Drivers of songbird territory density in the boundaries of a lowland arable farm

Abstract

Conventional farming in the UK has had adverse effects on farmland biodiversity, particularly during post-war intensification of agriculture. Efforts have been made in the reversal of these effects, with much of the literature reporting a mixture of findings. At a localised scale, these efforts have been noticeable with RSPB Hope Farm observing a 200% increase in bird territory numbers from 2000 to 2012, achieved with the wide implementation of agri-environment schemes (AES) on the farm. We aimed to investigate the spatio-temporal drivers of territory density in four hedgerow specialist bird species using a thirteen year (2000–2012) dataset of hedgerow management, in-field cropping and field boundary habitat records. Territory maps were used to calculate territory counts for each hedgerow across the time period. Generalised Linear Mixed Models were used to model territory counts for each habitat variable. These findings demonstrate that for Emberiza citrinella, Carduelis cannabina and Sylvia communis, presence of oilseed rape (OSR) is a strong predictor of higher territory numbers, leading to a doubling in territory density compared to absence of OSR. However, tree presence in hedgerows was a negative predictor of territory numbers for these species. Opposing trends were observed for Carduelis chloris, which exhibited significantly greater territory numbers in roadside hedgerows, hedges with trees and when adjacent fields were not sown with a main crop. Management of hedges was a weak predictor of S. communis territories. This demonstrates that crop type, AES features, tree presence and location of hedgerows are drivers of farmland bird territory numbers. These findings validate the usefulness of more sustainable, wildlife-friendly farming under previous CAP rules and have important implications for post-Brexit farming policy, such as the Agriculture Bill.