Changes in densities of Sahelian bird species in response to recent habitat degradation

Habitat loss in the Sahel region of West Africa has been pronounced, due to anthropogenic effects and (potentially) climate change. Although strong links have been found between conditions in the Sahel and subsequent breeding populations of certain Palaearctic migrants, the effects of these fluctuations upon Afrotropical species are unknown. We repeated bird censuses (Dec 1993 to Jan 1994, Dec 2001 and Dec 2002) at Watucal Forest Reserve, northern Nigeria, an area of rapidly degrading Sahelian woodland. We predicted declines in the abundance of woodland bird species with deforestation. For the purpose of setting up an experimental control, we also repeated bird censuses in adjacent farmland habitats that had already been deforested by the first census period: we predicted no change in abundance of farmland bird species. Tree density at Watucal decreased significantly by 82% over the eight-year period. The number of birds counted per point, the total number of species recorded per point, and the Shannon diversity index, all declined significantly in Watucal, but there was no significant change in adjacent farmland. Of those species that were reasonably abundant in either census period, 22% (n = 41) at Watucal showed a significant change in abundance between periods: all of these species showed a decline. In contrast, only 4% (n = 23) showed a significant change in abundance (a decline) on farmland. Of the seven species that disappeared from Watucal between periods, 100% were classified as broadly woodland species and, of the eight species that were only recorded in 2001/02 at Watucal, 63% were classified as scrub or open species. Given that Watucal is a protected area, the degree of deforestation and concomitant changes in bird abundance suggest that the Sahel is likely to be undergoing major changes in bird diversity.