A single fish, or even a school of them, swimming through the vast ocean isn’t an easy thing to keep track of, so scientists often rely on a little gadget called an acoustic tag. These tags give off ultrasonic “pings” that researchers pick up on hydrophones and other instruments and turn into digital data. By attaching them to or implanting them inside a fish, scientists can use them to monitor fish location, movement and survival rates.
Great care is always taken to make sure that these tags don’t hinder the animals that are being tracked, and fish don’t appear to be able to hear the pings. But that doesn’t mean other species can’t, and that might be a problem for both the fish and the scientists studying them.
Seals and sea lions have shown that they can hear fish tags’ pings from hundreds of feet away, but it wasn’t clear if the noises meant anything to them. Now, a new study suggests that the tags may be like little dinner bells for seals, helping them find tagged fish more easily and turning research subjects into easy prey.
Researchers from the UK, led by Amanda Stansbury, set up an experiment with 10 grey seals born on Scotland’s Isle of May. The seal pups were just three months old, didn’t associate sound with food, and had never even been in the ocean before. One by one, the seals were released into a long pool to find fish that the researchers had hidden in 20 boxes lining the sides. One box contained a tagged fish, one had an untagged fish in it, and the other 18 were empty. The pups searched around, poked their heads in the boxes and got a snack if they could find it.
After a few days—during which each seal got 20 turns in the pool—the seals all got faster at finding both types of fish. They not only reduced the time they needed to discover their prize, but also the number of boxes they had to check, even as the fish were moved from one hiding place to another. While the seals didn’t find the tagged fish much faster than the untagged ones, they did find them with fewer box checks and returned to the boxes with tagged fish twice as often as any of the other boxes. The researchers thought that the seals could have quickly learned to associate the tags’ sounds with food, but they might have also just been following their noses and not using sound that much during their searches.
To control for smell and other chemical cues, Stansbury and her team tried two variations of their original experiment. The first was a “tag only” trial where the seals explored the pool with just a fish tag, but no fish, in one box and all the others left empty. Even with no fish and no chemical cues to follow, the seals still checked the box with the tag in it for food faster than they did any of the other boxes. In the second “all fish” trial, the researchers filled all the previously empty boxes with fish that the seals couldn’t grab. With a tagged fish, an untagged fish, and 18 inaccessible fish all giving off odors in the pool, the seals again found the noisy fish faster than the silent one.
“Gray seals quickly learn that hearing pinging fish tags give away the location of a nice meal,” the researchers say, and they might rely on these sounds even more in the wild, where the scent of a live swimming fish would be harder to follow. This complicates things for scientists using acoustic fish tags. If tagged animals are more vulnerable to being eaten, that’s not only unfortunate for the fish, but could skew the data being collected and point researchers towards erroneous conclusions. There’s already some evidence that wild salmon wearing acoustic tags are easier pickings for predators and have lower survival rates than ones wearing silent tracking tags. And while noisy prey might make things easier for predators, a hunter that’s been tagged itself could alert its quarry and have a harder time finding something to eat. The researchers say that acoustic tagging is becoming more common in studies on sharks, and the tags could give them away to their seal prey (though shark researcher Michelle Jewell notes that the noisiness of seal colonies seems to leave them oblivious to the sounds of nearby tagged sharks).
Stansbury says that the results of the study show how important it is to consider all the effects, both good and bad, that an artificial sound might have in an environment. If acoustic tags alter the way predators and prey interact, that doesn’t mean that they’re no longer useful. Rather, finding this unintended consequence helps scientists fine tune their methods to save both themselves and the animals they’re studying a lot of trouble.
Though they're often described as "rats with wings" (a phrase popularized by the movie Stardust Memories), pigeons are actually pretty cool. From homing instincts to misleading rump feathers, here are 15 things you might not know about these avian adventurers.
1. THEY MIGHT BE THE FIRST DOMESTICATED BIRD.
The common city pigeon (Columba livia), also known as the rock pigeon, might be the first bird humankind ever domesticated. You can see them in art dating back as far as 4500 BCE in modern Iraq, and they've been a valuable source of food for thousands of years.
