Four calling male corncrakes have been recorded on Rathlin Island to date this year.
It is the first time since the late 1970s/early 1980s that four birds have been recorded.
One of the rarest birds on the island of Ireland - a red-listed species - it is a bird of high conservation concern.
Numbers have been in sharp decline since the 1980s and Rathlin is the only place in Northern Ireland home to this species.
For the last six years, at least one calling male has been heard.
This year, two males arrived in late April and are established on the island, with their behaviour indicating they have attracted mates, the Royal Society for the Protection of Birds (RSPB) said.
Two new males were recorded on Wednesday, so if these new arrivals remain and attract a mate, it will be “a real conservation coup”, the RSPB said.
RSPB Rathlin Island warden Liam McFaul said he was very happy that there was two calling males, but to hear four was quite something.
"There’s no doubt that there were four birds in four different locations. It would be nice if all four got mates and stayed on the island, but there’s always a chance that one or two might leave again and settle elsewhere.”
McFaul will continue to monitor the birds, which are all within a half-mile radius of each other.
At least three of the birds have been heard in nettle beds created over the last decade by RSPB NI staff and volunteers to attract corncrakes to the field margins of Church Bay.
The hope is to achieve a sustainable population of corncrakes, with four or five pairs regularly breeding.
The RSPB said one islander caught an extremely rare glimpse of a male and female corncrake side by side in a field on Tuesday 4 May.
Corncrakes have two broods; the first in June and the second in late July or early August. After the second brood hatches, the birds will migrate back to Africa in August or September.
Working with landowners
McFaul said that the RSPB has worked closely with landowners.
“With all the habitat work, we eventually had one bird coming back, then a few years later two birds, then one and now it’s up to four. So we’ve been working towards this for a long time.”
A Northern Ireland environment agency corncrake grant scheme is in place on the island and is administered by RSPB NI. The scheme works with farmers to ensure their lands remain safe for these protected birds.
The RSPB said corncrakes are easily spooked, so members of the public are asked not to try to get close to the birds, which are on private land.
“It is vitally important they are not disturbed and that this sensitive conservation effort is not compromised,” it said.