Effects of Agri-environmental and Game Management on the Productivity of Farmland Passerines.

Abstract

This thesis aims to contribute towards finding solutions to UK farmland passerine population declines by investigating the potential for aspects of agri-environment schemes (AES) and game-management to improve productivity. For six multi-brooded passerines from three lowland farmland sites, I investigated effects of predator removal and two AES options - conservation headlands (CHs) and wild bird cover (WBC) - on productivity components. Using productivity and population models, I assessed the population consequences of different management scenarios. I demonstrated a significant effect of predator removal on nest success in blackbird, chaffinch and yellowhammer, a possible effect in dunnock, but none in song thrush or whitethroat. In a blackbird case-study, predator removal appeared to have driven the breeding population trend, but this was unproven in the correlative analysis. Developing an individual-based re-nesting model, I demonstrated that in yellowhammer the effect could increase potential population growth rate by 23%, despite re-nesting compensation. Presence of WBC strips and CHs appeared to have little effect on productivity components of adjacent nests, except for a positive effect of presence of WBC strip on yellowhammer clutch size; a larger experimental study is required to confirm this effect. Population modelling predicted that in yellowhammer this could only lead to a 1% increase in population growth rate. Boundary-based AES may contribute somewhat towards mitigation of population declines, but are unlikely to provide a universal solution, and to achieve population recovery in the yellowhammer multiple management interventions that improve both survival and productivity will be required. In their current form, AES may fail to achieve this. Game-management could contribute as a self-motivated and sustainable system of management in which two components - predator removal and WBC - may benefit productivity. Methodologically, individual-based re-nesting models could be important in assessing the effects of management on seasonal productivity of farmland birds.