In September, I returned to Portal bringing with me the newest Ernest lab member, Erica Christensen. It was a bit cooler than usual for mid-September, but overall, a great time of year to be in the desert. We captured 263 rodents, most of which are still represented by the desert pocket mouse (Chaetodipus penicillatus) and Merriam’s kangaroo rat (Dipodomys merriami). It’s much less buggy than other years, and it was a really pleasant weekend. No complaints about desert fieldwork in the fall!
Posts Tagged ‘pocket mouse’
One of the best things about working in the desert (especially when you’re doing long-term ecology!) is that things are always changing. After the recent drought, we saw a decline in biodiversity at the site that rivaled anything seen throughout the course of the 35 years of study, including the dominance of the rodent community by a very small-sized species (Desert pocket mouse, Chaetodipus penicillatus) which surprised us all. After some decent rains in 2011, diversity is slowly returning to the rodent community as we have been seeing more of the generalist species return. These species seem to be more transient at the site, popping up when conditions are right for them. I was still a bit surprised, however, to catch several plain’s harvest mice (Reithrodontomys montanus) in January! This is a species that I hadn’t seen in a few years, so it took me a moment to determine what I was seeing.
Another of the generalist species that has been popping up this winter is the cactus mouse (Peromyscus eremicus). We even found a nesting pair in our trap shed this past month! They were pretty cute, but since our trap shed has recently been inundated with other living things–pack rats and most recently, at least one rattlesnake and a badger living underneath the shed, I chased them out. I really don’t want the shed to seem like a larder for our resident rattlesnake. Pictured below, is my volunteer of the month, Loren Sackett, from University of Colorado at Boulder.
Loren studies prairie dog populations, genetic divergence and pathogens in the southwest. You can read about her adventures at the prairie dog blog.
Meanwhile, the rain seems to have slowed from earlier in the winter but the plants are still growing! We’re headed down to the site again in March to have another rodent-trapping-plant-field-extravaganza.
Above, Rumex, Erodium, and Guterrezia all green up. The vegetation at the site seems hard to categorize and we’ve had trouble finding just one or two field guides to use when we do the plant surveys. Luckily, over 25 years of work at the site has led to the compilation of an amazing mini-herbarium of pressed plants and identifying characteristics that we can bring down with us when we do our plant surveys. I’m currently working to update this herbarium and have found several websites that are also really helpful for plant identification in the area, such as this NMSU website, this Arizona wildflowers website, and this New Mexico flora website. I’d love to hear any other suggestions of websites or books that are helpful for plants in the Portal area–please share!
Seed pods from Devil’s claw (Proboscidea parviflora) on the fence of a rodent exclosure, Chiricahua mountains in the background.
It was pretty small, but I’ve never seen a tarantula in January before!
Loren sets traps at sunset.
October is one of my favorite months to be at Portal. The day and night temperatures seem perfect and the days are long enough to enjoy the scenery of the desert. Because of this, it’s also one of the best times to introduce new Portal volunteers to the site. Throughout the project’s duration, many people have come to help with the rodent and plant censuses, and many of these people have not been graduate students or even biologists. This month, I was able to bring my mom, Mary Mohlman, who works at Lincoln Elementary School in Hastings, NE. Her students have actually been studying deserts this fall, so she was excited to learn about the rodents and to take lots of pictures to show the kids.
Our trap numbers continued to increase and we had nearly 200 individuals! In addition, some of our other species made a few cameos, including four cactus mice (Peromyscus eremicus), 4 southern grasshopper mice (Onychomys torridus), 2 silky pocket mice (Perognathus flavus), and even a new Bailey’s pocket mouse (Chaetodipus bailey)! We had one strange encounter with a very, very pregnant female kangaroo rat (Dipodomys merriami) who weighed over 60 grams (usually ~ 35-45 grams)! As soon as we let her go, she started making urgent squeaking noises and ran about 5 feet away from us towards the corner of the plot where she dug a hole, climbed inside, and covered the entrance. For the next 10 minutes, as we finished the rest of the traps on the plot, we could hear her squeaking while underground. I can’t say what was happening, but it was very strange behavior.
The rain seems to have stopped for the season and the vegetation was much drier than a few weeks ago when we completed the plant census. However, there were still plenty of very large centipedes (Scolopendra spp.) and texas horned lizards to be seen (Phrynosoma cornutum).
