A paw print in the snow contains enough genetic clues to identify the animal that made it, even if the track has been buried for five months.
That discovery may revolutionize and simplify wildlife monitoring in remote places. Instead of days of dangerous searching in winter conditions, anyone with a sharp eye, a little training and a clean water jug can confirm the presence of a wolverine or Canada lynx with courtroom precision.
Genomics scientist Kevin McKelvey at the U.S. Forest Service’s National Genomics Center for Wildlife and Fish Conservation in Missoula said the idea popped out of a lecture assignment he was trying to fix. After a decade refining the environmental DNA technique of finding fish evidence in samples of creek water, his lab could detect the presence of five little fish from a thousand yards away.
“The EDNA stuff was cool, but I’d be presenting a fish talk to wildlife guys,” McKelvey said. “So we got thinking outside the box and recognized the magic of EDNA wasn’t limited to water. We could do the same thing on land in snow.”
Each animal cell has about 200 strands of mitochondrial DNA inside, and the research station lab needs only one to identify a species. That single strand often will also give enough genetic information to determine the animal’s haplotype, or regional family marker. For example, it could tell if a grizzly bear came from the Northern Continental Divide Ecosystem or the genetically isolated Greater Yellowstone Ecosystem.
A single strand isn’t enough to tell whether the footprint came from a male or female animal, or identify a specific individual. For that, the lab would need much more genetic material, say, from a half-dozen hair follicles.
But it only takes a few days to cook an answer out of a jug of snow to know if a specific spot had a visit from a certain species of animal. That matters when especially rare critters like Canada lynx, wolverine or fisher appear in places they’re not expected. On the other hand, lynx and bobcat look similar, but there are nearly 1,000 bobcats for every lynx in Montana. Confirming that a threatened or endangered species wasn’t the critter in the picture can be equally useful to land managers.
Past practice had biologists finding a track in the snow, doing a best-guess visual identification, and then backtracking the trail in hopes of finding a tuft of hair or a scat that could provide a definite DNA marker. A field worker could spend hours snowshoeing through avalanche zones and alder thickets hoping to luck into such a trace.
“Now if you come across a track, you scoop it out and you know what it is,” said Jessie Golding, the research station’s carnivore research associate and co-author of the study. “It makes our field methods a lot more efficient.”
The new method not only cancels that backtracking hassle, it expands the time frame during which researchers can reliably gather data. Anyone who’s tried to ID a track in the snow knows how quickly some sunlight or wind degrades the details of claws or paw size. Using the new method, study lead author Thomas Franklin was able to identify a lynx in April from a paw print made in November.
“That was not a place we expected to find lynx,” McKelvey said. “But we thought, 'Hey, we can dig down and find the tracks and see what’s in them.' Snow is a perfect environment. It’s cold, dry, sterile, with no UV (ultraviolet light that degrades DNA). We had a picture from a remote camera, so we triangulated the track from the positions of the trees. The November signal was weak, but we were able to get it.”