Friday, November 21, 2014

Teaching mark-recapture with dor beetles

The key step in the planning of any good field course is to spend some time at the field site observing and asking questions. What is the habitat like, what lives there, what are the facilities, what are potential challenges or dangers to working there, etc? When I first went to do this at Svanninge Bjerge, the location of my zoology field course, I immediately started seeing big blue dung beetles all over the place. Bikuben Foundation, who operate the place, run cattle there. There is no lack of dung. These big plodding dor beetles (Geotrupidae) were all over the place, and it didn't take me long to decide I wanted to work them into the course. I wanted to introduce mark-recapture methods, and these seemed like perfect subjects. Mark-recapture methods involve catching animals, marking them in some way that would allow them to be recognized if re-sighted, letting them go, and then trying to recapture them. Such methods have a huge range of applications from tracking individual movements and estimating population sizes to monitoring growth and survival and studying behavior and sociality. To teach this in a field course, I wanted an invertebrate animal that wasn't too likely to leave the study area, that is easy to capture, mark and handle without damage, and that has enough charisma to capture students' attention. Dor beetles have all this. They are big and slow, and so easy to find and catch by hand. They don't bite or sting. They will collect in large numbers in pitfall traps baited with cow dung. They have big hard upper wings (elytra) that can be marked in any number or ways without harming them (we used this system with nail polish, but I've now got a battery-powered cautery). They are extremely numerous. They are shiny and blue. They can fly, but don't often do so.
Students mark a live beetle for release. Photo by Kim Lundgreen.
They make such an ideal intro to mark-recapture that I almost worry that I've given the student a false sense that this is easy, where in fact such studies are often very hard work. Still, if you want an efficient system for teaching mark-recapture methods and have beetles like this at your location, I strongly recommend them to you.

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