This week’s collection of science stories awaits your comments. Everyone is encouraged to share their 2¢ or articles, stories, and tweets. This is an open thread.

These female hummingbirds evolved to look like males — apparently to evade aggression

[…] “Why do some female jacobins look like males? It’s a mystery made up of multiple pieces,” said Jay Falk, a postdoctoral researcher at the University of Washington. “Is there a benefit? Is there a cost? Is it just appearance, or do these females also act like males?”

Now those pieces are falling into place. In research  published  Sept. 7 in the Proceedings of the Royal Society B, Falk and co-authors at the UW, Cornell University and Columbia University report that adult female white-necked jacobins with male-like plumage are mimicking male appearance — but not male behavior. In addition, their strength and body size are similar not to males, but to fellow females with muted plumage.

The study shows that the 1 in 5 adult females with male-like plumage are engaging in “deceptive mimicry”: They are essentially trying to pass themselves off as males, without acting like them. In the process they receive quite a benefit. As Falk and his colleagues  reported  in a  paper  published last year in Current Biology, females with male-like plumage suffer less aggression from males compared to females with the more typical muted plumage, and can hang out longer at feeders.

Warmer Earth could see smaller butterflies that struggle to fly, affecting food systems

New UBC research  has shown warmer temperatures can lead to smaller butterflies that collect less pollen and visit fewer flowers.

Dr. Michelle Tseng and recent graduate Erez Büyükyilmaz grew butterflies in the lab at different temperatures and found that the warmer the temperature, the smaller the butterfly, mimicking how increasing global temperatures due to climate change might affect the size of the insects. Then, using special equipment, they found smaller butterflies did not fly as far or as fast as the bigger ones, due to their smaller wings.

Refreezing poles feasible and cheap, new study finds

The poles are warming several times faster than the global average, causing record smashing heatwaves that were reported earlier this year in both the Arctic and Antarctic. Melting ice and collapsing glaciers at high latitudes would accelerate sea level rise around the planet. Fortunately, refreezing the poles by reducing incoming sunlight would be both feasible and remarkably cheap, according to  new research  published today in IOP Publishing’s  Environmental Research Communications.

Scientists laid out a possible future program whereby high-flying jets would spray microscopic aerosol particles into the atmosphere at latitudes of 60 degrees north and south – roughly Anchorage and the southern tip of Patagonia.  If injected at a height of 43,000 feet (above airliner cruising altitudes), these aerosols would slowly drift poleward, slightly shading the surface beneath.  “There is widespread and sensible trepidation about deploying aerosols to cool the planet,” notes lead author Wake Smith, “but if the risk/benefit equation were to pay off anywhere, it would be at the poles”.

Particle injections would be performed seasonally in the long days of the local spring and early summer. The same fleet of jets could service both hemispheres, ferrying to the opposite pole with the change of seasons.

Climate ‘points of no return’ may be much closer than we thought

Climate tipping points — the "points of no return" past which key components of Earth's climate will begin to irreversibly break down — could be triggered by much lower temperatures than scientists previously thought, with some tipping points potentially already reached. There are also many more potential tipping points than scientists previously identified, according to a new study.

In climatology, a tipping point is defined as a rise in global  temperature  past which a localized climate system, or "tipping element" — such as the  Amazon  rainforest or the Greenland ice sheet — starts to irreversibly decline. Once a tipping point has been reached, that tipping element will experience runaway effects that essentially doom it forever, even if global temperatures retreat below the tipping point. […]

In the new study, which was published Sept. 9 in the journal  Science, a team of researchers reassessed data from more than 200 papers on the subject of tipping points published since 2008. They found that there are now 16 major tipping points, almost all of which could reach the point of no return if  global warming  continues beyond 2.7 degrees Fahrenheit (1.5 degrees Celsius) above preindustrial levels.

A Volcano Erupted Without Warning. Now, Scientists Know Why.

Last year, one of the most dangerous volcanoes in Africa erupted without warning.

