Potential impacts of climate change on birds in the Albertine Rift: a baseline study of Bwindi, Echuya, Nyungwe and Kibira forests

Abstract

The Albertine region is an area of high endemism consisting of a network of mountainous protected areas of diverse habitat types. Birds were surveyed in Bwindi, Echuya, Nyungwe and Kibira forests using point counts along altitudinal gradients ranging from 1480 to 2937 metres above sea level. One hundred and sixty two (162) bird species were recorded during the surveys, including 24 species endemic to the Albertine Rift. Forty two (42) species including 14 endemics were examined in detail to relate their distribution to altitude and habitat, and to assess the potential impacts of climate change on their future range in the Albertine Rift. The distributions of many organisms, birds included, are often limited by altitude and by habitat requirements. Understanding these requirements is necessary to identify areas to prioritize for conservation and as an essential first step to protect them from the impacts of human induced environmental change. I used generalized additive models (GAM) to relate species occurrence to altitude and generalized linear models (GLM) to explore habitat relationships using presence/absence data of the bird species. To assess potential impacts of climate change on the birds, I used GAM models to relate species occurrence to climate (i.e. Species distribution models) and applied the resultant models to potential future climates to project future species distributions. Future climates were based on three general circulation models (GCMs): European Centre Hamburg Model (ECHAM5), Geophysical Fluid Dynamics Laboratory (GFDL2.1) and Hadley Centre Global Environmental Model (HADGEM) for three future time periods centred on the years 2025, 2055 and 2085. I demonstrate that altitude and habitat types contribute to the distribution of the birds and that climate change will influence the altitudinal distribution of birds in the Albertine rift. Most of the endemic species (64%) were encountered more frequently at higher altitudes (>2500m) while most of the widespread species (68%) were encountered more frequently at mid elevation altitudes (2000-2500m). Closed and mixed forest habitats were found to have more species than any other habitat, being positively related to the distribution of 28 and 23 species out of 42 species respectively. Bamboo and savannah woodland were found to have the least species; being important for 16 and 17 species respectively out of 42 species. Most endemic species were found to occur in closed and mixed forest habitats while most widespread species occurred in closed-forest, mixed-forest and swamp. Only two species; Kungwe Apalis Apalis agenta and Grey Apalis Apalis cinerea occurred in only one habitat type (closed-forest). The ratio of actual to potential evapotranspiration (APET) was the most important climate variable in determining species distributions (important in models for 40 of 42 species analysed) while mean temperature of the coldest month (MTCO) was the least important variable (important in models for 13 of 42 species). Most of the species relationships with both APET and MTCO were negative. Most of the endemic species were projected to shift their range upslope in future, especially in Nyungwe National Park, to track suitable climate. At other sites most of the endemics were projected to find limited suitable climates with altitude. Most widespread species were projected to shift their range downslope as more suitable climates were simulated for them at lower altitudes in future at the four study sites.