Specialist river birds as bioindicators of freshwater ecosystem health in the face of complex environmental change

Abstract

Rivers are one of the most important and sensitive ecosystems globally, subject to environmental pressures integrated across local, landscape and catchment scales. There is a growing need to effectively assess their ecological health to inform management strategies for their restoration and conservation, yet detecting the impacts of multiple integrated stressors is also challenging. Bioindicators can reflect the state of an environment and offer a relatively cheap alternative or complementary approach to traditional direct measures. Predatory, obligate riverine birds are promising candidates for indicating riverine health, with White-throated Dipper at the forefront of research due to their sensitivity to a broad range of pressures. However, other riverine specialists such as Grey Wagtail and Common Sandpiper that have divergent life histories and ecologies may improve capture of the intersection of riverine, riparian, and nearby terrestrial ecosystems that ultimately affect riverine health. This thesis examines the responses of these focal species to integrated stressors affecting riverine and riparian ecosystems in Britain, progressing our understanding of their potential role as broad indicators of ecological health. Chapter 2 explores the environmental drivers of spatial variation in occupancy and abundance of the three species. Findings demonstrate that occupancy, and to a lesser extent, abundance is controlled by underlying physiography and land cover at channel, local landscape, and catchment scales, upscaling existing knowledge to catchment-scale pressures. Chapter 3 examines responses to varying weather conditions. This analysis highlights the multiple direct and indirect pressures that temperature and rainfall impose, but the varying effects on these species likely reflects their contrasting breeding strategies. Chapter 4 investigates the association between Dipper breeding performance, breeding density and clutch initiation in a well-studied catchment. Findings suggest that clutch initiation date is a stronger driver of breeding performance than breeding density, but high variability within and among years may be obscured by overall trends.