Quantifying trade-offs between butterfly abundance and movement in the management of agricultural set-aside strips

Agri-environment schemes (AES) create small areas of habitat within agricultural landscapes to support biodiversity. Here, we study butterfly flight behaviour within linear AES features and examine whether differences in resource availability affect the speed, linearity, or directionality of local movements, thereby affecting their contribution to landscape connectivity. We surveyed butterflies within three basic (naturally regenerating) and three wildflower-sown linear field margin strips (0.09-0.15 ha) on a farm in North Yorkshire, UK, and mapped butterfly flight paths to quantify local displacement (movement speed), efficiency (linearity, turning angles), directionality (step orientation), and behaviour (time spent flying, nectaring). Butterfly species richness was similar between margin types {estimated asymptotic species richness of 21.9 [confidence interval (CI): 15.0-77.7] for basic margins and 14.2 (CI: 14.0-18.7) for wildflower-sown margins}, but abundance was 78% higher in wildflower-sown margins. For the three most common species [meadow brown, Maniola jurtina (L.); ringlet, Aphantopus hyperantus (L.); and small white, Pieris rapae (L.); n = 233 paths], movements within both margin types were highly linear (median turning angle 45 degrees) and generally oriented along the length of the margin strip (median step orientation 27 degrees). Movements in basic margins were slightly more orientated along the length of the margin but we found no differences between margin types in speed, path linearity, turning angles or the proportion of time spent flying or nectaring. We found strong channelling of movements along field margin strips regardless of management type, potentially aiding landscape connectivity. Providing field margin strips with additional foraging resources through wildflower-sowing increases butterfly abundance without impeding local movement rates or efficiency.