In a way, Nyiragongo, a vertiginous volcano in the Democratic Republic of Congo, is always erupting: The mountain is crowned by a rare, persistent lava lake constantly fed by churning magma below. But on May 22, 2021, its molten innards found another route to the surface. They oozed from fractures on the volcano’s flanks toward the metropolis of Goma, leading to the deaths of at least 31 people, injuring 750 others, displacing thousands more and leaving behind a trail of destruction.

Now, in a new study published this Wednesday in  Nature,  Delphine Smittarello, a geophysicist at the European Center for Geodynamics and Seismology in Walferdange, Luxembourg, and her colleagues articulated how the eruption managed to ambush everyone.

Mega-eruptions linked to most mass extinctions over past 500 million years

Mass extinctions litter the history of life on Earth, with about a dozen known in addition to the five largest ones — the last of which, at the end of the Cretaceous Period 66 million years ago, killed off the dinosaurs and 70% of all life on Earth.

A new study, led by scientists at Dartmouth College in New Hampshire, concludes that most of these mass extinctions had one thing in common: They occurred after mega-eruptions that spewed volcanic lava and toxic gases for hundreds of thousands of years, and some for as long as a million years.

The analysis linking mass extinctions throughout Earth’s history with major eruptions, characterized by lava and gas spilling from perhaps dozens of volcanoes and long fissure vents, confirms what many geologists have suspected for years. […] Massive amounts of sulfur dioxide emitted during the long-term eruption would have cooled the planet and caused the massive die-off seen in the fossil record.

U of M geologists discover major meteor crash site

Only 190 meteor impact sites have been confirmed worldwide, but a recent discovery by U of M researchers could soon add an ancient crater in Minnesota to that list.

“I’ve been mapping and studying the subsurface geology of Minnesota for the last 13 years … and have not come across something as exceptional as this before,” says crater co-discoverer Julia Steenberg. […]

The crater lies an average of 350 feet beneath Inver Grove Heights, a suburb on the Mississippi River, and appears to be at least 4 kilometers—2.5 miles—across. That means it should have an area 11 times the size of Meteor Crater, the iconic surface crater in Arizona, which measures 0.74 miles across.

On 26 September, an act of targeted violence will unfold 11 million kilometers from Earth, as a spacecraft about the size of a vending machine smashes into a small asteroid at 6 kilometers per second. Unlike some asteroids that stray worrisomely close to Earth’s orbit, Dimorphos—the 160-meter moon of a larger body—is an innocent bystander, posing no threat to our world. But the looming assault represents humanity’s first-ever field test of a planetary defense mission: NASA’s Double Asteroid Redirection Test, or DART.

The hope is that the collision will nudge Dimorphos into a closer orbit around its 780-meter partner, Didymos, shortening its nearly 12-hour orbital period by a few minutes. A successful strike would support the idea that, in the future, similar efforts could deflect threatening asteroids onto safer courses. But new simulations and lab experiments show the fate of the mission depends heavily on a crucial question: Are such small asteroids solid boulders or—as astronomers increasingly believe—loose heaps of rubble?

The answer, which should be revealed from the crater and ejecta produced by DART’s collision, could determine just how hard to hit an asteroid when the exercise is not a test.

On a warm August day, aquatic biologists Scott Girdner and Josh Sprague lie prone on the deck of the research vessel Neuston. Holding life jackets tented over their heads to block the sun’s glare, they gaze into the sapphire depths of Crater Lake, Oregon’s only national park. As they stare, Biological Science Technician Nate Akers operates a cable that lowers a black and white disk deep into the water.

“I’m out!” Sprague calls out, when he can no longer see the disk. Akers lowers the disk a few more meters, then starts pulling it back up.

“Out!” Sprague shouts again, once it comes into view.

This simple but elegant exercise, called the Secchi depth test, is used to measure the transparency of this incredibly clear, incredibly blue lake. The greater the depth at which a person can see the disk, the clearer the water.

U.S. declares disaster for tribal salmon fisheries on the West Coast

For generations upon generations, the Yurok tribe has relied on Chinook salmon from the Klamath River in Northern California for ceremonies, subsistence and commercial gain.

