Factors influencing nest site selection in a rapidly declining shorebird, the Eurasian curlew

Abstract

In this period of rapid human-induced environmental change, it is vital that influences of habitat on the distribution and productivity of threatened species are understood. Ground-nesting birds are declining more rapidly across Europe than any other group, with large-bodied birds at the greatest risk of extinction. Productivity and adult survival cannot both be maximised concurrently, and individuals will make decisions during the nest-placement phase which will favour one outcome or the other; however, under conditions of accelerating change, these decision processes may become decoupled from positive fitness outcomes. The Eurasian curlew Numenius arquata is Europe's largest wader and is showing steep declines in breeding productivity. Curlews are known to use a diverse range of habitats for nesting, where anthropogenic or natural features may influence distribution. There is an urgent need to understand the spatial scales of these impacts, and whether habitat characteristics have a positive or negative impact on nest survival. In our study site in southern England, curlew showed a marked preference for nesting in wetter habitats, primarily mire, and a weaker selection of dry heathland. Nest survival improved in wetter habitats, and the area of mire round a nest site was positively associated with increased levels of nesting success, whilst area of scrub had a negative association. Woodland significantly excluded curlew from potentially suitable breeding habitat, with an impact observed up to 2 km from the nest site, but nest survival did not improve with distance from woodland. Curlews strongly avoided nesting near a major road passing through the study site, despite seemingly suitable habitat nearby. Understanding landscape effects will assist in planning future habitat management for curlew, impacts of forestry and avoidance of additional pressures on a species of high conservation concern.