Why We Study Carnivores Using GPS Collars

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?
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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. 

Kitten tagged in June 2017 by tracking a collared female cougar in our Okanogan study area.

​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.

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​Investigating Kill-sites
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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. 

A deer’s body condition can be estimated with bone marrow color and condition. This bone marrow is pinkish and solid, indicating that the deer’s body fat reserves were in decline when it was killed by a collared cougar.

We can estimate a deer’s age by studying the number and shape of molar teeth in its jaw, and get exact age by sending an incisor tooth to the lab. The lab counts cementum annuli (annual cementum layers) in the tooth's root, like rings on a tree.

​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?
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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