Eden, Catrin and Sharp, Stuart and Broughton, Richard and Donato, Bart and Hewson, Chris M. (2025) Understanding the importance of aquatic habitats and migration strategies in the conservation of spotted flycatchers (Muscicapa striata). PhD thesis, Lancaster University.
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Abstract
Despite declines of Afro-Palearctic migrants spanning decades, little progress has been made in understanding the causes of population trends for most species. The complex annual cycle of migratory birds means that factors affecting population trends may act across an enormous geographic scale, but much research remains focussed on the breeding grounds due to limitations in tracking technology. Many migratory birds are insectivorous, and recent research suggests that aquatic habitats may play a crucial role by supplying nutrients through aquatic insect emergence, which is particularly relevant given reported declines in terrestrial insects. The spotted flycatcher (Muscicapa striata) is an obligate insectivorous Afro-Palearctic migrant in urgent need of conservation action, having declined by 93% in the UK since 1967. This thesis explores the role of aquatic habitats and the subsidies they provide in the ecology of spotted flycatchers, and aims to enhance our understanding of their movements outside the breeding season. In a UK-wide study, we found that occupancy and colonisation were positively correlated with river density, and loss was less likely when river density was high. At a local scale in Cumbria, we found that spotted flycatcher nests were more likely to occur near rivers, but this did not appear to influence nest survival, which was primarily driven by predation. However, adults and chicks were in better body condition when their blood contained higher concentrations of fatty acids associated with aquatic habitats, and nests that weren’t predated were more likely to fledge chicks during periods of higher aquatic insect availability. We also tracked individuals throughout a full annual cycle and present the first detailed account of spotted flycatcher migration and overwintering behaviour. We found that the species predominantly migrates in short hops between the UK and Namibia, necessitating access to frequently distributed high-quality habitats. Overall, we find that aquatic habitats may provide important refugia for insectivorous birds, and that broad-scale conservation strategies across the entire range may be most effective for this species and others facing similar challenges.