Mangrove forests attract many insectivorous birds. Bird density in West African mangroves in January–March 2014 is higher in Avicennia (21 birds/ha canopy) than in Rhizophora (11 birds/ha). The Palearctic species are dominant in the most northern mangroves (14–16°N), but further south resident birds become as numerous as migrants (11–12°N). The European Reed Warbler Acrocephalus scirpaceus is the most common winter visitor in West African mangroves between 12 and 16°N, with an estimated total of 4–6 million birds, which may account for 30–50% of the European population. The mortality of European Reed Warblers while crossing the Sahara desert in spring is higher when their Sudan-Guinean wintering areas have been drought-stricken in the preceding winter. European Reed Warblers wintering in mangroves suffer the same fate, because mangroves in the Sahel region massively die off in drought years.