Nectar: an energy drink used by European songbirds during spring migration

Nectar exploitation by European birds mainly refers to passerines feeding on exotic plants, although some recent studies described nectar-feeding by trans-Saharan passerines on local plants. We examined which birds and plants are involved in nectar consumption and investigated the consequences of nectar use on plasma blood glucose concentrations during spring migration at a stopover site in the central Mediterranean. We recorded 12 opportunistic nectar-feeding species, with Sylvia warblers in particular showing a marked nectarivory, and 6 plants used by birds, no one of which shows typical "bird flowers" features. Moreover, we demonstrated that nectar uptake led to an increase in plasma glucose concentrations and that nectar was drunk not only by birds in poor physical condition. The nectar consumption is fully in accordance with time-minimising migration models, allowing birds to obtain water and energy at stopover sites in a short time: nectar is easy to find and quick to digest.