Objectives of the Eidolon helvum colony counts
How many bats are there, and when?
The goal of this project is to monitor the populations of an ecological keystone species, Eidolon helvum or straw-coloured fruit bat, for vegetation regeneration across sub-Saharan Africa. Eidolon helvum stands out among African fruit bats for its long-distance migrations. However, we do not understand yet why the species migrates and what routes the bats take. Eidolon helvum is listed as "Near Threatened" by the international IUCN Red List, due to marked population declines. While our target species is threatened by unsustainable hunting, the negative perception it faces also plays its part, and too often we hear of roost destruction or targeted disturbances. Another important factor is deforestation. Monitoring through regular counts to assess population sizes as they also change as a result of migration will be key to develop effective conservation measures.
What have we found so far?
While E. helvum forms large colonies in many locations (at least seasonally), appearing to be a highly abundant species, previous count data confirm a steep decrease in numbers at several important roost sites (for example in Accra, Ghana). Regular and standardized colony counts in as many places as possible are crucial to better document and understand this population development.
We believe that concerted efforts are needed to protect E. helvum for the future, and to maintain its important ecosystem services. To achieve these goals and to increase awareness for the vulnerability even of common species in the global biodiversity crisis, we want this to become the largest monitoring program for a single species across Africa.
Our long term monitoring project depends on the support of multiple actors and committed local volunteers - from experienced scientists and upcoming conservationists to interested citizens. You know of an E. helvum roost near you, but you don't see it here? Then why not go and count it? Let us know - you are welcome to join us!
Further research goals
Seasonal E. helvum colonies appear to correspond with the initial greening of the landscape, here measured in NDVI (normalized difference vegetation index). We are using count data to explore if bats are "surfing the green wave," by tracking the instantaneous rate of green up across the landscape and arriving at large colony sites during peak green up.