Illegal killing associated with gamebird management accounts for up to three-quarters of annual mortality in Hen Harriers Circus cyaneus

Predators are frequently victims of wildlife crime due to conflicts with human interests. Where predators are protected, killing may occur covertly and novel methods, including satellite tracking, are often required to assess population consequences. Wildlife crime persists in the British uplands, where raptors are illegally killed on moorland managed for Red Grouse Lagopus lagopus scotica shooting. To understand impacts on one such species, the Hen Harrier Circus cyaneus, we analysed data from 148 individuals tracked across Britain between 2014 and 2021. Using remotely sensed land-use data and continuous-time survival methods, we quantified survival rates, contributions of natural causes and illegal killing to mortality, and spatial and temporal associations between mortality and land managed for grouse shooting. Annual survival was low, especially among first-year birds (males: 14 %; females: 30 %), with illegal killing accounting for 27-43 % and 75 % of mortality in first-year and subadult (1-2 years) harriers respectively. Illegal killing is likely attributable to grouse moor management because i) a 10 % increase in grouse moor use resulted in a 43 % increase in mortality risk; ii) a strong overlap existed between mortality and grouse moor extent in 20 km squares, identifying hotspots of illegal killing in northern England and northeast Scotland; iii) death due to natural causes showed different spatial and temporal patterns; and iv) timing of mortality peaked around the shooting season and during breeding territory establishment. Governments have failed to reduce illegal killing of Hen Harriers and other raptors in Britain and our results emphasise that further legislative reform is needed to tackle this enduring criminality.