Why do we put GPS collars on wolves, cougars, and other wildlife? Why are these collars effective research tools and what are we hoping to learn?
Research collars allow us to track individual animals. This can help us understand specific behaviors, such as the size of female cougar territories versus male territories, or how animals move around on the landscape. We can also use collars to locate animals for visual observation studies, such as by locating an elk herd and then watching those elk to see which plant species they choose to eat at certain times of year. Or we can use collars to find sites important for the species we follow, such as where they choose to den and raise young.
How do the collars work? Collars are programmed differently based on research goals. For this project, all of our collars record a GPS location every four hours, totaling six points per day. Each point takes a little bit of battery life, so we have to balance the detail of our data against the length of time we want the collar to last. Collar locations let us understand what wolves, cougars, deer, and elk do throughout the day and year, and in relation to one another. Are cougars and deer both resting in dense forests during the heat of the day? Are cougars following mule deer migrations or staying put? Collars can help us answer these questions.
Cougar GPS points in yellow. Each yellow dot represents a GPS point taken by the collar. The grouping of points in the center the of line is a "GPS cluster", and indicates that the cougar stayed in one location for several days, possibly to feed. Lines between points are drawn automatically but do not represent the actual path of the animal.
Collars can also help us find places where a cougar or wolf has killed an animal. When a predator makes a kill, it stays in the area for anywhere from a couple hours to a couple days to feed. When we see GPS points start to pile up, we hike in to those spots to see if the animal was just resting or if it was feeding on a kill. We call these spots “GPS clusters” and they help us find “kill-sites” where predators killed (or scavenged) prey. By investigating these spots, we can gather information on the species, age, and sex of prey by examining the bones left at sites. Age can be determined by looking at the pattern of teeth in the mandible (jaw) or by analyzing the deer’s incisor teeth for cementum annuli, which involves counting years of growth like rings on a tree. We can also get an estimate of the prey’s body condition by looking at bone marrow. White, solid bone marrow has a lot of fat, meaning the animal was not in critical condition. However, red jelly-like bone marrow indicates low fat reserves, suggesting that the animal was in very poor condition.
Information from clusters can help us understand which deer and elk are most at risk of being eaten by wolves and cougars. Is it young animals or older ones? Males or females? We can also learn how the landscape might influence predation. Do wolves steal or scavenge cougar kills that occur within their territories? Do cougars kill more deer in burned areas or unburned areas? Do wolves make more kills in areas with a lot of roads or in large blocks of undeveloped land?
All of this information will be used to understand how habitat, land management, terrain, and prey behavior influence wolf-cougar interactions in eastern Washington.
- Lauren Satterfield
January 2018 brought a new season of cougar captures for the Wolf-Cougar Project. When capturing cougars for research, winter is the best time to find these large felines. Snow makes tracking easier, and both cougars and the animals they eat congregate at lower elevations in valley bottoms to avoid the deep snow accumulating up high. Not to mention that a blanket of snow atop Washington’s conifer forests make for a scene worthy of a Bob Ross painting.
We catch cougars using either box traps or with the help of local houndsmen and trained hounds. Box trapping allows us to capture cougars in areas with more roads and private lands, whereas hounds help us cover larger amounts of ground in National Forests. Of sixteen cougars captured in 2016/2017, six were still alive in 2018. Ten were no longer part of the study due to either collar failure or mortalities caused by hunter harvest, agency removals, starvation, being killed by other cougars, or unknown factors.
Why Cougars Die
Hunting, agency removals, disease, starvation, and intra-species conflict can result in death for cougars in this region. The cougar hunting season runs throughout the winter in Washington, Idaho, and Canada, with many cougars taken when hunters are out looking for deer or elk. Young cougars stay with their mothers until approximately 18 months of age, looking like full-grown adults before they disperse. These “teenage” cats, known as subadults, sometimes do not have the hunting skills needed to make it through their first year on their own, while other times they wander into the territories of adult cats. Subadult male cougars in particular can die in territorial disputes with other adult males. Our research will allow us to better understand the different causes of mortality for cougars in Washington, and how a growing wolf population might be impacting cougar survival.
