Nectarivory of Palearctic migrants at a stopover site in the Sahara

Nectarivory of long-distance Palearctic migrants is known from Europe but there are few reports of nectar as a resource for migrants in Africa. Migrants feeding on nectar were regularly observed in the oasis of Ouadâne, a stopover site in the western Sahara, Mauritania, in spring 2003 and 2004. Migrant species observed consuming nectar were Eastern/Western Olivaceous Warbler Hippolais pallidalopaca, Orphean Warbler Sylvia hortensis, Common Whitethroat S. communis, Subalpine Warbler S. cantillans, Common Chiffchaff Phylloscopus collybita and Willow Warbler Ph. Trochilus, which took nectar from five tree species (Balanites aegyptiaca, Maerua crassifolia, Capparis decidua, Acacia raddiana, Ziziphus mauritiana). Flowering trees were available throughout the entire presumed migration period and, as well as providing nectar, they attracted many insects. We suggest that the phenology of flowering trees might be crucial for bird migration in spring, and might offer a solution to the phenomenon known as ‘Moreau’s paradox’, i.e. that migrants successfully lay down fuel reserves prior to spring migration during the dry season, when potential resources are thought to be at their lowest.