The Montagu's Harrier (MH) and the Lesser Kestrel (LK) are two threatened raptors overwintering in the Sahel. To ensure their conservation, it is essential to gain better knowledge on their winter ecology in order to predict their spatial distribution and estimate their respective population sizes. Combining information on raptors, their prey and habitats, collected over the 2009-2013 period in a 17,000 km(2) study area located in central Senegal, we assessed spatio-temporal variations of grasshopper density, and consequently estimated the abundance and distribution of MHs and LKs. The distribution of grasshoppers highlighted areas with contrasted densities, declining along a North East/South West gradient which constrained the spread of raptors. Moreover both species selected heterogeneous landscapes of savannah, mixing semi-natural and anthropogenized habitats. Population size reached 3360 and 36,000 individuals for MH and LK, which represents similar to 5% and 50% of their European breeding populations. The challenge for their conservation resides in their use of habitats suffering from anthropogenic perturbations, both during breeding and wintering. In Africa, this situation will be exacerbated in the near future due to interactions between food security, implying the control of grasshopper outbreaks and agricultural intensification, and to ongoing climate changes.