So we’ve been trapping the degus at Rinconada for about three weeks now, and we’re all getting a good rhythm going with our sampling. It may read a bit tedious, so feel free to skip over this section, but I’ll outline a typical day in the field: the drive out takes about an hour (depending on traffic), with the last ten minutes or so on a pretty bumpy dirt road. We arrive about 8:30, and depending on where we’re trapping we might have a short walk. We have about 160 traps, so we set them all up and bait them in about twenty minutes.
Then, we all spread out so all the traps are visible, and wait for the degus to emerge from their burrows. Usually by about 9am, give or take half an hour (again depending on the weather or the site), the degus are active and foraging. We scan the traps continuously until a degu gets caught, and then the closest handler—post-grads—and processer—graduate students—run to get the animal and procure the initial blood sample within three minutes of the trap closing. The blood is drawn from either leg after shaving the area around the targeted vein, and collected in a capillary tube which holds about 50 microliters, or 0.05 milliliters. Another non-time dependant blood sample is taken at the capture site for a different project, this time about 0.5 milliliters. We take the animal back to our “home base,” and mark the animal with two numbered ear tags. These make sure we know which individual each blood sample comes from, and we can easily ID recaptures (which we don’t re-bleed). We weigh the animals, which are typically about 150-180 grams. We measure the anal-genital distance, a proxy for many things including the degree of female masculinization due to intra-uterine positioning. Finally, we check the animal for ectoparasites by combing its fur with a certain standardized procedure; that’s the end of the first round of processing. We keep the animal caged while successive blood samples are taken over the next two hours, during which feces samples accumulate and are collected, and then we can release it. To avoid instant recaptures, we usually wait to release all the animals until the end of the day. In addition to trapping the degus, we also take some environmental data for different burrow systems: we measure soil hardness, sample vegetation biomass, and measure the distance to nearest cover.
That’s an outline of a day in the field. Depending on how quickly we’re catching animals and how many we want to catch, we’ll leave the site 2:30-5:30. Once we’re back in the city, we take the samples to the lab we use at the Pontifica Universidad Catòlica de Chile. All the samples are spun down in a centrifuge to separate the hematocrit (red blood cells) from the serum, where all the hormones we’re looking for will be. We measure the ratio of hematocrit to total blood volume, and then draw out the serum to store in a freezer until it can be analyzed back in the US. We also weigh all our feces and vegetation samples, which we’ll eventually dry out and re-weigh to determine water content. Again, depending on how many samples we have, this process can take up to an hour and a half.
There are many challenges to this whole process we’ve come across. I’ll just mention a couple: we usually don’t have any trouble getting the first bleed done, but some individuals
approach escape attempts with vigor and slow down the process a bit. If we catch lots of animals, there’s a lot of different bleeds to keep track of, and it’s easy to mix up samples. Also, particularly at the boulder field, we’ve had a couple of foxes come through the area we’re trapping and catch the degus. I think it’s safe to say monotony will be very unlikely in my two months here.
The first week and a half, we were trapping in an open field and along a hillside, and finished up catching about twenty individuals. We’ve now just finished trapping in a boulder field, which saw thirty individuals. Some days see more activity than others, depending largely on the weather conditions. Foggy and colder days tend to produce less captures than sunny and warmer days, and we don’t go out at all if it’s raining a lot. And, even though we’ve fallen into a good rhythm now, there’s still a lot to learn and exciting things happen every day. Sometimes foxes will come through the area we’re trapping and snatch up a degu (which could be an individual we’ve tagged). Also, I need to update my own post a bit: I mentioned that the grad students are the bleeders and the post-grads are the handlers, but the last couple of days I’ve been learning how to bleed myself! After a couple practice rounds, I took three real samples on Thursday.
Okay, so that’s an introduction to the work we’re doing here. Next time I’ll focus on play, i.e. a trip to the Andes we took last weekend and a trip we will be taking tomorrow. I’ve also added some more pictures to my album, so check it out!