Ten years on from a predator removal experiment in the English uplands: Changes in numbers of ground-nesting birds and predators.

Abstract

There are growing concerns that increasing generalist predators in the UK over the last few decades have contributed to declines in ground-nesting birds. Crow, Corvis corone and C. corvix combined, and Red Fox Vulpes vulpes abundances are either the highest or among the highest in any European country. These high densities are linked with a landscape of intensive agriculture and non-native woodland into which large numbers of non-native gamebirds are annually released, and from which several species of apex predators, which may otherwise limit mesopredators and scavengers, have been extirpated. Ground-nesting birds are particularly susceptible to predation and experimental legal removal of predators in North Northumberland during the 2000 s demonstrated a three-fold improvement in breeding success amongst ground-nesting birds, with subsequent increases in their abundance. Ten years after the experiment and cessation of predator control, the experimental plots were resurveyed to measure changes in numbers of four species of waders, three native wild gamebirds, two protected avian predators (Raven C. corax and Buzzard Buteo buteo) and two non-protected predators, Carrion Crow and Red Fox, whose abundances had been significantly reduced during the experiment. Carrion Crow abundance and a Red Fox index had increased by 78 % and 127 % respectively since the experiment, whilst Raven and Buzzard showed non-significant increases that paralleled UK trends for those species. Increases in non-protected and protected predators were associated with the local extinctions of Black Grouse Lyrurus tetrix and Grey Partridge Perdix perdix, together with significantly reduced Red Grouse Lagopus lagopus scotica (−71 %), Golden Plover Pluvialis apricaria (−81 %), Snipe Gallinago gallinago (−76 %), Curlew Numenius arquata (−24 %), and a non-significant reduction in Lapwing Vanellus vanellus (−49 %). These bird declines occurred whilst most habitat measures showed no change. They mirror patterns of decline amongst the same species across the UK. Continued lethal control of predators at landscape scales may be essential to help prevent further declines in birds of conservation concern, pending longer-term restructuring of habitat compositions at landscape scales to render them less predator friendly.