Hen harriers are on the brink of extinction in England after the number of breeding pairs fell to four last year, according to new figures.
The fifth national hen harrier survey showed the number of breeding pairs of the bird of prey in England fell from 12 in 2010 to just four in 2016.
Scotland - which is home to 80% of the UK population of hen harriers - saw its number of breeding pairs drop to 460 in 2016 from 505 six years previously.
The number of breeding pairs in Wales fell to 35 from 57 while Northern Ireland also experienced a drop from 59 to 46.
Hen harriers are the most threatened birds of prey in the UK due to illegal killings and destruction of heather moorland and forestry, their natural habitat.
RSPB conservation director Martin Harper said: "The latest figures back up a continued trend that we have seen for more than a decade - hen harrier numbers are on the decline throughout the UK.
"The illegal killing of this bird of prey is a significant factor behind the diminishing numbers and a large barrier stopping their recovery.
"Without purposeful action from all, including governments across the UK and the shooting industry, we may see hen harriers once again lost from more parts of the country."
Scottish Natural Heritage head of policy and advice Eileen Stuart said: "While Scotland remains the stronghold for hen harriers in the UK, the continuing decline is a serious concern, particularly the low numbers found in parts of the mainland."
Simon Wotton, lead author of the study, said: "We hope these results will convince all those who are in a position to help hen harriers to take positive steps to ensure their protection and rebuild the UK's hen harrier population for people to enjoy for generations to come."