observations, says Bryan Mendez, an astronomer at the University of California, Berkeley. But now, researchers will for the first time have actual samples of stardust to analyze and study.

This set of aerogel tiles collected comet grains and interstellar dust.

NASA/JPL

First, however, the researchers have to find the stardust. There will probably be only 45 or so particles in the aerogel. The width of each particle is less than that of a human hair, Mendez says. Looking for these particles in the sample tray is like looking for 45 ants on a football field.

So, Mendez and other scientists are seeking the public’s help.

The researchers will produce about 1.5 million “movies,” each one a set of images of a microscopic aerogel section no bigger than a grain of salt. Volunteer dust finders, who will be trained to spot stardust tracks, can then download and watch the micromovies on their Internet browsers.

Volunteers will be using their computers to do real science, Mendez says. “We need to find these particles in order to study them. With an army of volunteer scientists, we can do it pretty quickly.”

The micromovies won’t be ready until late March. But you can register to be a volunteer right now. Just go to stardustathome.ssl.berkeley.edu/. Astronomy buffs of any age can participate, Mendez says. All they need is a little bit of patience.

As a bonus, Mendez adds, anyone who finds a star speck will get to name it!

Going Deeper:

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Word Find: Stardust

Now, archaeologists tunneling deep in the ruins of a pyramid in Guatemala have discovered bits of the scribe’s writing. The text dates to between 300 B.C. and 200 B.C. It’s the earliest known example of Maya writing, the researchers say.

Painted hieroglyphs were found on a stone block buried in an ancient Maya temple in Guatemala.

© Science/Photograph by B. Beltrán

The hieroglyphs were originally part of a richly decorated room painted with colorful murals, the researchers say. The ancient Maya even painted a picture of their maize god on one of the doorjambs.

The hieroglyphic signs could have a religious meaning, but the archaeologists can’t be sure. The writing is so old that most of it is unrecognizable. One sign that the archaeologists can understand is an early version of the word for lord, noble, or ruler. The sign, pronounced “ajaw,” is probably part of a title.

This ancient Maya hieroglyph is probably an early version of the word for lord, noble, or ruler.

© Science/Drawing by D. Stuart

Another sign looks similar to a hand holding a brush or a sharp tool, the archeologists say. Perhaps the picture provides a clue to the hieroglyph’s meaning.

This mysterious hieroglyph resembles a hand holding a brush or a sharp tool.

© Science/Drawing by D. Stuart

The archaeologists found helpful clues about the age of the hieroglyphs from nearby pieces of burned wood. By comparing the amounts of different forms of carbon in a sample, researchers calculated the wood’s age. This is a process called radiocarbon dating. Once they knew how old the wood was, they estimated the age of the writing sample.

Before archaeologists found these hieroglyphs in San Bartolo, the oldest known examples of Maya writing were from between 100 B.C. and 100 A.D. The new discovery bumps back the date a few centuries.

It appears that the Maya were creating a writing system and painting hieroglyphs at the same time as other cultures to the north in Mexico.—K. Ramsayer

Going Deeper:

Bower, Bruce. 2006. Getting a read on early Maya writing. Science News 169(Jan. 21):45. Available at http://www.sciencenews.org/articles/20060121/note11.asp .

You can learn more about Maya writing at www.famsi.org/mayawriting/ (Foundation for the Advancement of Mesoamerican Studies) and www.civilization.ca/civil/maya/mmc04eng.html (Canadian Museum of Civilization).

Sohn, Emily. 2005. Stone tablet may solve Maya mystery. Science News for Kids (Oct. 12). Available at http://www.sciencenewsforkids.org/articles/20051012/Note2.asp .

Turck, Mary C. 2004. Maya math. In Mexico and Central America: A Fiesta of Cultures, Crafts, and Activities for Ages 8–12. Chicago: Chicago Review Press. Available at http://www.sciencenewsforkids.org/articles/20050119/LZActivity.asp .

The kakapo parrot, which can weigh more than 1.5 kilograms, forages at night. The birds can live about 60 years.

