Joshua Botti-Anderson - June 2018

In my previous report, I described the process we undertook to construct and place 16 trap-nests, which are being used to sample cavity-nesting bees and wasps in urban, as well as in agricultural and semi-natural habitats in and around Bozeman. At the time of writing, the project is in the midst of its data collection phase, where trap-nests are checked, and completed nests returned to the lab to be processed and stored. The plan is to continue this from now through September, since it matches the period of time in which cavity-nesters are active and ensures a more accurate diversity assessment. A narrower window of sampling, for instance, would likely only capture species that happen to be more active during just part of the summer. Prior to my first sampling excursion, I was informed that it is still fairly early in the season for cavity-nesters, at least in regard to their nest-provisioning activity. As such, I expected to observe few end caps, which signify a completed nest (and thereby sentence the nest to be harvested by me), during my first samplings of the nests. To my excitement, my visitations to the trap-nests have already yielded completed nests, albeit not (yet) from every location.

(Trap-nest with completed nests; photos courtesy of Joshua Botti-Anderson)

Important supplies that I bring along during my trap-nest visits include spare cardboard tubes (for replacement when completed nests are harvested), ventilated plastic bags, and a hemostat. Completed nests are identified by a cap of mud or debris, which I then pull from the trap-nest by grasping the edge of the tube with the hemostat. End cap composition can provide an indicator of which species provisioned the nest and, along with nest densities and diameters, will provide much of the data prior to that recorded following the emergences next spring. These are then transferred to a ventilated plastic bag labeled with the date and location. Once returned to the lab, these nests are isolated to their own glass tubes, which are ventilated with mesh that prevents emergent bees or wasps from chewing through. While most offspring will grow to their pre-diapause stage prior to a cool overwintering, some may complete development and emerge as ‘second generation’ adults during the summer. These early emergences may offer me an opportunity to begin identifying the nest occupants this summer, although I will have to wait for the vast majority next spring when they are reared following a winter cooling period.  

Urban areas are highly disturbed and constantly modified habitats, contrasting agricultural and semi-natural areas, which are likely more suitable for cavity nesting bees and wasps. Once the data has been collected, I will be guided by my mentors in data analysis, which will be conducted this fall, and next spring (when the identity of emerging adults is determined). I am excited to see results relating to nesting density, tube diameter, and species composition for different sites, as they will have implications for the habitat suitability and diversity of cavity-nesters in urban environments. As stated in my previous blog post, I hypothesize that urban locations will be less diverse and have fewer cavity-nesting bees and wasps than the semi-natural and agricultural sites sampled in this study. It will be interesting to see, after the data analysis is complete, how our results compare to previous work done on cavity-nesters in urban environments.

Besides checking the trap-nests for completed nests, a secondary part of routine visits to the field sites is to ensure that these biodiversity assessment tools are still ‘functioning’ properly. The usefulness of trap-nests for this kind of study relies on all of their essential components, especially the cardboard tubes used to harvest completed nests, remaining unaltered and securely in place. While not entirely unexpected, a simple but inevitable obstacle I have experienced is tampering by wildlife. An important aspect of the study design was to prevent human interference, but field sampling will always be subjected to the whims of mother nature. Birds will pull the cardboard tubes out of the trap-nests, and spiders will make their webs inside of them, effectively disturbing the cavity-nesters or confounding the sampling process. The latter effect would mainly be cavity-nesters constructing nests within the empty wood holes instead of the carboard tubes, preventing removal and replacement throughout the summer. Luckily, it is easy enough for me to clear out spider webs and replace or push in the cardboard tubes when I check each trap-nest.

(Left: nesting tubes pulled out of place - also, can you spot the visitor? Right: spider web in tube entrance; photos courtesy of Joshua Botti-Anderson)


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