Our fingerprints, patterns on whale flukes, and fur patterns on cheetahs are examples of the natural ways we can tell one individual animal from another. For an Amazonian treefrog called the egg-eating spiny-backed frog (Osteocephalus oophagus), we need to look into their eyeballs. Fine black radial lines cross their golden irises, and form a pattern similar to our fingerprints. A study recently published in the journal Herpetozoa details the discovery.

The project began with study co-author Mélissa Peignier, a behavioral ecologist at the University of Bern in Switzerland, admiring frog eyes. 

“At the time, I was doing my PhD, studying Allobates femoralis in the field in French Guiana,” Peignier said in a statement. “My first reaction was simply something along the lines of, ‘Wow, what beautiful eyes!’ That initial curiosity gradually turned into a genuine interest in the species, and I realised how little we actually know about them.”

There was also an ethical component. One of the standard ways to tell amphibians apart from one another is toe-clipping, where a section or all of a single toe is removed. This procedure can affect their survival, physiology, and behavior. 

“Other studies have used toe-clipping, which involves removing some of the digits. Personally, I was uncomfortable with this approach, especially given that these are arboreal frogs that rely on their limbs to climb trees.”

Looking for other markings could offer a more humane solution and a way to observe the animals natural behavior unimpeded.

For this study, fieldwork took place over three rainy seasons (2021 to 2023) on a river island in the Nouragues Nature Reserve in French Guiana. They identified 103 individual frogs over the course of the study.

During their later encounters, the team took pictures of each animal’s eyes without touching it and then compared the images with a reference library. This way, the recognised frogs were left undisturbed and their eyes appeared in their more natural state. The identifications were then independently verified using Wild-ID, a software package that analyzes photographic markings in animals.

They found highly distinctive iris patterns. Within one season, between 56 and 80 percent of the frogs were recaptured and reliably re-identified. According to the team, this indicates that the patterns on their eyes remain stable enough to monitor the frog in the short-term. Photographs could even be taken of frogs while in their mating embrace (called amplexus) without disrupting them. The team hopes that this method will spread. 

“In a world where biodiversity is declining at an alarming rate, it is essential that we minimise our impact on the animals we study,” added Peignier. “If we can reliably identify individuals using naturally occurring features, we may be able to reduce the need for more invasive marking techniques while still collecting the data needed to answer important scientific questions.”

While the reliability of the eye markings will vary between species, and should be done case by case, the team sees considerable promise for amphibians with complex irises. And working with them offers its own benefits. 

“Honestly, the frogs themselves are incredibly beautiful and surprisingly chill, which makes working with them a real pleasure,” Peignier said. 

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The swirling bluish-white mistrals, towering cypress trees, and glittery stars in Vincent van Gogh’s “The Starry Night” (1889) have captivated our imaginations for generations. Despite never selling a painting during his lifetime, van Gogh’s “The Starry Night” has since inspired a hit song in 1972, draws visitors to the Museum of Modern Art in New York City, and adorns everything from journals to scarves and tote bags.

But what particular night above Saint-Rémy-de-Provence, France, did the troubled post-impressionist painter actually put on the canvas? A new analysis points to July 22, 1889. During the early morning hours at that time of year, a waning crescent moon, the planet Venus, and the Hyades star cluster in Taurus appeared close together—all of which are seen in the painting. A study published today in the journal Scientific Reports details the findings. 

The story behind ‘The Starry Night’

According to the Metropolitan Museum of Art, van Gogh was inspired by the view from his window at the Saint-Paul-de-Mausole asylum in southern France. He spent twelve months there 1889–1890, seeking reprieve from his mental illnesses and was also diagnosed with a form of epilepsy. 

Like many of his paintings that year, “The Starry Night” was created in several sessions during the day, under different weather conditions. The village nestled below the hills was also based on other views, and could not be seen from his window. Although van Gogh reconstructed some of the features in the night sky as he saw them, he also altered the celestial shapes and added a sense of glow.

“Van Gogh assigned an emotional language to night and nature that took them far from their actual appearances,” the museum writes. “Dominated by vivid blues and yellows applied with gestural verve and immediacy, ‘The Starry Night’ also demonstrates how inseparable van Gogh’s vision was from the new procedures of painting he had devised, in which color and paint describe a world outside the artwork even as they telegraph their own status as, merely, color and paint.”

Looking to the stars

Using astronomy to pinpoint which day inspired the painting began with UCLA art historian Albert Boime in 1984 and Harvard University astronomer and astrophysicist Charles Whitney in 1986. The two scholars reached conflicting conclusions, and neither of them displaced the prevailing religious and symbolic interpretations of the painting. 

Historically, the painting has been dated based on a letter van Gogh wrote to his brother Theo around June 18, 1889. However, the waning gibbous moon from mid-June does not account for the slender crescent seen in the painting. By July 22, 1889, the Hyades star cluster rose in the eastern sky alongside Venus, and the moon’s shape looked closer to the crescent on the canvas. This new study uses observational geometry to find an answer.