2. THEY WON OVER CHARLES DARWIN—AND NIKOLA TESLA.
Pigeon-breeding was a common hobby in Victorian England for everyone from well-off businessmen to average Joes, leading to some fantastically weird birds. Few hobbyists had more enthusiasm for the breeding process than Charles Darwin, who owned a diverse flock, joined London pigeon clubs, and hobnobbed with famous breeders. Darwin's passion for the birds influenced his 1868 book The Variation of Animals and Plants Under Domestication, which has not one but two chapters about pigeons (dogs and cats share a single chapter).
Nikola Tesla was another great mind who enjoyed pigeons. He used to care for injured wild pigeons in his New York City hotel room. Hands down, Tesla's favorite was a white female—about whom he once said, "I loved that pigeon, I loved her as a man loves a woman and she loved me. When she was ill, I knew and understood; she came to my room and I stayed beside her for days. I nursed her back to health. That pigeon was the joy of my life. If she needed me, nothing else mattered. As long as I had her, there was a purpose in my life." Reportedly, he was inconsolable after she died.
3. THEY UNDERSTAND SPACE AND TIME.
In a 2017 Current Biologystudy, researchers showed captive pigeons a series of digital lines on a computer screen for either two or eight seconds. Some lines were short, measuring about 2.3 inches across; others were four times longer. The pigeons were trained to evaluate either the length of the line or how long it was displayed. They found that the more time a line was displayed, the longer in length the pigeon judged it to be. The reverse was true too: If the pigeons encountered a longer line, they thought it existed in time for a greater duration. Pigeons, the scientists concluded, understand the concepts of both time and space; the researchers noted "similar results have been found with humans and other primates."
It's thought that humans process those concepts with a brain region called the parietal cortex; pigeon brains lack that cortex, so they must have a different way of judging space and time.
4. THEY CAN FIND THEIR WAY BACK TO THE NEST FROM 1300 MILES AWAY.
The birds can do this even if they've been transported in isolation—with no visual, olfactory, or magnetic clues—while scientists rotate their cages so they don't know what direction they're traveling in. How they do this is a mystery, but people have been exploiting the pigeon's navigational skills since at least 3000 BCE, when ancient peoples would set caged pigeons free and follow them to nearby land.
Their navigational skills also make pigeons great long-distance messengers. Sports fans in ancient Greece are said to have used trained pigeons to carry the results of the Ancient Olympics. Further east, Genghis Khan stayed in touch with his allies and enemies alike through a pigeon-based postal network.
5. THEY SAVED THOUSANDS OF HUMAN LIVES DURING WORLD WARS I AND II.
Pigeons' homing talents continued to shape history during the 20th century. In both World Wars, rival nations had huge flocks of pigeon messengers. (America alone had 200,000 at its disposal in WWII.) By delivering critical updates, the avians saved thousands of human lives. One racing bird named Cher Ami completed a mission that led to the rescue of 194 stranded U.S. soldiers on October 4, 1918.
6. TWO PIGEONS ALMOST DISTRACTED FROM THE DISCOVERY OF EVIDENCE OF THE BIG BANG.
In 1964, scientists in Holmdel, New Jersey, heard hissing noises from their antenna that would later prove to be signals from the Big Bang. But when they first heard the sound, they thought it might be, among other things, the poop of two pigeons that were living in the antenna. "We took the pigeons, put them in a box, and mailed them as far away as we could in the company mail to a guy who fancied pigeons," one of the scientists later recalled. "He looked at them and said these are junk pigeons and let them go and before long they were right back." But the scientists were able to clean out the antenna and determine that they had not been the cause of the noise. The trap used to catch the birds (before they had to later be, uh, permanently removed) is on view at the Smithsonian Air & Space Museum.
7. YOU CAN TRAIN THEM TO BE ART SNOBS …
Japanese psychologist Shigeru Watanabe and two colleagues earned an Ig Nobel Prize in 1995 for training pigeons, in a lab setting, to recognize the paintings of Claude Monet and Pablo Picasso and to distinguish between the painters. The pigeons were even able to use their knowledge of impressionism and cubism to identify paintings of other artists in those movements. Later, Watanabe taught other pigeons to distinguish watercolor images from pastels. And in a 2009 experiment, captive pigeons he'd borrowed were shown almost two dozen paintings made by students at a Tokyo elementary school, and were taught which ones were considered "good" and which ones were considered "bad." He then presented them with 10 new paintings and the avian critics managed to correctly guess which ones had earned bad grades from the school's teacher and a panel of adults. Watanabe's findings indicate that wild pigeons naturally categorize things on the basis of color, texture, and general appearance.
