When my dog, Mollie, and I went out to enjoy the recent snow, she stopped in the yard and stared intensely down at the snow-covered ground. She suddenly plunged her nose into the snow, using it as a snowplow to try to track down whatever was underneath.
But was it her nose, her ears, or her eyes that tipped her to her prey? Often it’s a combination of all, and dogs do generally have better olfactory and hearing than humans (see sidebar), but what about their vision?
Over the years, I noticed my dogs were much better at detecting moving objects than I, while I could usually discern stationary objects more easily. I remember one such occurrence from years ago: I was walking my dog at the time, Mai Coh, on lead at Big Meadows, in Shenandoah National Park. I saw a doe with a young fawn standing still nearby, but Mai Coh obviously didn’t. I walked slowly toward the pair, and it wasn’t until we were a few yards from the deer, and they started to move off, that Mai Coh finally saw them, going on full alert. So why didn’t she see the pair when they were still?
Veterinarian researchers Paul E. Miller and Christopher J. Murphy (tinyurl.com/wi-dogvision), at the University of California-Berkeley, reviewed studies on dogs’ vision. They found one in which the most visually sensitive of 14 police dogs being studied could recognize moving objects from 810 to 900 meters away but could not recognize the same object when it was stationary unless it was much closer — 585 meters or less.
In another study, dogs could only begin to distinguish the details of a stationary object from 20 feet away that a person with normal vision could differentiate from 75 feet away — much like my experience with Mai Coh and the deer. In dim light, however, dogs showed better visual acuity than humans. Miller and Murphy point out that visually distinguishing the fine details in objects is less important for a dog’s lifestyle than it is for most people, and this holds true even for working dogs. The trade-off of being able to see better in the dark than we do enables dogs to “exploit an ecological niche inaccessible to us,” the researchers suggest.
Some dog breeds have been bred to have peak visual acuity. In one 2014 study (tinyurl.com/wi-2014study), other researchers found that dogs with long noses — such as sighthounds and wolves, from which dogs evolved — are better at detecting peripheral movement than dogs with short noses. These longer-nosed dogs have eyes situated more on the sides of their heads. In these breeds, the ganglion (nerve cell groups) in the retina that send visual information to the brain stretch out in a line called a “visual streak.” Dogs with eyes more in the front of their heads, such as pugs, have ganglions that are congregated more in the center of the retina.
There is an upside to having eyes that are more in the front of the head: they share a wider binocular field of vision, which means they provide increased depth perception. While a sighthound, with a 270-degree field of view has a wide field of monocular vision on either side, we humans have only a 180-degree view but have better binocular vision. Most dog breeds fall somewhere in between.
When it comes to distinguishing color, we humans see a wider spectrum. Miller and Murphy found that “the most striking differences in color vision between dogs and people is the dogs’ inability to differentiate among middle to long wavelengths of light, which appear to people as green, yellow-green, yellow, orange, or red, and their inability to distinguish greenish-blue from gray.”
Being able to see more colors wasn’t an issue until dogs joined forces with humans. As the researchers note, “restrictions in color vision are probably of limited consequence in dogs, as it is likely that dogs react only to colors of biological importance to them.” Color differentiation only becomes an issue, they write, when people try to teach their dogs a behavior that requires distinguishing among red, orange, yellow and green objects solely by color.
Dogs, along with a few other social mammals, share one aspect of vision with humans: the ability to follow the gaze of another animal. Mollie demonstrates this when she loses her frisbee on the ground and looks at me for help. Often just my looking at her Frisbee is enough to get her searching in the right direction. When that fails, I point to it, which almost always works. Recently scientists have found that the dog’s ability to follow others’ gaze does not extend into distant space, as it does in humans.
Because we have different strengths in sensing and interpreting the environment around us, dogs and humans work well together when it comes to finding wildlife. My first dog, Prince, taught me that when I was about six years old that. I looked to him for cues as to what critters he might have found when we were out discovering nature, and he looked to me for the same thing.
Prince’s cues that he found an animal were dramatic. He would freeze into a point, with tail horizontal, one leg up and nose pointed at the “prey” — true to the Irish setter half of his lineage. To him, prey encompassed, among other things, quail, rabbits, snakes and turtles but also our Thanksgiving turkey in the fridge and peanut butter sandwiches.
When Mollie and I are on a hike, we also check in visually with each other regularly. If I show any behavior signaling I’ve found something interesting, she will often come to see what has attracted my attention and vice versa. One way or another, we understand we work best as a team.
© 2017 Pam Owen
Dogs beat humans when it comes to smelling and hearing
As I wrote about in my Dec. 17, 2015, column, the dog’s nose is an amazing olfactory tool. It has, depending on the breed, about 300 million olfactory receptors, giving dogs a sense of smell 10,000 to 100,000 times as acute as ours. The long ears on bloodhounds, which have the keenest sense of smell, and other scenthounds also help channel scent to the nose.
Dogs also hear better than we do, especially in the high range. They can hear sounds four times farther away and more easily differentiate sounds and pinpoint their exact location. Ears are a factor in sound acuity, too: The dog’s ear has more muscles to better orient it to the sound, and some dogs have large, upright ears that enhance that ability.