D. Merton/VIREO

The population of kakapo parrots currently numbers about 86 birds. Scientists have been trying to find ways to increase the number of these hefty, green, flightless creatures.

About 5 years ago, conservationists noticed that females that they were feeding had far fewer female than male offspring. Fewer females mean fewer eggs in the future. But with such a small population to start with, the parrots need all the egg-laying females they can get.

To even out the number of male and female chicks, researchers found that they had to put some of the mama parrots on a diet.

In the wild, kakapos rummage around for plants from which they suck juices. Some years, they get extra helpings of tiny orange fruits from New Zealand’s rimu trees. In those fruit-filled years, the kakapos lay more eggs than they do in years when food is scarce.

Kakapos in captivity used to get extra treats as well. Their keepers fattened them up so the birds would produce babies with a better chance of survival. However, although the chicks were healthier, most of them were male.

Biologists suspected that the problem was related to the way kakapos find a mate. It isn’t easy for a male kakapo to attract a female. In the summer, male parrots carefully clear dirt patches and call out to potential partners for hours at night. Female parrots flock to the most impressive males. The other males are left completely out of the game.

According to evolutionary theory, well-fed mother parrots would have more sons because healthy males would have a better chance of catching the attention of female parrots. In contrast, scrawny sons would have a harder time attracting females, so under-fed mother parrots would have more daughters.

To test the idea, people breeding kakapos cut the chubbiest females’ menu. When the dieting parrots had chicks, 9 were male and 10 were female. Among the females that were already lean, the birds produced 7 male eggs and 9 female ones.

So, to ensure that there are going to be plenty of kakapos someday, perhaps these New Zealand birds should lay off of those yummy treats for a while. And, indeed, the population is already starting to recover from a shortage of female chicks.—K. Ramsayer

Going Deeper:

Milius, Susan. 2006. Dieting to save a species: Mother parrots that eat less avoid excess of sons. Science News 169(Jan. 21):36. Available at http://www.sciencenews.org/articles/20060121/fob3.asp .

You can learn more about the kakapo at www.kakapo.net/en/ (Kakapo.net).

TV crews wait for Mount St. Helens to erupt. Sound at low frequencies that people can’t hear could provide a warning that such a volcanic eruption is about to occur.

Kate Ramsayer

These silent sounds, or infrasound, are calling to some scientists. These researchers are using special microphones to eavesdrop on infrasound created by the world around us. The noisemakers include volcanoes, tsunamis, hurricanes, and even the turbulence that shakes airplanes.

“We’re learning more about how the planet operates by listening,” says Michael A. Hedlin. He studies sounds at the Scripps Institution of Oceanography in La Jolla, Calif.

Low notes

Like all types of sound, infrasound travels in waves. The sound waves have different heights, or amplitudes, which make them louder or softer. They also have different wavelengths, measured from the crest of one wave to the top of the next. And they have different frequencies, measured by the number of crests that pass by a particular position per second.

Short, rapid waves make high-pitched sounds, like a teapot’s whistle. Long, slow waves make low-pitched sounds, like a bass guitar in a rock band. And below the lowest note on a bass, below what people can hear, there’s infrasound.

An elephant generates and probably detects infrasound.

Infrasound is created when something, such as a bomb explosion or an earthquake, sets a large amount of air in motion. The resulting sound waves travel through the air, sometimes for thousands of kilometers.

Scientists originally started studying infrasound to make sure faraway countries weren’t testing nuclear bombs. Now, they’re using infrasound to check for natural events.

“We’re finding all these exotic sources [of infrasound] that we hadn’t thought of before,” Hedlin says.

Tsunami sounds

One of those infrasound sources is a gigantic wave called a tsunami. “We didn’t know that a tsunami produces infrasound,” says Milton Garcés. He runs the infrasound laboratory at the University of Hawaii, Manoa.

Earthquakes under the ocean can generate tsunamis. Special instruments on buoys, such as this one, can detect the resulting waves.