“To an observational astronomer, the cluster of stars in ‘The Starry Night’ is the Hyades in Taurus,” said study co-author Elijah Jeong-hyun Kim.  “But the moment I read the earlier studies explaining it as Aries, I heard the painting calling to me.” Kim is the CEO at South Korean robotic telescope company SLLAB and a PhD candidate at Kyung Hee University.

For this research, the team combined astronomical simulations and measurements of star positions, with historical weather records, and van Gogh’s own letters. They also used earlier sketches of the landscape to reconstruct the narrow field of view represented in “The Starry Night.”

According to the team, the crescent moon, Venus, and the Hyades star cluster in the constellation Taurus would have been visible around dawn on July 22, 1889. This configuration generally corresponds to what is portrayed in the painting. Weather records suggest that the night sky around July 22 would have been clear enough for this astronomical arrangement to be visible. Additionally, the frequent mentions of cicadas in van Gogh’s letters suggest that the region was seeing a period of hot weather, which matches the recorded temperatures in July 1889 better than in June.

The team also verified that the painter’s field of view in another painting titled “Starry Night over the Rhône” (1888) with photographs taken on site was painted when the sky was in Aries. Using the same method, the team also believes that the stars in “Café Terrace at Night” (1888) may be the Summer Triangle.

“I hope this work prompts a renewed, multidisciplinary look at the sequence and working methods of the Saint-Rémy paintings, and at Van Gogh’s movements that summer,” Kim said. “Our conversation with Van Gogh’s other skies is still ongoing. We plan to tell those stories one by one.”

The post What night is van Gogh’s ‘The Starry Night’? New analysis says it’s in July. appeared first on Popular Science.

Before giant manta rays (Mobula birostris) can grow to up to 30 feet long and 4,409 pounds, they must start small like most living things. Giant manta ray babies (called pups) in Central America don’t have their size to protect them from orca whales (Orcinus orca) and the numerous sharks in the open ocean. Their solution—sticking to the coast, where there is plenty of food to help them grow and defend themselves. A new study published today in the journal Frontiers in Fish Science details the baby rays’ behavior. 

“We show that manta rays’ lifestyle isn’t a one-size-fits-all behavior. Giant manta rays in Central America undergo a dramatic shift in space use as they mature,” Jeffry Madrigal-Mesén, a study co-author and project leader of Mantas Costa Rica, said in a statement. “Juveniles remained strictly within shallow nearshore waters that serve as coastal refuges, but most of the tracked adults executed long-distance transboundary migrations along the continental shelf break into Central America.”

Where the pups grow

In the study, the team used multiple methods to track and identify mantas at five locations between 2018 and 2025. Acoustic telemetry uses underwater sound pulses to monitor fish movements and allowed the team to track 59 individual rays. With satellite telemetry, transmitters track movement and behavior from a distance and helped the team track large-scale movements of 12 individuals. Lastly, photo identification helped to identify individual manta rays.

“If we hadn’t used all three technologies together, we simply wouldn’t have been able to piece this puzzle together,” explained Madrigal-Mesén. “Combining these tools turned fragmented data into a unified, undeniable story.”

The team ended up with a dataset of over 12,000 detections. The data showed that young mantas (those with a body about 10 feet or less) stick to shallow coastal refuges. In these more shallow spots, the pups have a safe place that doesn’t overlap with their predators’ hunting grounds. They have plenty of food and places to hide, and even get essential services like cleaning from reefs.

“Mature adults can rely on their massive body size and their ability to dive deep to evade threats. But juveniles don’t have that luxury,” said Madrigal-Mesén. “What is truly amazing is seeing how strictly young manta rays stick to coastal waters as long-term refuges. We see the same individuals more often than once a year. In fact, just recently, they were sighted again at the exact same tagging location. It is always a joy to see them again—they have truly become a part of the family.”

By comparison, nine mature mantas in the study went on expansive migrations along the continental shelf break. One manta ray nicknamed Mickey Mouse because of a spot pattern on his belly had movements that suggest the fish also continue to display loyalty to a particular site once they grow up. Unusually approachable for a manta, Mickey Mouse allowed the team tag him multiple times over several years, which provided a continuous dataset. In 2020, he logged 462 acoustic detections at a coastal hub called El Secreto. He returned to the same shelf in 2023, and stayed there for 38 days.

“Nearshore cleaning stations transcend basic hygienic function; they act as primary social hubs where courtship and reproductive interactions take place,” said Madrigal-Mesén. “Returning to a predictable coastal depot allows mature rays to prioritize social and cleaning needs before undertaking large-scale regional migrations.”

Traveling the manta swimway—safely

Once they leave coastal regions, adult manta rays face different dangers. Coastal areas are often legally protected marine reserves, but the open ocean is another story. They no longer have legal protection and are exposed to dangers from industrial fisheries and vessel strikes.

According to the team, this shows that marine protected areas alone are not enough to protect this highly mobile species as it swims across Central America. They say that multi-national “conservation swimways”  that link the domestic juvenile coastal refuges with adult migratory corridors could help keep the endangered rays safe. 

“This study opens a new chapter for manta ray research in Central America,” Madrigal-Mesén concluded. “We hope it sparks fresh enthusiasm and encourages future collaborators to join us in executing the new ideas and research projects we have planned for the conservation of this species.”

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