8. … AND TO DISTINGUISH WRITTEN WORDS.
In a 2016 study, scientists showed that pigeons can differentiate between strings of letters and actual words. Four of the birds built up a vocabulary of between 26 and 58 written English words, and though the birds couldn't actually read them, they could identify visual patterns and therefore tell them apart. The birds could even identify words they hadn't seen before.
9. FLUFFY PIGEON FEET MIGHT ACTUALLY BE PARTIAL WINGS.
A few pigeon breeds have fuzzy legs—which hobbyists call "muffs"—rather than scaly ones. According to a 2016 study, the DNA of these fluffy-footed pigeons leads their hind legs to take on some forelimb characteristics, making muffed pigeon legs look distinctly wing-like; they're also big-boned. Not only do they have feathers, but the hindlimbs are somewhat big-boned, too. According to biologist Mike Shapiro, who led the study, "pigeons' fancy feathered feet are partially wings."
10. SOME PIGEONS DISTRACT FALCONS WITH WHITE RUMP FEATHERS.
In a life-or-death situation, a pigeon's survival could depend upon its color pattern: Research has shown that wild falcons rarely go after pigeons that have a white patch of feathers just above the tail, and when the predators do target these birds, the attacks are rarely successful.
To figure out why this is, Ph.D. student Alberto Palleroni and a team tagged 5235 pigeons in the vicinity of Davis, California. Then, they monitored 1485 falcon-on-pigeon attacks over a seven-year span. The researchers found that although white-rumped pigeons comprised 20 to 25 percent of the area's pigeon population, they represented less than 2 percent of all the observed pigeons that were killed by falcons; the vast majority of the victims had blue rumps. Palleroni and his team rounded up 756 white- and blue-rumped pigeons and swapped their rump feathers by clipping and pasting white feathers on blue rumps, and vice versa. The falcons had a much easier time spotting and catching the newly blue-rumped pigeons, while the pigeons that received the white feathers saw predation rates plummet.
Close observation revealed that the white patches distract birds of prey. In the wild, falcons dive-bomb other winged animals from above at high speeds. Some pigeons respond by rolling away in midair, and on a spiraling bird, white rump feathers can be eye-catching, which means that a patch of them may divert a hungry raptor's focus long enough to make the carnivore miscalculate and zip right past its intended victim.
11. DODOS WERE RELATED TO TODAY'S PIGEONS.
Though most of this list focuses on the rock pigeon, there are 308 living species of pigeons and doves. Together, they make up an order of birds known as the columbiformes. The extinct dodo belonged to this group as well.
Flightless and (somewhat) docile, dodos once inhabited Mauritius, an island near Madagascar. The species had no natural predators, but when human sailors arrived with rats, dogs, cats, and pigs, it began to die out, and before the 17th century came to a close, the dodo had vanished altogether. DNA testing has confirmed that pigeons are closely related to the dodo, and the vibrant Nicobar pigeon (above) is its nearest genetic relative. A multi-colored bird with iridescent feathers, this near-threatened creature is found on small islands in the South Pacific and off Asia. Unlike the dodo, it can fly.
12. AT ONE POINT, MORE THAN ONE-QUARTER OF ALL THE BIRDS LIVING IN THE U.S. MAY HAVE BEEN PASSENGER PIGEONS.
Wild/feral rock pigeons reside in all 50 states, which makes it easy to forget that they're invasive birds. Originally native to Eurasia and northern Africa, the species was (most likely) introduced to North America by French settlers in 1606. At the time, a different kind of columbiform—this one indigenous—was already thriving there: the passenger pigeon (Ectopistes migratorius). As many as 5 billion of them were living in America when England, Spain, and France first started colonizing, and they may have once represented anywhere from 25 to 40 percent of the total U.S. bird population. But by the early 20th century, they had become a rare sight, thanks to overhunting, habitat loss, and a possible genetic diversity issue. The last known passenger pigeon—a captive female named Martha—died on September 1, 1914.
