Giant bearded vultures with wingspans of nearly three metres are sustainably reproducing in the Swiss Alps, researchers said on Thursday.
Lammergeyers, as the birds are also called, disappeared from their habitat a little more than a century ago after excessive hunting.
Scientists launched a reintroduction programme in 1986 by hatching lammergeyers in zoos and releasing two to ten young birds into the wild each year. The last lammergeyer was released in June 2008.
Since then, researchers at an ornithological station in canton Lucerne and scientists at Bern University have found that the natural death rate stands at four birds per year. The birth rate had outpaced that to create a population of about 20 resident birds.
Researchers warn however that the population is far from secure. If the death rate increases by two birds per year to six, the population will tumble irreparably without additional help.
Windmills on alpine passes and poison left illegally for wolves pose the greatest risks to the population, they said.
In April 2007, the first lammergeyer in 122 years was born in the wild in Switzerland. The last one happened in 1885, in canton Graubünden.