Marsh harriers have recovered dramatically in the UK from near-extinction in the 1970s through wetland habitat restoration, with current populations dependent on continued reed bed management and protection from disturbance.
Marsh harriers nesting in reed beds that dry out during summer find nesting substrate unstable and vulnerable to predator access. Human disturbance at reed bed edges by birdwatchers and reed cutters causes nest abandonment during incubation. Females disturbed during the brooding phase of chick-rearing leave young chicks exposed to cold. Prey availability in surrounding farmland — small mammals, water birds, and large insects — determines chick provisioning success and fledgling survival. Competition with other reed bed nesters including bitterns for prime nesting areas can cause nest displacement.