Some migratory birds that have to navigate across continents have an extremely useful tool at their disposal–an internal compass that points unerringly towards magnetic north. Researchers already knew that some birds possess these biological compasses, but their mechanism has been unclear. “This is basically the sixth sense of biology, but no one knows how it works…. The magnetic sense is by far the least understood sense in the natural world,” [Science News], says study coauthor Henrik Mouritsen.
Now, researchers have determined that light-sensing cells in the eye convey the crucial message to a special visual center of a robin’s brain, called cluster N. Special proteins called cryptochromes in the birds’ eyes may mediate this light-dependent magnetic sensing, Mouritsen says. Light hitting the proteins produces a pair of free radicals, highly reactive molecules with unpaired electrons. These electrons have a property called spin which may be sensitive to Earth’s magnetic field. Signals from the free radicals may then move to nerve cells in cluster N, ultimately telling the birds where north is [Science News].
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Even European eels enjoy a trip to the Bahamas, for mating season of course. The eel travels thousands of miles to the Sargasso Sea, in the Atlantic Ocean near the Bahamas, just to get a little action. Scientists wanted to see what the little eels were up to on their trek, so they equipped a few with satellite tags and tracked their journey, which surfaced in Science this week. The tags allowed researchers to follow 22 eels for the first 1,300 kilometers of their trek from the coast of Ireland to mating grounds near the Bahamas. Understanding the details of the eels’ journey may help to protect this critically endangered species, a favorite of sushi eaters [Science News].
The tags recorded location, speed, depth and direction of the eels for 6 months, before popping off and floating to the ocean’s surface to beam their data back to the laboratory. The researchers found the eels swim too slowly to get to the Sargasso Sea by the April spawning period. The researchers suggest this means the eels may gain speed and travel efficiency by entering the ocean currents that begin west of Africa and continue as part of the subtropical gyre system that flows to the Caribbean [BBC News]. The data also show that the eels swim in shallow, warm water at night and dive to depths of 3,200 feet during the day swims. Since the eels do not feed on their trip, scientists think swimming in warm water boosts metabolism, while the cold water helps slow sexual development until they reach the Sargasso Sea.
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Image: flickr / wwarby
A new experiment has shed light on how the monarch butterfly executes its impressive 2,000-mile migration every fall, and all it took was a lick of paint.
Researchers already knew that the butterflies use the sun to guide them to the exact same wintering spot in central Mexico. But because the sun is a moving target, changing position throughout the day, biologists have long speculated that in addition to having a “sun compass” in their brains, butterflies must use some kind of 24-hour clock to guide their migration [Wired.com]. In a new study, published in Science, researchers determined that the butterflies have a second circadian clock in their antennae, which sense light.
The researchers conducted the test by holding the butterfly wings gently and dipping their antennas in enamel paint. The ones with black paint were unable to orient to the south, they found, while butterflies whose antennas were coated with clear paint had no trouble navigating [AP]. This proved that the antennae had to be able to sense light for the butterflies’ navigation system to operate, and also showed that the butterflies weren’t navigating by scent, as both kinds of paint interfered with the insects‘ sense of smell.
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Image: Monarch Watch / Chip Taylor
Some dinosaurs coped with the cold of winter by venturing beneath the Earth’s surface, according to a study to be published in the journal Cretaceous Research. Three fossilized burrows found in southeastern Australia are the second group of such tunnels found on Earth and, dating back 110 million years, are the oldest.
When dinosaurs roamed the Earth, these burrows were within the Antarctic Circle and temperatures dipped below freezing during the winter. Also, periods of little sunlight likely led to cyclical shortages in vegetation. The burrows support the hypothesis that instead of migrating to escape the cold winters of the Cretaceous period, dinosaurs ventured underground, like modern animals such as alligators and coyotes. The only other known dinosaur burrow was discovered in 2005 in Montana, US. Described two years later, this burrow dated from 95 million years ago and contained the bones of an adult and two juveniles of a small new species of dinosaur called Oryctodromeus cubicularis [BBC News]. Burrows that snaked below the ground may have provided a haven offering protection from predators, along with stable temperatures, constant humidity levels and a place to tend to offspring.
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The blue whale, the biggest animal that has ever inhabited the planet, seems to be on the move in the Pacific Ocean in ways that could reflect the revival of old migratory patterns disrupted by decades of intensive whaling in the 20th century [The New York Times blog]. Although blue whale hunting was banned in 1965, the whales didn’t return to the northern Pacific waters off the coasts of British Columbia and Alaska, where they were once plentiful.
Whalers formerly caught hundreds of blue whales in the northern zones, landing 1300 between 1908 and 1965. Yet despite the ban, they seemed not to recover there [New Scientist]. Now a new study, published in the journal Marine Mammal Science, reports that 15 blue whales have been sighted in the northern waters over the last decade, and some of them were confirmed to be the same individuals previously spotted farther south, off the shores of California. Researchers can’t yet say what led to the renewed migration: It could be a sign of a booming population, or a response to global warming.
