A couple years ago, a shelter dog named Hank from Memphis traveled 11 miles over two days to return to his foster home after being moved to longer-term rescue care. The white shepherd had only been with his foster mom, Rachel Kauffman, for about six days before he was moved to a home across town. Even though he traveled to his new home by car and should not have instinctively known the route to Kauffman's house, Hank found his way back to her.

This is not the first time an animal has shown this amazing skill. In 2013, a house cat named Holly traveled 200 miles to return to her West Palm Beach home after being lost while traveling with her owners to Daytona Beach two months earlier. Some questioned whether or not the cat that showed up on the Richter's doorstep was, in fact, their beloved cat Holly. (I mean, really, 200 miles?) But Holly had an implanted microchip; it was definitely the same cat.

Sure, these are extreme cases of lost pets finding their way home, but it also brings up questions about the different ways that animals — especially house pets like cats and dogs — find their way around.

Looking for scents of home

dog sniffing ground Dogs have somewhere between 220 million to 2 billion olfactory receptor cells in their noses. (Photo: alexei_tm/Shutterstock)

It probably comes as no surprise that dogs rely heavily on their noses. When the wind is right, 11 miles isn't really that far for a dog with a good sniffer to travel. Dogs have somewhere between 220 million to 2 billion olfactory receptor cells for scents, reports PetMD. That's compared to the mere 12 to 40 millions that people have.

Each time your dog takes a walk around your neighborhood, he uses his nose to get familiar with the scents of home. There's the fire hydrants and the bushes, the sidewalks and the fences. And not only is he smelling as he goes, he's also leaving distinct scents behind, each time he puts down his paws.

But beyond the direct line of scent, dogs also use overlapping circles of scent to learn and plot a course. Maybe there's the smell of a familiar person or animal in the air, or a trash can or stop sign that's on his walking route. Any of these scents can help dogs zero in on the scent they are looking for — scents of home.

A few years ago, two schnauzers got lost in thick fog while hiking off leash in the U.K. After 96 hours of searching with volunteers and drones, the dogs' owners decided to grill up some sausages at the spot where the dogs had last been seen, reports The Telegraph. Moments later, the dogs came running.

"They absolutely love sausages," said owner Liz Hampson. "They have them every Sunday for breakfast, so if there was one food they were going to come back for, it was sausages."

Making a visual map

dog watching while on leash Dogs pay attention when they're walking so they create a picture of their neighborhood. (Photo: Rock and Wasp/Shutterstock)

But when you and your dog are out and about, there's a good chance your dog's nose isn't to the ground the entire time. He's likely looking around, taking in his surroundings too.

Although a dog's vision is nowhere near as good as his sense of smell, he's still using his eyesight to create a visual map of the world around him, veterinarian Wailani Sung tells PetMD.

"Research on wolves has indicated that they use visual landmarks to help guide their way around their territory," Sung points out. "Researchers have also found that some wolves have taken shortcuts to get from one point to another."

You may notice that as you get closer to your house on a walk, your dog either picks up the pace, happy to be home, or slows down because he doesn't want to end his outing yet. Your dog likely uses a combination of sights and smells to know that he's almost home.

A reason to come home

Cats have different navigation systems than dogs. They may use magnetic fields just like birds do to find their way north and south. In the case of Holly, the cat that traveled 200 miles, scientists speculate that she took a good guess when she got to the ocean and — possibly using her internal compass — turned right to head south to West Palm Beach. Then all she had to do was follow the ocean and keep on walking.

A pet's overall temperament plays a role in navigation too, Time points out. A dog that travels for miles and miles to find his way back home is likely trying to return to his owner. The dog-human connection, after all, is a powerful one. However, a cat that travels the same distance is likely just trying to get back to familiar turf.

Researchers caution that we shouldn't give animals too much credit. No matter how well they navigate, for every pet that makes the amazing trek back home, there are countless others that remain lost.

As for Hank, it looks like his long walk paid off in the form of a forever home. Kauffman, who already had two dogs and was fostering another, had no intention of adopting the young shepherd. But as she told WFTV news, “When it’s meant to be, it’s meant to be.”

Editor's note: This file has been updated since it was written in November 2015.

How do lost dogs find their way back home?
How does a dog travel 11 miles over two days to return to his foster home after being moved? Here's how your pet uses his senses to guide him like a GPS.