From: Kathleen M. Wong, California Academy of Sciences
Published December 17, 2004 12:00 AM

Sharks Can Detect Magnetic Fields and Other Stories

Sharks Can Detect Magnetic Fields


Sharks on migration swim arrow-straight lines across featureless ocean basins. How they navigate over such great distances has been a mystery. Now experiments by scientists at the University of Hawaii demonstrate that sharks are able to detect magnetic field changes, supporting theories that the predators can map their location by deciphering differences in Earth's magnetic field lines. Carl Meyer and colleagues trained captive sandbar and scalloped hammerhead sharks to associate an artificially induced magnetic field with the presence of food in a certain region of their tanks. When the field was turned on at random, the experimenters found that the sharks continued to swim over the target area whether or not food was present. Instead of continuing to swim around the perimeter of the tank, the sharks picked up speed and rapidly changed course to the target area. Sharks are known to correct their paths after encountering features such as seamounts, which perturb the earth's magnetic field. Pigeons and sea turtles are known to possess particles of magnetite in their bodies which allow them to tune in to the planet's magnetic fields. Sharks lack magnetite, but could use the electroreceptors in their heads instead. The work is reported in the journal Interface..


Wave Of Bird Extinctions To Come


Birds face a grim future. According to the latest estimates, about 14 percent of all bird species will go extinct by 2100. Cagan Sekercioglu of Stanford University based his model on the world's recent 1.1 percent extinction rate. Under his most optimistic scenario, all currently threatened species would go extinct, but no others. He reports in the Proceedings of the National Academy of Sciences that about 1,200 species will disappear in the next century. Countless ecosystem services such as plant pollination, insect control, and carrion cleanup will disappear along with them. Some areas are already feeling the strain. India's native vultures have suffered catastrophic declines in recent years, leaving carcasses to be devoured by mammalian scavengers instead, leading to skyrocketing rat and feral dog populations. At the same time, India accounted for 30,000 of the world's 50,000 rabies deaths. And many plants depend on certain species of birds for pollination, so their disappearance could drag trees, shrubs, and flowers with them. Until now, only 1.5 percent of birds have gone extinct since the year 1500.


San Andreas Fault Rumbles Down Deep


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Scientists have detected strange, lengthy tremors deep below the San Andreas Fault. The rumblings could presage a major earthquake in central California. Robert Nadeau of the University of California, Berkeley and colleagues recorded 110 tremors lasting between 4 and 20 minutes near the town of Parkfield. The second-largest earthquake recorded in California occurred there in 1857, when a 7.8 magnitude quake struck the military outpost of Fort Tejon. The new tremors occurred between 12.5 and 25 miles below the surface--beneath the fault itself, which is thought to lie approximately 10 miles down. Long-lasting, deep tremors have been recorded before along earthquake faults in Japan and the Pacific Northwest. However, those were subduction faults, sites where one plate in the earth's crust is diving below another. By contrast, the adjacent plates of the San Andreas slide horizontally past one another. The central California tremors were followed by microquakes of about magnitude 2.1 several months later, as well as one magnitude 6 quake. This portion of the San Andreas Fault has not moved much despite rising strain and is believed ripe for another big earthquake soon. The research was reported in the journal Science.


Lefties Make Better Fighters


Left-handedness may not be merely a neurological aberration. New evidence suggests the habit persisted in human populations because lefties make better fighters. Charlotte Faurie and Michel Raymond of the University of Montpelier, France, compared the prevalence of left-handedness in eight traditional societies with the number of homicides. The Yanomano of Venezuela, the Arctic Inuit, the Jimi of Papua New Guinea, the Ntumu of Cameroon, the Kreyol of Dominica, and Dioula speakers of Burkina Faso all tend to use knives or machetes rather than long-range weapons such as guns. Hand-to-hand combat, the researchers surmised, gives lefties the advantage. Opponents could get caught by surprise by a strong left-handed blow and lack a good defense. The scientists report in the Proceedings B of the Royal Society that the societies with the most murders also had the largest percentage of southpaws. The Yanomano topped the scale with four killings per 1,000 people and a whopping 22.6 percent of lefties. The relatively peaceful Dioula, with only three percent lefties, had a murder rate of only 0.01 per 1,000 people.


Mediterranean Fishing May Be Starving Dolphins


Bottle-nosed dolphins off the coast of Israel are alarmingly thin and may be starving. Researchers at the University of Haifa, Israel, point the finger at overfishing. Biologist Aviad Scheinin photographed 74 bottle-noses resident in national waters over a period of five years. He identified individuals by the unique shape and size of their dorsal fins. At least a third were so emaciated that their ribs were visible. Other populations of Mediterranean bottle-nosed dolphins have been declining, including in Greece, where up to 40 percent of dolphins are gaunt. Several lines of evidence point to overfishing as the cause. Several hundred bottle-nosed dolphins trail local fishing boats to snap up fish thrown back into the water. And fishermen themselves report smaller catches in recent years. The damming of the Nile River likely makes matters worse. Egypt's Aswan Dam has reduced the amount of organic nutrients entering the Mediterranean since its completion in the 1970s. Establishing no-fish zones around the Mediterranean would help the dolphins stay healthy.


Dusty Disks Surround Solar Systems Under Construction


New views of stars with their own planets are shedding light on of our own solar system's dusty past. The six stars, spotted by the Hubble and Spitzer Space Telescopes, are about the same size as our sun but slightly younger. Each had a thin disc of dust surrounding it. The material in the discs appears very similar to the debris orbiting our own solar system in the region beyond Neptune known as the Kuiper Belt. Dust discs are thought to be the raw materials from which planets form. Each sun is known to have at least one Jupiter-sized planet orbiting it. Gas giants like Jupiter are thought to be the first to coalesce from dust discs, while smaller, rocky planets such as Earth likely form later from accreted solid debris. Scientists say that at about 4 billion years old, the suns are probably too young to have formed any rocky planets. Our own solar system, now about 4.6 billion years old, may have looked much like these in its youth.


Crows Rival Great Apes In Smarts


Don't cross a crow. According to a new study in the journal Science, these brainy birds and their close relatives may be just as smart as great apes. Cambridge University biologists Nicola Clayton and Nathan Emery cite a long list of intellectual accomplishments for corvids such as crows, ravens, and jays. For example, crows will drop nuts in roads to be cracked by cars, and fashion custom tools from leaves and twigs to probe for insects. And Western scrub jays that steal from other birds' seed caches will move their own stash if they know other birds have watched them hide their treasures. This demonstrates the ability to guess another individual's state of mind--a talent not even chimpanzees are known to possess. The intellectuals of the animal world, which include some parrots and dolphins as well as corvids and primates, are all very social animals. The researchers propose that the need to understand complex social interactions may be the driving force behind the development of mental acumen.


Related Links:


Sharks Can Detect Magnetic Fields: BBC
Wave Of Bird Extinctions To Come: ABC News (Associated Press)
San Andreas Fault Rumbles Down Deep: San Francisco Chronicle / National Geographic / New Scientist
Lefties Make Better Fighters: Discovery.com
Mediterranean Fishing May Be Starving Dolphins: Los Angeles Times (Associated Press)
Dusty Disks Surround Solar Systems Under Construction: New Scientist / Yahoo Daily News (Reuters)
Crows Rival Great Apes In Smarts: National Geographic


Source: California Academy of Sciences


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