Six rare European bison bred in captivity in the Ireland and the UK have been sent to Romania to be reintroduced into the wild.
European bison were driven to extinction in the wild by the early 20th century as a result of hunting and destruction of their habitat, conservationists said.
Captive breeding programmes in European zoos and reintroductions have led to a gradual increase in numbers, and the project in Romania aims to establish a self-sustaining population there and boost the variety of wildlife in the region.
Reintroductions have already established free-ranging and semi-free herds in Poland, Lithuania, Belarus, Russia, Ukraine and Slovakia.
The six female captive-bred bison from Fota Wildlife Park, Cork, Ireland, Port Lympne and Howletts Wild Animal Park, Kent, and Highland Wildlife Park, Inverness-shire, were transported to Vanatori Neamt Nature Park in Romania's Carpathian Mountains.
The bison will be monitored with radio-collars and will become part of an existing herd of European bison introduced to the park from captive populations in Germany, Sweden and Switzerland.
The move of the six bison was carried out by the Aspinall Foundation in collaboration with the wildlife parks, and in partnership with the Vanatori Neamt Nature Park, the European Bison breeding programme and European Wilderness Society.
Sean McKeown, park director for Fota Wildlife Park, said: "It's great to see two young bison we have reared form part of this important reintroduction programme for this species that was once extinct in the wild in Romania."
Adrian Harland, animal director for Port Lympne Wild Animal Park said: "Following our involvement in the Aspinall Foundation's ground-breaking reintroduction projects in Africa, it is great to be able to continue our conservation efforts here in Europe by reintroducing a species that was once tragically made extinct in the wild."
Douglas Richardson, head of living collections for Highland Wildlife Park, said: "This project is an example of how zoos within the European Zoo Association's co-ordinated breeding programmes are helping save species from extinction and I am delighted Highland Wildlife Park's female bison Glen Rosa will be playing her part in the continuing reintroduction of a species that had become extinct in the wild less than a century ago."