Alarming declines in bird abundance in an Afromontane global biodiversity hotspot

Many natural ecosystems in tropical regions are under immense anthropogenic pressure, mostly connected with forest logging. However, several other factors may play important roles. From a conservation perspective, it is important to assess the impacts of these changes in biodiversity hotspots, but adequate data are scarce. We repeated point-count bird monitoring at 29 count-points in an Afromontane ecosystem near Big Babanki in NW Cameroon after a 13-year period. Between the censuses in 2003 and 2016, we found a decrease in bush cover and an increase in herb layer, whereas tree cover did not change. Consequently, we found a decrease in the total number of bird individuals per count-point driven by a decrease in the abundances of shrubland species, mainly nectarivores and granivores (e.g., Northern double-collared sunbird, Black crowned waxbill, Oriole finch, Thick-billed seedeater or Baglafecht weaver). In general, the decrease was found in nectarivore species that depend on flowering bushes (mainly Hypericum spp.). Similarly, we found a decrease in approximately half of the granivore species that often use bush cover for nesting and feeding. Additionally, one large fruit feeding bird, the Great blue turaco, became nearly extinct probably due to hunting activity. The observed contraction of bush cover accompanied by shrubland bird declines possibly results from a decrease in humidity in the area that was indicated by remote sensing. This may be caused by montane forest loss and fragmentation during the second half of the 20^th Century. Our findings uncover the long-term consequences of deforestation which are rarely considered, even though they impact key ecosystem functions.