A Night with the Pocket Mouse Field Crew

Each animal found in a trap is examined, weighed, marked, and released.

Each animal found in a trap is examined, weighed, marked, and released.

It’s 8 p.m., and I’m about two hours into my workday. The light is fading, and the moon isn’t yet up. It’ll probably rise around 1 a.m. a quarter full, waning. These changing details, which I’m mostly oblivious to during my “normal” life, are events of note out here, recorded faithfully in my field notebook every night. It’s spring now, and since the pocket mice are active this time of year—and nocturnal!—so am I.

A kangaroo rat leaves a trap.

A kangaroo rat leaves a trap.

We start about an hour and a half before dusk to open all our traps. They are spread over a couple of miles, about 200 traps in total. We snap open the doors, throw in some seeds for bait, and wait. Since our field site isn’t close to anything, really, we wait in the truck. We chat, read, eat dinner we packed, and relax for a bit.

At midnight it is time for the first trap check. We roll up to the first site, finding each numbered flag and it’s corresponding trap mostly by memory, with the help of little reflective tags and bright headlamps. I also carry maps of each site—it’s amazing how disorienting the dark can be! Tonight is pleasant: still, about 55 degrees Fahrenheit and not too windy.

The Pacific pocket mouse is the field crew's focus.

The Pacific pocket mouse is the field crew’s focus.

We come up to our first trap, which is shut. We carefully peak inside—a kangaroo rat! We move the animal from the trap and into a Ziploc bag to examine, weigh, mark, and release it. Each animal we catch is individually marked, and some are in the traps pretty regularly. Others we only catch once. Maybe they are only passing through, or they stay in the area but just won’t walk in again, or they end up as a meal for an owl or fox or snake. Life as a small rodent is full of dangers.

We repeat this process until we’ve checked every trap and handled every animal. We know who lives where, when they have their babies, and when they are active. We are also doing some behavioral observations with the different species to understand how they interact with each other. On average, it takes about two hours to go through all our traps. We hop back in the truck and can squeeze in a couple of hours of sleep. At 4 a.m. we wake up and do it all over again. This time we close the traps to make sure no more animals go in and record and release everyone we’ve caught. By 5:30 or 6 a.m., we are wrapping up, releasing the last animals before the sun comes up. The mice and my crew and I all head home to sleep for a few hours during the day, getting ready for another night in the field.

Rachel Chock is a graduate student and volunteer with San Diego Zoo Institute for Conservation Research’s Pacific pocket mouse project. Read her previous post, Where are Pocket Mice during Winter?

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