But in 2019, less than 40 percent of the usual number of salmon returned to the river — resulting in what tribal Chairman Joseph L. James  called  an “utter failure” of that year’s stock.

The Yurok tribe isn’t alone. Between 2014 and 2019, tribal salmon fisheries failed in Washington state rivers, too.

On Sept. 1, the Commerce Department  declared  fishery disasters for several West Coast tribes and allocated $17.4 million in disaster assistance in response. The assistance will be used to shore up everything from habitat restoration to commercial and subsistence fishers.

Sperm whales use distinct vocalizations to identify different whale clans, new research finds

Sperm whales in the Pacific Ocean make distinct vocalizations that help them identify whales in different clans, a new study from a team including an Oregon State University researcher found.

These vocalizations, called “identity codas,” are unique sequences of Morse code-like clicking sounds that function as symbolic markers of different social groups and are indicative of whale culture, researchers say.

“They’re all kind of using the same language, but phrasing things slightly differently,” said Mauricio Cantor, assistant professor in OSU’s Marine Mammal Institute and a co-author on the study,  published  last week in PNAS. “As symbolic markers, the identity codas would serve as a flag: an arbitrary but useful way to advertise membership of a particular group.”

Keeping trees near farmland pays environmental dividends

Both dead and alive, trees are an important ally for farmers in helping the environment, a new University of Alberta study shows. Preserving and planting shelterbelts and hedgerows — and keeping the deadwood they contain — next to cropland helps store carbon and reduce greenhouse gas emissions.

“Retaining those live and dead trees, and planting more trees where possible on agricultural lands, is a valuable way to help mitigate climate change,” says lead author Cole Gross, post-doctoral researcher at Yale University's School of the Environment, who conducted the study while completing his PhD in soil science in the  Faculty of Agricultural, Life & Environmental Sciences.

In the  three-year study, researchers looked at several central Alberta cropland sites and their nearby woodlands: shelterbelts, which are rows of planted trees, and hedgerows, which are naturally occurring trees and wild bushes. The results show that shelterbelts and hedgerows stored two and three times more carbon, respectively, than neighbouring fields of wheat, barley and canola.

How pollution changes a baby’s gut, and why it matters

Exposure to air pollution in the first six months of life impacts a child’s inner world of gut bacteria, or microbiome, in ways that could increase risk of allergies, obesity and diabetes, and even influence brain development, suggests new CU Boulder research.

The study,  published this month  in the journal  Gut Microbes, is the first to show a link between inhaled pollutants—such as those from traffic, wildfires and industry—and changes in infant microbial health during this critical window of development. Previous research by the same group found similar results in  young adults.

“This study adds to the growing body of literature showing that air pollution exposure, even during infancy, may alter the gut microbiome, with important implications for growth and development,” said senior author Tanya Alderete, assistant professor of Integrative Physiology at CU Boulder.

Bin-opening cockatoos enter 'arms race' with humans

Australia's crafty, sulphur-crested cockatoos appear to have entered an "innovation arms race" with humans, scientists say, as the two species spar over the rubbish in roadside bins. […]

Now, a new study says they have gone a step further by thwarting the escalating defences of fed-up humans.

The birds' and humans' behaviour may reveal a hitherto unexplored "interspecies innovation  arms race", said a study published Monday in Current Biology.

NASA’s Mars rover makes ‘fantastic’ find in search for past life

Since July, NASA’s Perseverance rover has drilled and collected four slim cores of sedimentary rock, formed in what was once a lake on Mars. They are the first of this type of rock to be gathered on another world — and scientists are excited because at least two of the cores probably contain organic compounds.

On Earth, organics, which are carbon-containing molecules, are often associated with living things, although they can be formed without the involvement of organisms.

Adding to the buzz over the rock samples, Perseverance collected them from an ancient delta in Mars’s Jezero Crater, where a river once deposited layers of sediment — and possibly other matter. River deltas on Earth often teem with living organisms.  If life ever existed in Jezero, these cores are probably NASA’s best chance of finding it.

