niffer dogs, commonly referred to as Human Remains Detection dogs (HRD) or more prosaically named “cadaver dogs”, are trained to specifically find the odor of decomposed human remains.
Trained dogs can distinguish between human remains, animal remains, and a wide range of other odors that would normally be expected to distract them. Human Remains Detection dogs are frequently used by police investigators to help out on crime scenes and on missing person cases that have been unsolved for decades.
Search and Rescue dogs assist in finding victims of natural or man-made disaster events. Most recently, their skills have been used in the wake of California’s catastrophic fires, or in the aftermath of the 2017 Puebla earthquake in Mexico.
A subset of HRD dog teams is called Historical Human Remains Detection (HHRD) dogs. These dogs are specifically trained to locate and alert on buried human bones rather than on soft-tissue decomposition as in the case of cadaver dogs.
The Indiana Jones Dogs
In 2018, a Croatian Archeologist called Vedrana Glavaš who studied prehistoric burial sites dated to the Iron Age, wondered how far back in time detection dogs could smell.
She teamed up with Andrea Pintar, a forensic detection dog trainer, to found out if dogs were capable of detecting human remains from archeological sites. What they did not expect was that Panda and Mali, two Belgian Malinois, would lead them to a human necropolis that radiocarbon dating confirmed to be 2,700 years old. In September 2019, the Journal of Archaeological Method and Theory published the results of their study.
The dogs uniquely enhanced the capability of typical grave-finding methods, such as geophysical surveys, aerial photography, infrared satellite imaging, and ground-penetrating radars (GPR).
So what exactly are canines detecting at archaeological sites? “Our dogs are not searching for bones,” Glavaš points out. “They are searching for the molecules of human decomposition.”
A dog’s nose
While the human brain is dominated by its visual system, dogs’ brains are mostly devoted to their noses. A dog’s nose can perform at least 10,000 times better than humans.
According to a 2016 study in Frontiers in Veterinary Science, canines can detect the equivalent of “one drop of a liquid in 20 Olympic-size swimming pools.”
Dogs can pick up on compounds that easily evaporate at room temperature and often carry an odor—what scientists call volatile organic compounds. Canines can detect one such part in every trillion and can follow scent trails for hours.
As a result, dogs have demonstrated uncanny olfactory abilities. Trained detection dogs are commonly used to find explosives, narcotics, oil leaks in pipelines, bed bugs and also detect early signs of disease in humans, such as breast cancer.
Any breed type can be trained as a detection dog, but some have a natural genetic advantage. Bloodhounds have almost three times more scent receptors than Dachshunds. In a famous experiments in the early 1960s, scientists placed a mouse in a one acre field. Beagles only took a minute to find it. Fox terriers took fifteen minutes to find the mouse, and Scottish Terriers were never successful. One actually stepped on the mouse. Border Collies or Retrievers usually take to training more quickly, but it comes down to the bond between dog and handler, as well as the unique drive and personality of the dog.
HDR dogs are typically trained as early as 9 months, and intensive training is conducted over several months in specialized centers that typically also train police dogs for narcotics and explosive detection. Each dog is assigned a handler who also becomes his owner, and trains as much as 40 hours per month.
What can dogs detect?
The ability of dogs to locate as little as 5–15 mg of human tissue, blood, or bone, exceeds the possibilities of our best instrumentation and defies rational explanation. In field trials, where the handlers were unaware of the sample size, the dog teams still had an astonishing 65%–95% success rate.
Researchers who study the canine olfactory system are still trying to pinpoint what organic compounds in human remains are detected by dogs. It is unclear what concentration of human remains a trained dog can detect, and which aspects of a given environment help retain the scent.
In the case of human remains, dogs could be sniffing for one of several specific molecules. One theory is that dogs detect the fatty acids in adipocere, also called “corpse wax”, a substance that scientists have known since the 17th century when studying Egyptian mummies. The molecules that dogs smell are created by organic decomposition. In the absence of oxygen, human fat is converted by bacteria into fatty acids, which then harden into the waxy-like adipocere that preserves bodies by mummifying them.
Adipocere can help scientists date corpses. This material has persisted on frozen remains estimated to be more than 300 years old, such as those found in glacier melt in northwestern British Columbia in Canada. In 2009, scientists reported on adipocere found on the 1,600-year-old remains of a child in Germany. In the United States, human remains detection dogs have aided discoveries at a variety of Native American burial sites.
Meet Fabel, the archeology dog
Fabel is a sociable and playful 7-year-old black German shepherd who loves playing with his green ball and eating popcorn.
Fabel was trained in detection by his handler, Swedish archeologist Sophie Vallulv, since he was a five-month-old puppy. Valluv came up with the idea of using a dog as a non-invasive prospection search method during her training to become an archaeologist, and wrote her master’s thesis in 2015 on “using a dog as an archaeological prospection method to locate human bones”.
Fabel is the world’s first scientifically tested archeology dog. The results of 120 searches and laboratory tests showed that he can distinguish between human and animal bones with a detection rate of 94.2%. Fabel can distinguish human bones from animal bones and can signal where old graves are located. He detected 400 years old human bones at the archeology site of an old mining settlement in northern Sweden, and 1,600-year-old human remains buried five feet deep a fortified settlement on the island of Öland.
Detection dogs remain a mystery to scientists. We understand the physiology of their amazing olfactory sense, but we still don’t know precisely what molecules they can detect.
Despite these mysteries, dogs continue to surprise us with new abilities in the field of detection and to collaborate with humans in ways we could not have imagined.
We had detective dogs, we now have Indiana Jones dogs.