Illegal killings are partly responsible for a fall in the number of hen harriers in Scotland, conservationists say.

There were 460 breeding pairs of the raptors identified during a survey last year, compared with 505 in 2010.

They are among the most threatened birds of prey in the UK and Scotland is home to about 80% of the population. They are ground nesting, making them particularly vulnerable.

Hen harriers are on the brink of extinction in England, according to the RSPB survey, with just four breeding pairs left. Twelve sets of mates were identified in 2010.

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."

Duncan Orr-Ewing, head of species and land management at RSPB Scotland, said urgent steps must be taken to stop killings.

"The hen harrier is an indicator of the health of our upland environment and the fact that its population continues to decline is of major concern," he said.

"The hen harrier is a high priority for our conservation work and urgent steps need to be taken to tackle illegal killing of this species and to improve their moorland breeding habitats."

Scottish Natural Heritage head of policy and advice Eileen Stuart added: "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."

The number of pairs also dropped in Wales, falling from 22 to 35, and Northern Ireland, down to 46 from 59.