Our goal for last winter was to deploy at least twelve more collars across our two study regions to help us understand how these large cats interact with wolves, the other large predator in the region. A typical winter day starts out by warming up snowmobiles and donning enough layers for a full day outdoors. Last winter, temperatures were markedly warmer, with most days around 30F instead of the frigid temps during the winter of 2016-2017 which could reach -15F. We do not capture cougars in temperatures below 5F, but we’re often out in colder temperatures looking for tracks and making plans for warmer days!
Cougars often walk down roads or cross them, so we spend the bulk of each capture day searching roads for fresh tracks. When we find tracks, we want to make the chase as short as possible for both the cougars and the hounds. We do as much of the work as we can ourselves, following tracks to see if they cross another road farther on or circle back on themselves, before letting the four-legged canine experts on the trail.
Once a cougar climbs up a tree we move the pursuing hounds back, set up a safety net to catch a potential fall, dart the animal with an anesthetic, and climb up the tree to lower the anesthetized cat to the ground. We weigh the cougar and then estimate its age based on a method called gumline recession. Older animals have a larger gap between the gum and where the canine tooth begins to taper.
Then, we affix small ear tags with an identification number to each ear and attach a global positioning system (GPS) collar that will allow us to track the animal for two to three years. After approximately 45 minutes, the cougar slowly begins to wake up and we leave. We surpassed our goal and put out seventeen new collars last winter, bringing our total to thirty-three cougars collared so far!
Summer field work recently came to a close for the Washington Predator-Prey Project. For my research (see community dynamics), this entailed deploying camera traps across both study areas to photo-capture medium- to large-bodied carnivore and ungulate species. After completing this first field season of my PhD work, I’ve come to appreciate the charms camera trapping has to offer.
The obvious perk of camera trapping is the incredible images you end up with. Given that we have 120 cameras placed across the two study areas and will leave them out year-round for the next 2 years, we will have quite a collection for photos by the end of the study. Each photo-capture of an animal gives us a wealth of information including the location, date, and time at which the animal was observed, the habitat it was using, and possibly even its age, sex, the number of individuals in its group, or behavior at that moment. In addition, because any passing animal will trigger a camera trap, we will end up with information on a wide variety of species. This is a huge advantage of camera trapping because we can collect data on multiple species with minimal additional effort.
To top it all off, we get to explore some of the most incredible places eastern Washington has to offer as we travel to and from the camera traps. This technology allows us to collect detailed data over large areas while still getting us out in the field to enjoy and appreciate Washington’s diverse ecosystems. We’re thrilled with the data we’ve collected up to this point and look forward to what we will catch on camera in the years to come.
Welcome to the Washington Predator-Prey Project Website. While various components of this research have been underway since 2016, we began large-scale data collection across the project this summer.
For my research on carnivore-ungulate interactions, this was the second season of collaring white-tailed deer fawns, and the first season collaring elk calves. Thanks to the hard work of our field crew and collaborators, we deployed 27 radio-tracking collars on fawns and 16 collars on elk calves this year. Combined with the 19 collars deployed on fawns last year, we have monitored a total of 62 neonates for the project so far.
So how do we find these newborn animals to study? Sometimes, we can identify if a doe or cow has young by closely observing her behavior, which can indicate the general location of a fawn or calf. We also monitor the locations of GPS (Global Positioning Satellite) collared adult deer and elk, and can often pinpoint a birth site by a substantial reduction in maternal movement. A subset of GPS collared does and cows are fit with transmitters that alert us when they’ve given birth and mark the location of the birth site. By carefully searching these areas we may find the newborn fawn to collar and study.
Once an animal has been collared, we listen to the radio signal periodically to locate the fawn or calf and check if it is alive. When the collar hasn’t moved for a pre-programmed period of time, the frequency of the radio signal changes to indicate a mortality or dropped collar. We follow this signal to locate the collar and investigate any mortalities to identify the cause of death. Incorporating these data into population models can help us identify which pressures the populations are most sensitive to.
For the next year, we will continue to monitor these and adult ungulate and investigate patterns of mortality and habitat use. Stay tuned to follow our progress get updates from the rest of the team.
- Taylor Ganz