Britain and Ireland support globally-important numbers of breeding seabirds, but these populations are under pressure from a suite of threats, including marine pollution, habitat loss, overfishing and highly pathogenic avian influenza. Climate change introduces additional threats, the magnitude of which is uncertain in the future, making it difficult to plan how to apportion conservation efforts between seabird species. Predicting how species’ numbers could change under different climate change scenarios helps clarify their future vulnerability to extinction, and thus assists in conservation planning.

Ongoing declines have been reported for many of our wader species, and there is an urgent need to both understand the reasons for these declines and assess the effectiveness of any associated conservation action. Intertidal habitats are often well-used by waders outside the breeding season, but some species also make use of other adjacent habitats during this period, including agricultural fields. Understanding the importance of these non-tidal habitats for waders is crucial, especially as such land is rarely included within the protected areas designated for these species. This study investigates the use of non-tidal habitats bordering The Wash – an estuary in eastern England – by Curlew and Bar-tailed Godwit, species which are designated as ‘Near Threatened’ by the IUCN. Information on the winter-feeding distribution of the two species was collated from resightings of individually colour-marked birds, initially caught and ringed at sites around The Wash by the Wash Wader Research Group. The sex of individual birds was determined from measurements taken in the field, and this provided an opportunity to determine if males and females differed in their use of the available habitats. The resightings revealed that Bar-tailed Godwits were only seen on intertidal habitats and none were observed feeding inland. In contrast, colour-marked Curlews were regularly observed feeding on agricultural fields, the colour-marks revealing that the majority of individuals were feeding on both fields and mud flats. Importantly, those Curlews seen feeding in fields were significantly more likely to be male and those on the estuary more likely to be female. Although there is a small degree of overlap, female Curlews have longer bills than males. The difference in habitat use evident in the resighting data probably reflects the fact that the longer-billed females can access more intertidal worms and are more efficient feeders when probing. Shorter-billed individuals may be better suited to feeding in the denser substrate typical of agricultural fields, and they may also struggle to find sufficient prey when using intertidal areas. That inland fields are used by increasing numbers of Curlews, particularly males, through the winter months has implications for existing conservation approaches. The Wash is protected by various national and international designations, but these relate primarily to the intertidal habitats; the inland fields are not protected and are subject to pressure on land for development. Should these inland feeding sites be lost this is likely to affect males (particularly those with the shortest bills) disproportionately, which may have implications for the wider Curlew population. The study’s findings suggest that consideration should be given to extending the area around The Wash receiving protection.

It is important for birds to maintain their plumage in good condition, something that is facilitated by the periodic moulting of their feathers. However, moulting feathers is energetically costly and can also compromise an individual’s ability to forage and avoid predators. Because of this, the timing of feather moult needs to be balanced against the demands imposed by other key events, such as breeding and migration.