Discrimination of small sugar concentration differences helps the nectar-feeding bat Leptonycteris yerbabuenae cover energetic demands.

Every day nectar-feeding animals face an energetic challenge during foraging: they must locate and select flowers that provide nectar with adequate amounts of sugar to cover their very high energy needs. To understand this decision-making process, it is crucial to know how accurately sugar concentration differences can be discriminated. In a controlled laboratory setting, we offered the nectar-specialist bat Leptonycteris yerbabuenae the choice between different sugar solutions covering the entire concentration range of bat-pollinated plants (3-33%). When feeding on solutions below 10% sugar concentration, L. yerbabuenae were unable to cover their energetic demands because of physiological constraints. Their ability to discriminate sugar concentrations was better than that of any other nectar-feeding animal studied to date. At sugar concentrations below 15%, L. yerbabuenae can discriminate solutions differing by only 0.5%. The bats may utilize this fine-tuned ability to select nectar from flowers with reward qualities that provide them with the necessary amount of energy to survive.