Testing a novel agri-environment scheme based on the ecology of the target species, Montagu's Harrier Circus pygargus

Farmland birds are in steep decline and agri-environment schemes (AES) to counteract these biodiversity losses are expensive and inefficient. Here we test a novel AES, ‘Birdfields’, designed using detailed ecological knowledge of the target species, Montagu's Harrier Circus pygargus. Current AES, such as field margins, that aim to improve foraging conditions (i.e. vole densities) for harriers are inefficient, as prey are difficult to capture in tall set-aside habitat. ‘Birdfields’ combines strips of set-aside to boost vole numbers and strips of alfalfa, as voles are accessible after alfalfa has been harvested. We found that vole numbers were generally highest in set-aside. Montagu's Harriers fitted with GPS-loggers used ‘Birdfields’ intensively after mowing, preferring mown to unmown strips. Thus, prey availability appeared more important than prey abundance. Thus, ‘Birdfields’, as a targeted AES for Montagu's Harriers, is more effective than previous AES due to increased prey accessibility. An additional advantage of ‘Birdfields’ is that it is considerably cheaper, due to the harvest of alfalfa. We advocate that AES should always include monitoring and research activities, aiming at a more adaptive conservation approach.