Nobody knows how it happened: an indoor housecat who got lost on a family excursion managing, after two months and about 200 miles, to return to her hometown.

Even scientists are baffled by how Holly, a 4-year-old tortoiseshell who in early November became separated from Jacob and Bonnie Richter at an R.V. rally in Daytona Beach, Fla., appeared on New Year’s Eve — staggering, weak and emaciated — in a backyard about a mile from the Richters’ house in West Palm Beach.

“Are you sure it’s the same cat?” wondered John Bradshaw, director of the University of Bristol’s Anthrozoology Institute. In other cases, he has suspected, “the cats are just strays, and the people have got kind of a mental justification for expecting it to be the same cat.”

But Holly not only had distinctive black-and-brown harlequin patterns on her fur, but also an implanted microchip to identify her.

“I really believe these stories, but they’re just hard to explain,” said Marc Bekoff, a behavioral ecologist at the University of Colorado. “Maybe being street-smart, maybe reading animal cues, maybe being able to read cars, maybe being a good hunter. I have no data for this.”

There is, in fact, little scientific dogma on cat navigation. Migratory animals like birds, turtles and insects have been studied more closely, and use magnetic fields, olfactory cues, or orientation by the sun.

Scientists say it is more common, although still rare, to hear of dogs returning home, perhaps suggesting, Dr. Bradshaw said, that they have inherited wolves’ ability to navigate using magnetic clues. But it’s also possible that dogs get taken on more family trips, and that lost dogs are more easily noticed or helped by people along the way.

Cats navigate well around familiar landscapes, memorizing locations by sight and smell, and easily figuring out shortcuts, Dr. Bradshaw said.

Strange, faraway locations would seem problematic, although he and Patrick Bateson, a behavioral biologist at Cambridge University, say that cats can sense smells across long distances. “Let’s say they associate the smell of pine with wind coming from the north, so they move in a southerly direction,” Dr. Bateson said.

Peter Borchelt, a New York animal behaviorist, wondered if Holly followed the Florida coast by sight or sound, tracking Interstate 95 and deciding to “keep that to the right and keep the ocean to the left.”

But, he said, “nobody’s going to do an experiment and take a bunch of cats in different directions and see which ones get home.”

The closest, said Roger Tabor, a British cat biologist, may have been a 1954 study in Germany which cats placed in a covered circular maze with exits every 15 degrees most often exited in the direction of their homes, but more reliably if their homes were less than five kilometers away.

New research by the National Geographic and University of Georgia’s Kitty Cams Project, using video footage from 55 pet cats wearing video cameras on their collars, suggests cat behavior is exceedingly complex.

For example, the Kitty Cams study found that four of the cats were two-timing their owners, visiting other homes for food and affection. Not every cat, it seems, shares Holly’s loyalty.

KittyCams also showed most of the cats engaging in risky behavior, including crossing roads and “eating and drinking substances away from home,” risks Holly undoubtedly experienced and seems lucky to have survived.

But there have been other cats who made unexpected comebacks.

“It’s actually happened to me,” said Jackson Galaxy, a cat behaviorist who hosts “My Cat From Hell” on Animal Planet. While living in Boulder, Colo., he moved across town, whereupon his indoor cat, Rabbi, fled and appeared 10 days later at the previous house, “walking five miles through an area he had never been before,” Mr. Galaxy said.

Professor Tabor cited longer-distance reports he considered credible: Murka, a tortoiseshell in Russia, traveling about 325 miles home to Moscow from her owner’s mother’s house in Voronezh in 1989; Ninja, who returned to Farmington, Utah, in 1997, a year after her family moved from there to Mill Creek, Wash.; and Howie, an indoor Persian cat in Australia who in 1978 ran away from relatives his vacationing family left him with and eventually traveled 1,000 miles to his family’s home.

Professor Tabor also said a Siamese in the English village of Black Notley repeatedly hopped a train, disembarked at White Notley, and walked several miles back to Black Notley.

Still, explaining such journeys is not black and white.

In the Florida case, one glimpse through the factual fog comes on the little cat’s feet. While Dr. Bradshaw speculated Holly might have gotten a lift, perhaps sneaking under the hood of a truck heading down I-95, her paws suggest she was not driven all the way, nor did Holly go lightly.

“Her pads on her feet were bleeding,” Ms. Richter said. “Her claws are worn weird. The front ones are really sharp, the back ones worn down to nothing.”

Scientists say that is consistent with a long walk, since back feet provide propulsion, while front claws engage in activities like tearing. The Richters also said Holly had gone from 13.5 to 7 pounds.

Holly hardly seemed an adventurous wanderer, though her background might have given her a genetic advantage. Her mother was a feral cat roaming the Richters’ mobile home park, and Holly was born inside somebody’s air-conditioner, Ms. Richter said. When, at about six weeks old, Holly padded into their carport and jumped into the lap of Mr. Richter’s mother, there were “scars on her belly from when the air conditioner was turned on,” Ms. Richter said.

Scientists say that such early experience was too brief to explain how Holly might have been comfortable in the wild — after all, she spent most of her life as an indoor cat, except for occasionally running outside to chase lizards. But it might imply innate personality traits like nimbleness or toughness.

“You’ve got these real variations in temperament,” Dr. Bekoff said. “Fish can by shy or bold; there seem to be shy and bold spiders. This cat, it could be she has the personality of a survivor.”

He said being an indoor cat would not extinguish survivalist behaviors, like hunting mice or being aware of the sun’s orientation.

The Richters — Bonnie, 63, a retired nurse, and Jacob, 70, a retired airline mechanics’ supervisor and accomplished bowler — began traveling with Holly only last year, and she easily tolerated a hotel, a cabin or the R.V.

But during the Good Sam R.V. Rally in Daytona, when they were camping near the speedway with 3,000 other motor homes, Holly bolted when Ms. Richter’s mother opened the door one night. Fireworks the next day may have further spooked her, and, after searching for days, alerting animal agencies and posting fliers, the Richters returned home catless.

Two weeks later, an animal rescue worker called the Richters to say a cat resembling Holly had been spotted eating behind the Daytona franchise of Hooters, where employees put out food for feral cats.

Then, on New Year’s Eve, Barb Mazzola, a 52-year-old university executive assistant, noticed a cat “barely standing” in her backyard in West Palm Beach, struggling even to meow. Over six days, Ms. Mazzola and her children cared for the cat, putting out food, including special milk for cats, and eventually the cat came inside.

They named her Cosette after the orphan in Les Misérables, and took her to a veterinarian, Dr. Sara Beg at Paws2Help. Dr. Beg said the cat was underweight and dehydrated, had “back claws and nail beds worn down, probably from all that walking on pavement,” but was “bright and alert” and had no parasites, heartworm or viruses. “She was hesitant and scared around people she didn’t know, so I don’t think she went up to people and got a lift,” Dr. Beg said. “I think she made the journey on her own.”

At Paws2Help, Ms. Mazzola said, “I almost didn’t want to ask, because I wanted to keep her, but I said, ‘Just check and make sure she doesn’t have a microchip.’” When told the cat did, “I just cried.”

The Richters cried, too upon seeing Holly, who instantly relaxed when placed on Mr. Richter’s shoulder. Re-entry is proceeding well, but the mystery persists.

“We haven’t the slightest idea how they do this,” Mr. Galaxy said. “Anybody who says they do is lying, and, if you find it, please God, tell me what it is.”

http://well.blogs.nytimes.com/2013/01/19/one-cats-incredible-journey/?src=me&ref=general