Optimal concentrations in nectar feeding

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra- tion makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We iden- tify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we deduce the dependence of the volume intake rate on the nectar viscosity and thus infer an optimal sugar concentration consistent with laboratory mea- surements. Our results provide the first rationale for why suction feeders typically pollinate flowers with lower sugar concentration nectar than their counterparts that use viscous dipping.