Red squirrels have been introduced at Castle Ward in a bid to establish a new population in the grounds of the Co Down property.
The first four have been released at the estate with more to follow.
The quartet were carefully transported by Belfast Zoo and Ulster Wildlife in hay-lined nest boxes to a soft-release pen in the estate to allow them to get used to their new surroundings, before taking their first leap into the wild.
The move is part of an ongoing effort between the National Trust, Ulster Wildlife, Belfast Zoo, Northern Ireland Environment Agency, and the Heart of Down Red Squirrel Group, to secure the long-term future of this increasingly rare mammal.
They were released into a specially selected location in the Castle Ward estate, picked for its woodland habitat as well as being free from invasive grey squirrels - the biggest threat to the red squirrel's survival.
Cormac Dolan, area ranger at National Trust Castle Ward, said the project shows how the native species can be given the chance to make a comeback.
"Our healthy population of pine marten at Castle Ward, alongside the work of local volunteers, has allowed for the absence of the invasive grey squirrel," he said.
"Greys are known to carry a fatal disease for our native reds and they also out-compete them for food and territory.
"The pine marten and red squirrel have evolved together in our local ecosystems and can much more easily share habitat.
"The work by everyone involved in this project is inspiring and shows how, with the right conditions and a little help, our native species can be given the chance to make a comeback."
Red squirrels have faced huge declines in the UK and Ireland due to the invasive grey, introduced from North America in the 19th century, and habitat loss.
However, alongside the spread of native pine martens and local conservation work, they are starting to recover locally.
Since 2012, Belfast Zoo has been breeding red squirrels and working with conservationists to release them into suitable woodlands, where these wild animals belong and can thrive.
Belfast Zoo manager, Alyn Cairns. said Castle Ward is their seventh release site and 35th zoo-bred squirrel to go out into the wild.
"We are hopeful that this National Trust site will prove to be a safe haven for reds and for future generations to enjoy in the coming years," she said.
Katy Bell, senior conservation officer at Ulster Wildlife, who has been at the forefront of this initiative, described the project as having been in the planning with partners for a number of years.
"We are delighted to see it finally come to fruition with the red squirrels now settled into their new home," she said.
"Partnership working is vital to helping ensure the long-term future of red squirrels and we hope to see this new population flourish, breed and spread out into other areas in County Down and beyond, with continued collaboration between organisations, landowners and volunteers.
"This work links into our ten-year Red Squirrel Conservation Strategy for Northern Ireland to support red squirrel recovery across the country."
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