This project was initiated in May 2013 to study populations of cavity-nesting bees at sites varying in elevation (and, thus, in temperature, phenology, and frost risk). The initial goal of the project was to determine the relative impacts of temperature variation and floral resource availability (which itself might be affected by temperature, via frost damage to flowers) on bee populations by monitoring the reproductive output of individual bees nesting in experimental trap-nests. However, it quickly became apparent that most of the flowers upon which the bees were most dependent were not particularly frost sensitive, such that frost was not likely to have a major impact on floral resource variation among sites or years. Thus, that aspect of the initial objectives was dropped, but the goal of understanding factors regulating bee populations remained. The initial results of this project (for Osmia iridis only) were published as Forrest & Chisholm 2017, Ecology. A subsequent paper (Wong & Forrest 2021, J. Animal Ecol.) includes a more comprehensive analysis of the reproductive output of multiple bee species, using the data up to 2018. Ongoing data collection aims to assess the impacts of drought on bee populations, and the effects of spring temperature on phenological synchronization between bees and their floral host-plants (as well as the fitness consequences for bees of any changes in synchrony). The project has also documented nesting phenology and abundance of cavity-nesting wasps (mainly eumenine vespids), though these have not been the primary focus.