Fig. 3. The daily timing of foraging flights in the nocturnal bee Megalopta genalis. Megalopta is active during two short time intervals each day, once in the morning (A) and once in the evening (B), when light levels at the nest (blue symbols) can be lower than 10^–4 cd m^–2. The number of bees leaving the nest (green bars) and returning to the nest (red bars) in 5 min intervals is shown relative to sunrise or sunset (0:00 h). Data were collected over several nights from several nests during two successive years on Barro Colorado Island (Panama). (A) The timing of foraging trips in the morning. The grey area indicates the time before astronomical twilight. (B) The timing of foraging trips in the evening. The grey area indicates the time after astronomical twilight. During the time interval between the onset of astronomical twilight in the evening and its offset in the morning, no light from the sun is present in the night sky. Modified with kind permission from Kelber et al. (Kelber et al., 2006).