National Oceanic and Atmospheric Administration

When a massive earthquake occurred off the coast of Indonesia in December 2004, for example, it sent a deadly wave across the Indian Ocean. When Garcés looked at infrasound data that were recorded near the tsunami, he found a big signal that corresponded to the wave. “It produced a wallop,” he says.

In the last year, Garcés and his colleagues have picked up sounds from two more tsunamis. One was a Japanese tsunami that produced “beautiful infrasound,” he says.

The researchers recently set up a tsunami infrasound project in Hawaii. “Whenever there’s a tsunami, we’re going to be looking at it very carefully,” Garcés says. The scientists hope to learn how the giant waves produce infrasound, which is currently a mystery.

Volcano rumbles

Garcés and others are also using infrasound to listen in on volcanoes.

On the Sakurajima volcano in Japan, Garcés discovered that stronger and stronger infrasound signals led up to the volcano’s eruption in 1998. If this happens all the time, scientists could use infrasound patterns to warn people if a nearby volcano is about to blow, he says.

The eruption of the Fuego volcano in Guatemala in 2003 generated strong infrasound, mostly below a frequency of 10 hertz (cycles per second). The pressure readings show that the strength of these sound waves can reach the equivalent of 120 decibels (rough

Jeffrey B. Johnson, University of Hawaii at Manoa

Detecting volcanic eruptions with infrasound would also be a useful tool for airplane pilots, because ash from an erupting volcano can dangerously damage a plane’s engines.

Infrasound stations are also keeping an ear on Mount St. Helens in Washington State. Hedlin can tell that gas is bubbling up in the volcano just by looking at the infrasound recordings.

The recordings also detect small earthquakes inside the volcano that push air around, as well as other events whose causes are yet unknown. Infrasound gives researchers a more complete picture of how volcanoes work, Hedlin says.

And scientists are always listening for new things to investigate, Hedlin adds.

Hedlin has recorded infrasound coming from sprites, which are short flashes of light in the atmosphere above thunderclouds. He’s also planning to set up a station to study winds off the coast of Africa, where hurricanes begin to form. To listen to the speeded-up sound of a sprite (so that you can hear it), click here.

The northern lights (auroras) generate infrasound by pushing the surrounding air outward.

Collection of Dr. Herbert Kroehl, NGDC, National Oceanic and Atmospheric Administration

Other researchers are using infrasound to detect avalanches, the northern lights, ocean waves, bumpy air that causes airplane turbulence, and mountains shaking from earthquakes.

Animal calls

While people are deaf to infrasound, other animals appear to use it to communicate. When elephants trumpet, for example, they also produce infrasound that can reach other elephants as far as 10 kilometers away, researchers discovered.

Elephants might even pick up these low rumblings through their feet, says Caitlin E. O’Connell-Rodwell. She’s a scientist at Stanford University in California.

Other researchers have suggested that whales, rhinos, and big birds called cassowaries can create or pick up infrasound. Even some dinosaurs might have had this ability.

A cassowary might pick up ultrasonic signals with its casque, a mysterious structure on top of its head. No one is yet sure what this structure is for.

Andrew L. Mack, Wildlife Conservation Society

In addition, it’s possible that people can detect infrasound in special ways. When elephants trumpet, “it’s such a powerful, low-frequency sound,” O’Connell-Rodwell says. “You really feel it resonating in your chest.”

In one experiment, researchers in England played infrasound during a music performance. Although listeners couldn’t hear the super-low notes, they seemed to have stronger emotions during the performance than did people who heard music without infrasound.

There certainly seems to be more to infrasound than meets the ear.

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Now, scientists have a better idea of how the brain makes sense of all these scents. Particular smells appear to turn on particular combinations of brain cells, researchers suggest.

When your nose catches a whiff of something, one of 1,000 different types of odor-receiving cells picks it up. These cells send an electrical signal to a region of the brain called the olfactory bulb. From there, the message is transmitted to a smell-specific section of the cortex, the part of the brain that handles thinking and perception.

