[Animals] Where will the animals that are guided by the stars go?

[MosterOfficial ☆]

 

On a moonless night just over a decade ago, Marie Dacke and Eric Warrant, animal vision experts at Lund University, Sweden, made a surprising discovery in South Africa. The researchers had been watching the nocturnal dung beetles, the miniature Sisyphus of the savannah, as they rolled gigantic dung balls. The beetles, or acatangas as they are also called, appeared to be able to roll in a surprisingly straight line, despite having no clear landmarks.

Humans are famous for this kind of thing. The stars attracted our species to cross the seas and ignited the sciences that later allowed us to climb toward them in rockets. From culture to culture, the Milky Way served as a backdrop and inspiration for stories about rivers, trees, gods, snakes, and of course, exploration.

 

But we weren't the only ones looking at her. Researchers like Dacke suspect that a large part of the animal world could sometimes navigate thanks to starlight. These animals could start to get lost as the lights of our cities drow out that glow. His team's most recent study, published in late July, reveals that dung beetles get confused when under light-flooded skies. The result is added to a small and scattered body of research, carried out over decades, on what the night sky can mean for other Earthlings who can perceive it. These experiments pose the same difficult questions: can animals see stars? Are they able to harness them? And what if they don't have them?

 

 

In the 1780s, astronomers William and Caroline Herschel scanned the skies for nebulae and found some that looked like spiral seashells. In the 1920s, Edwin Hubble, commanding a huge telescope, discovered that the spirals of the Milky Way, Andromeda, and Herschel were galactic islands in a vast cosmic sea. And in the mid-2000s, Nick, who is arguably a researcher in Cologne, Germany, swam to his own telescope and flopped into an underwater chair. Then he put his head into a tube and, if he saw a star, he would press an oar. He was rewarded with fish. Nick, a harbor seal, entered the annals of astronomical history when Guido Dehnhardt, a marine biologist now working at the University of Rostock, was studying how marine mammals orient themselves. Dehnhardt and his colleague Björn Mauck hypothesized that if seals could distinguish stars, that could help explain how these animals are capable of completing long journeys across seas that would otherwise have no characteristic features. To put the astronomical abilities of seals to the test, Mauck devised what must be two of the most surprising and wonderful experiments in the history of science. First, the team built their "focascope," a tube without a lens through which Nick gave a visual tour of the night sky. He constantly squeezed his paddle when bright spots like Venus, Sirius, and Polaris came into view. The researchers determined that he couldn't see as many faint stars as humans, but there were still plenty of celestial landmarks available to him. Then Mauck built something even bigger. This time he invited two seals to participate, Nick and his smarter brother, Malte. When they were brought back to the Cologne Zoo pool, the seals entered a 4.5-meter diameter dome, the rim of which rested on a floating ring. The interior of this custom-built aquatic planetarium was illuminated with 6,000 simulated stars. "Right away they were swimming around the planetarium and looking at the stars as if to say, 'Oh, what is that?'" Dehnhardt said. "You had the impression that they really recognized what it was."

 

Through the compound eyes of a dung beetle, stars appear as spots, not as points of light. But those same eyes are more sensitive than ours to faint objects, like the mottled patterns of the Milky Way. After its spinning scan, the beetle rolls its ball in a straight line away from the manure heap for a few minutes, in a random direction. (This seems to minimize the chance that two beetles will meet, which often results in a fight.) Dacke found that the beetles appear to keep rolling in a straight line by confirming that the intragalactic panorama they were heading towards still coincided with the previous reference image. But a curious thing happened when Dacke's team continued to study this behavior: They found it increasingly difficult to locate the Milky Way in the sky. “I ended up spending a night in the forest, when I was riding my bike,” says James Foster, who joined the project as a graduate student and is now doing a post-doctorate in zoology at the University of Würzburg, Germany. It is a common experience; About four in five Americans, two in three Europeans and one in three people in the world reside somewhere too bright at night for the Milky Way to be visible, a 2016 study showed, and the fraction of our planet that lights up at night increases every year. Dacke and Foster set out to see if washed-out skies were important to their study subjects, too. In their latest experiments, published in Current Biology, they illuminated the beetles with spotlights and brought them to the roof of the biology building at Wits University in downtown Johannesburg. They found two effects, neither of them good. When a beetle's sky was dominated by a single dazzling light, it could go straight ahead, but instead of rolling in a random direction, it was heading toward the lighthouse. More confusing were the featureless, light-flooded skies you'd expect in the suburbs - the beetles just circled. Other species can be affected in a similar way. Stars have always been more or less constant when other landmarks erode and the planet's magnetic field changes.

 

After completing their studies, the astronomical animals pioneers of science have followed other destinies. Some of the South African dung beetles now live in Lund's laboratory, where researchers sometimes study them under a fully simulated sky. Demlen kept the Betelgeuse indigo tiles in his laboratory through the winter and released them in the spring. Fortunately, he said, they recalibrated to true north before beginning their first migration. And the seal Nick is still actively collaborating in fields such as acoustics, hydrodynamics and optics, even though Malte died a few years ago. Nick now lives in a large harbor laboratory that opens onto the Baltic Sea; at night, he and the other seals in the enclosure can see fantastic skies overhead, says Dehnhardt.

 

Animals