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By Alexa Schwartz, Denver Zoo Teen Volunteer
The Bison project in the Rocky Mountain West is a long-term, experimental study working to document the impact of raising bison versus cattle on the Great Plains ecological system. Denver Zoo works with Rio Mora National Wildlife Refuge (a bison ranch), and Quintana Ranch (a cattle farm), in New Mexico, where Denver Zoo staff and volunteers track and document native plant and animal species within the different farms.
Conservation biologists at the zoo are investigating potential distinctions in the biodiversity of auxiliary species (not bison or cattle), in the hope of developing and promoting environmentally safe farming practices. In order to cover every environmental aspect, different trips focus on different groups of native species: small mammals, reptiles and amphibians, bird, invertebrates, and plants. Trapping and documenting indigenous animals allows us to discover variation in biodiversity and population density between the two ranches. With these results, Denver Zoo hopes to encourage farmers to use ecologically safe farming methods and conserve the animals and land in the Great Plains ecological system.
This is my third year participating in one of the Conservation Biology trips to New Mexico. During the summer, there are three conservation trips in the bison project that teen volunteers in Zoo Crew can participate in. Teen volunteers individually have the opportunity to participate in one of these trips per year. Teens apply between March and April, and are selected to participate in a trip based on interest, availability, and experience. Applications are due every April 1, and are reviewed by Teen Programs staff and returned within the following two weeks. Each year, we go with a group of up to six teen volunteers, one Denver Zoo Teen Programs staff, as well as one to two Denver Zoo zookeepers, who join us and lead the trips. All week, we work together twice a day to trap and track animals.
One type of bison trip focuses on tracking indigenous small mammals, predominantly mice and rats, but occasionally voles, and squirrels. Since small mammals are nearly impossible to find and track without capture, we use Sherman traps to temporarily catch the rodents, in order to systematically document biodiversity. To collect accurate data on the population density of animals in the two separate ranches, we use a trapping system set up in plots. In each plot, there are 121 traps, set up in rows of 11 in each direction to make a square. The traps are spaced 20 meters apart, and are each labeled with a number between 1 and 11, and a letter between A and K. This system helps us keep track of where animals are being captured and if they come back to the same trap later. Sherman traps are small metal boxes, with folding doors on either side. A door opens and latches on one side, and flips shut when the animal steps to the back of the trap on a metal plate called a trigger. We open traps in the evening, and document the animals found in them every morning before releasing them.
This year there are two plots in Rio Mora (the bison farm) and two in Quintana (the cattle farm). To process the animals, we ear tag the mice using a small metal earring labeled with a three-digit number. When measuring, we take the overall body length (tip of nose to base of tail), tail (base to last vertebra), ear (inner ear to tip), and hind foot (longest toe to heel) in millimeters. Finally, we take the weight of the animal in grams, and with the information, identify the species, approximate age, and gender of the mouse.
Everybody on the trip wakes between 4:00 am and 4:45, and together, we head out to the plots by 5:00. We have to get out early because we need check all of the traps, and release the animals before it gets too hot; therefore, we begin our checking before the sun is out. We break into two groups to save time, and each take one ranch. One group will set up and check in Quintana, while the other works in Rio Mora, then, we will switch for the next day. In the mornings, we check our traps for animals, and shake out any left over bait, which is peanut butter and oats.
We close off the traps after checking them all, and are usually done with the morning rounds by 8:30, and head back to the house. The house used for Denver Zoo personnel is situated in a beautiful valley in the middle of Rio Mora. During the hot hours of the day when mice would not be safe sitting in the traps, we participate in various activities around the ranch. At least once during the six-day trip, we help the reserve (Rio Mora) with a restoration project. On previous trips, projects included lifting rocks to make dams, trimming trees, checking rain gauges, and planting willows along the riverbank. This year we spent a few hours in the afternoon removing an invasive plant called cheat grass. Other days, teens and staff enjoy playing games, taking naps, looking for reptiles, taking hikes, or going on field trips to Las Vegas, New Mexico, or Fort Union, a nearby civil war military base.
At about 5:00 pm as the day cools down, we go back out to the plots to open them up and bait them. We keep a wad of polyfill (polyester stuffing) in the back of the traps to keep the animals warm and comfortable during the night. After opening the traps, we have dinner. Some nights we take night hikes, or night drives, to look for nocturnal animals. These are fantastic as well, since without the light pollution in the city, the stars are stunningly vibrant. We typically go to bed between 11:00 pm and 12:30 pm at night, only to get up a few hours later and repeat the process again.
Although these trips are full of strenuous work, they are extraordinary experiences. Every year, I am amazed by how much I learn, and enjoy participating in the trips. These trips provide a fantastic way to learn and engage in field conservation, and to experience conservation biology and research. We build strong friendships with all of the other participants on the trips, as well as learn about the ecological system we live in. After returning to the zoo, we strive to share our knowledge to further help our local environment.