2.2 Bee behaviour and Visitation Rates
To test if robbing leads to altered behaviour of bumblebees, we recorded several aspects of visitation. Firstly, we tested whether robbing would cause a change in visitation rates, by quantifying the number of visits per flower per hour on plants in both treatments when in full bloom. We also recorded the identity of bumblebee species that visited when conducting censuses. Plants were arranged in a line, separated by about 1 meter, with alternating treatments and the individuals within each treatment had their positions randomised. We recorded counts of each bumblebee species visiting flowers on control and robbed treatment plants and used 644 3-minute censuses to quantify visitation rates in 3-hour periods that covered different times of the day when floral visitors were active. Secondly, we also measured potential effects of robbing on the duration of floral visits by bumblebees. We recorded with a stopwatch the length of visits to individual flowers, defined as the time between entering a flower to feed and appearing at the mouth of the corolla to exit it.
Bumblebees typically visit several flowers on a foxglove inflorescence in each foraging bout, so to test whether robbing had an effect on a continuous foraging bout we measured the proportion of flowers on an inflorescence that individual bumblebees visited per foraging bout. Finally, we also recorded the number of times a plant in a treatment was ‘rejected’, defined as a bumblebee hovering near flowers and leaving without landing, or landing on the flower and leaving without entering.