The populations of many migrant birds have been in decline for decades, prompting research to understand the nature of these declines so that they can be addressed. The highly complex annual cycles of migrant birds, with their long migration routes and a dependence on different sites at different times of the year, makes it very difficult to identify the drivers of decline and to implement conservation action. While our knowledge is still incomplete, can we afford to wait until we have all of the answers?
The global long-term decline of migrant birds represents an important and challenging issue for conservation scientists and practitioners. This review draws together recent research directed at the Afro-Palaearctic flyway and considers its implications for conservation. The greatest advances in knowledge have been made in the field of tracking. These studies reveal many species to be highly dispersed in the non-breeding season, suggesting that site-level conservation at a small number of locations will almost certainly be of limited value for most species. Instead, widespread but ‘shallow’ land-sharing solutions are likely to be more effective but, because any local changes in Africa will affect many European populations, any impact will be extremely difficult to detect through monitoring in the breeding grounds. Targeted action to boost productivity in Europe may help to halt declines of some species but reversing declines for many species is also likely to require these ‘shallow’ land-sharing approaches in non-breeding areas. The retention or planting of native trees in the humid and arid zones within Africa may be a generic conservation tool, especially if planting is concentrated on favoured tree species. Overall, and despite a growing knowledge, we remain largely unable to progress beyond general flyway-level actions, such as maintaining suitable habitat across an increasingly anthropogenic landscape for generalists, targeted site-based conservation for specialists and at stop-over sites, protection of species from hunting, and individual species-level solutions. We remain unable to assess the cost-effectiveness of more specific conservation action, mainly because of uncertainty around how migrant populations are affected by conditions during passage and on the non-breeding grounds, as well as around the efficacy of implementation of actions, particularly in non-breeding areas. For advances in knowledge to develop and implement effective conservation, scientific approaches need to be better integrated with each other and implemented across the full annual cycle. However, we urge the immediate use of available scientific knowledge rather than waiting for a complete understanding, and that any action is combined with species monitoring and adaptive management across the flyway.
Developing solutions to tackle a population decline usually requires an understanding of whether the decline is being driven by poor breeding success or poor survival. The work that has been done so far for declining migrant birds has tended to focus on single species or single sites. Very little of this work has looked at small migrant passerines, so there are plenty of gaps in our current understanding.
This review paper examines the most recent research from the Afro-Palaearctic flyway, linking European breeding grounds with their African wintering areas, and assesses whether we have filled enough of the knowledge gaps to be able to take action now.
The study highlights the significant advances in the use of tracking technologies; meaning we now know much more about where our summer visitors spend the winter, and the routes and sites they use during migration. These tracking studies indicate that many migrants are highly dispersed during the winter months, rather than concentrated on a small number of wintering sites. This suggests that site-level conservation – locating and protecting key sites – is likely to be of limited value.
Instead, we need conservation solutions that improve the value of wintering habitats more widely across Africa. It will, however, be difficult to assess whether this approach is effective, not least because such measures would affect only a small part of any one European country’s breeding population, making it difficult to detect any benefits in the monitoring data being collected on the breeding grounds.
The study also identifies that targeted action to boost the productivity of European breeding populations may help to halt the declines of some species. However, such action will not, on its own, be enough to help other species without efforts to address the issues they face at staging sites and on the wintering grounds.
The study concludes that, despite a growing wealth of knowledge, we remain largely unable to deliver the necessary conservation action because of the knowledge gaps that remain. While better coordination of research efforts – working across the full annual cycle – will help, the authors argue that we need to use the scientific knowledge that we already have, and start to act now. If we wait until we have a complete understanding, it is likely to be too late.
Notes
We dedicate this review to Japheth Roberts, a brilliant young biologist from Ghana whose life was tragically cut short by illness. He made a major contribution to RSPB and Ghana Wildlife Society work in Africa – an area of work we highlight as a key ongoing priority. The review drew on discussion and insights generated at a workshop in Cambridge in 2019 generously funded by the Cambridge Conservation Initiative collaborative fund CCC-05-18-003 and RSPB and co-organized by J.V. and Susana Requena. We are grateful to all attendees for their invaluable input: Guy Anderson, Phil Atkinson, Olivier Biber, Claire Bissel, Graeme Buchanan, Malcolm Burgess, Andrew Callendar, Carles Carboneras, Nonie Coulthard, Nicola Crockford, João L. Guilherme, Jenny Gill, Borja Heredia, Vicky Jones, Felix Leichti, Alex Ngari, Abdoulaye N'Diaye, Will Peach, Rob Robinson, Tilman Schneider, Fernando Spina, David Stroud, Simon Wotton. We also thank the Editor Richard Fuller and Associate Editor Inês Catry and two anonymous referees for comments that greatly improved this review.
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