Seasonal interactions and rapid population declines in Afro-Palaearctic migratory birds

Across Europe, widespread and rapid population declines are currently being reported in many migratory bird species. For example, breeding populations of cuckoo, nightingale and spotted flycatcher in Britain have halved in the last 15 years. The causes of these declines are not understood, but the greater impact in long-distance (particularly sub-Saharan) migratory species has led to suggestions that they are being driven by changes on wintering sites. However, understanding population change in migratory species is complex because of the vast distances over which these species can travel, and the large number of locations on which they depend throughout their migratory ranges. Environmental changes in the breeding, migratory or winter locations could all be contributing to these population declines. Indeed, within the UK, we have previously shown that not all migrant populations are declining, and that both resident and migrant populations are faring better in the same areas. This suggests that changes on the breeding grounds, such as declines in habitat availability resulting from agricultural intensification, may be a primary driver of population trends (in both residents and migrants), but that changes in conditions on migration routes or winter locations may result in additional 'costs of being migrant'. As the resources and infrastructure available for conservation actions vary greatly between Europe and sub-Saharan Africa, it is extremely important to identify where resources may best be spent, before embarking on costly actions that may be difficult to implement.

Very little is known about the winter distribution and habitat use of the migratory bird species that travel to sub-Saharan Africa. However, these species are very well-monitored during the breeding season, thanks to volunteer-based bird surveys that are carried out across Europe to provide national estimates of the annual abundance of many species. In addition, volunteer-based constant effort bird ringing in many countries is used to monitor survival and recruitment into breeding populations. The Europe-wide scale of these data sources provides a powerful opportunity to address these issues, through within-species comparisons of (a) populations that breed across Europe but have different migratory routes, and (b) the consistency of these patterns among resident and migratory species.

We therefore propose to, for the first time, integrate these large-scale, long-term data, in order to explore the extent of the population declines across Europe, identify locations and habitats where declines are most severe, and quantify the demographic and environmental factors that are driving the population declines. Quantifying the relative contribution of breeding and non-breeding season processes to these declines will be key to identifying the most appropriate locations for targeted conservation actions for these species, and will provide the framework for species-specific research in complex migratory systems.

This research will be of particular relevance to conservationists and policy-makers involved with designing and implementing national and international conservation strategies, particularly among countries in Europe and Africa, and those that are Parties to the Convention on Migratory Species (CMS). The recent, rapid declines among Afro-Palearctic migratory bird species are a cause for great concern among policy-makers, conservationists and members of the public for whom these species hold great cultural value. Parties to the CMS are required to undertake actions to reduce habitat degradation, but it is not yet clear which part(s) of the migratory ranges of these species are likely to be contributing to these declines. Effort is currently focussed on sub-Saharan Africa, but this may be in vain if the problems in the European breeding areas are also contributing to these declines. Influencing the land-use changes that may be impacting migratory species is also likely to be substantially more feasible in Europe, given the established conservation community, infrastructure, resource availability (e.g. agri-environment funding) and public engagement. This study aims to identify the demographic changes driving these population changes, the extent to which this is related to breeding and non-breeding season conditions, and the geographic scale over which these changes are apparent. This information will therefore directly inform the development of international conservation strategies to tackle these issues. Our close links to government departments and NGOs responsible for the design and delivery of conservation policy, both nationally (RSPB, Natural England, Defra, JNCC) and internationally (CMS, EU Ornis Committee, Birdlife International), will facilitate communication and discussion of the study findings with relevant conservationists.