After trapping rodents August 26-28, it looks like the desert pocketmouse (Chaetodipus penicillatus, pictured below) is continuing do really well, as almost all the other species appear to be doing not-so-well, at least at our site!
Above, the desert pocket mouse is in a plastic bag (photo by S. Cobbold), before we take its measurements. Since we never know what is going to be inside a trap, putting it in a clear plastic bag before handling it gives us a chance to take a look at the animal and to get a good grip on it so it doesn’t escape. Sometimes we catch larger rodents (which can bite!) or other non-rodent animals (which could be venomous!).
Portal has been known for having very high diversity of rodents compared to many other locations; however, if someone had just begun trapping there this year, they would have concluded otherwise. For over a year now, we have been mostly capturing the desert pocket mouse and Merriam’s kangaroo rat (Dipodomys merriami), with only a handful of other species present (i.e. one or two grasshopper mice (Onychomys spp.), Ord’s kangaroo rat (Dipodomys ordii), or cactus mouse (Peromyscus eremicus). This month, there were ONLY Desert pocket mice and Merriam’s kangaroo rat and not a single individual of another species! I think this may be the only time this has ever happened in Portal Project history.
Stephanie Cobbold, a graduate student at Utah State University in the Jim MacMahon lab, helped out with trapping this month. She studies the sensitivity of species traits to habitat characteristics using spider communities, and we spent our free time looking for spiders, scorpions, and other small arthropods. Since there is a lot of vegetation right now, we saw lots of interesting webs and also saw a scorpion capturing a smaller scorpion! If you’re interested in this side of desert life, check out her great blog post on the spiders of Portal Arizona!
One thing that makes traveling to Portal each month so interesting is the speed at which the desert landscape can change. Southeastern Arizona has recently been in a major drought, but the arrival of summer monsoon rains seems to have helped green things up, at least temporarily.
Below, the first photo was taken on July 2, 2011 and the second photo was taken August 6, 2011. During that month approximately 11.4 cm of rain fell and transformed the dry, dusty ground into a carpet of green seedlings and flowers.
Some areas were covered in orange flowers (e.g., summer poppies, orange flame flower, and showy flame flower), purple flowers (e.g., silverleaf nightshade) and large caterpillars were abundant (I think mostly Sphinx moths).
In addition to the growth of new plant life, the summer rains have also led to flooding in the Chircahua Mountains where the fire left slopes unstable and vulnerable to washing away. Some of the forest roads remain closed and a short drive into Cave Creek Canyon makes it easy to see areas where the forest floor is buried under mud and debris washed down by flash flooding. Some locals, bloggers Azure Gate and Cave Creek Ranch, have posted updates and photos on conditions in the area.
In addition, the dry soil conditions and lack of vegetation on the bajada and in the valley seem to have allowed for increased erosion at our site as well. The gravel roads leading towards the Portal Project were washed out in places and erosion around the fenced plots meant that some gates were left > 12 cm above the actual soil surface or buried underneath mud and debris; both scenarios making it difficult or unlikely for rodents to actually find and use the gates. I’ll have to work at maintaining these gates over the next month as more rains are likely to occur.
Luckily, I had lots of help digging out rodent gates and collecting data by Elita Baldridge, a Ph.D. student in Ethan White’s lab who came to help out before we both headed to present at ESA after field work was finished.
I continue to be amazed at the “sea” of desert pocket mice (Chaetodipus penicillatus) that seem to be taking over–we’re even encountering control plots, where kangaroo rats should be dominant, with no kangaroo rats at all! Amazing.
Oh, and speaking of amazing…
Here is the belated spring update on Portal rodents. March, April and May were all months full of flowers! In May we began seeing scorpions, Mojave rattlers, and bee swarms. The site was beautiful as all the spring flowers took off, but the rodent numbers stayed low after winter. By May, we were still just below 50 animals! In addition, it appears some changes may be occurring within the community. We haven’t captured a banner-tailed kangaroo rat since late fall and Ord’s kangaroo rat is also doing quite poorly (2 or less all spring!). Perhaps most suprisingly, Bailey’s pocketmouse, which we usually capture throughout the colder months has also nearly disappeared. Very few were seen all winter, and by spring we were only capturing 1-2 each month. Instead, the smaller Desert pocketmouse is numerically dominant, along with Merriam’s kangaroo rat. Overall diversity is currently very low. Hopefully we can continue trapping, at least in some capacity, in order to see what happens as rodent numbers slowly rebound from near zero last winter!