Tracking the Cheeky Pocket Mouse
I sit in my truck in the dark. I have arrived at my field site on Camp Pendleton (north of San Diego, CA) and turned off the engine. It’s a big night. We are, for the first time ever, putting transmitters on the critically endangered Pacific pocket mouse. I designed the tiny data collectors, and I’m nervous. I flip on my headlamp and check and double check that I have everything that I need while I wait for my field assistants.
When they arrive, we strap on our snake guards and fanny packs, hop out of our trucks and walk to the trapping grid. It is 10 p.m. and the traps have been open for 4 hours, plenty of time for the little mice to find the seed path leading into the trap and set it off. We have been trapping for nearly two months and some mice have become so “trap happy” that once we release them and reset the trap, they immediately go back in for another cheek pouch full of seed!
After nearly 40 nights of trapping, we have a pretty good idea who we are going to find and where: pocket mice are territorial and once they claim a territory, they stay there for life.
We are looking for Male 22, an adult that weighs 6.4 grams, which is big for a “little pocket mouse,” and a regular visitor to our traps. We walk down the trap line where we normally catch him and sure enough, the trap—his trap—is closed.
I peek in to verify that it is a pocket mouse and am overwhelmed with a sense of wonder at this tiny creature. How is it possible that an animal smaller than a cat toy can play such an important role in the ecosystem? I snap back into my body, to the work at hand. We have to get him into our trap bag to check his identification colors. Using a black light, we read the fluorescent color code injected into his tail. Once we know it’s him, we set out our equipment and look for a tiny stick.
Though we have practiced on other nonendangered pocket mice, this time it really matters. The more we can learn about how these animals interact with each other and their environment, the more likely we are to save them from extinction. That’s why we are placing miniature backpacks on 10 pocket mice to track their movements and gather data on their behavior.
Despite the cold air, I’m sweating. I carefully hand little number 22 to my research technician in the cloth trap bag and he holds him as gently as possible on the ground. The other tech puts the tiny stick in the male’s mouth to keep him busy while I quickly and gently use the tweezers to lift his right arm and slip the loop of the backpack over his arm and slide it up to his armpit.
Next is the hard part. We have to hold the aspirin-sized transmitter in the middle of his back while using the tweezers to stretch the other loop of the harness over his left arm—any mistake could dislocate his tiny right arm.
We are tense and silent. It slipped. Darn! I take a deep breath and try again. We were so close last time; I just know we are going to fasten it on this time. Tiny 22 is closing his eyes tight. The first loop goes on quickly and…YESSS! This time we managed to stretch the second loop in place. We check him over and put him into a plastic aquarium for observation. Before freeing him, we have to make sure that he can move normally.
We take several minutes to allow everyone, including lucky number 22, to catch their breath, before we release him. One pocket mouse down, nine more to go!
Debra Shier, Ph.D., scientist at San Diego Zoo Institute for Conservation Research.
