Geolocator tracking has revealed the West African wintering grounds of UK-breeding Wood Warblers for the first time.
Wood Warbler is a Red-Listed summer visitor to the UK, where the breeding population has crashed by two-thirds since 1995.
Recent decades have seen serious declines in many migratory birds that spend the winter in Africa, but a lack of information about their lives after they leave Europe has hampered attempts to understand why this is.
Reasons for Wood Warbler's steep decline have so far remained unclear, but researchers from the British Trust for Ornithology (BTO) and RSPB hope that may be about to change, with knowledge provided by a recently published study set to help uncover the threats the birds face at each stage of their long annual journeys.
The UK's breeding population of Wood Warbler has declined by two-thirds since 1995 (Paul Coombes).
By fitting tiny geolocators to four Wood Warblers breeding on Dartmoor and in the New Forest, scientists found that the birds migrated in a clockwise loop that began with their departure from the UK in late July. They spent most of August in central-southern Europe before crossing the Sahara in a non-stop flight lasting around 36 hours.
After a short stop just south of the desert, the tracked Wood Warblers spent around two months at a stopover to the south-west in the Sahel. They then continued south-west to the tropical forests of Liberia and Sierra Leone, where they spent the rest of the winter. The data from one bird showed it did not return to Europe via its outbound route, but instead crossed the Sahara further west and continued north via Spain and France.
Assessing the threats migrant birds face throughout the year – not just after they arrive in the UK – is key to ensuring their continued survival. Now that the Wood Warbler's main stopover and wintering sites have been identified, conservationists are one step closer to understanding the true impact of climate change, habitat loss and other factors on this delightful woodland songster.
Dr Chris Hewson, BTO author on the paper, said: "Many of our most charismatic birds are essentially African species which migrate here to breed, but until recently we have known little about how they spend their lives away from these shores. Tiny tracking devices are now changing that, illuminating our lives with new understanding of these birds and hopefully moving us towards being able to do something about their declines."
Dr Malcolm Burgess, lead author, commented: "Most birds that migrate to sub-Saharan Africa have seen huge population declines over recent decades. Understanding why migrant birds are struggling is very challenging, partly because there are so many places to look for the problems that it can be hard to know where to start. This new research is an important step forward."
Burgess, M, Castello, J, Davis, T & Hewson, C. 2022. Loop-migration and non-breeding locations of British breeding Wood Warblers Phylloscopus sibilatrix. Bird Study. DOI: https://doi.org/10.1080/00063657.2022.2138825