Migratory birds are likely to be particularly vulnerable to climate change because they can be affected by changing conditions on the breeding grounds, wintering grounds or passage areas in between. Many long distance migrant birds that breed in the UK and winter in Africa are in severe decline, and previous BTO work has shown this can be related to changing conditions in Africa, which affect overwinter survival, and to conditions on British breeding grounds. New research by the BTO takes this further and considers the potential for changes in conditions in Africa to ‘carry-over’ and affect birds during the breeding season. Rainfall during the growing season in Africa is incredibly important for migrants that winter south of the Sahara as precipitation controls vegetation growth and therefore the abundance of herbivorous insects. Species such as warblers, flycatchers and chats rely heavily on berries and invertebrates to survive through the winter and fuel their journey back to the breeding grounds the following spring. Using a unique dataset collected by volunteers contributing to the Nest Record Scheme over a 46-year period, BTO scientists have demonstrated that the impact of African rainfall on migrant species that winter south of the Sahara does indeed carry-over and influence the subsequent timing of nesting of 19 species, including Sand Martin, Swallow and Redstart. In general, species laid their eggs earlier after wetter Sahel growing seasons, suggesting that they were in better condition and therefore able to leave earlier, travel faster or produce clutches more rapidly on arrival. However, the importance of this effect is relatively small when compared to the impact of spring temperature on the breeding grounds. This suggests that increasing temperatures in the UK are largely responsible for the observed trend towards earlier breeding, even in long-distance migrants. Warm springs are likely to stimulate early laying as they advance leaf growth and therefore the emergence of insects that birds depend on to provision their offspring; studies have shown that a failure to track these advances can have serious implications for breeding success. Changes in the numbers of eggs laid in each nest were also considered, but were largely unaffected by rainfall in Africa, and only weakly related to UK spring temperature. Overall, this research highlights the many factors determining how migrant species are responding to climate change, an understanding of which is vital if we are to effectively protect these birds and address population declines.

Protected area networks, where several sites are legally protected because of their importance for particular species or habitats, are one of the main conservation tools for reducing biodiversity loss. However, it is unclear how effective these networks might be as the species and habitats for which they are designated respond to climate change. New research led by the BTO and published in the prestigious journal Nature Climate Change, provides the most compelling evidence yet that while British bird populations are being affected by climate change, and will continue to be, the network of sites established to protect them under European law is resilient to these changes and will remain so. The UK is home to internationally important populations of breeding seabirds and wintering waterbirds. Sites holding particular numbers of these species are designated as Special Protection Areas (SPAs) under the EU Birds Directive. Scientists used high quality data on the abundance of 62 seabirds and waterbirds collected over 30 years to show that more than half the population trends during this time can be explained by climate change. They then used this information to predict trends until 2080 assuming 4?C global warming. This scenario produced population declines of at least 25% of more than half of species considered, and in some cases falls of more than 50%. Species such as the Arctic Tern, Guillemot, Eider and Bar-tailed Godwit were particularly badly affected. However, other species, like Avocet, Snipe and Common Tern, were projected to increase in numbers. These gains and losses have implications for the designation of SPAs. However, although many sites were projected to lose qualifying species as numbers dropped below the necessary threshold, they were also expected to gain other species, resulting in an overall change in the composition of species protected by a particular area. Such alterations highlight the need for efficient administration and regular assessment of the SPA network, so that it keeps pace with bird population trends.