Laursen K., Holm E. & Sorensen I. (1997) Pollen as a marker in migratory warblers, Sylviidae. ARDEA 85 (2): 223-231

Pollen were analysed in pollen horns accumulated at the base of the bill when birds forage in flowers. Among five warbler species, Sylviidae, caught in spring in Denmark, 1.8% (n = 766) of all individuals carried pollen horns from spring flowering plants, although the proportion of horns varied between species (ranged from 0.4 to 4.4%). In contrast, only one individual captured in autumn had pollen horns (n = 655) which contained pollen from spring flowering plants. The analysed horns contained predominantly pollen of plant genera Eucalyptus and Citrus restricted to the Mediterranean; these plant species occurred almost mutually exclusively amongst the collected pollen horns. The results indicate that the Mediterranean is an important stopover area for some warblers during spring migration, and demonstrate within and between species differences in feeding plant species.