Estimation of population density of Eidolon helvum on the island of Principe, Gulf of Guinea

Eidolon helvum is a widespread African fruit bat. It is migratory and can form colonies of millions of individuals. On Principe, in the Gulf of Guinea, there are seemingly large numbers of E helvum. Here, they have lost their migratory behaviour and rely on the availability of the year-round food resources on the island, which is small (128 km(2)) but is dominated by both primary rainforest and fruit-tree plantations. We visited the major roost for E helvum on the island. Exit counts carried out on two consecutive nights showed the roost was used by between 10,539 (SE +/- 67) and 14,160 (SE +/- 324) individuals. Compared to mainland Africa, the colony was small, no doubt constrained by the size of the island. Nonetheless, Principe still supports a considerable density of E helvum of between 82 and 111 bats/km(2), which is comparable with densities found on mainland Africa.