13. THEY'RE REALLY GOOD AT MULTITASKING.
According to one study, they're more efficient multitaskers than people are. Scientists at Ruhr-Universitat Bochum put together a test group of 15 humans and 12 pigeons and trained all of them to complete two simple jobs (like pressing a keyboard once a light bulb came on). They were also put in situations wherein they'd need to stop working on one job and switch over to another. In some trials, the participants had to make the change immediately. During these test runs, humans and pigeons switched between jobs at the same speed.
But in other trials, the test subjects were allowed to complete one assignment and then had to wait 300 milliseconds before moving on to the next job. Interestingly, in these runs, the pigeons were quicker to get started on that second task after the period ended. In the avian brain, nerve cells are more densely packed, which might enable our feathered friends to process information faster than we can under the right circumstances.
14. PIGEONS PRODUCE FAKE "MILK."
Only mammals produce genuine milk, but pigeons and doves (along with some other species of birds) feed their young with something similar—a whitish liquid filled with nutrients, fats, antioxidants, and healthy proteins called "crop milk." Both male and female pigeons create the milk in the crop, a section of the esophagus designed to store food temporarily. As is the case with mammal milk, the creation of crop milk is regulated by the hormone prolactin. Newly-hatched pigeons drink crop milk until they're weaned off it after four weeks or so. (And if you've ever asked yourself, "Where are all the baby pigeons?" we have the answer for you right here.)
15. ONE STUDY SUGGESTS THAT, GIVEN THE RIGHT CONDITIONS, THEY'RE AS GOOD AT IDENTIFYING CANCER AS DOCTORS.
We've already established that pigeons are excellent at differentiating between artists and words, but a 2015 study revealed they can also distinguish between malignant and benign growths in the right conditions. Researchers at University of California Davis Medical Center put 16 pigeons in a room with magnified biopsies of potential breast cancers. If the pigeons correctly identified them as either benign or malignant, they got a treat, According to Scientific American.
"Once trained, the pigeons' average diagnostic accuracy reached an impressive 85 percent. But when a "flock sourcing" approach was taken, in which the most common answer among all subjects was used, group accuracy climbed to a staggering 99 percent, or what would be expected from a pathologist. The pigeons were also able to apply their knowledge to novel images, showing the findings weren't simply a result of rote memorization."
Mammograms proved to be more of a challenge, however; the birds could memorize signs of cancer in the images they were trained on but could not identify the signs in new images.
No matter how impressive their results, "I don't anticipate that pigeons, no matter how good they become at pathology or radiology, will be playing a role in actual patient care—certainly for the foreseeable future," study co-author Richard M. Levenson told Scientific American. "There are just too many regulatory barriers—at least in the West."
Portions of the 16th-century Craignethan Castle in Scotland were shut down last week after a less-than-friendly badger holed up there and refused to leave. Historic Environment Scotland, which manages the site in South Lanarkshire, sent out a tweet last Friday notifying visitors that the property's cellar tunnel would remain closed over the weekend “due to the presence of a very angry badger.” Staff tried to coax it out with cat food and honey, but the badger did what it wanted, and they were unable to move the mammal.
A spokesman for HES told the BBC, "The castle is surrounded by woodland and we believe the badger may have become lost. Staff first spotted some dug-out earth on Wednesday evening, and later spotted the badger on closer inspection."
On Saturday, staff used a GoPro camera to check out the tunnel from a safe distance and learned that the badger had left voluntarily, but not before making a mess. The critter dug through both soil and stonework, according to The Scotsman. The castle, an artillery fortification erected around 1530, is already partly in ruins.
Badgers are not typically dangerous, but they can become aggressive if they feel cornered or threatened. They can be seen year-round in Scotland, especially during spring and summer. Earthworms, bird eggs, small mammals, fruit, and roots are among their favorite meals, and they can even be “tempted into your garden by leaving peanuts out—a tasty snack for our striped friends,” the Scottish Wildlife Trust says.