Sun halo on Mars! This Martian sky sight spotted by Perseverance rover was once thought to be impossible

NASA's Perseverance rover has spotted a phenomenon scientists had lost hope of ever seeing on Mars.

On Earth, when conditions are just right, ice crystals in the atmosphere can warp sunlight to create the appearance of a bright spot on either side of the  sun, or of a halo ringing it. And scientists have long thought that a similar optical trick could occur on other planets as well. But despite decades of robotic explorers on the surface of  Mars  capturing countless thousands of photographs of the skies, scientists hadn't seen any sign of a sun halo.

Until Dec. 15, 2021, that is. 

"Perseverance  really surprised us with some of the images that we got back in December," Mark Lemmon, a planetary scientist at the Space Science Institute, a nonprofit research institute in Boulder, told Space.com.

Saturn’s rings and tilt might have come from one missing moon

A single, doomed moon could clear up a couple of mysteries about Saturn.

This hypothetical missing moon, dubbed Chrysalis,  could have helped tilt Saturn over, researchers suggest September 15 in  Science. The ensuing orbital chaos might then have led to the moon’s demise, shredding it to form the iconic rings that encircle the planet today.

“We like it because it’s a scenario that explains two or three different things that were previously not thought to be related,” says study coauthor Jack Wisdom, a planetary scientist at MIT. “The rings are related to the tilt, who would ever have guessed that?”

Tiny ‘dragons’ flew through the trees of Madagascar 200 million years ago

Late  Permian Period  reptile  Coelurosauravus elivensis  (C. elivensis) won’t be laying colorful scaly eggs or burning down armies anytime soon, but it does have the title of the planet’s first flying reptile.

In a new study published in  Journal of Vertebrate Paleontology, researchers believe that the four-inch-long winged reptile evolved to glide between tree tops.  C. elivensis  was a  tetrapod  that lived during between 252 million to 260 million years ago in present-day Madagascar, and used a  patagium  (thin membranes extending from its torso to the front limbs) as a make shift pair of wings to travel above the tree canopy.

These unique features have earned the tiny lizard the title of “world’s first gliding reptile,”  according to researchers  from the French National Museum of Natural History in Paris and the Staatliches Museum für Naturkunde Karlsruhe in Karlsruhe, Germany. The first fossils of  C. elivensis  were unearthed in 1907  and sparked a spirited debate over how the reptile actually lived and how it evolved to have these wings. The team on this study created a near-perfect skeletal reconstruction of  C. elivensis  and the new research advanced knowledge of the tetrapod’s form and its habits. The team says that clues in the tree canopy of this extinct ecosystem have helped solve the puzzle.

Fire ant rafts form because of the Cheerios effect, study concludes

Fire ants might be the scourge of southern states like Georgia and Texas, but scientifically, they are  endlessly fascinating as an example of collective behavior. A few fire ants spaced well apart behave like individual ants. But pack enough of them closely together, and they act more like a single unit, exhibiting both solid and liquid properties. They can form rafts to survive flash floods, arrange themselves into towers, and you can even pour them from a teapot like a fluid.

"Aggregated, they can almost be thought of as a material, known as 'active matter,'" said  Hungtang Ko, now a postdoc at Princeton University, who began studying these fascinating creatures as a Georgia Tech graduate student in 2018. (And yes, he has been stung many, many times.) He's a co-author of two recent papers investigating the physics of fire ant rafts. The first,  published in  the journal Bioinspiration and Biomimetics (B&B), investigated how fire ant rafts behave in flowing water compared to static water conditions.

The second,  accepted for publication  in Physical Review Fluids, explored the mechanism by which fire ants come together to form the rafts in the first place. Ko  et al. were somewhat surprised to find that the primary mechanism appears to be the so-called "Cheerios effect"—named in honor of the tendency for those last remaining Cheerios floating in milk to clump together in the bowl, either drifting to the center, or to the outer edges.