DNA tracking is no longer reserved for the prime-time TV dramas and crime scene divisions.
Researchers working with predator/prey relationships have traditionally relied on guesswork, tracks, and behaviors when identifying a predator responsible for making a particular kill on a prey species. Even physical evidence such as scat left at a kill site can yield only marginal results; and doesn’t quite confirm the initial “killer”.
While seasoned veterans of the wild lands are pretty keen on subtle clues to identify depredation activity - primarily with characteristics like how an animal was killed - its no big secret that this method is unreliable, especially with smaller prey.
Researchers are seeking out new ways to track and confirm predatory kills when following predator and prey species, rather than trying to line up the proverbial candlestick with the butler in the parlor to solve the who-dun-it mystery.
Enter Laurel Peelle, a PhD student in environment and forest sciences at the University of Washington, who has focused research on tracking Canada Lynx and Hare depredation in the wilds of Washington State. Peelle, who conducted a new study as part of her master’s thesis, wanted to get a broader picture of the Canada lynx behaviors in Washington state.
She found that tracking methods normally utilized for larger carnivores like mountain lions, such as correlating kill sites with GPS or radio-collar data simply weren’t sufficient.
She found that medium-sized predators were simply not spending enough time at their kill sites to plot those locations via tracking data. So in order to find a more accurate way to determine a given predator responsible for a particular kill, Peele set out to track kills by tagging the prey instead. Hundreds of snowshoe hare were tagged and tracked throughout the Loomis State Forest and Okanogan National Forest in Washington from 2010 to 2014, and so the wait was on for the first recorded mortality.
The one hiccup - in the case of Lynx prey such as hare, the animal was consumed entirely. Upon arrival at the site of the first kill, she found all that remained was a tiny radio-collar and a tufts of hair.
With limits on tracks, scat, or even a carcass, Laurel Peelle set out to isolate the one piece of evidence that may have remained at the scene - DNA. She researched human forensic literature and worked to fine-tune a technique through trial and error to gather remaining saliva left behind at the scene, or, in some cases on those tiny radio-collars themselves.
Peelle discovered the best results came from swabbing the collars directly. Plastic radio-collars appeared to be a better alternative to traditional leather collars for the hares, as plastic’s non-porous surface doesn’t absorb saliva the same as leather. Swabbing the hair and carcasses left at kill sites is less than ideal, Peelle asserts, as this has the potential to mix prey DNA with that of prey species DNA.
The snowshoe hare is a primary prey species for many predators, including coyote, lynx, bobcat, fisher, and marten. (Photo NPS)
It was now time to put the plan in action to see if a determination could be made as to which predators were preying on hare - so off to the Rocky Mountain Research Station samples went for lab analysis.
Of an acquired 53 recent hare kills, researchers managed to get positive IDs on 31 of them. Of the remaining 22 that couldn’t be identified, Peelle believes the elements - such as rain or snow - may have deteriorated the DNA samples. She also confided that many were likely from raptors, which don’t have a lot of saliva to leave at a given kill scene.
As for those positive 31 samples, lynx (Lynx Canadensis), coyotes (Canis latrans), and bobcats (Lynx rufus) took the bulk of the kills, with Mountain lions (Puma concolor) and North American pine martens (Martes americana) also identified in a few of the samples.
While the research and accompanying study are certainly groundbreaking, the process is still not as simple as “track, swab, collect, and analyze cotton”.
For Peelle’s program, researchers still needed to use solutions particular to specific species.
In other words, the traditional observational skills approach to guesstimate a suspected predator at the scene was still applied. Either way the findings from Peelle et al, as published in the September 2019 Wildlife Society Bulletin are incredibly groundbreaking for conservation researchers.