Soundscapes and Dummy Caterpillars
... Fieldwork in the Forest Canopy
I have just finished my last field season collecting data in the ConFoBi plots. This was my third spring collecting soundscape recordings, which contain bird songs from the dawn chorus—a phenomenon where birds are most vocally active just before sunrise, which is not yet fully understood. Normally I make recordings in the understory by securing one recorder in each plot centre, about two meters high on a tree trunk. This field season, however, was different. I learned how to climb trees through an arborist course last autumn, and this spring was able to duplicate my recording process high in the forest canopy. We recorded trees with heights above 35 metres! Learning to tree climb was a long-term dream finally come true, and to do it for scientific research was even better. With this data, I will spend the next several months analyzing how canopy soundscapes differ from those recorded the understory, and why. Is it because of the physical properties affecting sound propagation? Is it because different bird species call from different heights, creating a series of vertically layered soundscapes in one forest plot?
Because canopy experiments are resource-intensive, we used the opportunity to simultaneously conduct a sentinel prey experiment pertaining to João Periera’s B6 project. Among other topics, João is interested in the predation of caterpillars by birds. In order to quantify such a relationship, we made dummy caterpillars and used wire to attach them to twigs amongst leaves. We collected them a week later to inspect them for bites and peck markings, which yields a relative predation rate per site. We selected beech (Fagus sylvatica) trees in ConFoBi plots that met specific criteria (sufficient ranges of DBH, height, crown size and neighboring tree species diversity, to name a few). In a ten metre radius around these trees, João placed 20 plasticine caterpillars in the understory and I replicated the experiment above. We did this in two teams, with the help of one research assistant and three other tree climbers. One week later, we revisited the same trees and tried to find all the caterpillars, which felt a little like searching for a green needle in a haystack. Often we were able to find them all, but we certainly hit unexpected stumbling blocks, for example due to rainy weather, which was relentless for six out of the eight fieldwork weeks. After the first week, we revisited our caterpillars to find empty wires… most of our caterpillars had dissolved! We switched to another water-resistant material and then we found not only our caterpillars, but some of them indeed had peck marks from birds! Now we will process all of our data and test our hypotheses. I hope this last field season with ConFoBi is just the beginning of lifelong research in the canopy, but no matter what this was certainly a field season I will never forget!
by Taylor Shaw (B7)
