Cadaver dogs have been searching the recent mudslide in Oso, Wash., to recover victims’ remains. But how do dogs sniff out the perfume of death? N.C. State associate English professor Cat Warren authored “What the Dog Knows: The Science and Wonder of Working Dogs,” a 2013 book (Simon & Schuster; $26.99) about her experience working with a cadaver dog, law enforcement and forensics experts. (Questions and answers have been edited.)
Q. What compounds are cadaver dogs sniffing out?
A. There are any number of volatile compounds that make up human remains. You want a dog who is trained to recognize a whole range of scents related to death, whether it’s coming from dried bones or the recently dead. Dogs exposed to this range in training have no trouble. The dog is trained to trek back and forth until it picks up the edge of a scent, then it tries to get to the spot where that scent is most concentrated. The dog’s body language changes, and the dog’s handler knows when the dog is “in scent”; they see the dog slow down, concentrate, and work its nose really hard. But the dog should also have a trained final indication, an alert. For both my dogs, Solo and Coda, they lie down.
Q. How do the dogs filter out carcasses of wild animals at a search site?
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A. In our North Carolina woods, we have a lot of what we call animal distractions: dead animals or their skeletal remains. You must train your dog to ignore these. Chemists aren’t yet certain of all the scent differences between humans and other animals, but they are different and a well-trained dog will rule out a deer skeleton pretty quickly.
Q. How do topography and weather affect a search?
A. Topography is critical in terms of where scent goes. The amount of scent that can be given off by a single body can literally travel over hills, or go into a creek where water pulls the scent downstream. Even vegetation can tend to trap or concentrate odor. An experienced searcher will look at the current weather and wind, but also what the conditions were like when the person went missing.
Q. Will scientists ever build an electronic nose that can out-scent a dog?
A. I love machines, but what we have in the dog is an amazing package: It consists not only of a nose, but four paws, a willingness to work, and an ability to get places where humans can’t always follow. Dogs may need rest, but they don’t break down like a machine or need to be calibrated. There’s no technological fix at this point that replaces dogs for all the things they do under a variety of circumstances.
Q. How accurate are well-trained cadaver dogs?
A. A well-trained cadaver dog can be very specific. And yet, due to conditions in the real world, that doesn't mean they can get their nose directly over where a person is buried. That said, there was a lovely little study done in Germany where people who died very recently were exposed to carpet squares for just a few minutes, then those carpet squares were placed among other carpet squares. The dogs were brilliant at detecting which carpet square had been with the dead bodies. This shows us that well-trained dogs can be enormously accurate in a lab setting with few distractions. In the real world, it gets more difficult. I think dogs are irreplaceable for narrowing down search areas.
Q. What is the time limit on cadaver dogs finding human remains?
A. There’s not a known time limit, but there’s some interesting work going on in the Mississippi Delta where dogs are helping find bones and remains from Mound civilization burials (a Native American culture) that go back 800 or 1,200 years. There is very little scent associated with these old bones. There’s much to be learned here in terms of exactly what the dogs are detecting in these bones. But there are enough positive alerts and recoveries that we know dogs are capable of doing this. Dogs have also been used to help find the remains of missing military personnel in Vietnam.
Q. Is there a specific breed that’s best for the job?
A. There isn't a certain breed that’s best, but the most frequently used are German shepherds, Labradors, Malinois (Belgian shepherds) and golden retrievers. I've also seen border collies, cattle dogs and mutts. What you want is a dog that has a lot of drive, an eagerness to work, and a nose that’s not so squashed inward that the dog gets hot and can’t breathe.
Q. What interests you most about how dogs use their nose?
A. The most interesting thing to me is how much we still don’t know about how dogs use their noses. It’s still a bit of a “black box.” We're getting to know so much about it, but there’s still so much to be learned.