Great spotted woodpeckers used to be like snakes – never seen in Ireland.
But since 2006 the striking woodland birds have colonised the entire eastern coast of Ireland from Co Antrim to Wexford and are even showing up as far west as Fermanagh and Kerry.
Earlier this year the distinctive drumming sound made by the woodpecker was heard in Belfast for the first time – at Belvoir Forest – suggesting the birds were poised to breed in the city.
The spread of the woodpecker is one of the success stories documented in the new Bird Atlas 2007-11, which drew on 40,000 volunteers to map all of Britain and Ireland's birds over four years.
The atlas revealed that in the last 40 years, 21 (18%) of Ireland's bird species have expanded their breeding range, 54 (47%) diminished and 41 (35%) stayed much the same. Meanwhile, 60% of overwintering birds are now found in more areas than three decades ago and 16% have decreased.
The corn bunting has disappeared from Ireland, while the overwintering pochard has seen a 49% reduction in range in 40 years.
In Northern Ireland, house martins, willow warbler, house sparrow and tree sparrow have all increased, while in south and east England they decreased.
Buzzards have undergone a massive 1976% expansion, spreading out from their stronghold in Northern Ireland 20 years ago and are now widespread across the eastern half of Ireland.
BTO Northern Ireland officer Shane Wolsey said: "The atlas also shows dramatic declines in our breeding waders.
"We now need to find out what is driving these changes so that we can better support birds that are in trouble."