African bird species could struggle to relocate to survive global warming because natural features of the landscape will limit where they can move to, according to new research published in June in Proceedings of the Royal Society B. As the global climate changes, some land bird species will be forced to move to new habitats, expanding and shifting their natural geographical 'range', in order to maintain suitable living conditions. The research team behind today's findings from Imperial College London says, however, that some sub-Saharan African species are in danger of getting trapped in environments that will become too hostile for them to survive. Birds may not be able to move across areas containing dramatically different kinds of landscapes, such as arid plains, tropical forests or mountain ranges. This is because these different natural features of Africa's landscape present such uniquely difficult survival challenges for species not already adapted to live across multiple habitats. This may prevent species from completing their journeys to new homes with suitable climates.
Lead author of the new study Lynsey McInnes, a PhD research student at the Grantham Institute for Climate Change at Imperial College London, explains: "As the climate changes and some habitats become inhospitable, bird species may start to move - stretching their ranges as they track the changing climate across the landscape, looking for new, agreeable habitats. "Our study suggests that these vital movements could run into difficulties if the birds' escape routes cross regions that they're not well adapted to survive in - such as mountain ranges, arid plains or tropical forests. These regions create barriers which many birds cannot cross because they do not provide the right kind of food and shelter."
Every species has a unique geographical range, which encompasses all the places it can be found. Ms McInnes and her colleagues from Imperial's Department of Life Sciences overlaid and analysed digital maps of the current geographical ranges of nearly 1900 species of sub-Saharan African land birds. They found a number of key locations where a large number of species' ranges come to an abrupt end, and realised that these 'barriers' correspond with dramatic changes in Africa's terrain, vegetation and topography. For example they found a large number of ranges, including those of the Congo Serpent Eagle and Violet-Tailed Sunbird, which end where the tropical rainforests of central Africa meet the surrounding savannah. Similarly they found that lots of species' ranges end on the slopes of the Eastern Arc Mountains of Kenya and Tanzania; examples include mountain-dwelling species such as the Usambara Eagle Owl and Udzungwa Forest Partridge, which do not expand their ranges into the surrounding lowlands.
The fact that so many species are currently constrained by these landscape barriers – even species such as the Namaqua Dove and Copper Sunbird whose naturally large ranges span a range of savanna and grassland habitats, but end at the boundaries of the rainforests - indicates that they may be almost impossible to pass. This is a concern if species need to make unusual journeys as the climate changes, says Dr David Orme from the Department of Life Sciences at Imperial College London: "We hope to combine our data showing the locations of these 'barriers' with African climate projections, so we can predict species which may be most at risk of getting stuck if they try moving to escape climate change. If we can pinpoint species that may run up against these natural barriers, conservationists may be able to help them across, perhaps through assisted migration programmes."
Professor Sir Brian Hoskins, Director of the Grantham Institute for Climate Change at Imperial, which funded the research, said: "This study highlights the scope of problems animals across the world are facing as the climate of their natural habitat changes. I hope that through studies like this, we can increase our understanding of these challenges and be better placed to help species adapt to the climatic changes we've caused, and that they will provide more ammunition for deciding to limit those changes as much as we can." - ICL