Using DNA metabarcoding to explore spatial and demographic variation in the diet of Hawfinch (Coccothraustes coccothraustes) populations

Many woodland bird species within Britain have shown population declines over recent years, with unclear reasons for declines. The Hawfinch (Coccothraustes coccothraustes) has been declining within the UK since the 1970's, while mainland Europe populations have remained stable. This PhD thesis used DNA metabarcoding and high-throughput sequencing (HTS) of Hawfinch faecal samples to describe plant and invertebrate dietary composition across core Hawfinch population ranges within the UK and mainland Europe. I investigated the degree of dietary composition difference between distinct populations of Hawfinch as well as between demographic groups. This was to elucidate the extent that Hawfinch show dietary plasticity, which can be a determining factor allowing species to adapt to environmental changes. Given the importance of diet, it is important to understand which taxa are preferred, especially for species which are showing population declines. Hawfinch plant dietary composition was analysed to reveal if the frequency of plants detected within their diet differed from their foraging environment, indicating selective foraging. UK Hawfinch dietary composition of plant (Chapter 2) and invertebrate (Chapter 3) taxa was found to vary spatially and between demographic groups, with mainland Europe populations showing similar patterns (Chapter 4). Analysis of the relative abundance of herbivorous taxa within UK woodlands compared with frequency of detection within Hawfinch diet (Chapter 5) indicated Hawfinch were showing selective foraging and were not consuming certain taxa relative to their availability. This PhD thesis provides novel insights into the dietary plasticity of a declining species across a broad geographical range. I provide a clear example of how DNA metabarcoding methodologies can be applied in studies of difficult to study species, as well as how dietary composition can be driven by environmental and demographic factors. Finally, this thesis shows that Hawfinch are selective, and are consuming plants disproportionally to their availability.