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Birds and vacationing humans aren’t the only animals to migrate south for the cold months of winter. It turns out that basking sharks do, too.
They are the ocean’s second largest fish, and live in temperate waters from late spring until early fall. But then they disappear, and until now scientists have only been able to guess where they go–some have even suggested that the sharks hibernate on the ocean floor. To find the real answer, the team tagged 25 basking sharks off the coast of Cape Cod and tracked them as they made their wintertime trip. The researchers found that the sharks headed south [to the Caribbean], some going as far as Brazil [Science News].
The basking shark is a benign behemoth. It swims at about three miles per hour with its four-foot-wide mouth gaping open, filtering through almost 500,000 gallons of water every hour for its plankton sustenance [Wired]. They can grow to 35 feet or longer, but aside from knowing the sharks spend most of their time in temperate waters, scientists have been mystified by these fish for years: no one has ever examined a newborn basking shark. No one has seen a pregnant female. No one knows where the animals give birth [Discovery News].
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A migrating bird has found a quick and effective way to boost its endurance for a grueling task, according to a new study, and it’s a tactic that would make human marathon runners jealous–provided they like seafood.
Like all migrating birds, the tiny sandpiper instinctively heads to warmer climates for the winter. The [1,900-mile] trek from the birds’ summer home in the Canadian Arctic to the South American coast includes 3 days of nonstop flight over open water. The journey is so arduous it can kill younger or weaker members of the flock [ScienceNOW Daily News]. Sandpipers prepare for the flight in a number of ways: Autumn’s shorter days and cooler weather trigger hormonal changes in the birds, causing their stomachs to stretch to hold more food. The birds also start flying more, as if exercising for their upcoming ordeal.
But the final, and arguably most important step seems to be a stop at the Bay of Fundy, where sandpipers spend two weeks gorging on mud shrimp, which have some of the highest levels of omega-3 fatty acids of any marine animal. Researchers say the feast drastically increases the birds’ endurance by making their muscles use oxygen more efficiently. These omega-3 fatty acids are the same fats shown to reduce the risk of cardiovascular disease and lower blood pressure in humans [CBC].
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The songbirds that live in the backyards and parks of the northeast United States have just earned a little more respect. Researchers strapped cutting-edge geolocator devises to the backs of purple martins and wood thrushes to track their migrations, and found that the diminutive warblers can fly more than 300 miles each day, tripling previous estimates. But researchers say the biggest achievement was proving that the new technology works, which lays the groundwork for future studies of small birds.
“Never before has anyone been able to track songbirds for their entire migratory trip,” explained co-author Bridget Stutchbury…. She said that most songbirds were too small to be fitted with conventional satellite tracking devices, so the team mounted miniature “geolocators” on the birds [BBC News]. Each tiny bird backpack weighs less than a dime, and contains light detectors that record each day’s sunrise and sunset times, and also record where the bird is in relation to the sun. When the researchers retrieved the monitors, they used that data to calculate where the birds had been, and when they were there.
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It’s a question that has fascinated scientists for decades: When sea turtles and salmon decides to give up the freedom of the open ocean and head back to their birthplaces to breed, how do they find their way back? Some species of sea turtle migrate thousands of miles across entire oceans back to their birthplaces after leaving more than 10 years earlier. And after hatching in rivers, salmon travel hundreds of miles out to sea before returning home to spawn years later [Press Association]. Now one researcher thinks he has the answer. Marine biologist Kenneth Lohmann believes that these marine animals can detect the distinctive magnetic fields of different spots and use them to navigate.
“What we’re proposing is the sea turtles and salmon, when they begin life, basically learn or imprint on the magnetic field that marks their home area,” he said. “They retain this information. And years later, when it is time for them to return, they are able to exploit this information in navigating back to their home area” [National Geographic News]. Lohman says this doesn’t contradict the existing theory that when salmon reach coastal waters, chemical scents guide them upriver to the particular stream where they were born; those olfactory cues probably have a limited range, he says, and couldn’t extend thousands of miles into the ocean to guide the salmon all the way home.
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The last woolly mammoths, who tromped around the Siberian tundra before going extinct about 10,000 years ago, had North American roots, according to a new genetic analysis. Scientists studied DNA from the remains of 160 mammoths from across North America and Eurasia, and determined that the last remaining mammoths were migrants who had come to Siberia via the Bering land bridge, and somehow replaced the endemic population.
Researchers believe that mammoths originally spread from Asia to North America via the land bridge, creating two genetically distinct populations. Now, they’re hypothesizing that some members of the North American group eventually made a return trip and proved hardier survivors than the Siberian group. “For some reason the North American guys went back over and became kings,” says [lead researcher] Hendrik Poinar [New Scientist].
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