To see what happens when smell messages hit the cortex, a group of scientists studied mouse brains. The researchers first exposed the mice to distinctive scents, such as vanilla, apples, or fish. They then examined thin slices of each mouse’s brain, looking for which brain cells had been turned on by each odor.

The scientists discovered that aromas activate a number of cells scattered throughout the smell cortex. Each scent produces a similar pattern of active cells in different mice. So, a certain combination of cells tells a mouse that it’s smelling vanilla, apples, fish, or any one of thousands of other odors.

The investigators also found that when mice smell a stronger scent, it activates more cells over a larger area. And when they looked at how mouse brains light up after the animals smell two scents that are similar, the patterns are similar as well.

This points to a sort of logic behind how smells activate the cortex, the researchers suggest. Scientists could use studies like this to create a map of which parts of the brain are activated by different smells.

Another smell scientist, however, says that researchers should also do studies on animals that don’t live in a lab, but have spent their lives smelling things in the natural world. With more smelling experience, they might show quite different patterns.—K. Ramsayer

Going Deeper:

Brownlee, Christen. 2005. Mapping aroma: Smells light up distinct brain parts. Science News 167(May 28):340-341. Available at http://www.sciencenews.org/articles/20050528/fob4.asp .

You can learn more about how smell works at science.howstuffworks.com/question139.htm (How Stuff Works).

Jupiter, Saturn, Uranus, and Neptune were once bunched together and closer to the sun, says an international team of scientists. Under the influence of gravity, the planets broke out of their original orbits and began violently rearranging the outer solar system.

A new theory suggests that the four giant planets, shown here in their current orbits around the sun, were once much closer together.

Nature

It’s “a fairy tale of the early solar system,” says Hal Levison. He’s a planetary scientist with the Southwest Research Institute in Boulder, Colo., and was one of the researchers who developed a computer simulation of the planets’ movements.

As the scientists tell it, the tale starts a few million years after the solar system’s birth. At first, the four giant planets had compact orbits. Neptune, for example, was only half as far away from the sun as it now. A slowly circulating band of ice, dust, and gas lay beyond these planets.

Ice, dust, and gas might not seem like much of a match for huge planets. But the researchers say that the pull of gravity between the particles and the planets caused the planets to gradually break out of their tight-knit group. Jupiter moved a bit closer to the sun, and the other three planets moved further away.

All was peaceful in the solar kingdom until the orbits of Saturn and Jupiter aligned so that Saturn took exactly twice as long as its neighbor to go around the sun. The increased gravitational tug of the two planets acting together caused an avalanche of effects.

Saturn’s orbit changed shape slightly, which threw off the orbits of Uranus and Neptune. The orbits of these two planets started looking like squished ovals. At times, the two planets even crossed paths.

And that’s when things got really crazy. Uranus and Neptune started hurtling through the band of ice, dust, and gas, scattering the debris throughout the solar system. The planets themselves ended up in their current orbits.

In the meantime, some of the scattered material became trapped around Jupiter, the scientists suggest. This could account for the presence of objects, known as the Trojan asteroids, that both lead and trail the planet.

Some of the debris could have been flung closer to our home, slamming into the moon and the solar system’s inner planets. This bombardment may have created the huge craters on the moon and elsewhere.

No one knows for sure whether all this really happened. But, by using computers to play complex games of “what if,” scientists can get a better sense of what might have happened to create the solar system as we know it.—K. Ramsayer

Going Deeper:

Cowen, Ron. 2005. Roaming giants: Did migrating planets shape the solar system? Science News 167(May 28):340. Available at http://www.sciencenews.org/articles/20050528/fob3.asp .

Sohn, Emily. 2004. Planets on the edge. Science News for Kids (April 7). Available at http://www.sciencenewsforkids.org/articles/20040407/Feature1.asp .

You can learn more about the birth of the solar system at www.earthsky.com/shows/shows.php?t=20050321 (Earth & Sky).

