Migrant 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 migrants 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, as well as to conditions on British breeding grounds. BTO research published last year showed that although conditions in Africa can ‘carry-over’ and affect the timing of nesting in this country, the most important factor influencing breeding was spring temperature in the UK. A new study by the BTO and the University of Sheffield builds upon the work by considering the impacts of climatic variation in passage regions, as well as the breeding and non-breeding grounds. It focuses on three declining migratory species of regional conservation concern in Europe - Redstart, Wood Warbler and Spotted Flycatcher. Long-term data from the Nest Record Scheme revealed that the strongest factor influencing timing of breeding was temperatures in the Mediterranean during spring migration, with warmer conditions leading to earlier breeding. This may be because warming enhanced food availability during stop-overs, increasing migration speed and improving birds’ condition upon arrival. Redstarts and Wood Warblers, but not Spotted Flycatchers, bred earlier in years with warmer springs in the UK. Overall the study showed that warmer Mediterranean temperatures during spring migration influenced breeding performance more than temperatures on the breeding grounds. It also confirmed the relatively weak effect of climatic conditions in Africa, although conditions in the Sahel influenced redstarts’ breeding success. The work has important implications for the conservation of these declining species and emphasises the importance of conditions during spring passage.

Scotland has a target to generate 100% of its energy from renewable sources by 2020. The country therefore has a large number of offshore sites where marine renewable developments (including wind, wave and tidal-stream installations) are proposed or under construction. As any existing developments have only become operational in recent years, and are only few in number, the effect they have on marine ecosystems is not yet properly understood. Scotland is home to over 60% of the world’s breeding Great Skuas, and principal colonies are protected under the European Birds Directive. Breeding success at many of these sites has been low in recent years and Great Skua numbers have fallen. The effect of marine renewable developments on these internationally important breeding populations could be detrimental, for example if birds fatally collide with wind turbines. It could also be beneficial if, for instance, installations act as fish aggregating devices that provide an abundant and predictable source of prey. A new study by the Environmental Research Institute at the University of the Highlands and Islands, the University of Amsterdam, the University of Glasgow and the BTO has examined these potential effects, using long-life GPS tags to reveal the movements of Great Skuas on Hoy (Orkney) and Foula (Shetland) throughout the breeding season and characterise their use of the marine environment. The study found that the movements of Great Skuas did not overlap to a great extent with areas of the sea where marine renewable developments are proposed. The largest overlap was with wave power installations, which are thought to pose a low risk to this species. However, the degree of overlap varied throughout the season and between colonies, with birds whose breeding attempts failed ranging over a larger area of sea than birds that were incubating or caring for chicks. Historical records of nest attendance also indicated that Great Skuas travel further during the breeding season than in the past – trips that took half an hour in the 1970s now take up to four hours. This could be linked to declines in sandeel abundance, a key prey species for Great Skuas, due to overfishing and climate change. Taken together, the findings of this study show that assessing the potential impact of marine renewable developments on Great Skuas is complex. This long-lived species uses different parts of the marine environment at different times of the year, and might be flexible in choosing where to go depending on prevailing conditions. Tracking can help to assess the effect of planned marine renewable developments, but long term studies in conjunction with thorough monitoring are essential to fully understand the conservation implications for Great Skuas and other seabirds.