Daily average plots of the foraging activity under continuous daylight conditions in the field. The top row shows daily average plots of the Bombus terrestris colonies observed at Kilpisjärvi Biological Station, Finland, in the summer of 2007 and the bottom row shows the data for the colonies observed in the summer of 2008 at the same location. Numbers in brackets indicate the number of tagged workers meeting the requirements to be included in the circadian analysis per colony. Each bar represents an hour of the day and the height of the bars indicates the level of activity.
Stelzer and Chittka BMC Biology 2010 8:93 doi:10.1186/1741-7007-8-93