The Amazing Science Behind Pets That Find Their Way Home
Kluger (Jeffrey)
Source: Time Magazine, Nov. 9, 2015
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  1. A dog that traveled 11 miles to find a former owner raises a familiar question
  2. A pity you can't ask a dog for the shortest route home when you're lost — or a cat or a seabird or a tortoise or a dung beetle, for that matter. Because if you could ask any of them how to get pretty much anywhere, odds are they'd know a lot more than you think.
  3. Animal navigation has long been something of a black box for scientists. The mystery of how nonhumans — without benefit of maps, language or GPS — manage to find their way from place to place, often over very great distances, presented itself anew1 recently when a dog walked 11 miles from its new home to return to a former foster owner. The feat was especially remarkable because the dog had been taken to its new location by car and had to find its way back on foot — meaning it hadn't had a chance to learn the route. Even more impressive was the 2013 tale of the geolocating2 cat that had been lost and found its way home after a journey of two months and 200 miles. So how do animals manage such prodigious — and precise — feats of travel?
  4. The kind of natural map any animal follows depends largely on the species. As TIME has reported, seabirds are believed to steer mostly by the sun and the stars, since if the animals are ever going to get lost, it tends to happen when the skies are overcast. The same is true of the unglamorous dung beetle. While naturalists have not extensively tracked the species' perambulations in the wild, they've studied them in — yes — planetariums. As long as the artificial Milky Way was in view, the beetle and its dung ball rolled right along. Throw the switch and change the stars, however, and the little critter was completely flummoxed.
  5. Many more animals navigate via Magnetism — orienting themselves along the north-south lines of Earth's magnetic fields. In one study of baby sea sea turtles, which typically migrate east after hatching, changing the orientation of magnetic generators around a swimming pool changed the direction in which the hatchlings swam too. Pigeons were thought to navigate the same way, especially since they have cells in their beaks that are heavy in iron. Later studies, however, found that those cells were related to the immune system, not navigation.
  6. Mammals — and particularly two of the species of mammals that humans love best: dogs and cats — have a range of ways to get around. Dogs, no surprise, are very big on scent, and that can take them a very long way.
  7. "An eleven-mile distance is actually not terribly long for a dog," says Bonnie Beaver, the executive director of the American College of Veterinary Behaviorists and a professor at Texas A&M University. "If the dog had walked both from and back to his home he'd be following his own scent trail." In this case, the dog was instead probably following an equally compelling smell: that of its owner, a type of navigation that is entirely possible over long distances as long as the wind is right.
  8. Dogs extend their scent range by moving among overlapping circles of familiar scents — much the way cell phone coverage relies on interconnected footprints from different cell towers. A dog that wanders out of its own immediate range might pick up the scent of, say, a familiar dog in the next circle. That might point it to a circle that contains a familiar person or tree or restaurant trash can, and so on.
  9. Cats, like other animals, might rely more on magnetic fields — a faculty that could turn out to be quite common in mammals. "There are some studies that show that the ears of most mammals contain iron," Beaver says. "That may cue them into the magnetic direction in the ground. There's work showing that cattle, deer and voles tend to orient in a north-south direction."
  10. The overall temperament of an animal — or, more broadly, of the species — can play a role in navigation too. A dog that travels a great distance to get home is likely trying to return to its owner, since the dog-human bond is a powerful one. Acat that travels the same distance is — sorry cat owners — probably just tying to return to its territory.
  11. No matter how well animals navigate, scientists caution against an observation bias that may make them seem better than they are. A dog or cat that finds its way halfway across the state makes news; the uncounted others that stay lost do not. What's more, some cases of remarkable returns may turn out to be matters of mistaken identity, unless there's a positive way to identify an animal like an implanted microchip that some owners use along with a collar.
  12. "You hear these stories about a three-legged black cat that came home and jumped into its favorite chair," says Beaver. "But it's real hard to be sure because they've been gone a long time and they look scruffy. And heck, that chair would be a comfortable one for any cat."
  13. Still, we shouldn't dismiss all the stories out of hand. That cat that traveled 200 miles in 2013? It did have an implanted microchip. So kudos to at least one kitty — and probably a whole lot more.

