(HealthDay) -- Jon Tumilson's dog, Hawkeye, was an important part of his life.
And, as it turns out, Tumilson was an important part of Hawkeye's life.
After the Navy SEAL was killed in Afghanistan last summer, more than a thousand friends and family attended the funeral in Rockford, Iowa, including his "son" Hawkeye, a black Labrador retriever who, with a heavy sigh, lay down in front of Tumilson's flag-draped casket. There, the loyal dog stayed for the entire service.
Hawkeye's reaction to his owner's death generated a lot of buzz online and in the media. But it's not unusual, according to pet experts, for some dogs to mourn the loss of a favorite person or animal housemate.
Grief is one of the basic emotions dogs experience, just like people, said Dr. Sophia Yin, a San Francisco-based veterinarian and applied animal behaviorist. Dogs also feel fear, happiness, sadness, anger, as well as possessiveness.
Dogs who mourn may show similar signs to when they're separated for long periods of time from the individual they're bonded to, she said. Of those signs, depression is the most common, in which dogs usually sleep more than normal, move slower, eat less and don't play as much.
The beginnings of such a strong inter-species bond between humans and dogs dates back some 15,000 years, when early man and the ancestor of today's dog roamed the Earth together.
Today, after thousands of years of friendship, there's a great deal of attunement between humans and dogs, not only in terms of comprehension of each other's gestures and body language but also emotionally, said Barbara King, a professor of anthropology at the College of William & Mary in Williamsburg, Va.
It's not just evolutionary logic, or reading peer-reviewed science literature that's convinced King that dogs (as well as cats) feel deep grief. Interviews with astute pet owners for her upcoming book, How Animals Grieve, and the power of observation, has also led her to this conclusion.
Case in point: a grainy video posted on YouTube that captured the image of a scruffy terrier running onto a busy highway in Chile to rescue another dog, hit moments earlier, by a car. As vehicles whiz by the terrier, he instinctively wraps his paws around the injured dog, dragging him off the road to safety.
"When you look at that sort of example, again, you see that these dogs are thinking and feeling creatures, and that sets the stage for grief," she said.
Through her research, King has found that in households with two dogs who've lived together for a number of years, some owners report that when one dog dies, the other gets depressed. Skeptics might point to a change in daily routine as the cause of depression or, perhaps, because the owner is upset and grieving. But King feels differently.
"The surviving dog is searching around the house for a lost companion -- looking in favorite places, going to places that they spent with their friend, very pointed actions that tell you the dog is missing his friend," she said.
In an effort to understand what dogs are thinking, researchers at Emory University in Atlanta are conducting brain scans of dogs using functional MRI (fMRI).
Gregory Berns, director of the Emory Center for Neuropolicy and lead researcher on the project, hopes their work will reveal secrets of the dog-human relationship, from the dog's perspective.
Even with high-tech tools, though, determining whether canines experience grief would be tough, he admitted, because he believes it's unknown how grief looks in the human brain. If it were known, however, Berns said researchers could then look for this emotion in the dog but it would require showing pictures, perhaps movies, of the deceased human or canine.
"It would be fascinating to figure out," said Berns, who normally uses fMRI technology to study how the human mind works. "If I were to speculate, I would guess that, like people, some dogs mourn and others don't."
King agrees. After all, she said, dogs possess unique personalities and react differently, even in the same situation. Whether a dog grieves hinges on a dynamic mix of life experiences, added King, including how they were raised and what their people or animal housemates were like.
If a pet mopes around the house after the death of a canine or human companion, Yin suggests the best thing owners can do is to get their dog's mind off the loss by engaging their pet in fun activities such as a game of fetch, brisk walks and play dates with other pets. "The activity depends on what the dog historically likes," she said.
Don't expect a quick fix. It may take anywhere from a few weeks to a few months, pet experts believe, before a dog's spirits begin to lift.
Explore further: Sexual selection isn't the last word on bird plumage, study shows
More information: For more on canine behavior, visit the American Veterinary Medical Association.