By Steffan Messenger BBC Wales Environment Correspondent
16 January 2017
Electronic tags have been fitted to one of Europe's rarest birds to understand its dramatic decline at a Powys reserve.
The RSPB estimates the population of Greenland white-fronted geese at Ynyshir has fallen by 83% since 1990.
The research project is being funded by Welsh Government.
It comes after a decision by ministers in August not to implement an outright ban on shooting the rare birds caused controversy.
Their movements will be monitored in real time, helping the charity and other partners to understand their needs and put conservation measures in place.
It is hoped the scheme will contribute towards international efforts to boost numbers of the threatened species.
The global population of Greenland white-fronted geese is estimated to be 18,879 - the lowest recorded since spring 1985 - and a marked decline on the last estimate of 20,797 in spring 2014.
The birds, which breed in Greenland, migrate in spring and autumn through south and west Iceland to wintering grounds in the British Isles.
The majority head for Ireland and western Scotland.