With time running out, I’m pressed to tell you more about my work in Yellowstone. In this post, I’m going to talk about cute and cuddly small mammals — well, kind of. You see, they are those fuzzy little creatures that we love to adore. However, some of them may carry something deadly. The Wildlife Health Program monitors certain small mammal species for disease that can affect animal populations and people visiting the park. I’ll tell you more about the program’s efforts and my experience with this project.
Since day one, Chad and I were doing rodent surveys. At first, we would assist Jess, our lab manager and lead on the rodent project. We accompanied her into the field to learn the ropes and help with data collection. As the summer went on, eventually, Chad and I were let loose to perform surveys on our own. These surveys provide an estimate of activity and abundance. Using this information, we identify sites that are suitable for trapping and sampling our species of interest.
Although a rodent survey could include any species in the order Rodentia, for our purpose, we focused on the Uinta Ground Squirrel (Spermophilus armatus) and the Deer Mouse (Peromyscus matriculates). Ground squirrels and their fleas are sometimes infected by Plague and occasionally, they can be a source of human infection. Additionally, Deer Mice may carry Hantavirus. The virus is found in the saliva, urine, and droppings and transmission to humans occurs when the virus is inhaled — think, cleaning an area with mouse poop.
In Yellowstone, ground squirrel habitat is found in meadows and residential areas. Timing is everything because they are only active for a short time in the year. First, we identify an area of activity and create an imaginary polygon with a GPS to identify the location. Then, we would walk parallel transects inside the polygon to count burrows or individuals. In areas of high abundance and activity, we may count individuals. More often, we count active burrows. While counting, a “clicker” or tally counter is our tool of choice. We record our findings on a data sheet along with environmental data, a drawing of our polygons, and any notes on ground squirrel activity.
Due to resource constraints, we trapped Deer Mice only once. This was done in an obscure maintenance area that was essentially a field where large equipment was stored — great habitat. In the evening, we deployed Sherman traps baited with oats and peanut butter and checked the traps in the morning. We donned our personal protective equipment when handling the animals — respirators, gloves, and long sleeves. Out of eighty traps, we caught nearly a dozen mice. In my experience, this was a successful trapping event. However, our captures alone do not indicate animal abundance.
Sampling rodents for these diseases requires collecting blood samples. The method we use is retro-orbital bleeding. Simply, this involves inserting a capillary tube between the eye ball and socket and scratching the capillaries behind the eye to obtain a small sample. Arguably, this method is least invasive, it is easy to learn and perform in the field, and it provides a quality blood sample. When done correctly, the tiny tube fills with enough blood for analysis and the eye is undamaged. Additionally, we record weight, sex, reproductive condition, and environmental data and attach an ear tag to identify the individual.
Although this procedure may sound harsh, keep in mind the necessity of monitoring for the presence of disease. Understanding disease ecology in Yellowstone National Park is fascinating but also important to the health of animal populations and the people who visit.