Carry-over effects from passage regions are more important than breeding climate in determining the breeding phenology and performance of three avian migrants of conservation concern

Wood Warbler. Photograph by Edmund Fellowes

Author(s): Finch, T., Pearce-Higgins, J.W., Leech, D.I. & Evans, K.L.

Published: January 2014  

Journal: Biodiversity and Conservation Volume: 23 ( part 10 )

Digital Identifier No. (DOI): 10.1007/s10531-014-0731-5

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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.

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