Breeding farmland birds and the role of habitats created under agri-environment schemes

Abstract

In this thesis, I aim to assess how farmland birds use insect-rich agri-environment scheme (AES) foraging habitats during the breeding season and how such birds might benefit from them. It is particularly focused on how the coverage and quality (measured by insect food levels and food accessibility) of AES habitats influence territory selection, foraging activities and breeding success. The thesis begins by explaining why farmland birds have declined, reviewing how AES may help reverse these trends, along with outlining why AES may fail to benefit breeding birds (Chapter one). I then investigated whether the addition of wildflowers to AES margins, boundary type, crop type, chick food availability or accessibility influenced the foraging activity of insectivores, mixed diet species and the passerine community in general (Chapter two). Next, I wanted to find out if territory selection by a declining farmland bird the yellowhammer Emberiza citronella related to the quantity of AES habitat available; models also accounted for chick food abundance, landscape diversity and nest site features (Chapter three). Subsequently I investigated how the availability of AES can affect chick diet and survival using the Eurasian tree sparrow Passer monatus as a focus species. I compared the abundance and diversity of tree sparrow chick food items between nest boxes with and without access to AES habitats aimed at foraging birds (Chapter four). I then documented whether tree sparrow productivity was limited by the availability of such invertebrate-rich foraging habitat (Chapter five). As the majority of AES studies use only short-term data sets, my final data chapter aimed to address this by linking trends in yellowhammer and common chaffinch Fringilla coelebs nest success to the total chick food abundance of available arable and AES habitats over an 10 year period (Chapter six). The thesis concludes by considering future research directions of AES and farmland bird studies in the United Kingdom (Chapter seven).