There are cranberry bogs, pecan orchards, cornfields, llama farms, peppermint fields, cattle ranches, rice paddies, and more. Along just one short stretch of road in California, farmers grow strawberries, lettuce, artichokes, and Brussels sprouts.

Atlantic salmon are raised on fish farms off the coasts of British Columbia, Washington State, New Brunswick, Norway, Scotland, Chile, and elsewhere around the world.

Timothy Knepp, U.S. Fish and Wildlife Service

Even venturing beyond the coast, you’d find farms in the water, producing fish, shellfish, and even seaweed. It’s called aquaculture.

About one-third of the fish that people eat already comes from such farms. The United Nations estimates that, in 25 years, aquaculture will produce more than half of our seafood.

“There’s simply not enough wild fish to supply the growing demand for seafood,” says Jennifer Dianto. She’s an environmental scientist with the Monterey Bay Aquarium in California.

This farm near Belzoni, Mississippi, produces catfish.

David Heikes, Agricultural Research Service, U.S. Department of Agriculture

Although fish farms could supply lots of food and save wild populations from dying out, there are serious concerns about these farms.

For example, fish could escape, says Paul Sandifer. He’s a scientist with the National Oceanic and Atmospheric Administration. Because the escapees often don’t normally live in the surrounding waters, they could have a bad effect on wild fish in the area.

Moreover, fish in a confined space produce a lot of waste, which can pollute nearby waters. Diseases can spread like wildfire within a farm and infect fish swimming nearby.

Despite such concerns, the U.S. Commission on Ocean Policy recently proposed that increased aquaculture would be a good thing—if it were managed properly. New technology can help solve the problems, says Sandifer, who was a commission member.

Friendly farms

Scientists are already testing new techniques for setting up environmentally friendly fish farms.

In the Caribbean, fish farmers are raising cobia in huge underwater cages. Cobia are long, slim fish that grow as heavy as 30 pounds. They prefer warm water and can often be found seeking shelter in harbors and near wrecks and reefs in the Florida Keys and elsewhere around the world.

Now farmed, cobia prefer to live in warm water in the Caribbean and elsewhere around the world.

National Oceanic and Atmospheric Administration

The idea is to have the cages offshore in deep waters where there are strong currents, says Daniel Benetti. He’s a scientist at the University of Miami.

He and his colleagues sank cages 90 feet below the surface, where more than 500 million gallons of water flows through a cage per day. These currents flush away the waste and leftover fish food that would otherwise collect beneath the cages.

When scientists tested the water near these farms, they found that the nearby water wasn’t significantly dirtier than water farther away, Benetti says.

In the much colder waters off eastern Canada, Thierry Chopin of the University of New Brunswick and his coworkers have experimented with combining salmon farming with other types of aquaculture.

“Don’t put all your salmon eggs in the same basket,” Chopin says. The waste from one species can be food for another.

Kelp thrives near salmon farms.

National Oceanic and Atmospheric Administration

The researchers have combined salmon farming with mussel and kelp farming. They found that mussels grew better right next to the fish cages, and kelp thrived when it grew a bit farther away.

At the same time, the shellfish and seaweed helped clean up waste generated by the salmon farms, Chopin says.

Attack of the sea lice

Still, many marine scientists are concerned about fish farms, especially salmon operations.

In 2002, the number of wild salmon along Canada’s west coast suddenly dropped sharply. Because there are a large number of fish farms along the coast, scientists looked for a connection between the farms and the population collapse.

They identified one possible culprit: sea lice. Sea lice are tiny parasites that thrive on farms, which often have a million salmon in one place.

Sea lice (dark shapes) cling to young wild pink salmon that have swum past a fish farm in British Columbia.

A. Morton, University of Alberta

“That represents a huge buffet to something like the sea lice,” says John Volpe. He’s a marine ecologist with the University of Victoria in British Columbia.

Whereas adult salmon can tolerate lice, young salmon, which weigh less than an ounce, are vulnerable. For such a small fish, having a sea louse attach itself is like having a 50-pound blood-sucking tick latch on to a 150-pound person, Volpe says. Imagine carrying that around!

