Overviews of the study sites, study design, and objectives can be found in Forrest & Chisholm (2017, Ecology, doi: 10.1002/ecy.1655) and Wong & Forrest (2021, Journal of Animal Ecology, doi: 10.1111/1365-2656.13460). Study sites are visited every 3-10 days throughout the growing season.
Temperature data are recorded hourly at each site by a HOBO pendant data-logger (light & temperature; Onset Computer, Bourne, Massachusetts, USA) attached to the bottom of one centrally located trap-nest (nesting block). The data-logger is not properly shielded from solar radiation, but it is shaded by the block. The light sensor faces out (=down). The logger is attached by a wire to the pipe-strapping that attaches the block to the tree, and it is additionally secured by another piece of pipe-strapping or wire mesh that supports it against the bottom of the trap-nest (so it isn’t dangling). Typically, the temperature data are downloaded once in the spring (May-June) and again at the end of summer (August). Batteries are replaced at the same time if necessary. Data from all sites and years are compiled into a single data file. One data-logger (at the VB site) failed over the winter of 2013-2014, so those readings are missing. Occasionally, single hourly readings were missed due to errors with time stamps or downloading being done at the time of temperature recording.
As soon as any bee activity or flowering is observed at a site, floral surveys begin at that site (though see below for exceptions). Surveys were done twice a week, as much as possible (once a week at the VB site), from 2013 to 2019. Floral data were not collected in 2020. As of 2021, surveys are done weekly at all sites. Surveys are occasionally delayed by a day or two because of poor weather. The specific flower taxa counted have changed slightly over the years, based on our growing knowledge of which taxa are
used by bees and of which taxa can be distinguished using their pollen. We have also grouped some taxa to simplify sampling, as shown in Appendix A. Floral densities are measured by counting the number of open flowers (or inflorescences, for Asteraceae) seen while walking in an expanding spiral from a fixed, central point; when 100 flowers are reached, we measure the distance from the centre of the site to this flower. Distances under 30 m are normally measured using a surveyor’s tape, to the nearest 0.1 m. Distances greater than 30 m are measured to the nearest metre using a Trimble GeoXH GPS unit. If 100 flowers are not reached within a 100m radius of the centre of the site, “>100m” is recorded for the distance and the number of flowers observed is recorded in the “notes” column. Distances are converted to densities using the fact that the measured distance represents the radius within which 100 flowers were observed.
In the first year of the project (2013), floral resources were quantified only once the first bees began nesting at a site, so floral densities prior to that point are unknown. In all years, the end of flowering may have been missed for some taxa because of the team’s departure from the field station in August. (The last date recorded for a given site in each floral abundance spreadsheet represents the last date on which floral surveys were conducted at that site in that year.)
