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Science Roundup: From a bird that is half male and half female to asymmetric dancing lights

The Northern and Southern Lights are asymmetric, scientists have discovered. You can imagine the two like mismatched dancers: viewed from space, the Northern Lights may contort and groove in one direction, while the Southern Lights could perform a routine that doesn’t quite sync up with its partner’s.

Research published in December in the Journal of Geophysical Research: Space Physics now reveals that the cause of this north-south auroral asymmetry is the angle at which the sun’s solar wind and magnetic field approaches Earth.

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Earth has two magnetic poles, a north and a south. From these two poles, bunched up magnetic field lines – invisible tendrils that represent the direction and strength of this planetary bar magnet – reach out into space as the planet travels on its orbit. Like fishing lines, they catch energetically excitable particles heading our way in the solar wind. These particles slam into our atmosphere, and energy is released in the form of the colourful auroras.

As these two geographically opposed magnetic poles are reflections of each other, it was once assumed that the auroras would be the same, too. However, scientists can now see more clearly that they not only have large-scale differences in shapes, but they crop up at slightly different locations around the magnetic poles, too.

Earth’s entire magnetic field is a bit like a bubble, one that is constantly being squashed by the sun’s magnetic field and solar wind. This causes the bubble to stretch out on Earth’s nightside in the shape of a magnetic tail. Space physicists have now found that when the sun’s magnetic field is heading towards Earth in a more east-west orientation relative to Earth’s magnetic poles, it compresses our magnetic tail in a peculiar way. This makes it tilt, which triggers distortions that produce differently shaped Northern and Southern Lights.

This new paper, led by Anders Ohma, a doctoral candidate at the University of Bergen, examined old images of both auroras taken at the same time by two separate satellites. By assessing the most up-to-date information about the two entities’ magnetic fields, they uncovered clear evidence that the asymmetry occurs because of the angle of the sun’s magnetic field compared to Earth’s field.

How human hunters kept desert animals alive

Australia’s bilby, bettong and rat kangaroo, as well as the brush-tailed possum and other medium-sized mammals, have disappeared from the Western Desert in recent decades. It was a mystery: typically bigger animals vanish first – often only after people show up.

But ask the people who lived in this desert for 48,000 years what happened and many will tell you: the small ones left first.

It’s easy for some to think of humans as the planet’s great destroyers. But in a study published recently in Human Ecology, scientists critique this notion of a human-free wilderness. By examining how an indigenous Australian community has shaped its land through traditional hunting, they present an example where it’s not all bad to have humans around.

“We can still see the ways that the Martu look after country,” says Stefani Crabtree, an archaeologist, ethnographer and an author of the study.

Their story of stewardship, Crabtree and colleagues say, could be applicable in other environments threatened by degradation.

The Martu are defined under Australian law as the traditional owners of more than 52,000 square miles of land in the Great and Little Sandy deserts. They hunt with fire, burning small patches of vegetation and returning after the flames subside to capture goannas and other small prey. But in the 1930s, they started trickling out of the desert into nearby missionary settlements and cattle ranches. By the 1960s, nearly all traditional hunters had left.

“It was in that time that you get this wave of extinctions,” says Doug Bird, an author of the study and an anthropologist at Penn State University. It seemed paradoxical to him: how could taking hunters out of the desert harm it?

In the 1980s, mining and exploration threatened their homeland, so the Martu returned to reclaim it and resume their hunting traditions.

The small hunting fires were vital for sustaining wild species. Without Martu people starting them year-round, seasonal lightning fires raged. Invasive predators thrived and mammals needing to travel long distances for food or water got hit hard. Even the goannas they hunted struggled without the Martu.

“The thing about fires is that they’re creating this patchy mosaic of really diverse vegetation,” says Rebecca Bliege Bird, an anthropologist also at Penn State and study co-author.

Yellowstone’s Steamboat geyser is gushing at a record pace

Late last year, Jeff Carter happened upon Steamboat geyser, the tallest active one in the world, just before it erupted.

“It was so much louder and higher and stronger than anything I had seen, almost frightening,” he says.

All but dormant for years, Yellowstone National Park’s Steamboat is erupting fairly frequently these days, and more people like Carter are seeing the spectacle.

While Old Faithful is a global icon of punctual eruption – it usually erupts every 90 minutes or so – it is the exception among geothermal features. Most of the park’s 1,000 or so geysers are far more unpredictable.

Many geysers, like Steamboat, are quiet and then suddenly come to life. Steamboat sometimes jets water to heights of 300ft to 400ft – far higher than Old Faithful’s top height of 185 feet – for anywhere from a few minutes to about an hour.