The researchers looked for lice infestations as young wild salmon migrated down a narrow channel, past a salmon farm, and out into the ocean. The infection rates were 73 times higher than normal when the young fish passed the farm, Volpe says.

When they pass by farms, baby fish pick up sea lice hitchhikers. And, if the fish survive, the lice they carry reproduce and infect even more fish as the schools migrate to the ocean. In the end, fewer fish make it to the ocean, and wild salmon populations drop.

The same problem could occur near salmon farms in Scotland, Ireland, Norway, and elsewhere.

Choosing seafood

If some fish farms appear to be hurting the environment and others seem to be okay, how does a hungry, but environmentally aware kid know which kind of seafood to eat?

That’s where publications such as the Monterey Bay Aquarium’s Seafood Watch guide come in handy. The guide lists fish in three, color-coded categories: best choices (green), good alternatives (yellow), and avoid (red). It covers both wild-caught and farmed fish.

These catfish come from a farm.

Peggy Greb, Agricultural Research Service, U.S. Department of Agriculture

For farmed fish, scientists look at how many wild fish it takes to make the fish meal and fish oil that feeds farmed fish. They look at the effect of fish farm escapees and whether the farms spread diseases or parasites. They look at what happens with fish waste and how the farms are managed.

“No one wants to be on the red list,” says Dianto, who’s the Seafood Watch program manager. And people seem to be paying attention. The Seafood Watch program has already distributed 5 million guides.

So, if you love catfish, tilapia, or mussels, there’s no problem. They’re all on the green list, which means they’re raised in a sustainable manner. Salmon lovers have to be more careful. Whereas wild-caught Alaskan salmon are in the green, salmon farms have a long way to go before their products would make the list.

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Word Find: Fish Farms

Such a loud, continuous racket may sound strange to snorkelers, but new experiments suggest that this reef noise attracts baby fish looking for a place to settle down.

Coral reefs snap, crackle, and click with the calls of various residents, and baby fish appear to home in on those sounds.

PhotoDisc

For a long time, biologists have wondered how reef fish find a home. Most reef fish spend the first part of their lives in open water. The baby fish, called larvae, are only about as big as a crumb.

Scientists used to think that, after hatching, larvae drifted wherever ocean currents took them, perhaps hundreds or thousands of miles away. The fish couldn’t control where they went. If the larvae were lucky, the currents carried them into a forest of coral where they could live.

It turns out that, although the larvae are small, they actually become pretty strong swimmers. With this skill, fish larvae might be able to control where they go. And, although little fish do venture into open water, they seem to stick closer to where they hatched than scientists had expected.

But, without a map of the ocean floor, how can these tiny critters find a reef to call home?

Sound can travel for long distances under water. So, Stephen Simpson of the University of Edinburgh and his coworkers proposed that baby fish can hear the racket made by reef creatures. If so, the fish could follow the noise to join the party.

To test their hypothesis, the scientists created a bunch of small, artificial reefs in the waters off Lizard Island in Australia’s Great Barrier Reef. In some coral clumps, they played recordings of fish and shrimp sounds throughout the night. In others, it was quiet.

A member of the cardinalfish family.

© Science

When the researchers checked back the next morning, they discovered that about twice as many young cardinalfish and damselfish had been lured to the noisy reefs as had come to the quiet reefs.

A member of the damselfish family.

© Science

So, like kids drawn by the shouts and laughter coming from a playground, baby fish seem to follow the noises of other reef dwellers to find a place where they want to be.—K. Ramsayer

Going Deeper:

Milius, Susan. 2005. Fish din: Reef clamor attracts young fish settlers. Science News 167(April 9):229-230. Available at http://www.sciencenews.org/articles/20050409/fob6.asp .

Click here to download a PowerPoint file that lets you hear some of the sounds of a coral reef. Courtesy of Stephen Simpson of the University of Edinburgh.

You can learn more about how reef noise may guide young fish home at www.cpa.ed.ac.uk/release/?FMRecord=1165 (University of Edinburgh).

