The scent of death has revealed the site of the grisly, cannibalistic end to a hopeful trip to California nearly 175 years ago. That’s thanks to cadaver-sniffing dogs, which seem to have proven their ability to detect death thousands of years after some burials at historic sites.
The Donner Party was a group of pioneers who attempted to migrate from Illinois to California in search of opportunity by wagon that partially followed the Oregon Trail beginning in the spring of 1846. Tragically, the expedition became “the worst disaster of overland migration to California,β According to Britannica.
A combination of inexperience, poor choices and bad luck contributed to the disaster for the families who originally started the van. The group was unable to complete their journey until winter set in and became stuck in deep snow in the Sierra Nevada mountains, where they built makeshift survival camps.
With the help of cadaver dogs, researchers have just fine-tuned some of the remains of those who died at this site β and elsewhere around the world. But how do these dogs do it?
Sniffing the mystery of the Donner Party
Dozens of the nearly 90 people who started the Donner Party expedition died, with the last survivor leaving the makeshift camp in April 1847. At least some of the survivors had resorted to cannibalism, eating the remains of those who died during the winter.
The exact location where many of the Donner party met their end is still not entirely clear.
“It was a place called the Death Camp,” says John Grebenkemper, a dog handler at Institute of Canine Forensics (ICF). The non-profit organization was founded 25 years ago in San Francisco to help discover ancient burials.
In recent years, Grebenkemper’s dog Cale, specially trained to sniff out corpses, may have identified several of the places where people from Donner’s party died based on a whiff of decay that lingered for nearly two centuries.
Dogs who dig history
Since first joining the ICF in 2007, Grebenkemper has worked on everything from tracking down unmarked Native American graves to searching for crash site of aviation hero Amelia Earhart on an uninhabited island in the Pacific Ocean.
But others have used cadaver dogs to track down truly ancient remains in Europe, sometimes dating back thousands of years.
Read more: Amelia Earhart’s final resting place
“Dogs have a wide range of uses,” says Grebenkemper.
A special kind of dog
Most dogs have a great sense of smell, but not every dog ββis suited to the type of training to discover ancient burials. The right personality usually requires a level of obsession that would be a fault with most pets.
“You want dogs that have a strong desire,” says Grebenkemper. When trainers are looking at a litter of puppies, they will select the ones that want toys more than the others for this type of work. “Of course the dog works for a reward.”
It takes several years to train a cadaver dog. Grebenkemper began his studies on human bones. “I have some very old bones that came from archaeologists in Europe,” he says. Other bones can be purchased commercially.
Dogs usually learn to detect the smell of bones fairly quickly. At this point, the trainers take them to old cemeteries to pass on the scent. Eventually, they stop giving them rewards every time, or the dog can learn to mistakenly give false positives – finding human remains when there aren’t any.
“Eventually, they really get into the game and just want to do it,” says Grebenkemper. “They don’t need a reward.”
Read more: Let’s travel through the mind of a dog
How it works
Researchers aren’t sure exactly what dogs smell. But at a basic level, the sense of smell is about chemical detection.
As the creatures die, some microbes that have always been inside them in smaller numbers begin to multiply, accelerating the rate of decomposition. As they eat meat, the microbes release chemical compounds that dogs can smell.
A certain mix of these compounds is probably unique to humans so that dogs don’t mistake humans for dead animals, Grebenkemper says. Dogs will sniff out these remains, often alerting their owners by sitting with their noses directly above the area of ββhighest odor concentration.
But that doesn’t always mean the location of the puppies is spot on. Depending on what is between the surface and the debris, the decaying compounds may not rise up in a straight line. The remains may be buried a few meters from where the dog alerted.
Archaeologists can also confirm where to dig using ground-penetrating radar. These devices can paint a more complete picture of what we can’t see below us, but they often work much slower than our four-legged friends.
In general, Grebenkemper says, dogs are best at finding remains that are up to several hundred years old.
When there’s almost nothing left
Although that doesn’t mean cadaver dogs can’t find older stuff. In fact, dogs have successfully found bones dating back millennia.
In Croatia, Belgian Malinois and German Shepherds are commonly used for criminal investigations coffins containing bones discovered and artifacts around a prehistoric hilltop fortress called DrviΕ‘ica.
The researchers first tested whether it would work by seeing if the dogs would find graves that had previously been found using other methods. When that worked, they let the dogs search more widely and found a number of other bones dating back nearly 3,000 years.
In the US, the ICF has found even older remains of Native Americans – some from 9,000 years ago.
Perhaps even more surprisingly, dogs can detect remains that are no longer there at all. In the 19th century, some Chinese immigrants buried their dead only temporarily before exhuming them and shipping them back across the sea to their native areas. The traces of human decomposition left in the soil were apparently enough for the dogs to detect, although most of the body was removedsays Grebenkemper.
It is even possible for dogs to detect cremated remains, despite the fact that burning destroys much of the chemical compounds produced by decomposition. ICF dogs helped locate remains of people burned in forest firesand Grebenkemper is working on blind tests to further test their ability to find these types of remains.
Preservation of undisturbed remains
The possibility of past burials has often caused conflict between developers and local communities, especially where there may be old bones in the area. “They don’t want their ancestors to be disturbed,” says Grebenkemper.
But where it’s not taboo, dogs can provide a non-invasive method of discovering past remains without even touching a shovel. Grebenkemper has worked on several of these cases, including a project with The Muwekma Ohlone tribe near San Francisco.
Read more: DNA from cemeteries reveals 2,000 years of tribal presence in California
Dogs can find lost burials important to living descendants. They can also help tribes plan for future development by marking potential burial sites.
Grebenkemper sees a positive future for the use of dogs in archaeology. Since the ICF started more than two decades ago, handlers have made great improvements in dog training. Now other groups around the world are training cadaver dogs.
“I suspect the technique will continue to evolve and the dogs will do better,” says Grebenkemper.