Trapping at Portal is usually done on the weekend closest to the new moon. This is done for a number of reasons: 1) trapping at the same time each month lends consistency to our methods, and 2) evidence suggests that rodent may be most active outside of the nest under the cover of the darkest time of the month (but then again, maybe not). This year, the new moon fell on the day after Thanksgiving and again on Christmas Eve. As much as I enjoy handling rodents, I pushed back the monthly Portal trips to the first (Dec 2-4) and third quarter (Dec 16-18) of the lunar calendar.
When the temperatures drop, many of our smaller species disappear for the winter as they enter torpor to save energy and remain warm in their burrows. Although larger species, such as the kangaroo rats and grasshopper mice stay active year round, they are still susceptible to cold desert nights, which commonly dip as low as 20 F in the winter! Getting wet, even a little bit, when it is so cold can kill even these larger individuals. So when I arrived in Arizona on Dec. 2nd to see rain clouds in the sky, I knew that trapping that weekend was just not going to happen.
Given the total lack of rain last winter in southeastern Arizona, and the nasty fire season they experienced this past summer, the rain is much needed. So although we weren’t able to set out traps, Tim Bean, visiting from UC Berkeley (where he studies the endangered giant kangaroo rat!), helped me with some site maintenance activities.
Erosion around the gates in our fences has continued as the rain falls, so we took advantage of the damp soil to rebuild little ‘ramps’ for the rodents to use to ensure that immigration and emigration from fenced plots can still happen.
While walking around all the plots, we also filled in holes that seemed to go under our fences. Here, a badger has successfully created a superhighway into one of our total rodent exclosure plots, right under the bottom of the buried wire mesh.
Here, Tim valiantly fills in the hole. Not a very good substitute for getting to see cute kangaroo rats, but it had to make do.
Germination has already begun, and if the rain keeps up, there should be a lot of vegetation this spring!
For the second December trip, I brought along ASU researcher with the CAP LTER, Julie Ripplinger, and we were lucky enough to be able to set traps one night, despite rain clouds lurking in the sky.
Julie is pictured here holding a cactus mouse (Peromyscus eremicus), which seem to be relatively abundant right now! We caught nearly all of them in pairs, one trap right next to the other and nearly all were in breeding condition. Cactus mice may breed year-round if conditions are right. They are also quite pretty mice with their orange-y sides, large ears, and very soft fur.
In addition, we continue to catch a solitary Bailey’s pocket mouse (Chaetodipus bailey); the species that was once our most dominant seems to be hanging around nearby…
Rain clouds hung around all day on Saturday (Dec 17) so we erred on the side of safety and didn’t set traps on our final night. Instead we completed more plot maintenance, this time focusing on stabilizing our trap shed. The shed is one of those snap-together plastic outdoor sheds which works fine for our purposes, but from time to time begins to fall apart and needs snapped back together. During the past two weeks, something dug a large hole underneath so it was completely destabilized. I wanted to take it completely off its cobbled-together rock base and rebuild it, but Julie stopped me when she saw the tail of a mojave rattlesnake poking from underneath the shed near my hand. Again deciding to err on the side of safety (snakes often overwinter in large groups, called a hibernaculum), I satisfied myself with carefully filling in the part of the hole I could see and stabilizing the roof of the shed.