The Royal Society for the Protection of Birds estimates that the number of calling males has risen from 480 to 570 over the past two years.
The corncrake, a relative of the moorhen which winters in south-east Africa, was a common farmland bird before the Second World War.
Many older people can still remember its rasping call. It has been a victim of the modernisation of farming, which has denied it the tall grass it needs through spring and most of summer.
It had held out in Northern Ireland as well as in the Scottish islands but the last time it bred in Ulster was in 1993. Numbers have risen recently in the Irish Republic, however.
RSPB experiments on the Hebridean island of Coll have shown that the timing and method of hay cutting are crucial for the survival of the corncrake nestlings in crofters' fields.
For the past four years it has joined with the Scottish Crofters' Union and the Government in running a scheme which pays crofters to not cut hay or silage until after 31 July.
To get the money, the crofters also have to mow in a way which reduces the risk of the young birds fleeing into the path of the mower. The scheme cost pounds 300,000 to run this year.
Stuart Housden of the RSPB said: "We have a real chance of halting the slide towards extinction."
He urged all farmers on land with corncrake potential to take up the payments.