After erupting, Steamboat – in Norris Geyser Basin, the park’s hottest – goes into a ferocious, churning steam phase that can last two days.

There were only very occasional eruptions until last March when Steamboat blasted off. It has erupted every week or two since. It set a record with 32 eruptions in 2018, besting its total of 29 in 1964. It has continued that pace of eruptions in 2019 and last erupted on 1 February.

Ear Spring geyser in the park’s Upper Geyser Basin also recently woke and Giant geyser in the park has also been unusually active.

What has stirred the geysers out of their years of slumber? It’s hard to say precisely. “These geysers are incredibly dynamic,” says Michael Poland, a federal geophysicist who studies the massive caldera for the Yellowstone Volcano Observatory. “Over time their conduit systems expand and contract as minerals precipitate in them and close them up, and the pressure builds and reams them out again.”

Add to that large annual swings in the amount of snow and rain, which can change the level of the below-ground reservoirs, and a constant jiggling of the landscape. “We have an average of 1,500 locatable earthquakes every year,” says Jeff Hungerford, a park geologist. “That acts as an agitator to the system and allows some of these geysers to keep open.”

Beaked whales are the deepest divers

Cuvier’s beaked whales are among the most mysterious and adept mammals on Earth.

They can dive deeper and hold their breath longer than any other marine mammal. But biologists still know very little about them, because they only surface for a few minutes between most dives, taxing the patience of whale experts, as well as the ability of electronic tags to upload information, before the whales plunge again into the depths.

Now a study, published recently in Royal Society Open Science, is the first to look at a population of these whales that lives off Cape Hatteras, North Carolina. Researchers tagged 11 Cuvier’s beaked whales for an average of a month, tracking the length and depths of their dives.

The whales dove almost continuously. They took deep dives of about one mile, swimming down for half an hour and then back up. These were followed by several shallower dives of about 918ft – nearly a fifth of a mile – lasting from 15 to 20 minutes, the study found. The whales would spend an average of just over two minutes at the surface, before plunging again.

At night, they sometimes spent longer intervals near the surface, perhaps because they were less concerned about being spotted by predators, says Jeanne Shearer, the paper’s lead author and a doctoral student at the Duke University Marine Lab.

Although diving capacity usually increases with size, Cuvier’s beaked whales dive longer and deeper than larger whales, and are about half the size of sperm whales, which are the second best deep-divers, Shearer says.

It’s not entirely clear how they manage to dive so deep, she says. Her team tracked a few dives of over 1.7 miles.

Diane Claridge, executive director of the Bahamas Marine Mammal Research Organisation, says recent evidence suggests that at least part of the answer may lie in the Cuvier’s muscles. “Basically, they’re made of this muscle that can store lots of oxygen,” Claridge says. The whales have little fat, especially around their midsections, which allows them to store more nitrogen, enabling deep dives.

The bird that’s half male, half female

The bird hopping on Shirley and Jeffrey Caldwell’s windowsill is the strangest they have ever seen.

Its left side is the taupe shade of female cardinals; its right, the signature scarlet of males.

Researchers believe that the cardinal frequenting the Caldwells’ birdfeeder in Erie, Pennsylvania, is a rare bilateral gynandromorph, half male and half female. Not much is known about the unusual phenomenon, but this sexual split has been reported among birds, reptiles, butterflies and crustaceans.

No one can be sure the bird is a gynandromorph without analysing its genes with a blood test or necroscopy, but the split in plumage down the middle is characteristic of the rare event, according to Daniel Hooper, an evolutionary biologist at the Cornell University Lab of Ornithology.

He says that gynandromorphs could theoretically be created through the fusion of two developing embryos that were fertilised separately.

It’s also possible that a female produces an egg that contains both copies of her sex chromosomes, Z and W, which is then fertilised by two sperm, each with a Z chromosome. (While human sex chromosomes are labelled XX for females and XY for males, female birds are ZW and males are ZZ.) Scientists aren’t precisely sure how such an egg yields a chick with both ZW and ZZ cells.

The split runs down the middle of the bird simply because vertebrates develop in a bilaterally symmetrical way. Although one side would largely be ZW and the other ZZ, previous research suggests there is some mixing of cells in the bird’s body.

But in essence, each side of the bird would be largely the brother or sister of the other. Genes other than those that confer gender also are affected. Sex determination in mammals is controlled by a gene on the Y chromosome that stimulates the development of testes, the hormones of which regulate development of the rest of the organism. That’s why gynandromorphism is so rarely seen in mammals, Dr Hooper says.

He doesn’t see any reason making cardinals more likely to be of mixed sex than other creatures, but their colour contrast by gender makes them particularly noticeable.

© New York Times


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