According to the scientific theory of evolution, apes and people have a common ancestor—one ancient animal from which both species evolved. At some time in the past, however, the creatures that would become humans started to differ from the creatures that would become apes and chimpanzees.

This computer reconstruction shows an ancient skull that its discoverers say is the earliest known human ancestor.

Michel Brunet, University of Poitiers/MPFT

A few years ago, anthropologists digging in the African country of Chad discovered some intriguing fossils. They found a skull, along with some teeth and jaw pieces, that was between 6 million and 7 million years old.

Because the face and teeth resembled those of later human ancestors, the scientists said that the fossils were those of a human-like, or hominid, species—even though the skull could hold only a chimp-sized brain. They called this creature Sahelanthropus tchadensis.

Not everyone agreed with this conclusion. Another group of anthropologists argued that the fossil pieces came from an ancient ape.

Now, the scientists who found the bones have dug up more fragments. And, because some of the original skull bits had been squished, the researchers used a computer program to unsquish the pieces and fit them together into a three-dimensional picture of the skull.

The newly found teeth look more human than chimp, the researchers say. Moreover, the computer image of the skull shows a human-like flat face.

The way the skull meets the spine and neck might also have allowed this primate to walk upright, they add. To confirm this, however, scientists would have to find leg bones as well.

The new information strengthens the view that the old bones belong to the earliest known human ancestor, the scientists conclude. This creature lived just after the split between the human and chimpanzee evolutionary families.

Here’s a model of what the head of the oldest known human ancestor might have looked like.

MPFT

Other anthropologists still aren’t convinced that this is our earliest ancestor. Humans and ancient apes looked a lot alike 7 million years ago, they say, and some features of the fossil skull are more ape-like than human-like.—K. Ramsayer

Going Deeper:

Bower, Bruce. 2005. Untangling ancient roots: Earliest hominid shows new, improved face. Science News 167(April 9):227. Available at http://www.sciencenews.org/articles/20050409/fob1.asp .

You can learn more about the Chad hominid fossils at www.sahelanthropus.com/ (Hominidae Project).

Information about evolution can be found at evolution.berkeley.edu/ (University of California, Berkeley).

He gently strokes the feathers on the bird’s forehead, right above its eyes. The owl, which had been flapping around as Diller held its feet, immediately calms down. It gazes up at Diller, almost in a trance, as the biologist measures its size and weight, makes sure it’s healthy, and slips an identification tag around its foot.

Biologist Lowell Diller soothes a captured northern spotted owl by stroking the feathers on the bird’s forehead.

Kate Ramsayer

He wants to make the owl feel as relaxed as possible. That way, if he needs to catch it again, the bird might remember the head massage and the free mice Diller feeds it and not immediately fly away.

Diller keeps track of spotted owls as part of his job. He’s a senior biologist at Green Diamond Resource Company, a timber company based in Seattle. Ever since 1990, when the United States government declared northern spotted owls a threatened species, timber companies must make sure they don’t harm or disturb the birds.

Northern spotted owl.

John and Karen Hollingsworth, U.S. Fish and Wildlife Service

On government lands, big chunks of owl-friendly habitat are set aside, off-limits to loggers.

But northern spotted owls are still in trouble. The number of owls is declining in many areas, and they face threats that won’t easily disappear. For example, the barred owl appears to be bullying spotted owls out of their territories. And some scientists are concerned that spotted owls might start dying from West Nile virus.

“Right now there’s more uncertainty than there has been, in my opinion, and it’s because of these two unknown threats,” Diller says. “We can’t predict how they’re going to turn out.”

Declining numbers

Northern spotted owls live in the western parts of northern California, Oregon, Washington, and British Columbia. They roost in stands of trees that are hundreds of years old.

In these old-growth forests, large trees mix with smaller trees, with dead trees called snags, and with trees having broken tops or holes in which the owls can make their nests. Some studies suggest that the owls can also live in forests made up of younger trees, as long as there’s still a variety of sizes and types of trees.