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In-Page Footnotes

Footnote 1: Dog Travels 2 Days and 11 Miles to Return to Foster Mom (Link (Defunct)):
  • "Sometimes dogs just pick their people"
  • A dog in Memphis, Tennessee, spent two days walking 11 miles to return to the woman who rescued him from a shelter just days before.
  • On October 22, Rachel Kauffman, a vet tech, saw a photo of Hank online and decided to adopt him for a few days, after which he would be moved to a longer-term foster care home, the Memphis Commercial Appeal reports, and Hank and Rachel became fast friends.
  • "When you get a new dog, they imprint pretty quickly. He would follow me around a lot, watch what I was doing," Kauffman told the paper. "I knew we had a good bond, but at that point, I couldn't predict he would do what he did."
  • Hank was transferred to another foster home on October 30, after just six days with Kauffman, but when his caretaker there left for the day, however, Hank unlocked the door and took off. By early Tuesday evening, two days after busting out, Hank had traveled 11 miles in a meandering path back to Kauffman's house.
  • "He traveled 11 miles to get back to me," said Kauffman. "I can't fathom how he traveled that far across town that fast to get back to me."
  • Time, Nov. 7, 2015
Footnote 2: How a Kitty Walked 200 Miles Home: The Science of Your Cat's Inner Compass (Link):
  • A house cat's long-distance journey raises new questions about how animals navigate.
  • When a battered, skinny tortoiseshell cat wandered into a yard in Florida earlier this year, she could have been any other stray, but she was nothing of the kind. She carried an implanted microchip — one put there by a loving owner — and it revealed an intriguing story: the cat belonged to a local family, had been lost on a trip two months earlier, and had traveled 200 miles (322 km) in that time to arrive back in her hometown. Her journey inspired a spate of articles looking for an explanation for how this one cat, and a few others who’ve made similar trips, managed such impressive feats of navigation. The response from many eminent animal researchers was the same: "No idea."
  • Cats' long-distance travels are relatively rare in the scientific literature, which explains the dearth of answers — at least so far. But that's not the case for the wanderings of sundry other creatures, especially those that migrate. Such extreme journeys — mapless, compassless, sometimes intercontinental, through places the animals have never seen before — seem nothing short of miraculous. That's the kind of mystery that gets scientists moving, and move they have, conducting all manner of experiments over the years — locking animals in planetariums, carrying them around in dark boxes, putting them in wading pools wrapped in magnets, and destroying various bits of anatomy to see which piece was the important one. These experiments have yielded fascinating insights into the animal brain and into a world beyond human sensation. Part of what navigating animals do is not entirely surprising. Planetarium studies reveal that some animals steer by the stars, an approach that's comfortingly familiar to Homo sapiens but practiced by organisms as distant as the nocturnal dung beetle, which, as one recent study revealed, can roll its precious gob of poo in a straight line only as long as the Milky Way is in view. One of the most accomplished animal navigation researchers of the twentieth century, naturalist Ronald Lockley, found that captured seabirds released far from their homes could make a beeline back so long as either the sun or the stars were visible; an overcast sky threw them off so much that many never made it back.
  • But plenty of other navigating animals are using something most humans regularly forget exists: the Earth's magnetic field. In illustrations, the field is usually depicted as a series of loops that emerge from the south pole and reenter the planet at the north pole, and extend out to the edges of our atmosphere, sort of like a cosmic whisk. Our compass needles are designed to align with the field, and in the last few decades it's become clear that numerous animals can find their way by feeling some of its various field.
  • Sea turtles, for example, don't use the field simply to tell north from south. According to experiments led by Kenneth Lohmann, a professor of biology at University of North Carolina, Chapel Hill, they are actually born knowing a magnetic map of the ocean. Newly hatched loggerhead turtles in the populations Lohmann studies journey 8,000 miles (12,900 km) from their hatching beaches around the Atlantic Ocean to reach feeding areas, and if they don't keep right on track, they do not survive. Lohmann learned early on that the turtles could sense the Earth's magnetism: he found that hatchlings from the Florida coast, which normally swim east in darkness to start their migration, swam the other way when they were put in a magnetic field that reversed north and south. That got Lohmann thinking that the turtles' long-distance navigation might be linked to their being able to respond to whorls and quirks in the planetary field they encounter along the way.
  • To study this, he and colleagues collected baby sea turtles a few hours before they would have left the nest on their own and put them in pools surrounded by magnetic coils. The coils were designed to reproduce the Earth's magnetic field at specific points along the turtles' migration. Reliably, the young turtles oriented themselves and swam in the direction relative to the magnetic field that, had they been in the open ocean, would have kept them on course. Lohmann has tested this with 8 different locations along their route, and in each case the turtles head in just the direction required to get them to their destination. The turtles may not know where they are in any big-picture way — as Lohmann says, they may not see themselves as blinking spots on a map — but they have inherited a sense that should they feel a particular pull from the magnetic field, well, better take a right.
  • The list of animals that navigate by magnetism, suspected and confirmed, is long, and includes a few mammals in addition to migrating birds and turtles. But our understanding of the mechanism behind that ability is sketchy: sea turtles tend to be threatened or endangered species, so scientists can study only their behavior, not their brains, and even in animals in which such work is possible, it's hard to tell what parts of the brain and other physical structures are involved.
  • Pigeons, one of the most intensively studied animal navigators, show how complex a question this is. One leading theory holds that iron-containing cells in the beak send magnetic information to the brain, since destroying the nerve that carries sensation from beak to brain seems to disrupt pigeons' navigation. However, last year it emerged that those beak cells are not neurons capable of sending messages, as had been supposed; they appear to be immune cells, throwing the beak theory into confusion. Another school of thought suggests that the magnetic field may be affecting chemical reactions in the birds' eyes, literally changing the way the world looks when they are oriented in a particular direction. And David Dickmann, a professor at the Baylor College of Medicine whose primary work is on a magical ability we humans often forget we have — our ability to sense gravity and constantly adjust our position to keep our balance — has lately published work showing that pigeons may have a magnetic-field sensor in their inner ears. No one knows yet which of these mechanisms, or what combination of them, is at the root of the pigeon's powers.
  • And lest we forget, the magnetic field is far from the only thing out there that navigating animals can sense and humans cannot. The heads of sharks are threaded with jelly-filled tubes, called the ampullae of Lorenzini, that allow them to detect extremely faint electric currents and may help them with navigation. Scents in the air, at concentrations far below human perception, are perceivable to numerous creatures that may use them to steer (in fact, pigeons that cannot smell seem oddly lost, even with their magnetic abilities intact). Bees can see patterns in sunlight invisible to the naked human eye and can use them to find their way.
  • We can see only the outcomes, never the workings, of whatever evolved systems animals use to orient themselves across hundreds or thousands of miles. But that hasn't stopped us from working to understand the feats of migrating reptiles, homing pigeons, and even lost pets. With reminders like the odyssey of the Florida housecat, how can we stop?
  • Veronique Greenwood, Feb. 11, 2013

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