A 9 year study suggests that controlling predators such as crows and foxes on moorland increased the breeding success of some birds. These birds includes the lapwing, curlew and golden plover.
The Game and Wildlife Conservation Trust found that controlling carrion crows and foxes increase ground feeding birds breeding succest by more than 3 times.
In Northumberland moorland and marginal farmland were studied. One area that was managed by a gamekeeper was compared with one which had not got a gamekeeper and two plots that removed predators and then stopped controling predator numbers.
Controlling predators doubled the numbers of meadow pipitsand increased the breeding numbers of red grouse
In some ways, it is obvious to me that if you control predators then more prey will live.
I have heard some people say that the field margins around fields are a haven for rats and are bad for ground nesting birds. The rats easily prey on many ground feeding birds nests. So this could be another reason some ground nesting birds are declining.