In Oregon, a logging method known as clear-cutting has completely removed trees from a portion of a forest where northern spotted owls could live.

Steve Hillebrand, U.S. Fish and Wildlife Service

But, as settlers moved into the Pacific Northwest, many cut down vast numbers of trees for timber. One study estimates that, since the early 1800s, people destroyed between 60 percent and 88 percent of potential spotted owl habitat.

The loss was so great that, when forest managers started protecting owl habitat 14 years ago, they suspected that the number of spotted owls wouldn’t immediately bounce back. Now, the number of owls in northern California and parts of Oregon is holding steady, but the owl population in Washington and British Columbia is getting smaller.

“Some of the populations are still continuing to decline,” says Rocky Gutierrez. He studies spotted owls as a professor at the University of Minnesota. “But others have shown a stabilizing trend,” he says. “We think that’s due to the protection of habitat.”

Bullying birds?

Scientists have a possible suspect for the decline.

“In the past 60 years or so, the barred owl has invaded the range of the northern spotted owl,” Gutierrez says. “The stage is set for competition to occur.”

And, so far, it looks like the barred owl is winning. Previously, barred owls lived in the eastern United States. Slowly but surely, they migrated across Canada and down the West Coast, into spotted owl territory.

Barred owl.

U.S. Fish and Wildlife Service

Barred owls are closely related to northern spotted owls, but they are slightly bigger. They live in the same habitats as spotted owls do and eat similar food, although they seem less finicky.

Barred owls are also more aggressive. Some scientists say that the barred owls are kicking spotted owls out of the few areas where spotted owls can live.

“The biggest wild card right now is the barred owl,” says Robin Bown. She’s a biologist with the U.S. Fish and Wildlife Service. “If you create the habitat, you don’t know if you’re going to get barred owls or spotted owls.”

Still, scientists can’t be sure that the barred owls are causing the decline in spotted owls. Right now, they only have observations, Bown says. They can see that there are fewer spotted owls in areas where there are more barred owls, but they don’t have any direct proof that barred owls are the culprit.

Gutierrez is interested in doing experiments to test the idea scientifically. He is planning to play recordings of barred owl calls and spotted owl calls near sites where spotted owls nest. He’ll play different combinations of the recordings to see if the spotted owls respond after the barred owl calls or if they keep quiet, not wanting to attract attention.

“At this point there’s a great deal of scientific uncertainty about how these two species interact,” he says.

But if barred owls turn out to be the bullies of old-growth forests, people can’t simply make rules to make them share the forest, as they did to slow down logging.

“The biggest problem is that there’s not much you can do,” Bown says. Instead, biologists can only hope that the two species of owls learn to live together. Or, perhaps spotted owls will settle into a habitat that their barred owl cousins don’t like. It’s an issue that scientists will keep a close eye on.

Other threats

Spotted owl biologists are also paying attention to other threats. Recently, West Nile virus has infected several birds of prey. While there haven’t been any known cases of West Nile among spotted owls, Diller says it could happen this spring.

An adult spotted owl watches visitors from its perch high in a tree.

Kate Ramsayer

Certain species of birds are resistant to West Nile and don’t get sick. But some birds die when infected. The biologists will just have to wait and see what happens with spotted owls.

Weather can also play a role in spotted owl survival. Rain ruffles the owls’ feathers so that they can’t fly as quietly to sneak up on their prey. If the spring is wet and owls can’t catch as many flying squirrels or dusky-footed woodrats, they might not have any chicks.

Although there are many factors that people can’t control, there are some factors they can control.

“Habitat is still an issue, and, if anything, it may be a bigger issue now because we’re losing spotted owl sites to barred owls,” Bown says.

So, forest managers are continuing to set aside patches of federal land for owls. On timber company lands, biologists such as Diller are drawing up habitat conservation plans to make up for areas the companies log.

Still, it looks like spotted owls will need help from all the friends they can get.

Going Deeper:

News Detective: Meeting an owl.

Word Find: Spotted Owls

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