Non invasive survey methods for carnivore conservation research include tracking, remote cameras, and hair snares. In my training to become a wildlife biologist, I’ve gotten a first-hand look at different techniques for carnivore monitoring and detection. (For the why and how of carnivore conservation, see part one of this series.)
Direct observation of animals and animal sign is minimally invasive but generally labor-intensive. Trackers visit likely habitat areas and look for distinctive signs. These include tracks, scat, scrapes, dens, and trees that have been scratched, among other indications.
Each species’ track has distinguishing characteristics, but these can sometimes be obscured by the quality of the substrate material or conditions since the track was made. For example, a track made in snow may appear larger after a week as rain or sun softens the print. As with humans, tracks between individuals of the same species can vary significantly in size, so scientists have collected size ‘guidelines’ to help trackers confirm the species based on width and length of the track as well as the distance between tracks.
Often, the trail itself (its stride length and grouping of tracks) may be more conclusive for identification than an individual track.
To prove to other scientists that a track is legitimate (especially important for rare species such as wolves, grizzles, wolverines, and fishers), it must be carefully documented. Trackers can photograph a print or create a cast. Other information might be recorded, such as a GPS location and the type and density of vegetation in the area.
Placing track plates, strips of material that record prints, is a less labor-intensive variation.
Scat (Science Talk for Poop!)
Scat is also an identifier for species, but likewise varies between individuals. Form, size, and composition of scat are key identifying features. Often, rain softens scat and makes it unidentifiable.
As an intern wildlife biologist at Santa Monica Mountains National Recreation Area (NRA) in Southern California, one of my weekly duties was walking ‘scatlines’. Scatlines are trails established by biologists along which we would look for scat at regular intervals. By having standardized locations, scientists could compare the data over time.
I was looking for bobcat and coyote scat. Bobcat and coyote scat can appear quite similar, but coyote scat sometimes contains berries, and bobcat scat can be divided into segments with an indentation at one end. I’m told bobcat scat has a lemony scent, but I took their word for it.
Photographing animals using remote cameras is a more expensive technique that remains minimally invasive but often provides more conclusive documentation. Scientists install cameras along likely trails and other habitat areas, often accompanied by “lure” to draw species to the camera.
“Lure” draws animals to the picture
Liquid lures include ‘delicious’-smelling concoctions in aromas like beaver castoreum and musks and urines from assorted animals. The lure is rubbed on a tree trunk or stump in front of the camera lens, drawing animals directly into the frame as they investigate. Lure application is a ‘hold-your-breath’ kind of operation. Different lures are used to attract different species. In Southern California, the Park biologists concocted their own recipes for bobcat lure for live traps.
Fresh carrion is another option to bait carnivores. When I set up remote cameras in the hopes of spotting martens, we attached a raw chicken to the tree, protected by chicken wire lashed around the carcass. At Santa Monica Mountains, we snagged fresh roadkill.
Visual lure also draws passing animals. Scientists tie feathers to nearby branches to flutter in the wind.
Photos are ‘tripped’ by heat and movement. To avoid disturbing animals, cameras often record infrared images at night, instead of using a visible flash. Cameras can now record video as well as individual images. Each image is time-stamped.
Potential issues with remote cameras
Choosing a location for the camera is essential. The camera should be placed somewhere animals are likely to pass, at an appropriate height, with no vegetation blocking the lens.
Since battery life and memory card size are limited, remote cameras do have to be checked periodically. A single squirrel can trigger the camera dozens of times if it spends a long time investigating the lure. Environmental conditions can sometimes trigger ‘false positives’ if there are rapid changes in light and movement. Scientists want to be sure not to miss the ‘target species’, the species they’re trying to document, through a dead battery or full memory card before the animal passes.
Shutter delay means the photo can sometimes miss the animal that triggered it entirely, if it walks out of the frame too quickly. Or it could capture inconclusive identification — was that bear rear end a black bear or a grizzly?
Cameras can be damaged by animals or sabotaged or stolen by people who find them.
Hair snares collect hair samples from animals indirectly, and the samples are identified by genetic testing. Lure draws animals to the snare, often an area surrounded by barbed wire that will capture hairs. I don’t have direct experience with hair snares, so forgive me for not elaborating.
Part 2: Non-Invasive Survey Methods (this post)
Part 4: Carnivore Conservation in Cascadia